All, One of my coworkers just pointed this out: "The amount of memory used in shared memory for WAL data. The default is 64 kilobytes (64kB). The setting need only be large enough to hold the amount of WAL data generated by one typical transaction, since the data is written out to disk at every transaction commit. This parameter can only be set at server start." http://www.postgresql.org/docs/9.0/static/runtime-config-wal.html That's quite incorrect. The wal_buffers are shared by all concurrent transactions, so it needs to be sized appropriately for all *simultaneous* uncommitted transactions, otherwise you'll get unnecessary flushing. Certainly performance testing data posted on this list and -hackers. bears that out. My suggestion instead: "The amount of shared memory dedicated to buffering writes to the WAL. The default is 64 kilobytes (64kB), which is low for a busy production server. Users who have high write concurrency, or transactions which commit individual large data writes, will want to increase it to between 1MB and 16MB. This parameter can only be set at server start." -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
