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Store -1 in attdisbursion to signal 'no duplicates in column'.

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Centralize att_disbursion readout logic.
This commit is contained in:
Tom Lane
1999-08-09 03:16:47 +00:00
parent 5af4b04f31
commit 14f84cd821
3 changed files with 43 additions and 102 deletions
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62
src/backend/commands/vacuum.c
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@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.117 1999/08/08 17:13:10 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.118 1999/08/09 03:16:47 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -2346,36 +2346,46 @@ vc_updstats(Oid relid, int num_pages, int num_tuples, bool hasindex, VRelStats *
}
else if (stats->null_cnt <= 1 && stats->best_cnt == 1)
{
/* looks like we have a unique-key attribute */
double total = ((double) stats->nonnull_cnt) + ((double) stats->null_cnt);
selratio = 1.0 / total;
}
else if (VacAttrStatsLtGtValid(stats) && stats->min_cnt + stats->max_cnt == stats->nonnull_cnt)
{
/* exact result when there are just 1 or 2 values... */
double min_cnt_d = stats->min_cnt,
max_cnt_d = stats->max_cnt,
null_cnt_d = stats->null_cnt;
double total = ((double) stats->nonnull_cnt) + null_cnt_d;
selratio = (min_cnt_d * min_cnt_d + max_cnt_d * max_cnt_d + null_cnt_d * null_cnt_d) / (total * total);
/* looks like we have a unique-key attribute ---
* flag this with special -1.0 flag value.
*
* The correct disbursion is 1.0/numberOfRows, but since
* the relation row count can get updated without
* recomputing disbursion, we want to store a "symbolic"
* value and figure 1.0/numberOfRows on the fly.
*/
selratio = -1;
}
else
{
double most = (double) (stats->best_cnt > stats->null_cnt ? stats->best_cnt : stats->null_cnt);
double total = ((double) stats->nonnull_cnt) + ((double) stats->null_cnt);
if (VacAttrStatsLtGtValid(stats) &&
stats->min_cnt + stats->max_cnt == stats->nonnull_cnt)
{
/* exact result when there are just 1 or 2 values... */
double min_cnt_d = stats->min_cnt,
max_cnt_d = stats->max_cnt,
null_cnt_d = stats->null_cnt;
double total = ((double) stats->nonnull_cnt) + null_cnt_d;
/*
* we assume count of other values are 20% of best
* count in table
*/
selratio = (most * most + 0.20 * most * (total - most)) / (total * total);
selratio = (min_cnt_d * min_cnt_d + max_cnt_d * max_cnt_d + null_cnt_d * null_cnt_d) / (total * total);
}
else
{
double most = (double) (stats->best_cnt > stats->null_cnt ? stats->best_cnt : stats->null_cnt);
double total = ((double) stats->nonnull_cnt) + ((double) stats->null_cnt);
/*
* we assume count of other values are 20% of best
* count in table
*/
selratio = (most * most + 0.20 * most * (total - most)) / (total * total);
}
/* Make sure calculated values are in-range */
if (selratio < 0.0)
selratio = 0.0;
else if (selratio > 1.0)
selratio = 1.0;
}
if (selratio < 0.0)
selratio = 0.0;
else if (selratio > 1.0)
selratio = 1.0;
attp->attdisbursion = selratio;
/*