Re: questions about a table's row estimates

[Ben Chobot <bench@xxxxxxxxxxxxxxx>]

On Feb 10, 2010, at 10:28 PM, Greg Smith wrote:

Ben Chobot wrote:

I'm looking at pg_stat_user_tables in 8.4.2, and I'm confused about n_live_tup. Shouldn't that be at least fairly close to (n_tup_ins - n_tup-del)? It doesn't seem to be, but I'm unclear why.

 

Insert 2000 tuples.
Delete 1000 tuples.
vacuum
Insert 1000 tuples. These go into the free space the deleted tuples used to be in.
analyze

n_tup_ins=3000
n_tup_del=1000
n_live_tup=3000

Say what? It's not documented terrible well (http://www.postgresql.org/docs/8.4/interactive/monitoring-stats.html is the best I can find) but I thought n_live_tup was basically the number of tuples visible to a new transaction. If my assumption is wrong, that might explain things.

And unfortunately, Tom, we're not resetting stats counters. :(