Search Postgresql Archives

Re: Partial Index Too Literal?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



use this

explain analyze select * from result where active = 't';

--- On Thu, 6/26/08, Phillip Mills <pmills@xxxxxxxxxxxxx> wrote:
From: Phillip Mills <pmills@xxxxxxxxxxxxx>
Subject: [GENERAL] Partial Index Too Literal?
To: pgsql-general@xxxxxxxxxxxxxx
Date: Thursday, June 26, 2008, 7:24 PM

Under somewhat unusual circumstances, rows in one of our tables have an 'active' flag with a true value.  We check for these relatively often since they represent cases that need special handling.  We've found through testing that having a partial index on that field works well.  What seems odd to me, however, is that the index gets used only if the query is a textual match for how the index was specified.

That is, using an index defined as 'where active = true':
dev=# explain analyze select * from result where active = true;
                                                             QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on result (cost=5.31..472.34 rows=4206 width=1126) (actual time=7.868..7.868 rows=0 loops=1)
   Filter: active
   ->  Bitmap Index Scan on result_active_idx  (cost=0.00..4.26 rows=2103 width=0) (actual time=4.138..4.138 rows=16625 loops=1)
         Index Cond: (active = true)
 Total runtime: 7.918 ms
(5 rows)

dev=# explain analyze select * from result where active is true;
                                                  QUERY PLAN
--------------------------------------------------------------------------------------------------------------
 Seq Scan on result (cost=0.00..537.26 rows=4263 width=1126) (actual time=55.631..55.631 rows=0 loops=1)
   Filter: (active IS TRUE)
 Total runtime: 55.668 ms
(3 rows)

This is version 8.2.6.  Is there something I'm missing that could make these queries ever produce different results?



[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Postgresql Jobs]     [Postgresql Admin]     [Postgresql Performance]     [Linux Clusters]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Postgresql & PHP]     [Yosemite]
  Powered by Linux