=?GB2312?B?RmVsaXgu0Ow=?= <ygnhzeus@xxxxxxxxx> writes: > //line 194 : In a "most common values" slot, staop is the OID of the "=" > operator used to decide whether values are the same or not. > //line 206 : A "histogram" slot describes the distribution of scalar data. > staop is the OID of the "<" operator that describes the sort ordering. > I don't understand the function of staop here, how is it used in optimizer, In principle a data type could have more than one sort ordering, and if we were to collect stats according to multiple orderings, staop would be needed to identify which ordering a particular set of statistics was created with. That flexibility isn't being used right now, at least not by any built-in code. There are types with more than one ordering (more than one btree opclass), but ANALYZE only collects stats for the default btree opclass. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
