> > But what kind of rows would satisfy heap_page_prune() and what would not? > > In my case all updates are doing the same thing (there is no HOT > updates, obviously), but why some updated rows are reported by > heap_page_prune() but the others are not? And it's also a random > issue. That means sometimes heap_page_prune() would report all > removable rows, and sometimes it reports no rows. >
I check the codes again. The heap_page_prune() would skip items if ItemIdIsDead() returns true. That means some obsoleted items are flagged dead before vacuum, and I found 3 places: 1) heap_page_prune_opt() --> heap_page_prune() --> ItemIdSetDead() 2) _bt_check_unique() --> ItemIdMarkDead() 3) _bt_killitems() --> ItemIdMarkDead() In my case, the first one happens most frequently. And it's interesting that it's invoked from select statement! 0x80ca000 : heap_page_prune_opt+0x0/0x1a0 0x80d030d : index_fetch_heap+0x11d/0x140 0x80d035e : index_getnext+0x2e/0x40 0x81eec9b : IndexNext+0x3b/0x100 0x81e4ddf : ExecScan+0x15f/0x290 0x81eed8d : ExecIndexScan+0x2d/0x50 0x81ddb20 : ExecProcNode+0x1f0/0x2a0 0x81dac6c : standard_ExecutorRun+0xfc/0x160 0x82d0503 : PortalRunSelect+0x183/0x200 0x82d17da : PortalRun+0x26a/0x3c0 0x82cf452 : PostgresMain+0x2282/0x2fc0 0x8097f52 : ServerLoop+0xb1b/0xec2 0x82793d7 : PostmasterMain+0x1237/0x13c0 0x8098b6c : main+0x48c/0x4d4 0xb754fa83 : __libc_start_main+0xf3/0x210 0x8098bd5 : _start+0x21/0x2c Regards, Jinhua Luo -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
