[HACKERS] free space map and visibility map
| От | Jeff Janes |
|---|---|
| Тема | [HACKERS] free space map and visibility map |
| Дата | |
| Msg-id | CAMkU=1wXkKUKBHWBYzET3D9OViyDg8DcVL-wKEqk2uyoMrzr_A@mail.gmail.com обсуждение исходный текст |
| Ответы |
Re: [HACKERS] free space map and visibility map
|
| Список | pgsql-hackers |
With some intensive crash-recovery testing, I've run into a situation where I get some bad table bloat. There will be large swaths of the table which are empty (all results from heap_page_items other than lp are either zero or NULL), but have zero available space in the fsm, and are marked as all-visible and all-frozen in the vm.
I guess it is a result of a crash causing updates to the fsm to be lost. Then due to the (crash-recovered) visibility map showing them as all visible and all frozen, vacuum never touches the pages again, so the fsm never gets corrected.
'VACUUM (DISABLE_PAGE_SKIPPING) foo;' does fix it, but that seems to be the only thing that will.
Is there a way to improve this, short of making updates to the fsm be a wal-logged operation?
It is probably not a very pressing issue, as crashes are normally pretty rare, I would hope. But it seems worth improving if there is a good way to do so.
Cheers,
Jeff
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