On Sat, 14 Nov 2009, Tom Lane wrote:
Matthew Wakeling matt...@flymine.org writes:
[ discussion about applying materialize to a mergejoin's inner indexscan ]
I have finally gotten round to doing something about this, and applied
the attached patch to CVS HEAD. Could you test it on your
to read in all
the rows where field1 = 'my_key', so that they can be sorted, but the sort
will be completely unpredictable because all the values will be the same.
If you wanted to grab any row, then remove the ORDER BY, and it will just
return the first one it finds.
Matthew
--
The best way
fairly soon, it
is better to just VACUUM, or autovacuum. Just make sure the free space map
can cope with it.
Matthew
--
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it, causing a surprising delay at unpredictable times
(although heavier near the start of the day).
There *is* a benefit of running VACUUM ANALYSE rather than just ANALYSE.
Matthew
--
I suppose some of you have done a Continuous Maths course. Yes? Continuous
Maths? menacing stares from audience Whoah
in the
WAL, effectively writing the data twice. As Euler said, the trick is to
tell Postgres that noone else will need to see the data, so it can skip
the WAL step:
BEGIN;
TRUNCATE TABLE foo;
COPY foo FROM ...;
COMMIT;
I see upward of 100MB/s over here when I do this.
Matthew
--
Patron: I
if there are
multiple rows with the same value.
Does that answer your question?
Matthew
--
The only secure computer is one that's unplugged, locked in a safe,
and buried 20 feet under the ground in a secret location...and i'm not
even too sure about that one. --Dennis
was used, and whether it was a disc sort or
an in-memory sort. As it is only an EXPLAIN, the query hasn't actually
been run, and we have no information about whether the sort would be
performed on disc or not.
Matthew
--
Hi! You have reached 555-0129. None of us are here to answer the phone
stable release is scheduled for the new year.
If you want the latest and greatest, then you can use Debian testing.
Matthew
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the references in
the actual row. Therefore, the order of columns should not matter.
Moreover, whether a row is used in an index should not make any
difference. The index stores the values too, right? Postgres will look up
in the index, and then fetch the rows, in two separate operations.
Matthew
rows=26341274
width=4)
(4 rows)
This query plan seems to me to be a little slow. Surely it could iterate
through the ten project rows and perform ten index lookups in the big
table?
Matthew
--
Riker: Our memory pathways have become accustomed to your sensory input.
Data: I understand - I'm
On Thu, 1 Oct 2009, Greg Smith wrote:
On Thu, 1 Oct 2009, Matthew Wakeling wrote:
For comparison, with Red Hat, you will need to upgrade to a whole new
distribution whenever you want updated software, which is a much bigger
undertaking.
This is somewhat true for larger packages, but it's
On Wed, 30 Sep 2009, Robert Haas wrote:
Er, wait... if you set the 'COST' parameter for the backing function,
does that work?
Ah, right. I was looking at CREATE OPERATOR, not CREATE FUNCTION.
Thanks,
Matthew
--
Bashir: The point is, if you lie all the time, nobody will believe you, even
new
distribution whenever you want updated software, which is a much bigger
undertaking.
As far as performance goes (and someone will probably contradict me here)
all the different Linux distributions should be roughly equivalent, as
long as they are up to date and well tuned.
Matthew
is quite reasonable for
what you are asking it to do.
To fix this, I suggest creating an index on NotReceivedTransport(SId, CId,
ShipperTransportNumber). Then, the index will be able to immediately see
that there are no rows to delete.
Matthew
--
We have always been quite clear that Win95
that the
EXPLAINs are correct. Is there a way to tell Postgres that an operator has
a large CPU cost? I can tell it what the join selectivity is, but I can't
find anything about CPU cost.
Matthew
--
Unfortunately, university regulations probably prohibit me from eating
small children in front of the lecture
a query will not fit neatly into work_mem. At this
point, Postgres will write the data to temporary files on disc. It is
harder to predict what size those will be. However, EXPLAIN ANALYSE will
sometimes give you a figure of how big a sort was for example.
Matthew
--
Reality is that which
floating point values, and bioseg (available from
http://www.bioinformatics.org/bioseg/wiki/ which I am maintaining at the
moment) will index integers.
Matthew
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up later.
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beneficial.
Alternatively, if you really want to force its hand (just for testing
purposes), then try running:
SET enable_seqscan TO off;
and see what happens.
Matthew
--
When I first started working with sendmail, I was convinced that the cf
file had been created by someone bashing their head
table were
cached already. Matthew, how big is this table compared to your RAM?
Were you testing a case in which it'd be in cache?
Oh, definitely. I have run this test so many times, it's all going to be
in the cache. Luckily, that's what we are looking at as a normal situation
in production
?
Matthew
--
Surely the value of C++ is zero, but C's value is now 1?
-- map36, commenting on the No, C++ isn't equal to D. 'C' is undeclared
[...] C++ should really be called 1 response to C++ -- shouldn't it
be called D?
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that it
uses this plan.
I'm using Postgres 8.4.0
Matthew
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If you have been so devious as to get this message, you will understand
it, and you deserve no sympathy. -- Knuth, in the TeXbook
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On Tue, 18 Aug 2009, Tom Lane wrote:
Matthew Wakeling matt...@flymine.org writes:
I'm seeing some interesting behaviour. I'm executing a query where I
perform a merge join between two copies of the same table, completely
symmetrically, and the two sides of the merge are sourced differently
BY
objectid, bin) as a;
?column?
-
57.5270393085641029
So on average, we will be rewinding by 57 rows each time. A materialise
step really does sound like a win in this situation.
Matthew
--
Patron: I am looking for a globe of the earth.
Librarian: We have a table-top
than process memory in the totals.
+1 on the idea that Linux memory reporting is incomprehensible nowadays.
Matthew
--
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that really was not very big
It was going quite fine
Till it reached the fourth line
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.
Matthew
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method of computation, where's the door?, then you are in luck. There are
some there, there, and by the side there. Oxygen masks will not drop from the
ceiling... -- Computer
On Thu, 13 Aug 2009, Greg Stark wrote:
On Thu, Aug 13, 2009 at 3:16 PM, Matthew Wakelingmatt...@flymine.org wrote:
Now, I'd like to get this done this side of Christmas, so I was wondering if
there's a neat trick I can use to get it to only consider the rows from s to
e, instead of having
The location_object_bioseg index is 182 MB
Matthew
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On Wed, 5 Aug 2009, Robert Haas wrote:
On Wed, Aug 5, 2009 at 6:20 AM, Matthew Wakelingmatt...@flymine.org wrote:
It is certainly doing a sequential scan. So are you saying that it will
start a sequential scan from a different part of the table each time, even
in the absence of other
. However, certainly for index creation,
tests on servers over here have indicated that running four CREATE INDEX
statements at the time runs four times as fast, assuming the table fits in
maintenance_work_mem.
Matthew
--
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.
Having said that, memory access latency is not scaling as quickly as CPU
speed, so over time SMT is going to get more important.
Matthew
--
Take care that thou useth the proper method when thou taketh the measure of
high-voltage circuits so that thou doth not incinerate both thee and the
meter
an explicit communication channel at all (I'm simplifying
massively here). A real interconnect is only needed between CPUs and
between different cores on a CPU, and of course to the outside world.
Scott's explanation of why SMT works better now is much more likely to be
the real reason.
Matthew
the whole query to complete within a few milliseconds.
Matthew
--
And why do I do it that way? Because I wish to remain sane. Um, actually,
maybe I should just say I don't want to be any worse than I already am.
- Computer Science Lecturer
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image format, even if it is cached.
The java program uses as near an on-disc format as Postgres does - just
held in memory instead of in OS cache.
Matthew
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structure is just too general,
because it needs to cope with the situation where a particular object type
does not have a well defined order, or where the order is unuseful for
indexing.
Matthew
--
A good programmer is one who looks both ways before crossing a one-way street.
Considering
.
Matthew
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I'm considering rewriting a postgres extension (GiST index bioseg) to make
it use version 1 calling conventions rather than version 0.
Does anyone have any ideas/opinions/statistics on what the performance
difference is between the two calling conventions?
Matthew
--
Patron: I am looking
On Fri, 17 Jul 2009, Peter Eisentraut wrote:
On Friday 17 July 2009 16:40:40 Matthew Wakeling wrote:
I'm considering rewriting a postgres extension (GiST index bioseg) to make
it use version 1 calling conventions rather than version 0.
Does anyone have any ideas/opinions/statistics on what
of the EXPLAIN result. Please read the manual at
http://www.postgresql.org/docs/8.4/interactive/using-explain.html
The width is the:
* Estimated average width (in bytes) of rows output by this plan node
Matthew
--
There once was a limerick .sig
that really was not very big
It was going quite fine
what it
returns. There are so many cross joins, outer joins, and inner joins
mixed up together, ugh.
Rather than trying to puzzle out why it is slow, rewrite it. It will be
faster than before on any version.
Matthew Hartman
Programmer/Analyst
Information Management, ICP
Kingston General Hospital
by case(c.category) when 1 then 'z' when 2 then 'a' then 3 then
'b' when 4 then 'w' when 5 then 'h' end;
Matthew Hartman
Programmer/Analyst
Information Management, ICP
Kingston General Hospital
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To make changes to your
on 10 minute
boundaries, rounding up their timeslot requirement. (The single odd
timeslot appointment will always waste 1 timeslot).
Now THAT is an interesting idea. I'll have to play with this in my head
a bit (during really boring meetings) and get back to you. Thanks!
Matthew Hartman
Programmer
and http://www.intermine.org/
3. HOT has been invented since then, and it won't play well with this
method.
Matthew
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enormous amount of fun! -- Computer Science Lecturer
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. To schedule an appointment, both the chair and
nurse have to be available for the required times at the same time,
while also respecting the pod/chair and pod/nurse assignments. It's more
than incrementing/decrementing the total available time.
Thanks,
Matthew Hartman
Programmer/Analyst
Information
. Perhaps you meant java.util.concurrent.ConcurrentHashMap?
Be very careful.
Matthew
--
Now, you would have thought these coefficients would be integers, given that
we're working out integer results. Using a fraction would seem really
stupid. Well, I'm quite willing to be stupid here - in fact
: interesting) problem.
In my current template there are 17 chairs and 7 nurses. Chairs are grouped
into pods of 2-4 chairs. Nurses cover one to many pods, allowing for a primary
nurse per pod as well as floater nurses that cover multiple pods.
Matthew Hartman
Programmer/Analyst
Information Management
);
There are indexes on matrix for timeslot,unit_id, timeslot,nurse_id, and
unit_id,nurse_id.
Matthew Hartman
Programmer/Analyst
Information Management, ICP
Kingston General Hospital
(613) 549- x4294
nature of using a loop suggests that another tool might be more
appropriate.
Matthew Hartman
Programmer/Analyst
Information Management, ICP
Kingston General Hospital
(613) 549- x4294
-Original Message-
From: pgsql-performance-ow...@postgresql.org
[mailto:pgsql-performance-ow
a
nested loop. Then you're getting upset because it isn't using a nested
loop. When you tell it to NEVER use anything (switching all join
algorithms off), it ignores you and chooses the right plan anyway.
Matthew
--
You can configure Windows, but don't ask me how. -- Bill Gates
--
Sent
.x
) nurse
Where chair.id = nurse.id
With matrix having 3,280 rows. Ugh.
I have tried various indexes and clustering approachs with little
success. Any ideas?
Thanks,
Matthew Hartman
Programmer/Analyst
Information Management, ICP
Kingston General Hospital
(613) 549- x4294
on a profiling build?
...the best bet is probably to make a test build of Postgres in which
your functions are linked directly into the main postgres executable.
I'll give that a try. Oprofile scares me with the sheer number of options.
Matthew
--
Prolog doesn't have enough parentheses. -- Computer
bioseg.so
bioseg_gist_consistent
I'm guessing my next step is to install a version of libc with debugging
symbols?
Matthew
--
Some people, when confronted with a problem, think I know, I'll use regular
expressions. Now they have two problems. -- Jamie Zawinski
btree_gist.sobtree_gist.so
gbt_num_consistent
A quick grep in the postgres source for mcount reveals no hits. No idea
what it does - there is no man page for it.
Matthew
--
I pause for breath to allow you to get over your shock that I really did cover
all that in only five
On Thu, 11 Jun 2009, Matthew Wakeling wrote:
A quick grep in the postgres source for mcount reveals no hits. No idea what
it does - there is no man page for it.
Ah - that's part of gprof. I'll recompile without --enable-profiling and
try again. Duh.
Matthew
--
What goes up must come down
nvidia_drv.so(no symbols)
19321 0.7527 bioseg.sobioseg.so
bioseg_gist_decompress
17365 0.6765 libmozjs.so.1d libmozjs.so.1d (no symbols)
Matthew
--
A good programmer is one who looks both ways before crossing a one-way street
On Fri, 5 Jun 2009, Robert Haas wrote:
On Thu, Jun 4, 2009 at 12:33 PM, Matthew Wakelingmatt...@flymine.org wrote:
Do you have a recommendation for how to go about profiling Postgres, what
profiler to use, etc? I'm running on Debian Linux x86_64.
I mostly compile with --enable-profiling
. Is
there someone here who can fix the problem?
Matthew
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be inconsistently inconsistent.
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On Wed, 10 Jun 2009, Guillaume Cottenceau wrote:
Matthew Wakeling matthew 'at' flymine.org writes:
It appears that I am being censored.
Do you seriously think that censorman would kill your previous
mails, but would let a It appears that I am being censored mail
go through?
If it's
On Wed, 10 Jun 2009, Gurjeet Singh wrote:
There is a limit on the size of the mail that you can send to different mailing
lists. Please try to remove/link your
attachments if you are trying to send any.
No, size is not an issue - it's only 3kB.
Matthew
--
Q: What's the difference between
On Wed, 10 Jun 2009, Scott Mead wrote:
Are you getting a bounce message? They usually have the reason in there.
No, I am not getting any bounce message. My email just goes into a black
hole, and does not appear on the web site archives either.
Matthew
--
The only secure computer is one
multiplying rows=361427 by rows=47.
That would only give 16987069 rows.
Any ideas/explanations?
Matthew
--
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To do is to be -- Nietzsche
To be is to do -- Sartre
Do be do be do -- Sinatra
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On Wed, 10 Jun 2009, Tom Lane wrote:
...the size of the join relation was estimated long before we even
started to think about nestloop-with-inner-indexscan plans.
That makes a lot of sense.
Matthew
--
Richards' Laws of Data Security:
1. Don't buy a computer.
2. If you must buy a computer
x86_64.
Matthew
--
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Jadzia: Oh yes, that's right. What's the 34th again?
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for this particular query+dataset.
Yeah, being bound by the ORM can be annoying. What version of Postgres is
this? Recent versions can sometimes do a bitmap index scan to satisfy an
OR constraint.
Matthew
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for this particular query+dataset.
Yeah, being bound by the ORM can be annoying. What version of Postgres is
this? Recent versions can sometimes do a bitmap index scan to satisfy an
OR constraint.
Matthew
--
I work for an investment bank. I have dealt with code written by stock
exchanges. I have seen
what you mean.
Matthew
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, but there may be a few situations where the reverse is
true.
Basically, the first option will only be faster if you are doing lots of
seeking (small requests) in a single thread. As soon as you go
multi-threaded or are looking at sequential scans, you're better off with
more discs.
Matthew
each set of
identical a and sort each by b.
Matthew
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To make
the index?
Or how about this query:
SELECT * FROM table1, table2 WHERE table1.fk = table2.id ORDER BY
table1.id, table2.id
where both id columns are UNIQUE with an index. Do we eliminate
table2.id from the ORDER BY in this case?
Matthew
--
Programming today is a race between software
your search is always going to be better than munging
together results from several indexes, even if the planner decides to turn
it into a bitmap index scan (which will be more likely in PG8.4 with
effective_concurrency set).
Matthew
--
I don't want the truth. I want something I can tell
of the tree under that,
because you are not constraining for street_id. A much better index to
answer your query is (city_id, house_id, floor_id) - then it can just look
up straight away. Instead of the index returning 20 rows to check, it
will return just the 2000.
Matthew
--
An ant
simpler
backend to start up each time. If you really want to get a decent
performance out of Postgres, then use long-lived connections (which most
real-world use cases will do) and prepare your queries in advance with
parameters.
Matthew
--
import oz.wizards.Magic;
if (Magic.guessRight
a bottleneck
given very short-lived connections.
Matthew
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of 45502) causes major planning problems. Also, why does the
BitmapAnd say zero actual rows?
I understand this probably isn't Priority No. 1, and there are some
interesting corner cases when n_distinct is higher than the histogram
width, but would it be possible to fix this one up?
Matthew
--
I
'::text)
- Bitmap Index Scan on geneflankingregion__distance_equals
(cost=0.00..1185.78 rows=91134 width=0)
(actual time=16.565..16.565 rows=91004 loops=1)
Index Cond: (lower(distance) = '10.0kb'::text)
Total runtime: 199.282 ms
(6 rows)
Matthew
--
It is better
too. I can't see any reason for this is the
GiST code - it all seems pretty tight to me. We probably need to do some
profiling.
Matthew
--
I suppose some of you have done a Continuous Maths course. Yes? Continuous
Maths? menacing stares from audience Whoah, it was like
have the directory_index option enabled on your ext3
filesystem.
Matthew
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The third years are wandering about all worried at the moment because they
have to hand in their final projects. Please be sympathetic to them, say
things like ha-ha-ha, but in a sympathetic tone of voice
it's not getting too out of hand.
I think quite a few systems do set it by default now.
Matthew
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On Wed, May 06, 2009 at 10:04:33PM +0800, Craig Ringer wrote:
Can the genetic query optimizer come into play on small queries?
On Wed, 6 May 2009, Kenneth Marshall wrote:
No.
Yes. But you would have had to have set some really weird configuration.
Matthew
--
And the lexer will say Oh look
afterwards.
Matthew
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Surely the value of C++ is zero, but C's value is now 1?
-- map36, commenting on the No, C++ isn't equal to D. 'C' is undeclared
[...] C++ should really be called 1 response to C++ -- shouldn't it
be called D?
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On Tue, 21 Apr 2009, Matthew Wakeling wrote:
Unfortunately, it seems there is another bug in the picksplit function. My
patch fixes a bug that reveals this new bug. The whole picksplit algorithm is
fundamentally broken, and needs to be rewritten completely, which is what I
am doing.
I have
On Wed, 22 Apr 2009, Matthew Wakeling wrote:
I will post a patch when I have ported my bioseg code over to the seg data
type.
Here is my patch ported over to the seg contrib package, attached. Apply
it to seg.c and all should be well. A similar thing needs to be done to
cube, but I haven't
, the different branches of the tree were
unselective, so new entries would just get stuffed in anywhere, leading to
a much more balanced tree.
I shall have a proper fix to this problem later today.
Matthew
--
It's one of those irregular verbs - I have an independent mind, You are
an eccentric, He
On Fri, 17 Apr 2009, Matthew Wakeling wrote:
I have done a bit of investigation, and I think I might have found the
smoking gun I was looking for.
I have found a bug in the contrib package seg, which has been copied into
the bioseg data type as well. It causes the index to be created
On Thu, 16 Apr 2009, Tom Lane wrote:
Matthew, can you put together a self-contained test case with a similar
slowdown?
I have done a bit of investigation, and I think I might have found the
smoking gun I was looking for. I just added a load of debug to the gist
consistent function
default_text_search_config = 'pg_catalog.english'
Anything I can do to solve this?
Matthew
--
Surely the value of C++ is zero, but C's value is now 1?
-- map36, commenting on the No, C++ isn't equal to D. 'C' is undeclared
[...] C++ should really be called 1 response to C++ -- shouldn't it
be called D
trivial for Postgres to do.
Matthew
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is to throw objects... If you're going to freak out... wait until party time
and invite me along -- Computer Science Lecturer
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On Thu, 16 Apr 2009, Grzegorz Jaśkiewicz wrote:
On Thu, Apr 16, 2009 at 11:37 AM, Matthew Wakeling matt...@flymine.org wrote:
I have a query that is executed really badly by Postgres. It is a nine table
join, where two of the tables are represented in a view. If I remove one of
the tables from
then?
Matthew
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incorporated into a
query that will constrain it and cause it to be evaluated a lot quicker.
This kind of scenario kind of guarantees a bad plan as soon as the number
of tables reaches from_collapse_limit.
Matthew
--
Failure is not an option. It comes bundled with your Microsoft product
be improved in the future?
Matthew
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use if you are in a hostile security environment. We absolutely do recognize
that the Internet is a hostile environment. Paul Leach pau...@microsoft.com
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On Thu, 16 Apr 2009, Kevin Grittner wrote:
Matthew Wakeling matt...@flymine.org wrote:
I have been doing some queries that are best answered with GiST
indexes
For what definition of best answered?
Since an index is only a performance tuning feature (unless declared
UNIQUE), and should never
in these queries, which are 14 seconds and 38 minutes
respectively.
Matthew
--
Doctor: Are you okay? You appear to be injured.
Neelix: Aaah!
Doctor: It's okay, it looks superficial.
Neelix: Am I going to die?
Doctor: Not unless you are allergic to tomatoes. This appears to be a sauce
On Thu, 16 Apr 2009, Tom Lane wrote:
Matthew, can you put together a self-contained test case with a similar
slowdown?
It isn't the smoking gun I thought it would be, but:
CREATE TABLE a AS SELECT a FROM generate_series(1,100) AS a(a);
CREATE TABLE b AS SELECT b FROM generate_series
location__key_all index: 334 MB
Matthew
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in the background in another thread,
while fully honouring flush calls. When it is using the database
connection is well-defined. I hope someone can find it useful.
Matthew
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On Wed, 15 Apr 2009, Matthew Wakeling wrote:
If anyone needs this code in Java, we have a version at
http://www.intermine.org/
Download source code: http://www.intermine.org/wiki/SVNCheckout
Javadoc: http://www.intermine.org/api/
Sorry, that should be http://www.flymine.org/api/
Matthew
that this join is redundant.
Because the join isn't redundant? You're making the assumption that for
every score.game_id there is exactly one game.id that matches. Of course,
you may have a unique constraint and foreign key/trigger that ensures
this.
Matthew
--
The third years are wandering about all
issue that correlation isn't actually that
good a measure of the cost of an index scan, but I'm not sure what is
better, and feasible.
Matthew
--
Our riverbanks and seashores have a beauty all can share, provided
there's at least one boot, three treadless tyres, a half-eaten pork
pie, some oil
to help you implement a test setup
for doing that, if you'd like.
You can always do binary-format COPY.
Matthew
--
An ant doesn't have a lot of processing power available to it. I'm not trying
to be speciesist - I wouldn't want to detract you from such a wonderful
creature, but, well, there isn't
single disc in the system that takes a long time to seek from
one place to another. This assumption fails on both RAID arrays and SSDs,
so I'd be interested to see some numbers to back that one up.
Matthew
--
import oz.wizards.Magic;
if (Magic.guessRight())... -- Computer Science
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