Re: [PERFORM] Query planner is using wrong index.
--- Tom Lane <[EMAIL PROTECTED]> wrote: > Brian Herlihy <[EMAIL PROTECTED]> writes: > > My options seem to be > > - Fudge the analysis results so that the selectivity estimate changes. I > > have tested reducing n_distinct, but this doesn't seem to help. > > - Combine the columns into one column, allowing postgres to calculate the > > combined selectivity. > > - Drop the (p2, p3) index. But I need this for other queries. > > Have you considered reordering the pkey to be (p2,p3,p1) and then > dropping the (p2,p3) index? > > regards, tom lane Hi Tom, I've considered it. Unfortunately I need to do lookups on (p1) and (p1,p2) as well as (p1, p2, p3). The solution I've gone with is to create an index on (p2 || '/' || p3). This is unique for each p2/p3 combination, because p2 cannot contain the '/' character. I'm assuming that this index will be no slower to generate than one on (p2, p3), as concatenation is very cheap. Having the index on an expression "hides" it from the optimizer, which is then forced to use the primary key instead. It works perfectly now! There were only 2 queries in the system which need this index, so it was no problem to change them. Thankyou very much for all your time and patience! Before I go, I have a question - From discussions on the Postgresql irc channel, and from reading the TODO list on the website, I am under the impression that there are no plans to allow optimizer hints, such as "use index table_pkey". Is this really true? Such a feature would make life inestimably easier for your end-users, particularly me :) Thanks, Brian ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PERFORM] Query planner is using wrong index.
Brian Herlihy <[EMAIL PROTECTED]> writes: > My options seem to be > - Fudge the analysis results so that the selectivity estimate changes. I > have tested reducing n_distinct, but this doesn't seem to help. > - Combine the columns into one column, allowing postgres to calculate the > combined selectivity. > - Drop the (p2, p3) index. But I need this for other queries. Have you considered reordering the pkey to be (p2,p3,p1) and then dropping the (p2,p3) index? 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: [PERFORM] Query planner is using wrong index.
--- Dave Dutcher <[EMAIL PROTECTED]> wrote: > > -Original Message- > > To: pgsql-performance@postgresql.org > > Subject: Re: [PERFORM] Query planner is using wrong index. > [Snip] > > I am really surprised that I have to go through such contortions just > to > > use > > the primary key! This area of Postgres needs improvement. > > > > > Of course you mentioned that you are using 7.4.7. You might want to try > upgrading to 8.1.3. There have been a lot of improvements to the > performance since 7.4. I don't know if your specific problem was fixed, > but it's worth a try. > > Also you might want to at least upgrade to 7.4.12 for the bug fixes. Thanks for the suggestions. I've verified the same problem in 8.1.3 as well, after my initial post. It was actually in 8.1.3 that I first discovered the problem. I noticed this item in the TODO list: - Allow accurate statistics to be collected on indexes with more than one column or expression indexes, perhaps using per-index statistics This is what I need! But until that is added, I need a way to use the primary key with the current version :) Thanks, Brian ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PERFORM] Query planner is using wrong index.
> -Original Message- > From: [EMAIL PROTECTED] [mailto:pgsql-performance- > [EMAIL PROTECTED] On Behalf Of Brian Herlihy > Sent: Thursday, April 06, 2006 6:56 PM > To: pgsql-performance@postgresql.org > Subject: Re: [PERFORM] Query planner is using wrong index. [Snip] > I am really surprised that I have to go through such contortions just to > use > the primary key! This area of Postgres needs improvement. > Of course you mentioned that you are using 7.4.7. You might want to try upgrading to 8.1.3. There have been a lot of improvements to the performance since 7.4. I don't know if your specific problem was fixed, but it's worth a try. Also you might want to at least upgrade to 7.4.12 for the bug fixes. ---(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: [PERFORM] Query planner is using wrong index.
--- Ragnar <[EMAIL PROTECTED]> wrote: > On fös, 2006-04-07 at 00:01 +1000, Brian Herlihy wrote: > > Index Scan using p2_p3_idx on t (cost=0.00..6.02 rows=1 width=102) > (actual > > time=2793.247..2793.247 rows=0 loops=1) > >Index Cond: (((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = > > 'web/results?itag=&q=&kgs=&kls='::text)) > >Filter: ((p1)::text = 'a'::text) > > Total runtime: 2793.303 ms > > (4 rows) > > try to add an ORDER BY clause: > > explain analyze > select * from t > WHERE p1 = 'a' > and p2 = 'uk.altavista.com' > AND p3 = 'web/results?itag=&q=&kgs=&kls=' > ORDER BY p1,p2,p3; > > this might push the planner into using the primary key > > gnari > Thankyou very much, that works very well for select. However, I need it to work for update as well. Is there an equivalent way to force use of an index for updates? Here are the results for select: db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls=' order by p1,p2,p3; QUERY PLAN -- Index Scan using t_pkey on t (cost=0.00..6.02 rows=1 width=102) (actual time=32.519..32.519 rows=0 loops=1) Index Cond: (((p1)::text = 'a'::text) AND ((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = 'web/results?itag=&q=&kgs=&kls='::text)) Total runtime: 32.569 ms (3 rows) db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls='; QUERY PLAN --- Index Scan using p2_p3_idx on t (cost=0.00..6.02 rows=1 width=102) (actual time=2790.364..2790.364 rows=0 loops=1) Index Cond: (((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = 'web/results?itag=&q=&kgs=&kls='::text)) Filter: ((p1)::text = 'a'::text) Total runtime: 2790.420 ms (4 rows) But I cannot add an "order by" to an update. The other idea I came up with last night was to change p2_p3_idx so it indexes a value derived from p2 and p3, rather than p2 and p3 themselves. This would "hide" this index from the optimizer, forcing it to use the primary key. I am really surprised that I have to go through such contortions just to use the primary key! This area of Postgres needs improvement. Thanks, Brian ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
For a DSS type workload with PostgreSQL where you end up with single long running queries on postgresql with about 100GB, you better use something like Sun Fire V40z with those fast Ultra320 internal drives. This might be perfect low cost complete database in a box. Sun Fire T2000 is great for OLTP where you can end up with hundreds of users doing quick and small lookups and T2000 can crank simple thread executions far better than others. However when it comes to long running queries you end up using 1/32 of the power and may not live up to your expectations. For example consider your PostgreSQL talking to Apache WebServer all on T2000... You can put them in separate zones if you have different administrators for them. :-) As for PostgreSQL on Solaris, I already have the best parameters to use on Solaris based on my tests, the default odatasync hurts performance on Solaris, so does checkpoint segments, others are tweaked so that they are set for bigger databases and hence may not show much difference on performances... That said I will still be interested to see your app performance with postgreSQL on Sun Fire T2000 as there are always ways of perseverence to improve performance :-) Regards, Jignesh Juan Casero (FL FLC) wrote: Because I plan to develop a rather large (for us anyway) data warehouse with PostgreSQL. I am looking for the right hardware that can handle queries on a database that might grow to over a 100 gigabytes. Right now our decision support system based on postgresql 8.1.3 stores retail sales information for about 4 four years back *but* only as weekly summaries. I want to build the system so it can handle daily sales transactions also. You can imagine how many more records this will involve so I am looking for hardware that can give me the performance I need to make this project useable. In other words parsing and loading the daily transaction logs for our stores is likely to take huge amounts of effort. I need a machine that can complete the task in a reasonable amount of time. As people start to query the database to find sales related reports and information I need to make sure the queries will run reasonably fast for them. I have already hand optimized all of my queries on the current system. But currently I only have weekly sales summaries. Other divisions in our company have done a similar project using MS SQL Server on SMP hardware far outclassing the database server I currently use and they report heavy loads on the server with less than ideal query run times. I am sure I can do my part to optimize the queries once I start this project but there is only so much you can do. At some point you just need more powerful hardware. This is where I am at right now. Apart from that since I will only get this one chance to buy a new server for data processing I need to make sure that I buy something that can grow over time as our needs change. I don't want to buy a server only to find out later that it cannot meet our needs with future database projects. I have to balance a limited budget, room for future performance growth, and current system requirements. Trust me it isn't easy. Juan -Original Message- From: Josh Berkus [mailto:[EMAIL PROTECTED] Sent: Thursday, April 06, 2006 2:57 AM To: pgsql-performance@postgresql.org Cc: Juan Casero (FL FLC); Luke Lonergan Subject: Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3 Juan, Ok that is beginning to become clear to me. Now I need to determine if this server is worth the investment for us. Maybe it is not a speed daemon but to be honest the licensing costs of an SMP aware RDBMS is outside our budget. You still haven't explained why you want multi-threaded queries. This is sounding like keeping up with the Joneses. -- Josh Berkus Aglio Database Solutions San Francisco ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
Hi Leigh inline comments Leigh Dyer wrote: Luke Lonergan wrote: Juan, We've got a Sun Fire V40z and it's quite a nice machine -- 6x 15krpm drives, 4GB RAM, and a pair of Opteron 850s. This gives us more than enough power now for what we need, but it's nice to know that we can shoehorn a lot more RAM, and up it to eight CPU cores if needed. The newer Sun Opteron systems look nice too, but unless you're using external storage, their little 2.5" hard drives may not be ideal. Thats because Sun Fire V40z had write cache turned on while the 4200/4100 has the write cache turned off. There is a religious belief around the "write cache" on the disk in Sun :-) To really compare the performance, you have to turn on the write cache (I believe it was format -e and the cache option.. but that could have changed.. need to verify that again.. Same goes for T2000 SAS disks too.. Write cache is turned off on it so be careful before you compare benchmarks on internal drives :-) -Jignesh Thanks Leigh - Luke ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster ---(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 ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PERFORM] CURSOR OR OFFSET/LIMIT
On Apr 6, 2006, at 10:48 AM, Kaloyan Iliev wrote: If I use cursors it's better but my problem is that cursors live only in the current transaction. So when the Web Server finish I've lost the transaction and the cursor. Cursors can live outside the transaction if you declare them WITH HOLD specified. But that still may not help you in a web environment if you want to break the results into pages served on separate requests (and possibly different connections). http://www.postgresql.org/docs/8.1/interactive/sql-declare.html Is there a way to save the cursor between separe Browser request (and to give it time to live)? Sure, but you need to add a lot of connection management to do this. You would need to keep track of the cursors and make sure a subsequent request uses the right connection. John DeSoi, Ph.D. http://pgedit.com/ Power Tools for PostgreSQL ---(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: [PERFORM] Query planner is using wrong index.
On fös, 2006-04-07 at 00:01 +1000, Brian Herlihy wrote: > --- Ragnar <[EMAIL PROTECTED]> wrote: > > > On fim, 2006-04-06 at 19:27 +1000, Brian Herlihy wrote: > > > > > Yes, the primary key is far better. I gave it the ultimate test - I > > dropped > > > the (p2, p3) index. It's blindingly fast when using the PK, > > > > I have problems understanding exactly how an index on > > (p1,p2,p3) can be faster than and index on (p2,p3) for > > a query not involving p1. > db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' > AND p3 = 'web/results?itag=&q=&kgs=&kls='; this is different from what you said earlier. in your original post you showed a problem query without any reference to p1 in the WHERE clause. this confused me. > Index Scan using p2_p3_idx on t (cost=0.00..6.02 rows=1 width=102) (actual > time=2793.247..2793.247 rows=0 loops=1) >Index Cond: (((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = > 'web/results?itag=&q=&kgs=&kls='::text)) >Filter: ((p1)::text = 'a'::text) > Total runtime: 2793.303 ms > (4 rows) try to add an ORDER BY clause: explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls=' ORDER BY p1,p2,p3; this might push the planner into using the primary key gnari ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
Juan, On 4/6/06 7:01 AM, "Matthew Nuzum" <[EMAIL PROTECTED]> wrote: >> Apart from that since I will only get this one chance to >> buy a new server for data processing I need to make sure that I buy >> something that can grow over time as our needs change. I don't want to >> buy a server only to find out later that it cannot meet our needs with >> future database projects. I have to balance a limited budget, room for >> future performance growth, and current system requirements. Trust me it >> isn't easy. > > Isn't it about time we had our annual "what kind of server can I get > for $8k" thread? Based on Juan's description, here's a config that will *definitely* be the fastest possible in an $8K budget: Buy a dual opteron server with 8 x 400GB SATA II disks on a 3Ware 9550SX RAID controller with 16GB of RAM pre-installed with Centos 4.3 for $6,000 here: http://www.asacomputers.com/ Download the *free* open source Bizgres here: http://bgn.greenplum.com/ Use bitmap indexes for columns with less than 10,000 unique values, and your system will fly through 100GB. This is the fastest OSS business intelligence kit for the money, guaranteed. - Luke ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
On Apr 6, 2006, at 12:47 AM, Leigh Dyer wrote: I'm sure those little SAS drives would be great for web servers and other non-IO-intensive tasks though -- I'd love to get some X4100s in to replace our Poweredge 1750s for that. It's a smart move overall IMHO, For this purpose, bang for the buck would lead me to getting Dell 1850 with hardware RAID and U320 drives. The quick-n-dirty tests i've seen on the FreeBSD mailing list shows the disks are much faster on the 1850 than the X4100 with its SAS disks. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
On Apr 5, 2006, at 9:11 PM, Marcelo Tada wrote: What are you think about the Sun Fire X64 X4200 Server? I use the X4100 and like it a lot. I'm about to buy another. I see no advantage to the X4200 unless you want the extra internal disks. I use an external array. ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
On Apr 5, 2006, at 5:58 PM, August Zajonc wrote: Most involve some AMD Opertons, lots of spindles with a good raid controller preferred to one or two large disks and a good helping of ram. Be interesting to get some numbers on the sunfire machine. I can highly recommend the SunFire X4100, however the only dual- channel RAID card that fits in the box is the Adaptec 2230SLP. It is not quite as fast as the LSI 320-2x when running freebsd, but is sufficient for my purpose. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
[PERFORM] CURSOR OR OFFSET/LIMIT
Hi, I am working on Web Based application using Perl and Apache. I have to show to the users some query results by pages. Some time the result can be over 1000 rows (but can be more). The question is how to make this. The one way is to use OFFSET and LIMIT. That's OK but every time the whole query must be parsed and executed. If I use cursors it's better but my problem is that cursors live only in the current transaction. So when the Web Server finish I've lost the transaction and the cursor. There is some software written from my coleagues that on every server request open a transaction and cursor. Move to the requested page and show the result(After that the script finishes, so is the transaction). So my question is. Should I rewrte this by using OFFSET/LIMIT or it is better every time to create the cursor and use it to get the rows. Is there a way to save the cursor between separe Browser request (and to give it time to live)? Or After all OFFSET and LIMIT? Thanks in advance. Kaloyan Iliev ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Query planner is using wrong index.
--- Ragnar <[EMAIL PROTECTED]> wrote: > On fim, 2006-04-06 at 19:27 +1000, Brian Herlihy wrote: > > > Yes, the primary key is far better. I gave it the ultimate test - I > dropped > > the (p2, p3) index. It's blindingly fast when using the PK, > > I have problems understanding exactly how an index on > (p1,p2,p3) can be faster than and index on (p2,p3) for > a query not involving p1. > can you demonstrate this with actual EXPLAIN ANALYZES ? > something like: > EXPLAIN ANALYZE select * from t where p2 = ? and p3 = ?; > BEGIN; > DROP INDEX p2p3; > EXPLAIN ANALYZE select * from t where p2 = ? and p3 = ?; > ROLLBACK; > > maybe your p2p3 index needs REINDEX ? > Here's the output. The timings after caching are repeatable (varying only by 10% or so). Query before caching: db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls='; QUERY PLAN --- Index Scan using p2_p3_idx on t (cost=0.00..6.02 rows=1 width=102) (actual time=2793.247..2793.247 rows=0 loops=1) Index Cond: (((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = 'web/results?itag=&q=&kgs=&kls='::text)) Filter: ((p1)::text = 'a'::text) Total runtime: 2793.303 ms (4 rows) Query after caching: db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls='; QUERY PLAN --- Index Scan using p2_p3_idx on t (cost=0.00..6.02 rows=1 width=102) (actual time=0.617..0.617 rows=0 loops=1) Index Cond: (((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = 'web/results?itag=&q=&kgs=&kls='::text)) Filter: ((p1)::text = 'a'::text) Total runtime: 0.665 ms (4 rows) === At this point I did "DROP INDEX p2_p3_idx" Query after dropping index: db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls='; QUERY PLAN -- Index Scan using t_pkey on t (cost=0.00..6.02 rows=1 width=102) (actual time=95.188..95.188 rows=0 loops=1) Index Cond: (((p1)::text = 'a'::text) AND ((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = 'web/results?itag=&q=&kgs=&kls='::text)) Total runtime: 95.239 ms (3 rows) Query after dropping index, fully cached: db# explain analyze select * from t WHERE p1 = 'a' and p2 = 'uk.altavista.com' AND p3 = 'web/results?itag=&q=&kgs=&kls='; QUERY PLAN -- Index Scan using t_pkey on t (cost=0.00..6.02 rows=1 width=102) (actual time=0.030..0.030 rows=0 loops=1) Index Cond: (((p1)::text = 'a'::text) AND ((p2)::text = 'uk.altavista.com'::text) AND ((p3)::text = 'web/results?itag=&q=&kgs=&kls='::text)) Total runtime: 0.077 ms (3 rows) And one where the query planner chooses the primary key instead. Both p2 and p3 are present as Most Common Values in pg_statistics: Query before fully cached: db# explain analyze SELECT * FROM t WHERE p1 = 'b' AND p2 = 'www.google.com' AND p3 = 'search?hl=&lr=&q='; QUERY PLAN -- Index Scan using t_pkey on t (cost=0.00..6.02 rows=1 width=102) (actual time=212.092..212.100 rows=1 loops=1) Index Cond: (((p1)::text = 'b'::text) AND ((p2)::text = 'www.google.com'::text) AND ((p3)::text = 'search?hl=&lr=&q='::text)) Total runtime: 212.159 ms (3 rows) Query after fully cached: db# explain analyze SELECT * FROM t WHERE p1 = 'b' AND p2 = 'www.google.com' AND p3 = 'search?hl=&lr=&q='; QUERY PLAN --
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
On 4/6/06, Juan Casero (FL FLC) <[EMAIL PROTECTED]> wrote: > Because I plan to develop a rather large (for us anyway) data warehouse > with PostgreSQL. I am looking for the right hardware that can handle > queries on a database that might grow to over a 100 gigabytes. You need to look for a server that has fast I/O. 100 GB of data will take a long time to scan through and won't fit in RAM. > Right > now our decision support system based on postgresql 8.1.3 stores retail > sales information for about 4 four years back *but* only as weekly > summaries. I want to build the system so it can handle daily sales > transactions also. You can imagine how many more records this will > involve so I am looking for hardware that can give me the performance I > need to make this project useable. Sounds like you need to be doing a few heavy queries when you do this, not tons of small queries. That likely means you need fewer CPUs that are very fast. > In other words parsing and loading > the daily transaction logs for our stores is likely to take huge amounts > of effort. I need a machine that can complete the task in a reasonable > amount of time. See my previous comment > As people start to query the database to find sales > related reports and information I need to make sure the queries will run > reasonably fast for them. Get more than one CPU core and make sure you have a lot of drive spindles. You will definately want to be able to ensure a long running query doesn't hog your i/o system. I have a server with a single disk and when we do a long query the server load will jump from about .2 to 10 until the long query finishes. More cpus won't help this because the bottle neck is the disk. > I have already hand optimized all of my > queries on the current system. But currently I only have weekly sales > summaries. Other divisions in our company have done a similar project > using MS SQL Server on SMP hardware far outclassing the database server > I currently use and they report heavy loads on the server with less than > ideal query run times. I am sure I can do my part to optimize the > queries once I start this project but there is only so much you can do. > At some point you just need more powerful hardware. This is where I am > at right now. You say "this is where I am at right __now__" but where will you be in 9 months? Sounds like you will be i/o bound by the time you get above 10GB. > Apart from that since I will only get this one chance to > buy a new server for data processing I need to make sure that I buy > something that can grow over time as our needs change. I don't want to > buy a server only to find out later that it cannot meet our needs with > future database projects. I have to balance a limited budget, room for > future performance growth, and current system requirements. Trust me it > isn't easy. Isn't it about time we had our annual "what kind of server can I get for $8k" thread? -- Matthew Nuzum www.bearfruit.org ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PERFORM] freebsd/softupdates for data dir
On Apr 5, 2006, at 6:07 PM, Jim Nasby wrote: More importantly, it allows the system to come up and do fsck in the background. If you've got a large database that's a pretty big benefit. That's a UFS2 feature, not a soft-updates feature. ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [PERFORM] Intel C/C++ Compiler Tests (fwd)
> > On 3/22/06 5:56 AM, "Spiegelberg, Greg" <[EMAIL PROTECTED]> wrote: > > > > > Has anyone tested PostgreSQL 8.1.x compiled with Intel's Linux C/C++ > > > compiler? > > > > We used to compile 8.0 with icc and 7.x before that. We found very good > > performance gains for Intel P4 architecture processors and some gains for > > AMD Athlon. > > > > Lately, the gcc compilers have caught up with icc on pipelining > > optimizations and they generate better code for Opteron than icc, so we > > found that icc was significantly slower than gcc on Opteron and no > > different > > on P4/Xeon. > > > > Maybe things have changed in newer versions of icc, the last tests I did > > were about 1 year ago. EnterpriseDB is seeing the same thing, that gcc4 now has the same performance as icc, and is more flexible. -- Bruce Momjian http://candle.pha.pa.us + If your life is a hard drive, Christ can be your backup. + ---(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: [PERFORM] Query planner is using wrong index.
On fim, 2006-04-06 at 19:27 +1000, Brian Herlihy wrote: > --- Ragnar <[EMAIL PROTECTED]> wrote: > > > On fim, 2006-04-06 at 12:35 +1000, Brian Herlihy wrote: > > ... > > > PRIMARY KEY (p1, p2, p3) ... > > > > > > I have also created an index on (p2, p3), as some of my lookups are on > > > these only. ... > > > db=# explain select * from t where p2 = 'fairly_common' and p3 = > > > 'fairly_common'; > > please show us an actual EXPLAIN ANALYZE > > > I would like the query planner to use the primary key for all of these > > lookups. > > > > have you tested to see if it would actualy be better? > > > Yes, the primary key is far better. I gave it the ultimate test - I dropped > the (p2, p3) index. It's blindingly fast when using the PK, I have problems understanding exactly how an index on (p1,p2,p3) can be faster than and index on (p2,p3) for a query not involving p1. can you demonstrate this with actual EXPLAIN ANALYZES ? something like: EXPLAIN ANALYZE select * from t where p2 = ? and p3 = ?; BEGIN; DROP INDEX p2p3; EXPLAIN ANALYZE select * from t where p2 = ? and p3 = ?; ROLLBACK; maybe your p2p3 index needs REINDEX ? > My options seem to be > - Fudge the analysis results so that the selectivity estimate changes. I > have tested reducing n_distinct, but this doesn't seem to help. > - Combine the columns into one column, allowing postgres to calculate the > combined selectivity. > - Drop the (p2, p3) index. But I need this for other queries. > > None of these are good solutions. So I am hoping that there is a better way > to > go about this! I think we must detemine exactly what the problem is before devising complex solutions gnari ---(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: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
Because I plan to develop a rather large (for us anyway) data warehouse with PostgreSQL. I am looking for the right hardware that can handle queries on a database that might grow to over a 100 gigabytes. Right now our decision support system based on postgresql 8.1.3 stores retail sales information for about 4 four years back *but* only as weekly summaries. I want to build the system so it can handle daily sales transactions also. You can imagine how many more records this will involve so I am looking for hardware that can give me the performance I need to make this project useable. In other words parsing and loading the daily transaction logs for our stores is likely to take huge amounts of effort. I need a machine that can complete the task in a reasonable amount of time. As people start to query the database to find sales related reports and information I need to make sure the queries will run reasonably fast for them. I have already hand optimized all of my queries on the current system. But currently I only have weekly sales summaries. Other divisions in our company have done a similar project using MS SQL Server on SMP hardware far outclassing the database server I currently use and they report heavy loads on the server with less than ideal query run times. I am sure I can do my part to optimize the queries once I start this project but there is only so much you can do. At some point you just need more powerful hardware. This is where I am at right now. Apart from that since I will only get this one chance to buy a new server for data processing I need to make sure that I buy something that can grow over time as our needs change. I don't want to buy a server only to find out later that it cannot meet our needs with future database projects. I have to balance a limited budget, room for future performance growth, and current system requirements. Trust me it isn't easy. Juan -Original Message- From: Josh Berkus [mailto:[EMAIL PROTECTED] Sent: Thursday, April 06, 2006 2:57 AM To: pgsql-performance@postgresql.org Cc: Juan Casero (FL FLC); Luke Lonergan Subject: Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3 Juan, > Ok that is beginning to become clear to me. Now I need to determine > if this server is worth the investment for us. Maybe it is not a > speed daemon but to be honest the licensing costs of an SMP aware > RDBMS is outside our budget. You still haven't explained why you want multi-threaded queries. This is sounding like keeping up with the Joneses. -- Josh Berkus Aglio Database Solutions San Francisco ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [PERFORM] Query planner is using wrong index.
--- Ragnar <[EMAIL PROTECTED]> wrote: > On fim, 2006-04-06 at 12:35 +1000, Brian Herlihy wrote: > > > I have a problem with the choice of index made by the query planner. > > > > My table looks like this: > > > > CREATE TABLE t > > ( > > p1 varchar not null, > > p2 varchar not null, > > p3 varchar not null, > > i1 integer, > > i2 integer, > > i3 integer, > > i4 integer, > > i5 integer, > > d1 date, > > d2 date, > > d3 date, > > PRIMARY KEY (p1, p2, p3) > > ); > > > > I have also created an index on (p2, p3), as some of my lookups are on > these > > only. > > > All the integers and dates are data values. > > The table has around 9 million rows. > > I am using postgresl 7.4.7 > > > > I have set statistics to 1000 on the p1, p2 and p3 columns, and run vacuum > full > > analyse. However, I still see > > query plans like this: > > > ... > > db=# explain select * from t where p2 = 'fairly_common' and p3 = > > 'fairly_common'; > > > QUERY PLAN > > > --- > > Index Scan using p2p3 on t (cost=0.00..6.01 rows=1 width=102) > >Index Cond: (((p2)::text = 'fairly_common'::text) AND ((p3)::text = > > 'fairly_common'::text)) > > (3 rows) > > please show us an actual EXPLAIN ANALYZE > this will show us more. > > > I would like the query planner to use the primary key for all of these > lookups. > > How can I enforce this? > > How would that help? have you tested to see if it would > actualy be better? > > gnari > Yes, the primary key is far better. I gave it the ultimate test - I dropped the (p2, p3) index. It's blindingly fast when using the PK, which is what I expect from Postgresql :) This query is part of an import process, which has been getting increasingly slow as the table has grown. I first discovered the problem when I noticed queries which should be simple PK lookups taking up to 2.5 seconds on an idle system. I discussed this problem in the Postgres IRC channel, and it turns out to be due to an inaccurate selectivity estimate. The columns p2 and p3 are highly correlated, which is why I often get hundreds of rows even after specifying values for both these columns. However, the query optimizer assumes the columns are not correlated. It calculates the selectivity for each column seperately, then multiplies them to get the combined selectivity for specifying both p2 and p3. This results in an estimate of 1 row, which makes the (p2,p3) index look as good as the (p1,p2,p3) index. I'm aware now that there is no way to force use of a particular index in Postgres. I've also been told that there is no way to have the optimizer take into account correlation between column values. My options seem to be - Fudge the analysis results so that the selectivity estimate changes. I have tested reducing n_distinct, but this doesn't seem to help. - Combine the columns into one column, allowing postgres to calculate the combined selectivity. - Drop the (p2, p3) index. But I need this for other queries. None of these are good solutions. So I am hoping that there is a better way to go about this! Thanks, Brian ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
Hi, Juan, Juan Casero (FL FLC) wrote: > Ok that is beginning to become clear to me. Now I need to determine if > this server is worth the investment for us. Maybe it is not a speed > daemon but to be honest the licensing costs of an SMP aware RDBMS is > outside our budget. When postgresql starts does it start up a super > server process and then forks copies of itself to handle incoming > requests? It starts a super server process (Postmaster) and some background processes (background writer, stats collector). For each incoming connection, the postmaster forks a single-threaded backend process, which handles all queries and transactions on this connection, and terminates when the connection terminates. So as a thumb-rule, each connection can utilize only a single CPU. You can utilize a few more CPUs than you have simultaneous connections, due to the background processes and the OS needing CPU for I/O, but thats rather marginal. AFAIK, Bizgres MPP has extended the backend processes to be multi threaded, so a single connection can utilize several CPUs for some types of queries (large data sets, sorting/joining/hashing etc.). Btw, I presume that they might offer you a free test license, and I also presume their license fee is much lower than Oracle or DB/2. > Or do I have to specify how many server processes should be > started up? You can limit the number of server processes by setting the maximum connection limit. > I figured maybe I can take advantage of the multiple cpu's > on this system by starting up enough postgres server processes to handle > large numbers of incoming connections. I have this server available for > sixty days so I may as well explore the performance of postgresql on it. Yes, you can take advantage if you have multiple clients (e. G. a wep app, that's what the T2000 / Niagara were made for). You have a Tomcat or Jboss sitting on it, each http connection forks its own thread. Each customer has its own CPU :-) Then use a connection pool to PostgreSQL, and you're fine. The more customers, the more CPUs are utilized. But beware, if you have floating point maths, it will be very slow. All 8 CPUs / 32 Threads share a single FPU. So if you need floating point (e. G. Mapserver, PostGIS geoprocessing, Java2D chart drawing or something), T2000 is not the right thing for you. HTH, Markus -- Markus Schaber | Logical Tracking&Tracing International AG Dipl. Inf. | Software Development GIS Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org ---(end of broadcast)--- TIP 6: explain analyze is your friend
[PERFORM] Maintenance_work_mem influence on queries
Hello, I am doing some test with differents values for the parameter maintenance_work_mem in order to ameliorate the time for the creation of index and and the use of vacuum and analyse. I read in the doc that this parameter is just for create index, vacuum and analyse and foreign key . But when i test 2 queries with differents values the result are twice big : for mwm to 64 Mo the query 1 last 34 min and the query 2 41 min for mwm to 512 mo the query 1 last 17 min and the query 2 21 min So my question is in what condition the parameter maintenance_work_mem influence on the execution of queries. Thanks ,
Re: [PERFORM] Query planner is using wrong index.
On fim, 2006-04-06 at 12:35 +1000, Brian Herlihy wrote: > I have a problem with the choice of index made by the query planner. > > My table looks like this: > > CREATE TABLE t > ( > p1 varchar not null, > p2 varchar not null, > p3 varchar not null, > i1 integer, > i2 integer, > i3 integer, > i4 integer, > i5 integer, > d1 date, > d2 date, > d3 date, > PRIMARY KEY (p1, p2, p3) > ); > > I have also created an index on (p2, p3), as some of my lookups are on these > only. > All the integers and dates are data values. > The table has around 9 million rows. > I am using postgresl 7.4.7 > > I have set statistics to 1000 on the p1, p2 and p3 columns, and run vacuum > full > analyse. However, I still see > query plans like this: > ... > db=# explain select * from t where p2 = 'fairly_common' and p3 = > 'fairly_common'; > QUERY PLAN > --- > Index Scan using p2p3 on t (cost=0.00..6.01 rows=1 width=102) >Index Cond: (((p2)::text = 'fairly_common'::text) AND ((p3)::text = > 'fairly_common'::text)) > (3 rows) please show us an actual EXPLAIN ANALYZE this will show us more. > I would like the query planner to use the primary key for all of these > lookups. > How can I enforce this? How would that help? have you tested to see if it would actualy be better? gnari ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
[PERFORM] Query planner is using wrong index.
Hi, I have a problem with the choice of index made by the query planner. My table looks like this: CREATE TABLE t ( p1 varchar not null, p2 varchar not null, p3 varchar not null, i1 integer, i2 integer, i3 integer, i4 integer, i5 integer, d1 date, d2 date, d3 date, PRIMARY KEY (p1, p2, p3) ); I have also created an index on (p2, p3), as some of my lookups are on these only. All the integers and dates are data values. The table has around 9 million rows. I am using postgresl 7.4.7 I have set statistics to 1000 on the p1, p2 and p3 columns, and run vacuum full analyse. However, I still see query plans like this: db=# explain select * from t where p1 = 'something' and p2 = 'fairly_common' and p3 = 'fairly_common'; QUERY PLAN --- Index Scan using p2p3 on t (cost=0.00..6.01 rows=1 width=102) Index Cond: (((p2)::text = 'fairly_common'::text) AND ((p3)::text = 'fairly_common'::text)) Filter: ((p1)::text = 'something'::text) (3 rows) The problem appears to be this: db=# explain select * from t where p2 = 'fairly_common' and p3 = 'fairly_common'; QUERY PLAN --- Index Scan using p2p3 on t (cost=0.00..6.01 rows=1 width=102) Index Cond: (((p2)::text = 'fairly_common'::text) AND ((p3)::text = 'fairly_common'::text)) (3 rows) The query planner thinks that this will return only 1 row. In fact, these index lookups sometimes return up to 500 rows, which then must be filtered by p1. This can take 2 or 3 seconds to execute for what should be a simple primary key lookup. For VERY common values of p2 and p3, the query planner chooses the primary key, because these values are stored explicitly in the analyse results. For rare values there is no problem, because the query runs quickly. But for "fairly common" values, there is a problem. I would like the query planner to use the primary key for all of these lookups. How can I enforce this? Thanks, Brian ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
Miguel wrote: Excuse me for this off topic, but i notice that you are very excited about the sun's hardware, what os do you install on them , slowlaris?, has that os improved in some espectacular way that i should take a look again?, i used it until solaris 9 and the performance was horrible. im a happy freebsd user now (using hp and dell hardware though) I'm running Debian Sarge AMD64 on mine, and it works wonderfully. I'm not a Solaris person, and I never plan on becoming one, but Sun's Opteron hardware is quite nice. The remote management was one of the features that sold me -- full control over power, etc. and serial-over-LAN, through an SSH interface. Sun don't support Debian officially (but we don't have a software support contract anyway, so I'm not too fussed), but I'm pretty sure they support at least SLES and RHEL. Thanks Leigh ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PERFORM] bad performance on Solaris 10
Chris Mair wrote: Ok, so I did a few runs for each of the sync methods, keeping all the rest constant and got this: open_datasync 0.7 fdatasync 4.6 fsync 4.5 fsync_writethrough not supported open_sync 0.6 in arbitrary units - higher is faster. Quite impressive! Chris, Just to make sure the x4100 config is similar to your Linux system, can you verify the default setting for disk write cache and make sure they are both enabled or disabled. Here's how to check in Solaris. As root, run "format -e" -> pick a disk -> cache -> write_cache -> display Not sure how to do it on Linux though! Regards, -Robert ---(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: [PERFORM] Sun Fire T2000 and PostgreSQL 8.1.3
Mark Kirkwood wrote: The newer Sun Opteron systems look nice too, but unless you're using external storage, their little 2.5" hard drives may not be ideal. Yes - but they end-of-lifed the V20z and V40z! That's quite disappointing to hear -- our V40z isn't even six months old! We're not a big company, so external storage solutions are outside our price range, but we still wanted a nice brand-name box, and the V40z was a great deal compared to smaller boxes like the HP DL385. One big problem with the sun line in general is the tiny internal storage capacity - already too small on the V40z at 5/6 drives, now ridiculous at 4 SAS drives on the galaxy series. I'm sure those little SAS drives would be great for web servers and other non-IO-intensive tasks though -- I'd love to get some X4100s in to replace our Poweredge 1750s for that. It's a smart move overall IMHO, but it's certainly not great for database serving. Excuse me for this off topic, but i notice that you are very excited about the sun's hardware, what os do you install on them , slowlaris?, has that os improved in some espectacular way that i should take a look again?, i used it until solaris 9 and the performance was horrible. im a happy freebsd user now (using hp and dell hardware though) --- Miguel ---(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
