how reliable is pg_rewind?

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how reliable is pg_rewind?

Curt Kolovson
When trying to resync an old primary to become a new standby, I have found that pg_rewind only works occasionally. How reliable/robust is pg_rewind, and what are its limitations? We have observed that approx half our FPIs in the WALs are due to XLOG/FPI_FOR_HINT. The only reason we've set wal_log_hints=on is so that we can  use pg_rewind. But if pg_rewind is unreliable, we would rather turn off wal_log_hints. Any info on the reliability of pg_rewind and its limitations would be appreciated.

Thanks, Curt 
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Re: how reliable is pg_rewind?

Michael Paquier-2
On Sat, Aug 01, 2020 at 10:35:37AM -0700, Curt Kolovson wrote:
> When trying to resync an old primary to become a new standby, I have found
> that pg_rewind only works occasionally. How reliable/robust is pg_rewind,
> and what are its limitations? We have observed that approx half our FPIs in
> the WALs are due to XLOG/FPI_FOR_HINT. The only reason we've set
> wal_log_hints=on is so that we can  use pg_rewind. But if pg_rewind is
> unreliable, we would rather turn off wal_log_hints. Any info on the
> reliability of pg_rewind and its limitations would be appreciated.

FWIW, we use it in production to accelerate the redeployment of
standbys in HA configuration for 4 years now in at least one product,
and it is present in upstream for since 9.5, for 5 years now.  So the
tool is rather baked at this stage of the game.
--
Michael

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Re: how reliable is pg_rewind?

Paul Förster
Hi Curt, hi Michael,

> On 03. Aug, 2020, at 03:58, Michael Paquier <[hidden email]> wrote:
>
> On Sat, Aug 01, 2020 at 10:35:37AM -0700, Curt Kolovson wrote:
>> Any info on the reliability of pg_rewind and its limitations would be appreciated.
>
> FWIW, we use it in production to accelerate the redeployment of
> standbys in HA configuration for 4 years now in at least one product,
> and it is present in upstream for since 9.5, for 5 years now.  So the
> tool is rather baked at this stage of the game.

same here. We use it with Patroni in failover cluster setups for about 2-3 years now. It has not failed us yet.

Cheers,
Paul



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Re: how reliable is pg_rewind?

Curt Kolovson
Thanks, Paul and Michael. I forgot to mention that we're using postgres v10.12. 

On Sun, Aug 2, 2020 at 10:29 PM Paul Förster <[hidden email]> wrote:
Hi Curt, hi Michael,

> On 03. Aug, 2020, at 03:58, Michael Paquier <[hidden email]> wrote:
>
> On Sat, Aug 01, 2020 at 10:35:37AM -0700, Curt Kolovson wrote:
>> Any info on the reliability of pg_rewind and its limitations would be appreciated.
>
> FWIW, we use it in production to accelerate the redeployment of
> standbys in HA configuration for 4 years now in at least one product,
> and it is present in upstream for since 9.5, for 5 years now.  So the
> tool is rather baked at this stage of the game.

same here. We use it with Patroni in failover cluster setups for about 2-3 years now. It has not failed us yet.

Cheers,
Paul

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Re: how reliable is pg_rewind?

Paul Förster
Hi Curt,

> On 03. Aug, 2020, at 08:25, Curt Kolovson <[hidden email]> wrote:
> Thanks, Paul and Michael. I forgot to mention that we're using postgres v10.12.

11.6 and 12.3 here.

Also, please don't top-post, thanks.

Cheers,
Paul