| From: | Stephen Frost <sfrost(at)snowman(dot)net> |
|---|---|
| To: | Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Checksums by default? |
| Date: | 2017-01-26 00:30:08 |
| Message-ID: | 20170126003008.GY9812@tamriel.snowman.net |
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| Lists: | pgsql-hackers |
* Peter Geoghegan (pg(at)heroku(dot)com) wrote:
> On Wed, Jan 25, 2017 at 3:30 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> > As it is, there are backup solutions which *do* check the checksum when
> > backing up PG. This is no longer, thankfully, some hypothetical thing,
> > but something which really exists and will hopefully keep users from
> > losing data.
>
> Wouldn't that have issues with torn pages?
No, why would it? The page has either been written out by PG to the OS,
in which case the backup s/w will see the new page, or it hasn't been.
Our testing has not turned up any issues as yet. That said, it's
relatively new and I wouldn't be surprised if we need to do some
adjustments in that area, which might be system-dependent even. We
could certainly check the WAL for the page that had a checksum error (we
currently simply report them, though don't throw away a prior backup if
we detect one).
This isn't like a case where only half the page made it to the disk
because of a system failure though; everything is online and working
properly during an online backup.
Thanks!
Stephen
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