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Add a GUC parameter seq_page_cost, and use that everywhere we formerly

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assumed that a sequential page fetch has cost 1.0.  This patch doesn't
in itself change the system's behavior at all, but it opens the door to
people adopting other units of measurement for EXPLAIN costs.  Also, if
we ever decide it's worth inventing per-tablespace access cost settings,
this change provides a workable intellectual framework for that.
This commit is contained in:
Tom Lane
2006-06-05 02:49:58 +00:00
parent a837851dc0
commit eed6c9ed7e
8 changed files with 243 additions and 187 deletions
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10
src/backend/utils/misc/postgresql.conf.sample
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@ -175,12 +175,12 @@
# - Planner Cost Constants -
#seq_page_cost = 1.0 # measured on an arbitrary scale
#random_page_cost = 4.0 # same scale as above
#cpu_tuple_cost = 0.01 # same scale as above
#cpu_index_tuple_cost = 0.001 # same scale as above
#cpu_operator_cost = 0.0025 # same scale as above
#effective_cache_size = 1000 # typically 8KB each
#random_page_cost = 4 # 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 -