Greg Smith <g...@2ndquadrant.com> wrote: > You can easily quantify if the BGW is aggressive enough. Buffers > leave the cache three ways, and they each show up as separate > counts in pg_stat_bgwriter: buffers_checkpoint, buffers_clean > (the BGW), and buffers_backend (the queries). Cranking it up > further tends to shift writes out of buffers_backend, which are > the ones you want to avoid, toward buffers_clean instead. If > buffers_backend is already low on a percentage basis compared to > the other two, there's little benefit in trying to make the BGW do > more. Here are the values from our two largest and busiest systems (where we found the pg_xlog placement to matter so much). It looks to me like a more aggressive bgwriter would help, yes? cir=> select * from pg_stat_bgwriter ; -[ RECORD 1 ]------+------------ checkpoints_timed | 125996 checkpoints_req | 16932 buffers_checkpoint | 342972024 buffers_clean | 343634920 maxwritten_clean | 9928 buffers_backend | 575589056 buffers_alloc | 52397855471 cir=> select * from pg_stat_bgwriter ; -[ RECORD 1 ]------+------------ checkpoints_timed | 125992 checkpoints_req | 16840 buffers_checkpoint | 260358442 buffers_clean | 474768152 maxwritten_clean | 9778 buffers_backend | 565837397 buffers_alloc | 71463873477 Current settings: bgwriter_delay = '200ms' bgwriter_lru_maxpages = 1000 bgwriter_lru_multiplier = 4 Any suggestions on how far to push it? -Kevin
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