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Re: Does PostgreSQL check database integrity at startup? - Mailing list pgsql-general

From Jan Wieck
Subject Re: Does PostgreSQL check database integrity at startup?
Date
Msg-id CAGBW59eqjmsymYJUFO6q0Yya3G2AonSi-h0vUiUCYKYUsLLM_w@mail.gmail.com
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In response to Re: Does PostgreSQL check database integrity at startup?  (Stephen Frost <sfrost@snowman.net>)
Responses Re: Does PostgreSQL check database integrity at startup?
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This whole discussion left out the critical point of

how on earth did that file end up having zero bytes?

There is the possibility that this is due to a bug in PostgreSQL. But over the 20+ years I've been using and hacking it, that has never happened.

OP never told us what type of OS, hardware and specifically storage subsystem that "slave" was running on. Filesystems zapping files to zero after a catastrophic IO failure (no longer throwing them into lost+found) isn't unheard of.


Regards, Jan


On Fri, Dec 29, 2017 at 8:13 PM, Stephen Frost <sfrost@snowman.net> wrote:
Greetings,

* Edson Carlos Ericksson Richter (richter@simkorp.com.br) wrote:
> There should be a "catalog" that point where tables are stored in physical
> files (I think, at least, because at some point PostgreSQL need to know from
> where to read the data).

Yes, it's pg_class.  Specifically, the relfilenode.

> Based on information from this catalog, would I have a tool (perhaps, a C
> function) that check that data is really there?

You could write such a function, but it wouldn't be able to be general
purpose as a zero-byte file is, in fact, a valid file.  You could just
as easily do a 'select 1 from table limit 1;' and make sure that you get
back a successful, single-row, result, if you wish to verify that certain
tables in your database always have at least 1 row.

Thanks!

Stephen



--
Jan Wieck
Senior Postgres Architect

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