pg_class.reltuples VS pg_stat_all_tables.n_live_tup for estimation of table

Hello,

Does anyone which is a more accurate estimate of a table's live
rows: pg_class.reltuples (
http://www.postgresql.org/docs/current/static/catalog-pg-class.html)
OR pg_stat_all_tables.n_live_tup (
http://www.postgresql.org/docs/current/static/monitoring-stats.html#PG-STAT-ALL-TABLES-VIEW)?
In my test database their values are not the same.

- Is pg_class.reltuples an estimation of live tuples only, or is it of
all tuples (both live and dead)? I would guess it's live only but that is a
guess
- In the database I am testing:
- pg_class.reltuples <> pg_stat_all_tables.n_live_tup
- pg_class.reltuples <> (pg_stat_all_tables.n_live_tup
+ pg_stat_all_tables.n_dead_tup)

I understand that pg_stat_all_tables is probably the more expensive view to
query but I am already querying both so I only care which is more accurate.

Thanks!
Will

*Will J. Dunn*
*willjdunn.com <http://willjdunn.com>*