*
* 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
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;