Re: Less than ideal error reporting in pg_stat_statements

On Tue, Sep 22, 2015 at 4:40 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I wonder whether the real problem here is failure to truncate statement
> texts to something sane. Do we really need to record the whole text of
> multi-megabyte statements? Especially if doing so could render the entire
> feature nonfunctional?

I recently encountered a 9.4 customer database that had an insanely
large query text stored by pg_stat_statements, apparently created as
part of a process of kicking the tires of their new installation. I
don't know how large it actually was, but it caused psql to stall for
over 10 seconds. Insane queries happen, so truncating query text could
conceal the extent of how unreasonable a query is.

I think that the real problem here is that garbage collection needs to
deal with OOM more appropriately. That's the only way there could be a
problem with an in-flight query as opposed to a query that looks at
pg_stat_statements, which seems to be Nasby's complaint.

My guess is that this very large query involved a very large number of
constants, possibly contained inside an " IN ( )". Slight variants of
the same query, that a human would probably consider to be equivalent
have caused artificial pressure on garbage collection.

--
Peter Geoghegan