Re: Set visibility map bit after HOT prune

On 16 December 2012 14:41, Andres Freund <andres@2ndquadrant.com> wrote:
> On 2012-12-16 13:23:56 +0530, Pavan Deolasee wrote:
>> Another idea could have been to NOT clear the visibility bit when a
>> HOT update happens. Such tuple can get pruned by HOT prune, so we
>> don't need vacuum per se, and the index-only scans are not affected
>> because the update was a HOT update, so the index keys did not change
>> either. So index-only scans would continue to return the same result.
>> Don't know if this would work with hot standby, probably not.
>
> For IOSs that sounds like an interesting and itself easy to implement
> idea, you basically only would need to add a single !use_hot_update in
> the if blocks doing the PageClearAllVisible in heap_update.
> This probably could make IOSs far more likely in some scenarios.

Doing that would completely change the meaning of the visibility map
from a heap visibility map into an index-only map.

IndexOnly scans would still work, but nothing else would ever and it
would be hard to confirm the validity of the vm.

-1

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 Simon Riggs                   http://www.2ndQuadrant.com/
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