From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Greg Smith <greg(at)2ndquadrant(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Enabling Checksums |
Date: | 2012-12-17 21:42:54 |
Message-ID: | CA+U5nM+5M-VeARvEeqcbKzLsE6LoXrnbFkt=6JoLY9hh085QbQ@mail.gmail.com |
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Lists: | pgsql-hackers |
On 17 December 2012 19:29, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>> Discussing this makes me realise that we need a more useful response
>> than just "your data is corrupt", so user can respond "yes, I know,
>> I'm trying to save whats left".
>
>> We'll need a way of expressing some form of corruption tolerance.
>> zero_damaged_pages is just insane, much better if we set
>> corruption_tolerance = N to allow us to skip N corrupt pages before
>> failing, with -1 meaning keep skipping for ever. Settable by superuser
>> only.
>
> Define "skip".
Allow data access, but accept that the answer is silently incomplete.
Not really much difference from zero_damaged_pages which just removes
the error by removing any chance of repair or recovery, and then
silently gives the wrong answer.
> Extra points if it makes sense for an index.
I guess not, but that's no barrier to it working on heap pages only,
in my suggested use case.
> And what about things like pg_clog pages?
SLRUs aren't checksummed because of their lack of header space.
Perhaps that is a major point against the patch.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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