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Update comments about attdisbursion. NO code change.

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This commit is contained in:
Tom Lane 1999-08-09 02:45:56 +00:00
parent 1ecb43a40c
commit e9054829a2
1 changed files with 10 additions and 3 deletions
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13
src/include/catalog/pg_attribute.h
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@ -7,7 +7,7 @@
*
* Copyright (c) 1994, Regents of the University of California
*
* $Id: pg_attribute.h,v 1.48 1999/07/31 19:07:25 tgl Exp $
* $Id: pg_attribute.h,v 1.49 1999/08/09 02:45:56 tgl Exp $
*
* NOTES
* the genbki.sh script reads this file and generates .bki
@ -53,8 +53,15 @@ CATALOG(pg_attribute) BOOTSTRAP
float4 attdisbursion;
/*
* attdisbursion is the disbursion statistic of the column, or zero if
* the statistic has not been calculated.
* attdisbursion is the disbursion statistic of the column (0.0 to 1.0),
* or zero if the statistic has not been calculated, or -1.0
* if VACUUM found that the column contains no duplicate entries
* (in which case the disbursion should be taken as 1.0/numberOfRows
* for the current table size). The -1.0 hack is useful because the
* number of rows may be updated more often than attdisbursion is.
* We assume that the column will retain its no-duplicate-entry
* property. (Perhaps this should be driven off the existence of a
* UNIQUE index for the column, instead of being a statistical guess?)
*/
int2 attlen;