| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Michael Paquier <michael(at)paquier(dot)xyz>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Stephen Frost <sfrost(at)snowman(dot)net>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Online verification of checksums |
| Date: | 2019-03-04 14:01:46 |
| Message-ID: | 090a264c-f6ba-ae69-86df-41408df66293@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On 3/4/19 4:09 AM, Michael Paquier wrote:
> On Sun, Mar 03, 2019 at 07:58:26AM +0100, Fabien COELHO wrote:
>> I agree that having a server function (extension?) to do a full checksum
>> verification, possibly bandwidth-controlled, would be a good thing. However
>> it would have side effects, such as interfering deeply with the server page
>> cache, which may or may not be desirable.
>
> In what is that different from VACUUM or a sequential scan? It is
> possible to use buffer ring replacement strategies in such cases using
> the normal clock-sweep algorithm, so that scanning a range of pages
> does not really impact Postgres shared buffer cache.
> --
But Fabien was talking about page cache, not shared buffers. And we
can't use custom ring buffer there. OTOH I don't see why accessing the
file through SQL function would behave any differently than direct
access (i.e. what the tool does now).
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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