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From: Mihail Nikalayeu <[email protected]>
To: Antonin Houska <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Pg Hackers <[email protected]>
Cc: Robert Treat <[email protected]>
Subject: Re: Adding REPACK [concurrently]
Date: Thu, 18 Dec 2025 03:05:00 +0100
Message-ID: <CADzfLwWm-6WpLiif3dUZ98jHH0D+z6b-PcDuez74Cpk6Gj8mmQ@mail.gmail.com> (raw)
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Hello, Antonin!

On Sat, Dec 13, 2025 at 8:39 PM Antonin Houska <[email protected]> wrote:
> > ---
> > > SpinLockAcquire(&shared->mutex);
> > > valid = shared->sfs_valid;
> > > SpinLockRelease(&shared->mutex);
> >
> > Better to remember last_exported here to avoid any races/misses.
>
> What races/misses exactly?

Just as some way to reduce a number of potential scenarios/states
between parallel actors.

> > ---
> > > bool       done;
> >
> > bool exit_after_lsn_upto?
>
> Not sure.

I think it should be named in some way to signal it is a request, not a report.

> > Also, should we add some kind of back pressure between building
> > indexes/new heap and num of WAL we have?
> > But probably it is out of scope of the patch.
>
> Do you mean that the decoding worker should be less active if the amount of
> WAL doesn't grow too fast?

In the previous version (without background) we have some kind of
back-pressure during the scan part (if we have too muchWAL delayed
because of us - we process it).
But it is not more true with a background worker. At the same time -
it never was during the index building phase...

Best regards,
Mikhail.





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