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Re: strange query behavior

From: "Tim Jones" <TJones(at)optio(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: strange query behavior
Date: 2006-12-13 22:08:44
Message-ID: 47668A1334CDBF46927C1A0DFEB223D39F7A98@mail.optiosoftware.com (view raw or flat)
Thread:
Lists: pgsql-performance
Version 8.1

Here are the planner constraints I believe we changed
effective_cache_size and random_page_cost
BTW this is an AIX 5.2 

#-----------------------------------------------------------------------
----
# QUERY TUNING
#-----------------------------------------------------------------------
----

# - Planner Method Configuration -

#enable_bitmapscan = on
#enable_hashagg = on
#enable_hashjoin = on
#enable_indexscan = on
#enable_mergejoin = on
#enable_nestloop = on
#enable_seqscan = on
#enable_sort = on
#enable_tidscan = on

# - Planner Cost Constants -

#effective_cache_size = 10000       # typically 8KB each
effective_cache_size = 400000
random_page_cost = 3.8          # units are one sequential page fetch
                    # cost
#cpu_tuple_cost = 0.01          # (same)
#cpu_index_tuple_cost = 0.001       # (same)
#cpu_operator_cost = 0.0025     # (same)

# - Genetic Query Optimizer -

#geqo = on
#geqo_threshold = 12
#geqo_effort = 5            # range 1-10
#geqo_pool_size = 0         # selects default based on effort
#geqo_generations = 0           # selects default based on effort
#geqo_selection_bias = 2.0      # range 1.5-2.0

# - Other Planner Options -

#default_statistics_target = 10     # range 1-1000
#constraint_exclusion = off
#from_collapse_limit = 8
#join_collapse_limit = 8        # 1 disables collapsing of explicit
                    # JOINs


Thanks

Tim Jones
Healthcare Project Manager
Optio Software, Inc.
(770) 576-3555

-----Original Message-----
From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us] 
Sent: Wednesday, December 13, 2006 4:59 PM
To: Tim Jones
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] strange query behavior 

"Tim Jones" <TJones(at)optio(dot)com> writes:
> The tables for theses queries are vacuumed and analyzed regularly. I 
> just did an analyze to be sure and here are the results ...

There's something pretty wacko about the choice of plan in the slow case
--- I don't see why it'd not have used the same plan structure as for
the IN case.  It's coming up with a cost a lot higher than for the
other, so it certainly knows this isn't a great plan ...

Which PG version is this exactly?  Are you running with any nondefault
planner parameters?

			regards, tom lane

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Subject: Re: Optimizing a query
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