X-Original-To: pgsql-performance-postgresql.org@postgresql.org Received: from localhost (mx1.hub.org [200.46.208.251]) by postgresql.org (Postfix) with ESMTP id 90E8E9FB206 for ; Thu, 27 Jul 2006 16:19:43 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.208.251]) (amavisd-new, port 10024) with ESMTP id 42909-03 for ; Thu, 27 Jul 2006 16:19:38 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey- Received: from web55902.mail.re3.yahoo.com (web55902.mail.re3.yahoo.com [216.252.110.63]) by postgresql.org (Postfix) with SMTP id 966819FA5FC for ; Thu, 27 Jul 2006 16:19:06 -0300 (ADT) Received: (qmail 9613 invoked by uid 60001); 27 Jul 2006 18:55:08 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.ca; h=Message-ID:Received:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=DSpzySxpsd/y/hpCyUBadko4X5fwuf7TWvD2ITgrZRqCYFyJpUpLf/jEVaVHqMN2uh4s19LLUhTgSEhcF4hQ8Y/ZPc2VkDpelH0whxY2zNUIAKWwHyjxM2jSRiolIie09kkCLOQXKOM0ImJO/G2E66YeLUOEBbuLa8oUi+IuWJM= ; Message-ID: <20060727185507.9604.qmail@web55902.mail.re3.yahoo.com> Received: from [207.164.182.8] by web55902.mail.re3.yahoo.com via HTTP; Thu, 27 Jul 2006 14:55:06 EDT Date: Thu, 27 Jul 2006 14:55:06 -0400 (EDT) From: Ioana Danes Subject: Re: Query plan issue when upgrading to postgres 8.14 (from To: Ioana Danes Cc: pgsql-performance@postgresql.org In-Reply-To: <20060718160253.46375.qmail@web55912.mail.re3.yahoo.com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1884499080-1154026506=:99742" Content-Transfer-Encoding: 8bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.201 tagged_above=0 required=5 tests=DNS_FROM_RFC_ABUSE, HTML_MESSAGE X-Spam-Level: X-Archive-Number: 200607/247 X-Sequence-Number: 20107 --0-1884499080-1154026506=:99742 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Hi everyone, I posted this question some time ago and I did not get any answer so here I am again. Does anyone now what the problem is with the following select when upgrading to postgresql 8.1.4 the query plan does not use the indexes as in postgresql 8.0.3. Here are the results of my query for postgresql 8.0.3 and 8.1.4. For postgresql 8.1.4 there are 2 results, one for test table having the same indexes as in 8.0.3 and the second one for a new index on test table by (testtype,testid) that will speed up my query. This last index will fix my problem for this particular query. In the Test table there are 19,494,826 records and 11,090 records have testtype = 1455. The data on both servers is identical. And on both servers I run vacuum analyze prior executing this queries. As it can be seen the result in postgresql 8.1.4 is very slow and I am wondering why is that. Bug, missing configuration, ... 1. Result on Postgresql 8.0.3: ------------------------------------- # explain analyze select max(TESTID) from TEST where TESTTYPE = 1455; Aggregate (cost=391.56..391.56 rows=1 width=8) (actual time=94.707..94.711 rows=1 loops=1) -> Index Scan using ix_test_testtype on test (cost=0.00..355.18 rows=14551 width=8) (actual time=0.036..51.089 rows=11090 loops=1) Index Cond: (testtype = 1455) Total runtime: 94.778 ms (4 rows) # select max(TESTID) from TEST where TESTTYPE = 1455; max ---------- 18527829 (1 row) Time: 13.447 ms 2. Result on Postgresql 8.1.4 (with the same indexes as in 8.0.3): ------------------------------------------------------------------------------------------ Result (cost=32.78..32.79 rows=1 width=0) (actual time=1865.406..1865.408 rows=1 loops=1) InitPlan -> Limit (cost=0.00..32.78 rows=1 width=8) (actual time=1865.378..1865.381 rows=1 loops=1) -> Index Scan Backward using pk_testid on test (cost=0.00..464069.25 rows=14155 width=8) (actual time=1865.371..1865.371 rows=1 loops=1) Filter: ((testid IS NOT NULL) AND (testtype = 1455)) Total runtime: 1865.522 ms (6 rows) # select max(TESTID) from TEST where TESTTYPE = 1455; max ---------- 18527829 Time: 1858.076 ms 3. Result on Postgresql 8.1.4 (after creating an index by testtype, testid ): ----------------------------------------------------------------------------------------------------- # explain analyze select max(TESTID) from TEST where TESTTYPE = 1455; Result (cost=1.71..1.72 rows=1 width=0) (actual time=0.069..0.070 rows=1 loops=1) InitPlan -> Limit (cost=0.00..1.71 rows=1 width=8) (actual time=0.055..0.056 rows=1 loops=1) -> Index Scan Backward using ix_test2 on test (cost=0.00..24248.92 rows=14155 width=8) (actual time=0.050..0.050 rows=1 loops=1) Index Cond: (testtype = 1455) Filter: (testid IS NOT NULL) Total runtime: 0.159 ms # select max(TESTID) from TEST where TESTTYPE = 1455; max ---------- 18527829 Time: 1.029 ms Thank you in advance, Ioana --------------------------------- Be smarter than spam. See how smart SpamGuard is at giving junk email the boot with the All-new Yahoo! Mail --0-1884499080-1154026506=:99742 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Hi everyone,

I posted this question some time ago and I did not get any answer so here I am again.
Does anyone now what the problem is with the following select when upgrading to postgresql 8.1.4 the query plan does not use the indexes as in postgresql 8.0.3.

Here are the results of my query for postgresql 8.0.3 and 8.1.4. For postgresql 8.1.4 there are 2 results, one for test table having the same indexes as in 8.0.3 and the second one for a new index on test table by (testtype,testid) that will speed up my query. This last index will fix my problem for this particular query.

In the Test table there are 19,494,826 records and 11,090 records have testtype = 1455. The data on both servers is identical. And on both servers I run vacuum analyze prior executing this queries.

As it can be seen the result in postgresql 8.1.4 is very slow and I am wondering why is that. Bug, missing configuration, ...

1. Result on Postgresql 8.0.3:
-------------------------------------
# explain analyze select max(TESTID) from TEST where TESTTYPE = 1455;

 Aggregate  (cost=391.56..391.56 rows=1 width=8) (actual time=94.707..94.711 rows=1 loops=1)
   ->  Index Scan using ix_test_testtype on test  (cost=0.00..355.18 rows=14551 width=8) (actual time=0.036..51.089 rows=11090 loops=1)
         Index Cond: (testtype = 1455)
 Total runtime: 94.778 ms
(4 rows)

# select max(TESTID) from TEST where TESTTYPE = 1455;

   max
----------
 18527829
(1 row)

Time: 13.447 ms


2. Result on Postgresql 8.1.4 (with the same indexes as in 8.0.3):
------------------------------------------------------------------------------------------
 Result  (cost=32.78..32.79 rows=1 width=0) (actual time=1865.406..1865.408 rows=1 loops=1)
   InitPlan
     ->  Limit  (cost=0.00..32.78 rows=1 width=8) (actual time=1865.378..1865.381 rows=1 loops=1)
           ->  Index Scan Backward using pk_testid on test  (cost=0.00..464069.25 rows=14155 width=8) (actual time=1865.371..1865.371 rows=1 loops=1)
                 Filter: ((testid IS NOT NULL) AND (testtype = 1455))
 Total runtime: 1865.522 ms
(6 rows)

# select max(TESTID) from TEST where TESTTYPE = 1455;
 
   max
----------
 18527829

Time: 1858.076 ms


3. Result on Postgresql 8.1.4 (after creating an index by testtype, testid ):
-----------------------------------------------------------------------------------------------------
# explain analyze select max(TESTID) from TEST where TESTTYPE = 1455;
 Result  (cost=1.71..1.72 rows=1 width=0) (actual time=0.069..0.070 rows=1 loops=1)
   InitPlan
     ->  Limit  (cost=0.00..1.71 rows=1 width=8) (actual time=0.055..0.056 rows=1 loops=1)
           ->  Index Scan Backward using ix_test2 on test  (cost=0.00..24248.92 rows=14155 width=8) (actual time=0.050..0.050 rows=1 loops=1)
                 Index Cond: (testtype = 1455)
                 Filter: (testid IS NOT NULL)
 Total runtime: 0.159 ms

# select max(TESTID) from TEST where TESTTYPE = 1455;

   max
----------
 18527829

Time: 1.029 ms

Thank you in advance,
Ioana

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