Re: [HACKERS] Selecting a constant question
Ühel kenal päeval, E, 2007-06-11 kell 22:55, kirjutas Dann Corbit: -Original Message- ... I hope someone who truly understands database interfaces will read this thread and address the issue. For now we will have to special case postgres in our application until it is addressed. or redesign your application so that it allocates memory as needed and won't waste client memory by allocating maximum possible amount for each and every grid cell weather needed or not ;) As I understand from this discussion you are writing some kind of middleware (i.e. tools), and I'd expect toolmakers to do the right thing. In this case the middleware is: ODBC/JDBC/OLEDB/.NET data drivers for PostgreSQL. There are other related tools, but the above is the product for which the bug needs corrected. You mean you use some kind of Grid inside JDBC/.NET drivers , and it needs to know max size for a column ? can't you replace it with a dynamically allocated Grid component, which would also work well for other expressions, not just constants ? allocating as much as possibly ever needed is something that would be excusable in quick-n-dirty end user application, but not in a tool. It's a requirement of the ODBC/JDBC/OLEDB/.NET specifications. Is that a requirement only for constants or for any expression, say SELECT substring(reallybigblob, 1, random(100)) from somebigtable ? I suppose we could scan the table twice to figure out how large a column might be, but that would make the PostgreSQL driver run at 1/2 speed. Not a very appetizing solution. by scanninc twice you find out how big the largest column _is_, not might be . None of the other database vendors has any trouble reporting this information correctly. By this information you mean the max possible size of data returned by and expression ? - Hannu ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Selecting a constant question
Again, the issue is not our tool, but the deficiency in libpq/postgres ... even mysql gets its right .. why not Postgres? Its not hard for a database to report metadata properly. if I issue a sql statement: select '123' from any table the database should report that the maximum length of the 1st column in the resultset is 3 ... it cant be any more plain than that. Thanks lm From: Hannu Krosing [mailto:[EMAIL PROTECTED] Sent: Mon 6/11/2007 10:43 PM To: Larry McGhaw Cc: Tom Lane; Alvaro Herrera; Dann Corbit; Gregory Stark; Martijn van Oosterhout; pgsql-hackers@postgresql.org Subject: Re: [HACKERS] Selecting a constant question Ühel kenal päeval, E, 2007-06-11 kell 22:11, kirjutas Larry McGhaw: As far as I am aware these statements are true. If you have a specific example you could provide to the contrary that would be interesting. Even if there are such conditions it does not change the fact that libpq and/or postgresql is deficient in this area. For any query, the database should be capable of describing the metadata for the columns, which includes 1) the column type and 2) the column maximum length. This is such a basic database interface principle that I very disappointed that someone has not recognized this and simply said yes, we see the issue we will work on it. Again, *all* other major relational databases do this ... even blob fields have a maximum length reported from the database. I hope someone who truly understands database interfaces will read this thread and address the issue. For now we will have to special case postgres in our application until it is addressed. or redesign your application so that it allocates memory as needed and won't waste client memory by allocating maximum possible amount for each and every grid cell weather needed or not ;) As I understand from this discussion you are writing some kind of middleware (i.e. tools), and I'd expect toolmakers to do the right thing. allocating as much as possibly ever needed is something that would be excusable in quick-n-dirty end user application, but not in a tool. Hannu
Re: [HACKERS] ecpg compile error in regression tests
On Mon, Jun 11, 2007 at 07:03:05PM +0200, Magnus Hagander wrote: I get the following error when trying to build the sql/parser.pgc test: c:\prog\pgbin\pgsql\bin\ecpg --regression -o parser.c parser.pgc parser.pgc:26: ERROR: syntax error at or near NULLS Any pointers for where to look? (Kinda seems it could be the ecpg binary not being up-to-date, but I did a make clean and rebuild of it) I get the same error IF I try using an 8.2 parser, be it in the backend or in ecpg. With 8.3 however it works nicely. Could it be that you have some older versions around? Yes, you did a rebuild, but still. Michael -- Michael Meskes Email: Michael at Fam-Meskes dot De, Michael at Meskes dot (De|Com|Net|Org) ICQ: 179140304, AIM/Yahoo: michaelmeskes, Jabber: [EMAIL PROTECTED] Go SF 49ers! Go Rhein Fire! Use Debian GNU/Linux! Use PostgreSQL! ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] ecpg compile error in regression tests
On Tue, Jun 12, 2007 at 09:57:17AM +0200, Michael Meskes wrote: On Mon, Jun 11, 2007 at 07:03:05PM +0200, Magnus Hagander wrote: I get the following error when trying to build the sql/parser.pgc test: c:\prog\pgbin\pgsql\bin\ecpg --regression -o parser.c parser.pgc parser.pgc:26: ERROR: syntax error at or near NULLS Any pointers for where to look? (Kinda seems it could be the ecpg binary not being up-to-date, but I did a make clean and rebuild of it) I get the same error IF I try using an 8.2 parser, be it in the backend or in ecpg. With 8.3 however it works nicely. Could it be that you have some older versions around? Yes, you did a rebuild, but still. I'll try to blow away my tree and do a fresh cvs checkout later. I'll go ahead with what I for now and get it in thoguh, don't want to throw my changes out. And since the problem is not actually with the regression test *engine*, it's with the tests themselves.. :-) //Magnus ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question
Larry McGhaw wrote: Again, *all* other major relational databases do this ... even blob fields have a maximum length reported from the database. So what are you doing with the max length? Not all data types and values have a meaningful max length, so you have to be able to deal with variable length data anyway. For blobs, exactly what max length would you like to get; 1GB? 1TB? Why, what good is that for? -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Autovacuum launcher doesn't notice death of postmaster immediately
Alvaro Herrera [EMAIL PROTECTED] wrote:
No, I meant a while (sleep 1(or 10) and counter longtime) check for
exit instead of sleep longtime.
Ah; yes, what I was proposing (or thought about proposing, not sure if I
posted it or not) was putting a upper limit of 10 seconds in the sleep
(bgwriter sleeps 10 seconds if configured to not do anything). Though
10 seconds may seem like an eternity for systems like the ones Peter was
talking about, where there is a script trying to restart the server as
soon as the postmaster dies.
Here is a patch for split-sleep of autovacuum_naptime.
There are some other issues in CVS HEAD; We use the calculation
{autovacuum_naptime * 100} in launcher_determine_sleep().
The result will be corrupted if we set autovacuum_naptime to 2147.
In another place, we use {autovacuum_naptime * 1000}, so we should
set the upper bound to INT_MAX/1000 instead of INT_MAX.
Incidentally, we've already had the same protections for
log_min_duration_statement and log_autovacuum.
I hope this patch could fix those large-autovacuum_naptime problems.
Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center
autovacuum_naptime_overflow.patch
Description: Binary data
---(end of broadcast)---
TIP 7: You can help support the PostgreSQL project by donating at
http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question
Again, *all* other major relational databases do this ... even blob fields have a maximum length reported from the database. So what are you doing with the max length? Not all data types and values have a meaningful max length, so you have to be able to deal with variable length data anyway. Imho it has a lot to do with optimizing the interface. If you know, that the max length is e.g. 16 bytes in UTF-8 for the 3 chars, you will probably not want any on the fly allocation smarts and preallocate and bind those 16 bytes. When the max length value gets larger, and it is a variable lenght type, the overhead of varlen allocation smarts starts to pay off. A generic interface should keep the sql parsing smarts at a minimum, thus it cannot know that a returned column is actually a text constant. Imho the request for a max length is very reasonable, but has no value once it exceeds a certain size e.g. 64k. Andreas ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] Autovacuum launcher doesn't notice death of postmaster immediately
Alvaro Herrera wrote: Zeugswetter Andreas ADI SD escribió: The launcher is set up to wake up in autovacuum_naptime seconds at most. Imho the fix is usually to have a sleep loop. This is what we have. The sleep time depends on the schedule of next vacuum for the closest database in time. If naptime is high, the sleep time will be high (depending on number of databases needing attention). No, I meant a while (sleep 1(or 10) and counter longtime) check for exit instead of sleep longtime. Ah; yes, what I was proposing (or thought about proposing, not sure if I posted it or not) was putting a upper limit of 10 seconds in the sleep (bgwriter sleeps 10 seconds if configured to not do anything). Though 10 seconds may seem like an eternity for systems like the ones Peter was talking about, where there is a script trying to restart the server as soon as the postmaster dies. There is also one wild solution. Postmaster and bgwriter will connect with socket/pipe and select command will be used instead sleep. If connection unexpectedly fails, select finish immediately and we are able to handle this issue asap. This socket should be used also in some special case when we need wake up it faster. Zdenek ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Selecting a constant question
Larry McGhaw [EMAIL PROTECTED] writes: The database *knows* this size of the char constant (obviously), and should report the size via a metadata call, as all other relational databases do. I'm not even clear whether you and Dan are talking about the same thing. He's talking about the number of bytes required hold the constant. You seem to be talking about the character length of strings. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question
Dann Corbit wrote: -Original Message- From: Hannu Krosing [mailto:[EMAIL PROTECTED] Since libpq function PQfsize returns -2 for all constant character strings in SQL statements ... What is the proper procedure to determine the length of a constant character column after query execution but before fetching the first row of data? Why not just get the first row and determine the width from it before you actually use any of tha data ? What if the second row is 1000x longer? Thats exactly the point. Consider select mytext from mytable ; How can PostgreSQL possibly know the maximum length of the returned values *before* it has scanned the whole table? greetings, Florian Pflug ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] Autovacuum launcher doesn't notice death of postmaster immediately
On Tue, Jun 12, 2007 at 12:23:50PM +0200, Zdenek Kotala wrote: Alvaro Herrera wrote: Zeugswetter Andreas ADI SD escribió: The launcher is set up to wake up in autovacuum_naptime seconds at most. Imho the fix is usually to have a sleep loop. This is what we have. The sleep time depends on the schedule of next vacuum for the closest database in time. If naptime is high, the sleep time will be high (depending on number of databases needing attention). No, I meant a while (sleep 1(or 10) and counter longtime) check for exit instead of sleep longtime. Ah; yes, what I was proposing (or thought about proposing, not sure if I posted it or not) was putting a upper limit of 10 seconds in the sleep (bgwriter sleeps 10 seconds if configured to not do anything). Though 10 seconds may seem like an eternity for systems like the ones Peter was talking about, where there is a script trying to restart the server as soon as the postmaster dies. There is also one wild solution. Postmaster and bgwriter will connect with socket/pipe and select command will be used instead sleep. If connection unexpectedly fails, select finish immediately and we are able to handle this issue asap. This socket should be used also in some special case when we need wake up it faster. Given the amount of problems we've had with pipes on win32, let's try to avoid adding extra ones unless they're really necessary. If split-sleep works, that seems a safer bet. //Magnus ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] Selecting a constant question
Thats exactly the point. Consider select mytext from mytable ; How can PostgreSQL possibly know the maximum length of the returned values *before* it has scanned the whole table? I think this focuses too much on those cases where it is not possible. When it is not feasible like with a text column, clients deal with it already (obviously some better than others). It is for those cases where it would be feasible, like constants (or concateneted columns), where the max length if properly returned could be used to improve performance. Andreas ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [HACKERS] Selecting a constant question
Zeugswetter Andreas ADI SD wrote: Thats exactly the point. Consider select mytext from mytable ; How can PostgreSQL possibly know the maximum length of the returned values *before* it has scanned the whole table? I think this focuses too much on those cases where it is not possible. When it is not feasible like with a text column, clients deal with it already (obviously some better than others). It is for those cases where it would be feasible, like constants (or concateneted columns), where the max length if properly returned could be used to improve performance. I doubt there's any measurable performance benefit here. You might as well allocate a buffer of say 128 bytes, and enlarge it from there when you see a value larger than that. Even in the worst case, you'll only need to enlarge the buffer a few times per query until you reach the real max length. Actually, if you're in such a high throughput, client-side CPU-intensive situation that this makes any difference, why are you copying the value to another buffer in the first place? Just access it directly in the libpq buffer returned by PQgetvalue, and move on. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question
Heikki Linnakangas wrote: Actually, if you're in such a high throughput, client-side CPU-intensive situation that this makes any difference, why are you copying the value to another buffer in the first place? Just access it directly in the libpq buffer returned by PQgetvalue, and move on. That's a *very* good point. The original design for the pgAdmin query tool made it's own copy of the data to display in the grid which is exactly why we used to get complaints about having a query time and a display time. The modern versions use a virtual table which enables the grid to retrieve the data directly from the libpq buffer when it needs to draw each cell which has effectively eliminated that display time. Regards, Dave. ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Autovacuum launcher doesn't notice death of postmaster immediately
Magnus Hagander wrote: On Tue, Jun 12, 2007 at 12:23:50PM +0200, Zdenek Kotala wrote: Alvaro Herrera wrote: Zeugswetter Andreas ADI SD escribió: The launcher is set up to wake up in autovacuum_naptime seconds at most. Imho the fix is usually to have a sleep loop. This is what we have. The sleep time depends on the schedule of next vacuum for the closest database in time. If naptime is high, the sleep time will be high (depending on number of databases needing attention). No, I meant a while (sleep 1(or 10) and counter longtime) check for exit instead of sleep longtime. Ah; yes, what I was proposing (or thought about proposing, not sure if I posted it or not) was putting a upper limit of 10 seconds in the sleep (bgwriter sleeps 10 seconds if configured to not do anything). Though 10 seconds may seem like an eternity for systems like the ones Peter was talking about, where there is a script trying to restart the server as soon as the postmaster dies. There is also one wild solution. Postmaster and bgwriter will connect with socket/pipe and select command will be used instead sleep. If connection unexpectedly fails, select finish immediately and we are able to handle this issue asap. This socket should be used also in some special case when we need wake up it faster. Given the amount of problems we've had with pipes on win32, let's try to avoid adding extra ones unless they're really necessary. If split-sleep works, that seems a safer bet. Ok It should be problem. But I'm afraid split-sleep is not good solution as well. It should generate a lot of race condition in start/stop scripts and monitoring tools. Much better should be improve pg_ctl to perform clean up (pg_ctl cleanup) when postmaster fails. I think we must offer deterministic way to packagers integrator how to handle this issue. Zdenek ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
[HACKERS] comparing index columns
Hi, As per HOT design, a necessary condition to do HOT updates is that an index column must not be updated. I am invoking the type specific equality operator to compare two index columns, something like this (which I think I had copied from ri_KeysEqual(), but that too have changed now): typeid = SPI_gettypeid(relation-rd_att, attrnum); typentry = lookup_type_cache(typeid, TYPECACHE_EQ_OPR_FINFO); if (!OidIsValid(typentry-eq_opr_finfo.fn_oid)) ereport(ERROR, (errcode(ERRCODE_UNDEFINED_FUNCTION), errmsg(could not identify an equality operator for type %s, format_type_be(typeid; /* * Call the type specific '=' function */ if (!DatumGetBool(FunctionCall2((typentry-eq_opr_finfo), oldvalue, newvalue))) return true; Heikki pointed out that this may not work correctly with operator classes where we should actually be using the operator from the given operator class instead of the default operator of the type. I don't have much insight into the operator classes and operator families and how they work. Where should I look for the related code ? Is there anything else we should be worried about as well ? Any help is appreciated. Thanks, Pavan -- Pavan Deolasee EnterpriseDB http://www.enterprisedb.com
Re: [HACKERS] Selecting a constant question
On Tue, Jun 12, 2007 at 12:47:55PM +0200, Zeugswetter Andreas ADI SD wrote: I think this focuses too much on those cases where it is not possible. When it is not feasible like with a text column, clients deal with it already (obviously some better than others). It is for those cases where it would be feasible, like constants (or concateneted columns), where the max length if properly returned could be used to improve performance. For constants there is a basic problem that Postgres, if at all possible, doesn't even analyse the string at all. If it's not part of a join or sort, then in every likelyhood it's passed through the entire execution untouched and comes out the other end as type unknown. The length indicator of -2 indicates a null-terminated string, postgres never even bothered calculating the length of it. For the situation of concatinating varchar columns, it's a fairly special case. The typmod, in the *special case* of varchar is the maximum length, but for other types it means something else. Additionally, the planner doesn't know that || is concatination, a consequence of the user-defined operators. So to make this work you need to change the planner so that: 1. It special cases varchar to know what the typmod means 2. It special cases the || operator to add the typmods together. 3. Has to take special care not to break user-defined operators All a pile of hacks and special cases to handle something that, to be honest, the vast majority of people never notice. So no, no patch is going to be accepted to handle this special case, because it's far too hacky for a corner case. On the other hand, if you can piggyback it into something like the user-defined typmod stuff, it may have a better chance, though I really think the first problem is basically won't fix from an optimisation point of view. Hope this clarifies things a bit, -- Martijn van Oosterhout [EMAIL PROTECTED] http://svana.org/kleptog/ From each according to his ability. To each according to his ability to litigate. signature.asc Description: Digital signature
Re: [HACKERS] Selecting a constant question
Larry McGhaw wrote: Again, the issue is not our tool, but the deficiency in libpq/postgres ... even mysql gets its right .. why not Postgres? Its not hard for a database to report metadata properly. if I issue a sql statement: select '123' from any table the database should report that the maximum length of the 1st column in the resultset is 3 ... it cant be any more plain than that. Making assertions like this does not make your case for you. If you think it's that easy then send in a patch. I suspect that doing what you want in the cases where it could be supported would require a protocol change, with possibly an extra field in the RowDescription object. If that's true you'd need to make a very good and compelling case indeed for such a change. If this is so vital I'm curious to know why driver authors haven't been screaming about it until now. I'm not dismissing what you want, but just waving your hand and saying it's not hard really won't do. cheers andrew ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Command tags in create/drop scripts
David Fetter wrote: On Fri, Jun 08, 2007 at 08:12:22PM -0500, Jim C. Nasby wrote: On Tue, Jun 05, 2007 at 05:52:39PM -, Andrew Hammond wrote: On Jun 5, 9:19 am, [EMAIL PROTECTED] (Alvaro Herrera) wrote: Zdenek Kotala wrote: Tom Lane wrote: Bruce Momjian [EMAIL PROTECTED] writes: Is this a TODO? I don't think so; there is no demand from anybody but Zdenek to remove those programs. Has it ever even come up before? Personally I found really strange to have createuser and createdb shipped by Postgres when I started using it. I just didn't complain. +1. Given the prevalence of the pg_foo convention, those names are clunky. So is initdb. I'm less creative than Zdenek, so I'd suggest simply renaming to pg_createuser and friends with the same command line options as the originals. Have the binaries check $0 and emit a warning about using the deprecated name to STDERR if called by a name that doesn't have the pg_ prefix. Default to symlinking the old names for backwards compatibility until 9.0. +1 +1 It's a lot easier just to prefix the names than to do something clever. I agree that it is easier to implement. But my original idea was create one command which should be easy expandable. For example add LIST command which it allow to get list of users, roles, langs, databases (instead of psql -l). There is also no way how to create table space? Will we add command pg_createtablespace ? I think better is keep it in one binary instead extend list of deliverable object. I think for people is better to remember pg_cmd --help instead looking for pg_something command. And a lot of code is share anyway. The nice example is ZFS implementation. You need only know two commands (ZPOOL and ZFS) to configure everything include NFS sharing. Zdenek ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] comparing index columns
Pavan Deolasee [EMAIL PROTECTED] writes: I don't have much insight into the operator classes and operator families and how they work. Where should I look for the related code ? Primary opclass members are stored right in the Relation data struct for you. Since (I trust) you're only supporting this for btree, you could just use rd_supportinfo[0] which will not even cost an fmgr lookup. See index_getprocinfo() and callers. regards, tom lane ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
[HACKERS] regress changes
Hi, Quick report from the front lines. I've been IM'ing with Magnus and he already fixed most problems with the regression tests. The buildfarm should slowly start turning green again. There is a remaining problem though, which is that it doesn't work at all on VPATH builds. The problem seems to be that we are neglecting to symlink the files into the builddirs. I am looking into that. I failed to notice this previously because my regular cleanup procedure left the symlinks in place. I think this is something that we should hack make distclean to remove. I'll have a look at that as well. -- Alvaro Herrera Valdivia, Chile ICBM: S 39º 49' 18.1, W 73º 13' 56.4 No hay hombre que no aspire a la plenitud, es decir, la suma de experiencias de que un hombre es capaz ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] regress changes
Alvaro Herrera wrote: There is a remaining problem though, which is that it doesn't work at all on VPATH builds. The problem seems to be that we are neglecting to symlink the files into the builddirs. I am looking into that. The problem is that the files are only symlinked on make install, and I had forgotten to do that. So this is just pilot error. I did correct a minor buglet in the ecpg makefile. Everything seems to be working now, and all tests (main, contrib, pl and ecpg) pass on my machine. Thanks to Joachim and Magnus for reworking this stuff. -- Alvaro Herrera http://www.PlanetPostgreSQL.org/ No deja de ser humillante para una persona de ingenio saber que no hay tonto que no le pueda enseñar algo. (Jean B. Say) ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
[HACKERS] regression driver changes vs resultmap
This patch appears to have randomly changed the format of the resultmap file. Please either undo that, or update the documentation (regress.sgml) to describe what it is now. regards, tom lane ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] regression driver changes vs resultmap
Tom Lane wrote: This patch appears to have randomly changed the format of the resultmap file. Please either undo that, or update the documentation (regress.sgml) to describe what it is now. Not randomly - it needs to be able to use paths including /, so it can't be a separator anymore. Will update docs - missed that they were there. Sorry about that. //Magnus ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question
I'm really frustrated by this process I'm not trying to attack anyone here. I'm just surprised that no one will even entertain the idea that this is an issue that needs to be addressed. Instead nearly all of the responses have been attacking the applications that rely on the metadata. Let me back up and explain the situation. This issue came to light for us when we were using a query tool to examine performance of postgres queries. We were not only measuring the performance of the database itself, but also the TCP/IP transport, And the rendering of the data .. Comparing SQL Server, Oracle, and Postgres head to head with the same queries. We noticed inexplicably that when we used a constant with a postgres query, our records per second dropped From 60,000 records per second to 600 records per second, so we started digging into the issue. We discovered that libpq was not describing the metadata properly for the constant column, and it appears That the 3rd party grid control was relying on that metadata somehow .. The bottom line is that there was A huge performance drag. * OK ... I agree that the memory handling in the grid control could be better, but I would imagine that this issue is not an isolated to this one particular control, and that other applications and controls that rely on resultset metadata may have this issue. Bottom line, we only reported this problem because we thought you would be interested in doing everything possible to make postgres more mainstream and conform to SQL standards. In the past such suggestions have been absorbed with zeal. I have no vested interest in you improving the interface or not, and I'm not going to plead a case for you To do something that every other commercial database has done out of the box. It is in your hands now :) Thanks lm -Original Message- From: Andrew Dunstan [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 4:50 AM To: Larry McGhaw Cc: Hannu Krosing; Tom Lane; Alvaro Herrera; Dann Corbit; Gregory Stark; Martijn van Oosterhout; pgsql-hackers@postgresql.org Subject: Re: [HACKERS] Selecting a constant question Larry McGhaw wrote: Again, the issue is not our tool, but the deficiency in libpq/postgres ... even mysql gets its right .. why not Postgres? Its not hard for a database to report metadata properly. if I issue a sql statement: select '123' from any table the database should report that the maximum length of the 1st column in the resultset is 3 ... it cant be any more plain than that. Making assertions like this does not make your case for you. If you think it's that easy then send in a patch. I suspect that doing what you want in the cases where it could be supported would require a protocol change, with possibly an extra field in the RowDescription object. If that's true you'd need to make a very good and compelling case indeed for such a change. If this is so vital I'm curious to know why driver authors haven't been screaming about it until now. I'm not dismissing what you want, but just waving your hand and saying it's not hard really won't do. cheers andrew ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question
Hi, Nobody is tring to attack anyone, but we're all surprised this is an issue since you're the first person to have mentioned it. I have some a query to test below: On Tue, Jun 12, 2007 at 10:21:09AM -0700, Larry McGhaw wrote: We noticed inexplicably that when we used a constant with a postgres query, our records per second dropped From 60,000 records per second to 600 records per second, so we started digging into the issue. We discovered that libpq was not describing the metadata properly for the constant column, and it appears That the 3rd party grid control was relying on that metadata somehow .. The bottom line is that there was A huge performance drag. What I don't understand is *why* it's complaining about the constant column and not, for example, any other variable length column. There are a very small number of cases where a useful length is returned, 99% of the time it doesn't, yet you're obviously not get any performance problems there. Just a quick test, does the problem go away if you do: SELECT '1'::varchar FROM table; If that fixes it then the bug is (probably) that the middleware thinks that a length of -2 means it's 65534 bytes long. Note, in the test query I gave, it will return -1 for the length. I don't want to blame the middleware, but I want to make sure we're diagnosing the problem correctly. If that query has the same problem, then we really need to think of something else. Have a nice day, -- Martijn van Oosterhout [EMAIL PROTECTED] http://svana.org/kleptog/ From each according to his ability. To each according to his ability to litigate. signature.asc Description: Digital signature
Re: [HACKERS] Selecting a constant question
Larry McGhaw wrote: I'm really frustrated by this process I'm not trying to attack anyone here. I'm just surprised that no one will even entertain the idea that this is an issue that needs to be addressed. Instead nearly all of the responses have been attacking the applications that rely on the metadata. Having been following this debate, I think what people have really been attacking is the idea that the metadata for: SELECT '1' AS varchar_column; should be different from the metadata for: SELECT varchar_column FROM really_big_table; or for: SELECT varchar_column FROM really_small_table; Or at least that's what I've taken away from the dicussion- it's not so much that the metadata shouldn't be relied on, it's that the metadata may be more generic than theoretically necessary. And that the metadata may not contain the length of a variable length field even when that length is known. Brian ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [HACKERS] Selecting a constant question
What I don't understand is *why* it's complaining about the constant column and not, for example, any other variable length column. There are a very small number of cases where a useful length is returned, 99% of the time it doesn't, yet you're obviously not get any performance problems there. The statement above is contrary to my actual results. The proper length is returned in all non-const cases. Here is a specific example: test=# create table test1 ( a varchar(20), b char(10), c integer ); CREATE TABLE test=# Note .. The table is empty, and contains no data at this point: Select a, b, c, '123' , '123'::char(3), '123'::varchar(3) from test1 For column a libpq returns the following: Pqfsize returns -1 Pqfmod (-4) returns 20 For column b libpq returns the following: Pqfsize returns -1 Pqfmod (-4) returns 10 For column c libpq returns the following: Pqfsize returns 4 For constant '123' libpq returns the following: Pqfsize returns -2 Pqfmod returns -1 For constant '123'::char(3) libpq returns the following: Pqfsize returns -1 Pqfmod (-4) returns 3 For constant '123'::varchar(3) libpq returns the following: Pqfsize returns -1 Pqfmod returns -1 Thanks lm -Original Message- From: Brian Hurt [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 11:09 AM To: Larry McGhaw Cc: pgsql-hackers@postgresql.org Subject: Re: [HACKERS] Selecting a constant question Larry McGhaw wrote: I'm really frustrated by this process I'm not trying to attack anyone here. I'm just surprised that no one will even entertain the idea that this is an issue that needs to be addressed. Instead nearly all of the responses have been attacking the applications that rely on the metadata. Having been following this debate, I think what people have really been attacking is the idea that the metadata for: SELECT '1' AS varchar_column; should be different from the metadata for: SELECT varchar_column FROM really_big_table; or for: SELECT varchar_column FROM really_small_table; Or at least that's what I've taken away from the dicussion- it's not so much that the metadata shouldn't be relied on, it's that the metadata may be more generic than theoretically necessary. And that the metadata may not contain the length of a variable length field even when that length is known. Brian ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] one click install?
The problem here is that there aren't really very many defined defaults, or that these defaults vary (sometimes greatly) between the different flavors of UNIX. For example, please tell me: 1) Where should PGDATA default to? 2) How do you want to handle logging output from the postmaster? There are plenty of options... 3) Where should those log files get written? 4) For 1 and 3, will that support multiple major versions of PostgreSQL? (ie, can I have 8.2.latest and 8.1.latest installed at the same time) 5) How about multiple postmasters (on different ports)? I think that the community would be well served by standardizing on these things, at least for basic installations. On 6/11/07, Timasmith [EMAIL PROTECTED] wrote: Hi, I can probably figure it out on linux but I would like to do a one click install based upon defined defaults for the Postgresql database (creating it as a service and load my sql file which creates the database) - has anyone written such a how to? thanks Tim ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Selecting a constant question
Larry McGhaw wrote: For constant '123'::varchar(3) libpq returns the following: Pqfsize returns -1 Pqfmod returns -1 That one certainly looks odd. cheers andrew ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question
That one surprised me as well. Thanks lm -Original Message- From: Andrew Dunstan [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 12:00 PM To: Larry McGhaw Cc: Brian Hurt; pgsql-hackers@postgresql.org Subject: Re: [HACKERS] Selecting a constant question Larry McGhaw wrote: For constant '123'::varchar(3) libpq returns the following: Pqfsize returns -1 Pqfmod returns -1 That one certainly looks odd. cheers andrew ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Selecting a constant question
Larry McGhaw [EMAIL PROTECTED] writes: The statement above is contrary to my actual results. The proper length is returned in all non-const cases. Here is a specific example: test=# create table test1 ( a varchar(20), b char(10), c integer ); CREATE TABLE It's not returning a length at all though. It's returning the typmod, ie, the thing in the parentheses above. In that respect it's perfectly correct to return -1 for the '123' case as well since it's interpreted as an unbounded string and has no maximum length. It happens to only be three characters but then the values in the table could happen to be much less than the 10 or 20 characters you declared them as. The reason you might want to get this has more to do with understanding the semantics of the data you're receiving than optimizing storage. If you queried a Numeric column you would get something very different from the length from which you could extract the maximum precision and scale. This might help you display or work with the results maintaining the precision and scale a user expects. One reason why it might be useful to add an actual measure of the expected length (Postgres does make guesses about the length for planning purposes) would be to so a driver could size buffers appropriately. For example, in psql where we use cursors to process rows, we might want to automatically use a fetch count calculated to be large enough to receive approximately one ethernet frame of data. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [HACKERS] .conf File Organization
Tom, Do you have a better organizing principle than what's there now? It's mostly detail stuff: putting VACUUM and Autovac together, breaking up some subsections that now have too many options in them into grouped. Client Connection Defaults has somehow become a catchall secton for *any* USERSET variable, regardless of purpose. I'd like to trim it back down and assign some of those variables to appropriate sections. On the more hypothetical basis I was thinking of adding a section at the top with the 7-9 most common options that people *need* to set; this would make PostgreSQL.conf much more accessable but would result in duplicate options which might cause some issues. -- Josh Berkus PostgreSQL @ Sun San Francisco ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] .conf File Organization
Josh Berkus [EMAIL PROTECTED] writes: On the more hypothetical basis I was thinking of adding a section at the top with the 7-9 most common options that people *need* to set; this would make PostgreSQL.conf much more accessable but would result in duplicate options which might cause some issues. Doesn't sound like a good idea, but maybe there's a case for a comment there saying these are the most important ones to look at? regards, tom lane ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Avoiding legal email signatures
All, Perhaps we make a policy that corporate-style (disclaimered) mail is encouraged to seek support via corporate-style channels (e.g. is pointed at the commercial support companies). I'm uncomfortable with such a policy, but it'd be better than ignore these nasty corporate victims, which is what the proposal so far sounds like to me. First off, I'm not clear on why we're discussing this on -hackers; -www would be the appropriate list. So I'm cross posting; please reply any additional messages to -www. Second, I'm not sure why we care. I don't believe that e-mail confidentiality notices are in fact enforceable, or at least they haven't been in some high-profile cases which made the news. IANAL, of course. However: Haven't we been over this at least once before? Greg is right, just document the point and leave it alone. If you want to get really picky about, make the confirmation email from the subscription process specifically state that confirming subscription is an acceptance of the PostgreSQL.Org usage policies which can be found here (insert link). This is a good idea anyway. We should have a list usage policy, and we should link to if from the subscribe confirmation and from the web subscription page. In addition to letting people know that e-mail confidentiality footers will be ignored, we can tell them how the lists are moderated, how to unsubscribe (can't have this in enough places), not to use HTML mail, etc. So, who wants to write it? The only additional idea I have is that we ought to simply strip away any e-mail footer over 4 lines from the archives. Not only would this purge the confidentiality footers, it would save us some space in general. -- Josh Berkus PostgreSQL @ Sun San Francisco ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] .conf File Organization
Tom, Doesn't sound like a good idea, but maybe there's a case for a comment there saying these are the most important ones to look at? Yeah, probably need to do that. Seems user-unfriendly, but loading a foot gun by having some options appear twice in the file seems much worse. I'll also add some notes on how to set these values. -- Josh Berkus PostgreSQL @ Sun San Francisco ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] one click install?
On 6/13/07, Andrew Hammond [EMAIL PROTECTED] wrote: The problem here is that there aren't really very many defined defaults, or that these defaults vary (sometimes greatly) between the different flavors of UNIX. For example, please tell me: 1) Where should PGDATA default to? 2) How do you want to handle logging output from the postmaster? There are plenty of options... 3) Where should those log files get written? 4) For 1 and 3, will that support multiple major versions of PostgreSQL? (ie, can I have 8.2.latest and 8.1.latest installed at the same time) 5) How about multiple postmasters (on different ports)? Exactly :} ... all very good points... and then there's still the ownerships of processes and directories/files, and their perms. And integration with the init-scripts. And how e.g. the environment variables for users should be handled. I think that the community would be well served by standardizing on these things, at least for basic installations. But whose decision should that be? The postgres' developers? I think that the defaults that the configure script suggests are quite sane, and happily use them in my Slackware installations. Linux File system Hierarchy standards? Which major distro(s)? And what about the BSDs (or the commercial Unices supported)? And while at it: who would define what a basic installation is? :) -- Cheers, Andrej ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [pgsql-www] [HACKERS] Avoiding legal email signatures
Josh Berkus wrote: The only additional idea I have is that we ought to simply strip away any e-mail footer over 4 lines from the archives. Not only would this purge the confidentiality footers, it would save us some space in general. The effort it would take to write some code to extract the messages from the archive mboxes, break up the messages into their component parts, strip excess sig lines, reconstruct the messages, reconstruct the mboxes and then regenerate the archives would probably equate in dollar value to the disk space required for another 40 or 50 years worth of archives. I vote 'lets not bother' :-) /D ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [pgsql-www] [HACKERS] Avoiding legal email signatures
Dave Page [EMAIL PROTECTED] writes: Josh Berkus wrote: The only additional idea I have is that we ought to simply strip away any e-mail footer over 4 lines from the archives. Not only would this purge the confidentiality footers, it would save us some space in general. The effort it would take to write some code to extract the messages from the archive mboxes, break up the messages into their component parts, strip excess sig lines, reconstruct the messages, reconstruct the mboxes and then regenerate the archives would probably equate in dollar value to the disk space required for another 40 or 50 years worth of archives. A more serious objection is that any automated tool would probably get it wrong sometimes, and strip important text. I vote 'lets not bother' Right. I agree with Josh's idea about mentioning list policies in the subscription confirmation message, though. regards, tom lane ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question
For what its worth .. Your statement about why we are the first people to mention this problem really got me thinking. Anyone who would attempt to write an ODBC driver for Postgres would run into the exact same issue. So I installed the official Postgres ODBC driver, and ran the identical query and here are my results: I probably should have looked at this first There is a whole Postgres ODBC dialog dedicated to the very subject of this thread: Handling of unknown data sizes. The pgodbc driver is configured to treat unknowns as varchar(255) by default, As shown by my example below. This can be configured up or down as desired. SQLExecDirect: In: hstmt = 0x003C18E0, szSqlStr = Select a,b,c, '123' , '123'::char(3), '123'::varchar(3) from..., cbSqlStr = -3 Return: SQL_SUCCESS=0 Describe Column All: icol, szColName, *pcbColName, *pfSqlType, *pcbColDef, *pibScale, *pfNullable 1, a, 1, SQL_VARCHAR=12, 20, 0, SQL_NULLABLE=1 2, b, 1, SQL_CHAR=1, 10, 0, SQL_NULLABLE=1 3, c, 1, SQL_INTEGER=4, 10, 0, SQL_NULLABLE=1 4, ?column?, 8, SQL_VARCHAR=12, 255, 0, SQL_NULLABLE=1 5, bpchar, 6, SQL_CHAR=1, 3, 0, SQL_NULLABLE=1 6, varchar, 7, SQL_VARCHAR=12, 255, 0, SQL_NULLABLE=1 From psqlodbc.h #define MAX_VARCHAR_SIZE255 /* default maximum size of * varchar fields (not including null term) */ So I guess the bottom line is that we are not the first to encounter this problem .. Its just been covered up by assigning An arbitrary maximum size .. So I guess we will do the same and make it configurable like the official postgres driver. Thanks lm -Original Message- From: Martijn van Oosterhout [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 10:43 AM To: Larry McGhaw Cc: Andrew Dunstan; Hannu Krosing; Tom Lane; Alvaro Herrera; Dann Corbit; Gregory Stark; pgsql-hackers@postgresql.org Subject: Re: [HACKERS] Selecting a constant question Hi, Nobody is tring to attack anyone, but we're all surprised this is an issue since you're the first person to have mentioned it. I have some a query to test below: On Tue, Jun 12, 2007 at 10:21:09AM -0700, Larry McGhaw wrote: We noticed inexplicably that when we used a constant with a postgres query, our records per second dropped From 60,000 records per second to 600 records per second, so we started digging into the issue. We discovered that libpq was not describing the metadata properly for the constant column, and it appears That the 3rd party grid control was relying on that metadata somehow .. The bottom line is that there was A huge performance drag. What I don't understand is *why* it's complaining about the constant column and not, for example, any other variable length column. There are a very small number of cases where a useful length is returned, 99% of the time it doesn't, yet you're obviously not get any performance problems there. Just a quick test, does the problem go away if you do: SELECT '1'::varchar FROM table; If that fixes it then the bug is (probably) that the middleware thinks that a length of -2 means it's 65534 bytes long. Note, in the test query I gave, it will return -1 for the length. I don't want to blame the middleware, but I want to make sure we're diagnosing the problem correctly. If that query has the same problem, then we really need to think of something else. Have a nice day, -- Martijn van Oosterhout [EMAIL PROTECTED] http://svana.org/kleptog/ From each according to his ability. To each according to his ability to litigate. ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
[HACKERS] Selecting a constant question: A summary
First a comment: At CONNX Solutions Inc., we believe sincerely that we should do whatever is necessary to make our customers prosper. This means creation of excellent tools and being responsive to customer needs. Secondly, we believe that we should treat the customers the way that we want to be treated. I think that the PostgreSQL group has managed the first objective, but not the second. Of course, that is only an opinion, but I think that success hinges on both factors. Our objective in this issue has also been to improve PostgreSQL so that it can become more useful to the end users and not to denigrate the work of the engineers that have toiled on it. I will also admit that frustration has caused our tone to become sharp at times. This is clearly a mistake on our part and for this, I apologize. Next, the problem: According to SQL/CLI and ODBC 3.5, we should bind the length of a character column. Here are some references from the relevant documentation (SQL/CLI and ODBC are clones of one another): == ANSI/ISO/IEC 9075-3-1999 for Information Technology Database Language SQL Part 3: Call-Level Interface (SQL/CLI) Section 6.5 BindCol Along with function SQLBindCol from the ODBC specification http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odbc/ht m/odbcsqlbindcol.asp This bit should be sufficient to explain what we are after: BufferLength [Input] Length of the *TargetValuePtr buffer in bytes. The driver uses BufferLength to avoid writing past the end of the *TargetValuePtr buffer when returning variable-length data, such as character or binary data. Note that the driver counts the null-termination character when returning character data to *TargetValuePtr. *TargetValuePtr must therefore contain space for the null-termination character or the driver will truncate the data. When the driver returns fixed-length data, such as an integer or a date structure, the driver ignores BufferLength and assumes the buffer is large enough to hold the data. It is therefore important for the application to allocate a large enough buffer for fixed-length data or the driver will write past the end of the buffer. SQLBindCol returns SQLSTATE HY090 (Invalid string or buffer length) when BufferLength is less than 0 but not when BufferLength is 0. However, if TargetType specifies a character type, an application should not set BufferLength to 0, because ISO CLI-compliant drivers return SQLSTATE HY090 (Invalid string or buffer length) in that case. == Now, there are times when (according to the spec) we have to defer binding. However, this causes great problems for end user tools and should only be done in what is basically a dire emergency. In the case of a SELECT query that selects a fixed constant of any sort, it would be a definite improvement for PostgreSQL to give some sort of upper maximum. For example: SELECT Eastern Division, sum(Inventory_level), sum(Inventory_backorder), Manager_last_name FROM table_name WHERE division_id = 9 GROUP BY Manager_last_name Will return 3 columns of data. The first column is of unknown length. Imagine if you are a spreadsheet in OpenOffice: http://www.openoffice.org/ which happens to support ODBC connections. You would like to fill out a report for the president of your company. Unfortunately, the first column is of unknown length That makes it a bit difficult to format this spreadsheet. Now, I will admit that we may not know a-priori if Eastern Division is character or Unicode or MBCS. But in the worst case scenario it will be (16 + 1) * element_width bytes in length. For some Unicode character sets, element_width can be as much as 4, so that leaves 68 octets as an upper possible maximum. Now, you might protest, 68 bytes might be much too large. That is true, but I know that if I allocate 68 bytes we will not have data truncation. It is no worse than a varchar(255) field that has a largest item 15 characters wide in it. The grid will successfully bind and we will be able to produce the report. Generally speaking, grids are smart enough to automatically resize themselves to max_length(grid_column_title, grid_column_data) and so the report will look very nice. It is also true that it is possible for us to work around the problem. We certainly can know the exact type information about the constants in our queries and reformat the PostgreSQL queries to decorate them with things like: SELECT Eastern Division::char(16), sum(Inventory_level)::Numeric(16,4), sum(Inventory_backorder) ::Numeric(16,4), Manager_last_name FROM table_name WHERE division_id = 9 GROUP BY Manager_last_name But it would be very nice if the database could provide a good estimate for us so that PostgreSQL could work like all of the other database systems. Code full of
Re: [HACKERS] Selecting a constant question
-Original Message- From: Larry McGhaw Sent: Tuesday, June 12, 2007 1:40 PM To: Martijn van Oosterhout Cc: Andrew Dunstan; Hannu Krosing; Tom Lane; Alvaro Herrera; Dann Corbit; Gregory Stark; pgsql-hackers@postgresql.org Subject: RE: [HACKERS] Selecting a constant question For what its worth .. Your statement about why we are the first people to mention this problem really got me thinking. Anyone who would attempt to write an ODBC driver for Postgres would run into the exact same issue. So I installed the official Postgres ODBC driver, and ran the identical query and here are my results: I probably should have looked at this first There is a whole Postgres ODBC dialog dedicated to the very subject of this thread: Handling of unknown data sizes. The pgodbc driver is configured to treat unknowns as varchar(255) by default, As shown by my example below. This can be configured up or down as desired. SQLExecDirect: In: hstmt = 0x003C18E0, szSqlStr = Select a,b,c, '123' , '123'::char(3), '123'::varchar(3) from..., cbSqlStr = -3 Return: SQL_SUCCESS=0 Describe Column All: icol, szColName, *pcbColName, *pfSqlType, *pcbColDef, *pibScale, *pfNullable 1, a, 1, SQL_VARCHAR=12, 20, 0, SQL_NULLABLE=1 2, b, 1, SQL_CHAR=1, 10, 0, SQL_NULLABLE=1 3, c, 1, SQL_INTEGER=4, 10, 0, SQL_NULLABLE=1 4, ?column?, 8, SQL_VARCHAR=12, 255, 0, SQL_NULLABLE=1 5, bpchar, 6, SQL_CHAR=1, 3, 0, SQL_NULLABLE=1 6, varchar, 7, SQL_VARCHAR=12, 255, 0, SQL_NULLABLE=1 From psqlodbc.h #define MAX_VARCHAR_SIZE 255 /* default maximum size of * varchar fields (not including null term) */ So I guess the bottom line is that we are not the first to encounter this problem .. Its just been covered up by assigning An arbitrary maximum size .. So I guess we will do the same and make it configurable like the official postgres driver. Of course, the downside here is that choosing a default will truncate the data when the actual data is larger than the default chosen. ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question: A summary
Dann Corbit wrote: First a comment: At CONNX Solutions Inc., we believe sincerely that we should do whatever is necessary to make our customers prosper. This means creation of excellent tools and being responsive to customer needs. Secondly, we believe that we should treat the customers the way that we want to be treated. I think that the PostgreSQL group has managed the first objective, but not the second. Of course, that is only an opinion, but I think that success hinges on both factors. Our objective in this issue has also been to improve PostgreSQL so that it can become more useful to the end users and not to denigrate the work of the engineers that have toiled on it. I will also admit that frustration has caused our tone to become sharp at times. This is clearly a mistake on our part and for this, I apologize. Woah, now this is interesting. This morning, I read this whole thread, wondering what in the world could possibly be taking so long ;). I will admit that many of us in the community tend to try to provide a solution without actually understanding the problem. I think it kind of comes with the territory, a lot of times it seems like FOSS is all about the work around versus the solution because the solution takes longer. Perception is a powerful thing. Personally, I didn't see any of the community doing anything but trying their best to help you with the problem you were experiencing. What I did see, is a lot of tenseness from your side, to what basically amounts to free support. Remember that we are here, at no cost to you. Lastly, the PostgreSQL community doesn't have customer. You have customer, CMD has customers, the PostgreSQL community does not. The best correlation I can give you is this. We (the community) are all a team. You are part of that team. We are not your vendor. Sincerely, Joshua D. Drake -- === The PostgreSQL Company: Command Prompt, Inc. === Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240 Providing the most comprehensive PostgreSQL solutions since 1997 http://www.commandprompt.com/ Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate PostgreSQL Replication: http://www.commandprompt.com/products/ ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question: A summary
Dan, Secondly, we believe that we should treat the customers the way that we want to be treated. I think that the PostgreSQL group has managed the first objective, but not the second. I just read this whole thread, and I feel that the sort of comment above is completely unjustified, and counterproductive to your goal of adding a feature to PostgreSQL which will make your driver work better. You'll be a lot more likely to persuade people in the community to work with you if you're not trying to convince them to change the project culture at the same time. You are on the developer mailing list for an open, community-based open source project and *not* a commercial company. Therefore we do not have customers and your paradigm is wrong. The PostgreSQL developers *are* treating you exactly has they expect to be treated; as a developer, meaning that you argue things out and defend your desire for a change. If you read anybody else's discussion on this list you'll see that's how everyone else interacts. If anything you've gotten more than your fair share of attention ... 40+ posts from 1/2 dozen senior developers in less than 48 hours! If you would prefer a more formal customer-vendor relationship, then I suggest that you sign up as a customer of EnterpriseDB, Red Hat, Sun, Command Prompt, SRA etc. or similar. Now, that aside: According to SQL/CLI and ODBC 3.5, we should bind the length of a character column. This is a much better approach. Standards are always nice. But it would be very nice if the database could provide a good estimate for us so that PostgreSQL could work like all of the other database systems. Code full of kludges is harder to maintain. Do you have any information about how binding works in other databases? A clear roadmap would make it easier for eventual developer implementation, and obviously this is a solved problem elsewhere. And so I hope that we can get off on a better foot this time. If the answer is No, the priority for this sort of thing is low, and we do not consider it important for our customers. Again, we don't have customers. So your desire to implement a change in behavior is dependant on: 1. Getting this list to agree on the specification; 2. Convincing an *individual* PostgreSQL developer or contributing company that this issue is in their high priority interest to fix, OR Fixing it yourself and submitting the patch to PostgreSQL.org. Then we will have to work around it. Hopefully, at least, it will get put into a queue of future enhancements. Getting it on the TODO list is a good first step. However, that doesn't get it implemented until it becomes some other developer's problem as well. -- Josh Berkus PostgreSQL @ Sun San Francisco ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [pgsql-www] [HACKERS] Avoiding legal email signatures
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 6/12/07, Tom Lane wrote: A more serious objection is that any automated tool would probably get it wrong sometimes, and strip important text. I vote 'lets not bother' Right. I agree with Josh's idea about mentioning list policies in the subscription confirmation message, though. Why? If the legal mumbo-jumbo has already got some precedence as being un-enforcable (even if it's only in a handful of jurisdictions), why give it even a patina of credibility by addressing it in a policy? Saying that it's not applicable here implies that is is applicable elsewhere. To quote Ghandi first they laugh at you, then they ignore you, then they fight you, then you win. I say we stick with the laughing. To that end, I propose should have a policy about being pelted with scathing sarcasm when the signal to boilerplate ratio drops below 10:1. Andrew -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (Darwin) iD8DBQFGbxln+zlEYLc6JJgRAuaNAJsECSRrgIqR1f5c15P7OszVa34lVgCghWSb io55WHyChKGQVHCQ9R+z2ec= =KNyQ -END PGP SIGNATURE- ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] Selecting a constant question: A summary
Dann Corbit [EMAIL PROTECTED] writes: In the case of a SELECT query that selects a fixed constant of any sort, it would be a definite improvement for PostgreSQL to give some sort of upper maximum. What's the point? You keep reminding us that your code is middleware that can't assume anything much about the queries you're dealing with. Therefore, I see no real value in fixing up one corner case. Your argument about space allocation falls to the ground unless we can provide a guaranteed, and usefully tight, upper bound on the column width in *every* situation. If we cannot (which we can't), you're still going to need those client-side kluges. In my opinion, variable-length data is a fact of life and you should endeavor to make your code deal with it gracefully. There are bits of the SQL spec that assume fixed-width data specifications are useful, but to be blunt that's all a holdover from 1960s 80-column-punch-card thinking. It's no way to design a modern application. BTW, the reason I'm resistant to even thinking about this is that Postgres is designed as an extensible system. Trying to do what you want is not a matter of fixing literal constants and concatenation and one or two other places --- it's a matter of imposing a new and potentially hard-to-meet requirement on every datatype under the sun, including a lot of user-written code that we don't control and would break by adding such a requirement. So it's not even likely that we'd think very hard about making this work, let alone actually do it. regards, tom lane ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [pgsql-www] [HACKERS] Avoiding legal email signatures
Andrew Hammond wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 6/12/07, Tom Lane wrote: A more serious objection is that any automated tool would probably get it wrong sometimes, and strip important text. I vote 'lets not bother' Right. I agree with Josh's idea about mentioning list policies in the subscription confirmation message, though. Why? If the legal mumbo-jumbo has already got some precedence as being un-enforcable (even if it's only in a handful of jurisdictions), why give it even a patina of credibility by addressing it in a policy? We are addressing the whole using postgresql.org mailing lists issue. The legality issue is only part of it. It is always a good idea to document against stuff like this, just in case. Joshua D. Drake Saying that it's not applicable here implies that is is applicable elsewhere. To quote Ghandi first they laugh at you, then they ignore you, then they fight you, then you win. I say we stick with the laughing. To that end, I propose should have a policy about being pelted with scathing sarcasm when the signal to boilerplate ratio drops below 10:1. Andrew -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (Darwin) iD8DBQFGbxln+zlEYLc6JJgRAuaNAJsECSRrgIqR1f5c15P7OszVa34lVgCghWSb io55WHyChKGQVHCQ9R+z2ec= =KNyQ -END PGP SIGNATURE- ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org -- === The PostgreSQL Company: Command Prompt, Inc. === Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240 Providing the most comprehensive PostgreSQL solutions since 1997 http://www.commandprompt.com/ Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate PostgreSQL Replication: http://www.commandprompt.com/products/ ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] one click install?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 6/12/07, Andrej Ricnik-Bay wrote: On 6/13/07, Andrew Hammond wrote: The problem here is that there aren't really very many defined defaults, or that these defaults vary (sometimes greatly) between the different flavors of UNIX. For example, please tell me: 1) Where should PGDATA default to? 2) How do you want to handle logging output from the postmaster? There are plenty of options... 3) Where should those log files get written? 4) For 1 and 3, will that support multiple major versions of PostgreSQL? (ie, can I have 8.2.latest and 8.1.latest installed at the same time) 5) How about multiple postmasters (on different ports)? Exactly :} ... all very good points... and then there's still the ownerships of processes and directories/files, and their perms. And integration with the init-scripts. And how e.g. the environment variables for users should be handled. I think that the community would be well served by standardizing on these things, at least for basic installations. But whose decision should that be? The postgres' developers? I think that the defaults that the configure script suggests are quite sane, and happily use them in my Slackware installations. They're reasonable for a system which only wants a single version of the binaries installed at any given time. Generally I want to have at least two binaries on a production server at any given time: the one I'm running and either the one I'm upgrading to or the one I just upgraded from. Adding slony into the mix makes things even more complicated along those lines. Linux File system Hierarchy standards? Which major distro(s)? And what about the BSDs (or the commercial Unices supported)? I think a cage match would be a good way to settle this, and we could use money collected by selling the even to pay-per-view to fund development of Optimizer Hints. Seriously though, just having some suggestions about where these things belong in the docs wouldn't hurt and might actually lead to some convergence. And while at it: who would define what a basic installation is? :) I'd be willing to take a stab at that one (since it's pretty easy). A basic installation is any install where the person or software doing the install doesn't care about anything more than getting postgres running (NB: no mention of version numbers, performance requirements, or... well... anything a serious use would care about). Andrew -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (Darwin) iD8DBQFGbxz3+zlEYLc6JJgRAnEQAJ9o24X5zzn6CK05G3DpBF2j5ckQiwCginrc SjIbaI5I80rzWpicvtQR4Yo= =R4hG -END PGP SIGNATURE- ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Selecting a constant question: A summary
As Dann pointed out we were one of the first companies to port Postgres to windows many many years ago (7.1 days), and part of that porting work is in the current postgresql product. As I pointed out in a prior post, for the ODBC specification at least (probably others), a maximum upper bound on returned data *must* be reported and determined ahead of time when using binding ... A technique where the client application allocates memory for the data and supplies a pointer to that memory location for the driver. Postgres unlike other databases shifts the burden of determining this maximum size to the client and/or driver. Our company specializes in access to wide variety of databases, both relational and non relational, including SQL Server, Oracle, DB2, Sybase, Informix, etc. Postgres sticks out as the only database that we have encountered with this behavior .. Which is why we posted the original message. Also as Dann pointed out even if this issue was addressed, it does not help us because every existing installation of Postgres has the metadata bug, so we *have* to bandaid it at the client/driver level anyway. At least we have a record of the issue, so the next time a developer in the community runs across the same oddity hopefully they will find this and won't be scratching their heads like we were for a bit :) Thanks lm -Original Message- From: Tom Lane [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 12, 2007 3:11 PM To: Dann Corbit Cc: pgsql-hackers@postgresql.org; Larry McGhaw Subject: Re: [HACKERS] Selecting a constant question: A summary Dann Corbit [EMAIL PROTECTED] writes: In the case of a SELECT query that selects a fixed constant of any sort, it would be a definite improvement for PostgreSQL to give some sort of upper maximum. What's the point? You keep reminding us that your code is middleware that can't assume anything much about the queries you're dealing with. Therefore, I see no real value in fixing up one corner case. Your argument about space allocation falls to the ground unless we can provide a guaranteed, and usefully tight, upper bound on the column width in *every* situation. If we cannot (which we can't), you're still going to need those client-side kluges. In my opinion, variable-length data is a fact of life and you should endeavor to make your code deal with it gracefully. There are bits of the SQL spec that assume fixed-width data specifications are useful, but to be blunt that's all a holdover from 1960s 80-column-punch-card thinking. It's no way to design a modern application. BTW, the reason I'm resistant to even thinking about this is that Postgres is designed as an extensible system. Trying to do what you want is not a matter of fixing literal constants and concatenation and one or two other places --- it's a matter of imposing a new and potentially hard-to-meet requirement on every datatype under the sun, including a lot of user-written code that we don't control and would break by adding such a requirement. So it's not even likely that we'd think very hard about making this work, let alone actually do it. regards, tom lane ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [pgsql-www] [HACKERS] Avoiding legal email signatures
Joshua D. Drake [EMAIL PROTECTED] writes: Andrew Hammond wrote: Why? If the legal mumbo-jumbo has already got some precedence as being un-enforcable (even if it's only in a handful of jurisdictions), why give it even a patina of credibility by addressing it in a policy? It is always a good idea to document against stuff like this, just in case. If push came to shove, which I sure hope it never does, being able to say you agreed to these terms of use of the mailing lists would be an excellent defense. They'd have to argue that's not binding because we didn't legally agree, whereupon we could reply sure, and your disclaimer is equally not binding because we didn't agree to it. Whereupon they slink away quietly. Without such a reply they might manage to get a court to listen for awhile before throwing them out. If there's anything I've learned about matters legalistic, it's that it's always better to have more than one line of defense. regards, tom lane ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [HACKERS] Selecting a constant question: A summary
On 6/12/07, Josh Berkus [EMAIL PROTECTED] wrote: Tom, What's the point? You keep reminding us that your code is middleware that can't assume anything much about the queries you're dealing with. Therefore, I see no real value in fixing up one corner case. Your argument about space allocation falls to the ground unless we can provide a guaranteed, and usefully tight, upper bound on the column width in *every* situation. If we cannot (which we can't), you're still going to need those client-side kluges. Hmmm? I thought that Dann was just talking about constants, and not column results. Am I confused? BTW, the reason I'm resistant to even thinking about this is that Postgres is designed as an extensible system. Trying to do what you want is not a matter of fixing literal constants and concatenation and one or two other places --- it's a matter of imposing a new and potentially hard-to-meet requirement on every datatype under the sun, including a lot of user-written code that we don't control and would break by adding such a requirement. So it's not even likely that we'd think very hard about making this work, let alone actually do it. I'd think it would be possible to do this in an abstract way ... having a DisplayLength() call for each data type and value. That would require casting the constant, though, or computing all uncast constants as text. The simplest formulation of this problem appears to be that constant strings that are uncast are treated as type unknown. The connx guys seem to think that they should be implicitly cast to char(n) where n is the length of the string. Is that a reasonable description, or are you guys looking for something more general? If you're just talking about the strings, then here are the thoughts I've gleaned from the preceding thread. - This makes possible some performance tweaks for drivers - It achieves spec compliance (albeit for a stupid part of the spec) - Implicit casting of unknown to char(n) or anything else seems rather sketchy to me, but I can't see any specific objection, except that... - I don't know when the right time to do the cast is. And doing it too early seems obviously wrong. - This only helps in corner case of string constants that are 1. not already cast and 2. not manipulated in any way And that seems like a very small corner case with little or no practical use. I guess if you have some code that turns query output into some flavor of pretty-print, it'd make sense to have a constant column as output of a CASE statement or something. - The corner case must already be correctly handled by the general case for arbitrary sized text, or alternatively phrased: there is no way to conform to the standard while supporting arbitrary sized text. Unless you're willing to pay the cost of scanning twice, or maintaining biggest entry data for each variable length column. - I don't know how much effort it would require to implement this, nor how much complexity it would add to the code base. Clearly both of these would be non-zero values. Given the above, I agree with Tom: this seems like corner case where the returns are marginal at best, compared to the cost to implement and maintain. Is there something I'm getting wrong in this summary? Andrew ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question: A summary
Josh Berkus [EMAIL PROTECTED] writes: What's the point? You keep reminding us that your code is middleware that can't assume anything much about the queries you're dealing with. Hmmm? I thought that Dann was just talking about constants, and not column results. Am I confused? Well, the specific example he was on about was a constant, but I don't think it does him any good for us to fix just that one case. He'll still have to deal with columns of indeterminate width in a whole lot of other cases. If there were a reasonable path for us to report a useful width bound in *every* case, then I could see spending time on it ... but there's not. BTW, it would certainly be trivial to extend libpq to report the actual max width of a column within an already-retrieved PGresult. This isn't anything the client code can't compute for itself, of course, but libpq could get it in somewhat fewer cycles. However, I'm under the impression that Dann wants the number at statement prepare time, and we simply haven't got the information then. I'd think it would be possible to do this in an abstract way ... having a DisplayLength() call for each data type and value. That would require casting the constant, though, or computing all uncast constants as text. No, the point is about predicting the max width of a column of a query result in advance of actually running the query. After you've got the values in hand, it's not a very interesting problem. Before, well, consider these examples: select repeat(text_col, int_col) from my_table; select repeat(text_col, int_col * random()) from my_table; select repeat(text_col, some_user_defined_function(int_col)) from my_table; The problem's really not soluble unless you want to dumb Postgres down to approximately the capabilities of SQL89 -- no user-defined functions, let alone user-defined types, plus pull out a whole lot of the built-in functions that don't have readily predictable result widths. regards, tom lane ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] Selecting a constant question: A summary
Andrew Hammond [EMAIL PROTECTED] writes: - Implicit casting of unknown to char(n) or anything else seems rather sketchy to me, but I can't see any specific objection, except that... - I don't know when the right time to do the cast is. And doing it too early seems obviously wrong. Well, I don't see any reason that we'd consider an implicit cast to char(N) without context to drive us in that direction. The system is currently biased to prefer casts to text. You could make a reasonable case for forcing a cast to text if the constant's type is still unresolved at the end of parsing, and indeed people have proposed that off and on just so that clients would have one less type to think about. In itself it doesn't do anything for Dann's problem though, because unspecified width is unspecified width. I've been thinking lately about trying harder to unify the text and varchar types; I'm not sure about details yet, except that text should be *exactly* the same thing as unconstrained-width varchar, rather than almost the same except we claim it's a different type. The reason I'd been thinking about this was mainly to get rid of the complexity and runtime overhead that comes from having RelabelType nodes all over the place when someone uses varchar instead of text. But if we did that, we could also arrange that unknown literals coerce to varchar(N) with N equal to their actual width, rather than coercing to text, and not create any weird corner-case behaviors in the type system. But at the end of the day this all would only solve Dann's problem for the specific case of a SELECT with an undecorated literal constant in its target list. He's still going to have to deal with unknown-width columns in an enormous variety of cases, and so I completely fail to see the point of changing the system's behavior for this one case. regards, tom lane ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Selecting a constant question
Ühel kenal päeval, T, 2007-06-12 kell 13:40, kirjutas Larry McGhaw: For what its worth .. Your statement about why we are the first people to mention this problem really got me thinking. Anyone who would attempt to write an ODBC driver for Postgres would run into the exact same issue. So I installed the official Postgres ODBC driver, and ran the identical query and here are my results: I probably should have looked at this first There is a whole Postgres ODBC dialog dedicated to the very subject of this thread: Handling of unknown data sizes. The pgodbc driver is configured to treat unknowns as varchar(255) by default, As shown by my example below. This can be configured up or down as desired. BTW, what is the reason you are writing your own ODBC driver ? What problems in the official one are you trying to solve ? -- Hannu ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question: A summary
Just a curiosity question: Why is the type of a literal '1' unknown instead of varchar(1)? Wouldn't varchar(1) cast properly to any use of the literal '1'? What is the benefit of assuming it's an unknown? ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Selecting a constant question: A summary
Chuck McDevitt [EMAIL PROTECTED] writes: Just a curiosity question: Why is the type of a literal '1' unknown instead of varchar(1)? Because, for instance, it might be intended as an integer or float or numeric value. Change the content a little, like '(1,2)' or '12:34', and maybe it's a point or time value. There are plenty of contexts in which the intended type of a literal is obviously not text/varchar. We assign unknown initially as a way of flagging that the type assignment is uncertain. Once we have a value that we think is varchar (a table column for instance), the rules for deciding to cast it to a different type get a lot more stringent. regards, tom lane ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Selecting a constant question
Hannu Krosing wrote: Ühel kenal päeval, T, 2007-06-12 kell 13:40, kirjutas Larry McGhaw: For what its worth .. Your statement about why we are the first people to mention this problem really got me thinking. Anyone who would attempt to write an ODBC driver for Postgres would run into the exact same issue. So I installed the official Postgres ODBC driver, and ran the identical query and here are my results: I probably should have looked at this first There is a whole Postgres ODBC dialog dedicated to the very subject of this thread: Handling of unknown data sizes. The pgodbc driver is configured to treat unknowns as varchar(255) by default, As shown by my example below. This can be configured up or down as desired. BTW, what is the reason you are writing your own ODBC driver ? They aren't I don't think. I think they are using the ODBC driver as an example. Joshua D. Drake What problems in the official one are you trying to solve ? -- Hannu ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq -- === The PostgreSQL Company: Command Prompt, Inc. === Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240 Providing the most comprehensive PostgreSQL solutions since 1997 http://www.commandprompt.com/ Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate PostgreSQL Replication: http://www.commandprompt.com/products/ ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
