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help / color / mirror / Atom feedFrom: Greg Sabino Mullane <[email protected]>
To: Jon Zeppieri <[email protected]>
Cc: Nick Cleaton <[email protected]>
Cc: [email protected]
Subject: Re: Possible causes of high_replay lag, given replication settings?
Date: Fri, 25 Jul 2025 19:12:26 -0400
Message-ID: <CAKAnmm+jtytmNAYDjBkiQvCHQVwtskUzvp3J_=5mUsFvaOkRVA@mail.gmail.com> (raw)
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References: <CAKfDxxwF03mouH7GqdZ0AqpGKz2wTj4T3F6ei_ubEQnNtErfGA@mail.gmail.com>
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On Fri, Jul 25, 2025 at 9:57 AM Jon Zeppieri <[email protected]> wrote:
> Thanks for the response, Nick. I'm curious why the situation you describe
> wouldn't also lead to the write_lag and flush_lag also being
> high. If the problem is simply keeping up with the primary, wouldn't you
> expect all three lag times to be elevated?
>
No - write and flush are pretty quick and simple, it's just putting the WAL
onto the local disk. Replay involves a lot more work as we have to parse
the WAL and apply the changes, which means doing a lot of I/O across many
files. Still, *hours* to me indicates more than just a lot of extra
traffic. Check that recovery_min_apply_delay is still 0, then log onto the
replica and see what's going on with regards to open transactions and locks.
Cheers,
Greg
--
Crunchy Data - https://www.crunchydata.com
Enterprise Postgres Software Products & Tech Support
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Subject: Re: Possible causes of high_replay lag, given replication settings?
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