"Day, David" <dday@xxxxxxxxxx> writes: > There seems to be an unbounded growth of memory usage by the backend postgres process representing a "permanent" session in our system. It's hard to evaluate this report with so little information, but there are at least three possible explanations: 1. Many people misunderstand "top"'s output and believe they are seeing memory bloat when they aren't. This happens because top only charges pages of shared memory to a process after the process has first physically touched those pages. So a PG process's claimed use of shared memory will gradually grow from nothing to the whole shared-memory area, as it has occasion to make use of different shared buffers, lock table entries, etc. You can correct for this by subtracting the SHR (shared) column from the process's reported size, but people often fail to. (Note: it's possible that FreeBSD's implementation doesn't suffer from this problem, but the issue definitely exists on e.g. Linux.) 2. If, over time, the queries issued to the process touch many different tables (I'm talking thousands of tables), or execute large numbers of distinct plpgsql functions, etc, then you will get bloating of the internal caches that hold copies of that catalog data. PG generally operates on the principle that cached is better than not cached, so it doesn't try to limit the size of those caches; but in some installations that can cause problems. If this is your situation, then indeed restarting the sessions periodically may be necessary. 3. Or you might have found an actual memory leak. PG's memory usage conventions are such that true leaks that persist across transactions are pretty rare ... but I won't say it doesn't happen. If you've eliminated point 1 and want to try to look into the other theories, you could do this: attach to a recently-started session with gdb, and execute call MemoryContextStats(TopMemoryContext) quit This will cause a memory usage map to get dumped to stderr (hopefully you are starting the postmaster in such a way that that gets captured to a log file rather than sent to /dev/null). Save that. Wait until you see bloat, reattach and repeat, compare the memory maps. Let us know what you see. If possible, compare maps taken at points where the session is idle and waiting for input. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
