On 29 May 2015 at 11:35, Tom Lane <t...@sss.pgh.pa.us> wrote: > Craig Ringer <cr...@2ndquadrant.com> writes: > > It's sometimes desirable to collect auto_explain data with ANALYZE in > order > > to track down hard-to-reproduce issues, but the performance impacts can > be > > pretty hefty on the DB. > > > I'm inclined to add a sample rate to auto_explain so that it can trigger > > only on x percent of queries, > > That sounds reasonable ... >
Cool, I'll cook that up then. Thanks for the sanity check. > > and also add a sample test hook that can be > > used to target statements of interest more narrowly (using a C hook > > function). > > You'd have to be pretty desperate, *and* knowledgeable, to write a > C function for that. Can't we invent something a bit more user-friendly > for the purpose? No idea what it should look like though. > I've been that desperate. For the majority of users I'm sure it's sufficient to just have a sample rate. Anything that's trying to match individual queries could be interested in all sorts of different things. Queries that touch a particular table being one of the more obvious things, or queries that mention a particular literal. Rather than try to design something complicated in advance that anticipates all needs, I'm thinking it makes sense to just throw a hook in there. If some patterns start to emerge in terms of useful real world filtering criteria then that'd better inform any more user accessible design down the track. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
