When we checkpoint we write out all dirty buffers. But ISTM we don't really need to write out buffers which are dirty but which have an LSN older than the previous checkpoint. Those represent buffers which were dirtied by a non-wal-logged modification, ie, hint bit setting. The other non-wal-logged operations will sync the buffer themselves when they're done.
I guess it doesn't really buy much, probably just a slight delay in writing out the page until bgwriter gets around to it. Conceivably you could have a hot buffer with many missing hint bits which will get written out on several checkpoints but how many of those can you have? And extending the checkpoint doesn't seem like much of a concern. On the other hand it wouldn't be hard to check would it? -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
