| From: | Greg Stark <stark(at)mit(dot)edu> |
|---|---|
| To: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, simon(at)2ndquadrant(dot)com, tgl(at)sss(dot)pgh(dot)pa(dot)us, alvherre(at)commandprompt(dot)com, david(at)fetter(dot)org, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Page Checksums + Double Writes |
| Date: | 2011-12-28 14:45:11 |
| Message-ID: | CAM-w4HMnX=KV+wnuh1Js=LG05ae-jBG5q5DKvXOSWf9MkVi0YQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Dec 27, 2011 at 10:43 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> I bet if you kept a judicious number of
> clog pages in each local process with some smart invalidation you
> could cover enough cases that scribbling the bits down would become
> unnecessary.
I don't understand how any cache can completely remove the need for
hint bits. Without hint bits the xids in the tuples will be "in-doubt"
forever. No matter how large your cache you'll always come across
tuples that are arbitrarily old and are from an unbounded size set of
xids.
We could replace the xids with a frozen xid sooner but that just
amounts to nearly the same thing as the hint bits only with page
locking and wal records.
--
greg
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