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In some cases, exiting out of a plpgsql statement due to an error, then catching the error in a surrounding exception block, led to leakage of temporary data the statement was working with, because we kept all such data in the function-lifespan SPI Proc context. Iterating such behavior many times within one function call thus led to noticeable memory bloat. To fix, create an additional memory context meant to have statement lifespan. Since many plpgsql statements, particularly the simpler/more common ones, don't need this, create it only on demand. Reset this context at the end of any statement that uses it, and arrange for exception cleanup to reset it too, thereby fixing the memory-leak issue. Allow a stack of such contexts to exist to handle cases where a compound statement needs statement-lifespan data that persists across calls of inner statements. While at it, clean up code and improve comments referring to the existing short-term memory context, which by plpgsql convention is the per-tuple context of the eval_econtext ExprContext. We now uniformly refer to that as the eval_mcontext, whereas the new statement-lifespan memory contexts are called stmt_mcontext. This change adds some context-creation overhead, but on the other hand it allows removal of some retail pfree's in favor of context resets. On balance it seems to be about a wash performance-wise. In principle this is a bug fix, but it seems too invasive for a back-patch, and the infrequency of complaints weighs against taking the risk in the back branches. So we'll fix it only in HEAD, at least for now. Tom Lane, reviewed by Pavel Stehule Discussion: <17863.1469142152@sss.pgh.pa.us> |
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