| From: | Stephen Frost <sfrost(at)snowman(dot)net> |
|---|---|
| To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
| Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, 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 00:31:08 |
| Message-ID: | 20170126003108.GZ9812@tamriel.snowman.net |
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| Lists: | pgsql-hackers |
* Michael Paquier (michael(dot)paquier(at)gmail(dot)com) wrote:
> On Thu, Jan 26, 2017 at 9:14 AM, 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?
>
> Why? What do you foresee here? I would think such backup solutions are
> careful enough to ensure correctly the durability of pages so as they
> are not partially written.
I believe his concern was that the backup sw might see a
partially-updated page when it reads the file while PG is writing it.
In other words, would the kernel return some intermediate state of data
while an fwrite() is in progress.
Thanks!
Stephen
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