Re: How much expensive are row level statistics?

"Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> writes:
>> The cost depends on your usage patterns. I did tests with one of
>> my applications and saw no significant performance difference for
>> simple selects, but a series of insert/update/delete operations ran
>> about 30% slower when block- and row-level statistics were enabled
>> versus when the statistics collector was disabled.

> That approximately confirms my results, except that the penalty may even
> be a little bit higher in the worst-case scenario. Row level stats hit
> the hardest if you are doing 1 row at a time operations over a
> persistent connection.

IIRC, the only significant cost from enabling stats is the cost of
transmitting the counts to the stats collector, which is a cost
basically paid once at each transaction commit. So short transactions
will definitely have more overhead than longer ones. Even for a really
simple transaction, though, 30% seems high --- the stats code is
designed deliberately to minimize the penalty.

regards, tom lane