Tomas Vondra <tomas.von...@2ndquadrant.com> writes: > On 02/06/2016 08:39 PM, Andres Freund wrote: >> FWIW, I've done that at some point. Noticeable speedups (that's what >> I cared about), but a bit annoying to use. There's many random >> pfree()s around, and then there's MemoryContextContains(), >> GetMemoryChunkContext(), GetMemoryChunkSpace() - which all are >> pretty fundamentally incompatible with such an allocator. I ended up >> having a full header when assertions are enabled, to be able to >> detect usage of these functions and assert out. >> >> I didn't concentrate on improving memory usage, but IIRC it was even >> noticeable for some simpler things.
> I think the hassle is not that bad when most of the fragments have the > same life cycle. With hashjoin that's almost exactly the case, except > when we realize we need to increase the number of buckets - in that case > we need to split the set of accumulated tuples in two. Yeah, I think that a context type that just admits "we'll crash if you try to pfree" would only be usable for allocations that are managed by just a very small amount of code --- but the hashjoin tuple table qualifies, and I think there would be other use-cases, perhaps tuplesort/tuplestore. Andres' idea of adding a chunk header only in assert builds isn't a bad one, perhaps; though I think the near-certainty of a core dump if you try to use the header for anything might be good enough. pfree and repalloc are an ironclad certainty to crash in a pretty obvious way, and we could likely add some assert checks to MemoryContextContains and friends to make them 99.99% certain to fail without paying the price of a chunk header. regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers