Date: Fri, 09 Nov 2012 09:28:10 +0100 From: Frank Broniewski <brfr@metrico.lu> To: freebsd-questions@freebsd.org Subject: Postgresql related memory question Message-ID: <509CBE9A.5020007@metrico.lu>
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Hi, I recently had a discussion of PostgreSQLs memory usage on FreeBSD, notably the display of the different memory types in top, on the PostgreSQL mailing list [1]. My server has 32GB ram, of which approx. 8GB vanish from tops display after a while. My question was wether there is a memory problem on FreeBSD or if top is not capable of dealing well with PostgreSQLs memory handling, eg. the shared_buffers. We used a perl script [2] to get a better understanding of the current memory usage on FreeBSD and a line from the scripts output caught my eye: > mem_gap_vm: + 8812892160 ( 8404MB) [ 26%] Memory gap: UNKNOWN I don't have a good understanding of the different types of system memory, so the question is, in relation with PostgreSQL, if the mem_gap_vm value can be considered normal or if it is a sign of memory leak. Since this question is more of a FreeBSD question, we decided to move the discussion here in order to get more insight on the system internals :-) This value equals more or less the shared buffers (shared_buffers=8GB) setting of PostgreSQL and is stable, which means, it doesn't change anymore after reaching its peak value. I did post already some system configuration information in the thread on the PostgreSQL list, but I am happy to provide all the information necessary to shed some light on this matter. Many thanks, Frank [1] http://postgresql.1045698.n5.nabble.com/Memory-issue-on-FreeBSD-td5730651.html [2] http://www.cyberciti.biz/faq/freebsd-command-to-get-ram-information/ -- Frank BRONIEWSKI METRICO s.à r.l. géomètres technologies d'information géographique rue des Romains 36 L-5433 NIEDERDONVEN tél.: +352 26 74 94 - 28 fax.: +352 26 74 94 99 http://www.metrico.lu
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