| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Merlin Moncure <mmoncure(at)gmail(dot)com> |
| Subject: | Re: Do we need so many hint bits? |
| Date: | 2012-11-17 01:19:23 |
| Message-ID: | 1353115163.14335.196.camel@sussancws0025 |
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| Thread: | |
| Lists: | pgsql-hackers |
On Fri, 2012-11-16 at 16:09 +0100, Andres Freund wrote:
> As far as I understand the code the crash-safety aspects of the
> visibilitymap currently rely on on having the knowledge that ALL_VISIBLE
> has been cleared during a heap_(insert|update|delete). That allows
> management of the visibilitymap without it being xlogged itself which
> seems pretty important to me.
It looks like the xlrec does contain a "cleared all visible" flag in it,
and it uses that to clear the VM as well as PD_ALL_VISIBLE.
So, it still seems achievable, and maybe not even a large patch, to do
away with PD_ALL_VISIBLE without a lot of performance risk.
Regards,
Jeff Davis
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