database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-03 20:02:46 +03:00
Code Activity

Make the planner estimate costs for nestloop inner indexscans on the basis

Browse Source 
that the Mackert-Lohmann formula applies across all the repetitions of the
nestloop, not just each scan independently.  We use the M-L formula to
estimate the number of pages fetched from the index as well as from the table;
that isn't what it was designed for, but it seems reasonably applicable
anyway.  This makes large numbers of repetitions look much cheaper than
before, which accords with many reports we've received of overestimation
of the cost of a nestloop.  Also, change the index access cost model to
charge random_page_cost per index leaf page touched, while explicitly
not counting anything for access to metapage or upper tree pages.  This
may all need tweaking after we get some field experience, but in simple
tests it seems to be giving saner results than before.  The main thing
is to get the infrastructure in place to let cost_index() and amcostestimate
functions take repeated scans into account at all.  Per my recent proposal.

Note: this patch changes pg_proc.h, but I did not force initdb because
the changes are basically cosmetic --- the system does not look into
pg_proc to decide how to call an index amcostestimate function, and
there's no way to call such a function from SQL at all.
This commit is contained in:
Tom Lane
2006-06-06 17:59:58 +00:00
parent 05631354f3
commit 8a30cc2127
14 changed files with 340 additions and 202 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
src/backend/optimizer/util/pathnode.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.127 2006/03/05 15:58:31 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.128 2006/06/06 17:59:57 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -420,8 +420,8 @@ create_seqscan_path(PlannerInfo *root, RelOptInfo *rel)
* 'indexscandir' is ForwardScanDirection or BackwardScanDirection
* for an ordered index, or NoMovementScanDirection for
* an unordered index.
* 'isjoininner' is TRUE if this is a join inner indexscan path.
* (pathkeys and indexscandir are ignored if so.)
* 'outer_rel' is the outer relation if this is a join inner indexscan path.
* (pathkeys and indexscandir are ignored if so.) NULL if not.
*
* Returns the new path node.
*/
@ -431,7 +431,7 @@ create_index_path(PlannerInfo *root,
List *clause_groups,
List *pathkeys,
ScanDirection indexscandir,
bool isjoininner)
RelOptInfo *outer_rel)
{
IndexPath *pathnode = makeNode(IndexPath);
RelOptInfo *rel = index->rel;
@ -445,7 +445,7 @@ create_index_path(PlannerInfo *root,
* don't really care what order it's scanned in. (We could expect the
* caller to supply the correct values, but it's easier to force it here.)
*/
if (isjoininner)
if (outer_rel != NULL)
{
pathkeys = NIL;
indexscandir = NoMovementScanDirection;
@ -466,10 +466,10 @@ create_index_path(PlannerInfo *root,
pathnode->indexclauses = allclauses;
pathnode->indexquals = indexquals;
pathnode->isjoininner = isjoininner;
pathnode->isjoininner = (outer_rel != NULL);
pathnode->indexscandir = indexscandir;
if (isjoininner)
if (outer_rel != NULL)
{
/*
* We must compute the estimated number of output rows for the
@ -505,7 +505,7 @@ create_index_path(PlannerInfo *root,
pathnode->rows = rel->rows;
}
cost_index(pathnode, root, index, indexquals, isjoininner);
cost_index(pathnode, root, index, indexquals, outer_rel);
return pathnode;
}
@ -515,6 +515,9 @@ create_index_path(PlannerInfo *root,
* Creates a path node for a bitmap scan.
*
* 'bitmapqual' is a tree of IndexPath, BitmapAndPath, and BitmapOrPath nodes.
*
* If this is a join inner indexscan path, the component IndexPaths should
* have been costed accordingly, and TRUE should be passed for isjoininner.
*/
BitmapHeapPath *
create_bitmap_heap_path(PlannerInfo *root,
@ -560,7 +563,7 @@ create_bitmap_heap_path(PlannerInfo *root,
pathnode->rows = rel->rows;
}
cost_bitmap_heap_scan(&pathnode->path, root, rel, bitmapqual, false);
cost_bitmap_heap_scan(&pathnode->path, root, rel, bitmapqual);
return pathnode;
}