Recent changes for power reduction mean that we now issue a wakeup call to the bgwriter every time we set a hint bit.
However cheap that is, its still overkill. My proposal is that we wakeup the bgwriter whenever a backend is forced to write a dirty buffer, a job the bgwriter should have been doing. This significantly reduces the number of wakeup calls and allows the bgwriter to stay asleep even when very light traffic happens, which is good because the bgwriter is often the last process to sleep. Seems useful to have an explicit discussion on this point, especially in view of recent performance results. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 1adb6d3..310cd95 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -654,6 +654,10 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, FlushBuffer(buf, NULL); LWLockRelease(buf->content_lock); + /* The bgwriter may need to be woken. */ + if (ProcGlobal->bgwriterLatch) + SetLatch(ProcGlobal->bgwriterLatch); + TRACE_POSTGRESQL_BUFFER_WRITE_DIRTY_DONE(forkNum, blockNum, smgr->smgr_rnode.node.spcNode, smgr->smgr_rnode.node.dbNode, @@ -2368,9 +2372,6 @@ SetBufferCommitInfoNeedsSave(Buffer buffer) VacuumPageDirty++; if (VacuumCostActive) VacuumCostBalance += VacuumCostPageDirty; - /* The bgwriter may need to be woken. */ - if (ProcGlobal->bgwriterLatch) - SetLatch(ProcGlobal->bgwriterLatch); } } }
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