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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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15
src/include/optimizer/cost.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/cost.h,v 1.73 2006/03/05 15:58:57 momjian Exp $
* $PostgreSQL: pgsql/src/include/optimizer/cost.h,v 1.74 2006/06/05 02:49:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -21,12 +21,14 @@
/* defaults for costsize.c's Cost parameters */
/* NB: cost-estimation code should use the variables, not these constants! */
/* If you change these, update backend/utils/misc/postgresql.sample.conf */
#define DEFAULT_EFFECTIVE_CACHE_SIZE 1000.0 /* measured in pages */
#define DEFAULT_SEQ_PAGE_COST 1.0
#define DEFAULT_RANDOM_PAGE_COST 4.0
#define DEFAULT_CPU_TUPLE_COST 0.01
#define DEFAULT_CPU_INDEX_TUPLE_COST 0.001
#define DEFAULT_CPU_OPERATOR_COST 0.0025
#define DEFAULT_EFFECTIVE_CACHE_SIZE 1000.0 /* measured in pages */
/*
* prototypes for costsize.c
@@ -34,11 +36,12 @@
*/
/* parameter variables and flags */
extern double effective_cache_size;
extern double random_page_cost;
extern double cpu_tuple_cost;
extern DLLIMPORT double seq_page_cost;
extern DLLIMPORT double random_page_cost;
extern DLLIMPORT double cpu_tuple_cost;
extern DLLIMPORT double cpu_index_tuple_cost;
extern double cpu_operator_cost;
extern DLLIMPORT double cpu_operator_cost;
extern double effective_cache_size;
extern Cost disable_cost;
extern bool enable_seqscan;
extern bool enable_indexscan;