If the stats collector is 'lossy ' i will not be able to use it, can anyone confirm that it is ? So maybe my best option is to write a simple trigger that just increments a counter (value in a separate table) after an insert/update/delete and then add this trigger to each table i want to record the stats for. Would this new approach work ( i.e. be "lossless") ?
Cheers,
Andy
On 11/01/07, Richard Huxton <dev@xxxxxxxxxxxx> wrote:
Andy Dale wrote:
> Hi,
>
> I turned on the stats_row_level in the postgresql.conf file and now the the
> calls to the stats functions work. I want to get the inserted, updated,
> and
> deleted numbers on a given database, so i have written a query to do so:
>
> SELECT
> sum(pg_stat_get_tuples_inserted(c.oid)) AS inserted,
> sum(pg_stat_get_tuples_updated(c.oid)) AS updated,
> sum(pg_stat_get_tuples_deleted(c.oid)) AS deleted
> FROM
> pg_class c, information_schema.tables i
> WHERE
> i.table_catalog = 'testdb' AND
> i.table_schema= 'public' AND
> i.table_name = c.relname
>
> I had to use the information schema as i could not figure out a way to
> fetch
> the tables of a particular database using only pg_* tables.
It's the pg_class table you'll want to start with. If you start psql
with -E and then do \dt you'll see the queries it uses.
> What i am
> really now concerned is reliability, is it possible that the stats can be
> incorrect ? and are they never reset ?. Also does using row level stats
> have a serious effect on the performance ?
Well, I'm not sure about incorrect. AFAIK the stats gatherer is "lossy",
so there's not a 100% guarantee that every read/write is measured.
Performance shouldn't be an issue unless you're already pushing the
limits of your hardware.
--
Richard Huxton
Archonet Ltd
