Atsushi Ogawa <[EMAIL PROTECTED]> writes: > Tom Lane wrote: >> Why is this better than the fix already in place?
> Because per-tuple context is reset many times. If per-tuple context is > never used, the following codes of AllocSetReset become effective. > /* Nothing to do if context has never contained any data */ > if (block == NULL) > return; Hm. It's still pretty ugly though, since fixing only those two places isn't very exciting. I went back and looked at your AllocSetReset patch from last May, and liked it better on second consideration. The point I had missed before is that even though we're adding an instruction to palloc, it's only needed in the "slow" paths. The cases that we have to be worried about, IMHO, are: 1. Loop containing palloc(s) and pfree(s). 2. Loop containing palloc(s) and MemoryContextReset. 3. Loop containing only MemoryContextReset. (We need not worry about cases doing only palloc since that is obviously not sustainable over any long period.) Case 1 is the one that was bothering me, but in practice, once the loop is rolling the pallocs should mostly be reusing previously-pfreed chunks. That is the "fast" path through AllocSetAlloc, and it doesn't need any extra overhead because it doesn't need to clear the alloc-set-is-empty flag --- the set is clearly already nonempty if it has free chunks. There's enough instructions in the other paths that one more isn't going to hurt. In case 2 we're adding instructions to both palloc and MemoryContextReset, for no gain :-( ... but again, these are in code paths that aren't the fastest possible. I don't think it'll hurt noticeably. I notice also that MemoryContextIsEmpty could return a better answer if we maintained a flag like this. This is not real important in the current scheme of things, but might be more interesting someday. I'll fix up the old patch and apply it. I think that's a better answer than kluging up the aggregate functions themselves. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq