Joshua Reich <[EMAIL PROTECTED]> writes: > I lurk... I don't know if I'm a 'statistics jock', but I may be > valuable if only I had a better understanding of how the optimizer > works. I have been following this thread with interest, but could really > do with a good pointer to background information beyond what I have read > in the main postgres manual. Does such information exist, and if so, > where ?
Well, there's the 20000-foot view here: http://developer.postgresql.org/pgdocs/postgres/planner-optimizer.html but after that you have to start reading code. The optimizer README file may be useful: http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/README but it goes into a lot of details that probably aren't interesting for your purposes. Most of the planner is just mechanism associated with generating different possible plans. The policy that determines which plan is chosen is the cost-estimation equations, and those are all in costsize.c and selfuncs.c: http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c The division between these two files is a bit historical, but roughly speaking selfuncs.c knows about the behavior of specific WHERE-clause operators and index access methods, while costsize.c knows about the behavior of particular plan types. I'd like to think that costsize.c is well enough commented that you can follow it even without any C knowledge, but selfuncs.c may be a bit more daunting. Still, the comments are pretty extensive, and feel free to ask questions on pg-hackers. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
