Re: crash-safe visibility map, take five

On Wed, Jun 22, 2011 at 10:40 PM, Jeff Davis  wrote:
> 1. Torn pages -- not a problem because it's a single bit and idempotent.

Right.

> 2. PD_ALL_VISIBLE bit makes it to disk before a WAL record representing
> an action that makes the page all-visible. Depending on what action
> makes a page all-visible:
>  a. An old snapshot is released -- not a problem, because if there is a
> crash all snapshots are released.
>  b. Cleanup action on the page -- not a problem, because that will
> create a WAL record and update the page's LSN before setting the
> PD_ALL_VISIBLE.

Lazy VACUUM is the only thing that makes a page all visible.  I don't
understand the part about snapshots.

-- 
Robert Haas
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