Re: Very low performance on table with only 298 rows

Andreas Joseph Krogh wrote:
> nbeweb=> EXPLAIN select count(*) from onp_web_index;
> QUERY PLAN
> -----------------------------------------------------------------------------
> Hi all.
> I have a problem with a table which only has 298 rows in it. A select count(*)
> takes forever and CTRL-C also takes a long time canceling the query. There
> are only 298 rows in the table when count(*) returns. How come it takes such
> a long time counting only 298 rows? Here is EXPLAIN ANALYZE:
>
> nbeweb=> EXPLAIN ANALYZE select count(*) from onp_web_index;
> QUERY PLAN
> -----------------------------------------------------------------------------------------------------------------------------------
> Aggregate (cost=205759.52..205759.52 rows=1 width=0) (actual
> time=179748.910..179748.913 rows=1 loops=1)
> -> Seq Scan on onp_web_index (cost=0.00..205455.41 rows=121641 width=0)
> (actual time=179735.956..179747.821 rows=298 loops=1)
> Total runtime: 179748.993 ms

Why does PG think you have 121641 rows in this table?
How often do you vacuum it?
How often do you analyse it?
Does "vacuum full verbose" show a lot of dead rows being removed?

I'm suspecting a *lot* of dead rows need to be removed.

--
Richard Huxton
Archonet Ltd