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If we don't have any stats for a boolean column, assume

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the disbursion is 0.5, not something small.
This commit is contained in:
Tom Lane 2000-02-16 01:00:23 +00:00
parent deee4e1612
commit 68be513f8b
1 changed files with 15 additions and 3 deletions
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18
src/backend/utils/cache/lsyscache.c vendored
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.39 2000/01/26 05:57:17 momjian Exp $ * $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.40 2000/02/16 01:00:23 tgl Exp $
* *
* NOTES * NOTES
* Eventually, the index information should go through here, too. * Eventually, the index information should go through here, too.
@ -183,6 +183,7 @@ double
get_attdisbursion(Oid relid, AttrNumber attnum, double min_estimate) get_attdisbursion(Oid relid, AttrNumber attnum, double min_estimate)
{ {
HeapTuple atp; HeapTuple atp;
Form_pg_attribute att_tup;
double disbursion; double disbursion;
int32 ntuples; int32 ntuples;
@ -197,10 +198,21 @@ get_attdisbursion(Oid relid, AttrNumber attnum, double min_estimate)
relid, attnum); relid, attnum);
return min_estimate; return min_estimate;
} }
att_tup = (Form_pg_attribute) GETSTRUCT(atp);
disbursion = ((Form_pg_attribute) GETSTRUCT(atp))->attdisbursion; disbursion = att_tup->attdisbursion;
if (disbursion > 0.0) if (disbursion > 0.0)
return disbursion; /* we have a specific estimate */ return disbursion; /* we have a specific estimate from VACUUM */
/*
* Special-case boolean columns: the disbursion of a boolean is highly
* unlikely to be anywhere near 1/numtuples, instead it's probably more
* like 0.5.
*
* Are there any other cases we should wire in special estimates for?
*/
if (att_tup->atttypid == BOOLOID)
return 0.5;
/* /*
* Disbursion is either 0 (no data available) or -1 (disbursion * Disbursion is either 0 (no data available) or -1 (disbursion