Alvaro Herrera <[EMAIL PROTECTED]> wrote: > Tom Lane wrote: > > > It may boil down to whether we would like the identity > > n_live_tup = n_tup_ins - n_tup_del > > to continue to hold, or the similar one for n_dead_tup. The problem > > basically is that pgstats is computing n_live_tup and n_dead_tup > > using those identities rather than by tracking what really happens.
On a relevant note, there is a variance in the calculation of auto-analyze threshold between documentation and implementation in HEAD. (Only HEAD; It is ok in 8.2 or before) Our documentation says | analyze threshold = analyze base threshold | + analyze scale factor * number of tuples | is compared to the total number of tuples inserted, updated, or deleted | since the last ANALYZE. http://momjian.us/main/writings/pgsql/sgml/routine-vacuuming.html#AUTOVACUUM but deleted tuples are not considered in the total number, because the delta of {n_live_tuples + n_dead_tuples} is not changed by DELETE. We add the number of DELETE into n_live_tuples and subtract it from n_dead_tuples. | pgstat.c | t_new_live_tuples += tuples_inserted - tuples_deleted; | t_new_dead_tuples += tuples_deleted; | autovacuum.c | anltuples = n_live_tuples + n_dead_tuples - last_anl_tuples; There is no delete-only database in the real world, so this is not so serious problem probably. We'd better to fix the documentation if it is intention. Regards, --- ITAGAKI Takahiro NTT Open Source Software Center ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
