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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! |
