From: | dafNi <dzaf88(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | optimizer's cost formulas |
Date: | 2013-04-06 10:51:52 |
Message-ID: | 515FFE48.6090307@gmail.com |
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Thread: | |
Lists: | pgsql-general |
Hello everybody!
I'm trying to understand the the query planner's cost estimator.
I was not able to find anywhere the formulas that estimate the cost
of each operation that the optimizer produces.
I only found this for the sequential scan:
SEQ SCAN = ( cpu_tuple_cost * rows ) + ( number of pages * seq_page_cost )
where :
cpu_tuple_cost=0.01
seq_page_cost=1.0
and "rows" and "number of pages" are given in the query plan (via
EXPLAIN ANALYZE)
I am wondering where could I find the rest formulas for the rest operations
(e.g. HashAggregate, Nested Loop, Hash Join, Index Scan, Sort, etc)
I also looked at costsize.c but could not find a formula like the above
or maybe I
couldn't make sense of it
Thank you in advance!
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