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Add a quick index page estimation

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This commit is contained in:
Julien Rouhaud 2015-03-16 20:50:03 +01:00
parent 63af004299
commit 0c16484267
1 changed files with 15 additions and 2 deletions
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17
pg_hypo.c
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@ -20,6 +20,7 @@
#include "storage/bufmgr.h"
#include "tcop/utility.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
PG_MODULE_MAGIC;
@ -256,6 +257,7 @@ addHypotheticalIndex(PlannerInfo *root,
{
IndexOptInfo *index;
int ncolumns, i;
int ind_avg_width = 0;
/* create a node */
@ -283,6 +285,7 @@ addHypotheticalIndex(PlannerInfo *root,
for (i = 0; i < ncolumns; i++)
{
index->indexkeys[i] = entries[position].indexkeys;
ind_avg_width += get_attavgwidth(relation->rd_id, index->indexkeys[i]);
switch (index->relam)
{
case BTREE_AM_OID:
@ -328,12 +331,22 @@ addHypotheticalIndex(PlannerInfo *root,
if (index->indpred == NIL)
{
index->pages = rel->tuples / 10; // Should compute with col width and other stuff, WIP
index->tuples = rel->tuples; // Same
/* very quick and pessimistic estimation :
* number of tuples * avg width, with ~ 50% bloat, plus 1 block
*/
index->pages = (rel->tuples * ind_avg_width * .5 / BLCKSZ) + 1;
/* partial index not supported yet, so assume all tuples are in the index */
index->tuples = rel->tuples;
}
/* obviously, setup this tag.
* However, it's only checked in selfuncs.c/get_actual_variable_range, so
* we still need to add hypothetical indexes *ONLY* in an
* explain-no-analyze command.
*/
index->hypothetical = true;
/* add our hypothetical index in the relation's indexlist */
rel->indexlist = lcons(index, rel->indexlist);
}