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From: Bertrand Drouvot <[email protected]>
To: Michael Paquier <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: [email protected]
Subject: Re: [BUG]: the walsender does not update its IO statistics until it exits
Date: Wed, 1 Oct 2025 14:21:22 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Hi,

On Wed, Oct 01, 2025 at 07:43:31AM +0900, Michael Paquier wrote:
> On Tue, Sep 30, 2025 at 10:05:43AM +0000, Bertrand Drouvot wrote:
> > On Tue, Sep 30, 2025 at 04:37:25PM +0900, Michael Paquier wrote:
> >> Or perhaps you think that the pending data of a stats kind could be
> >> different if a kind allows transactional and non-transactional
> >> flushes? 
> > 
> > Yeah that was my thought: one stats kind could have metrics that are transactional
> > and some metrics that are non-transactional. This could be possible for
> > both variable and fixed stats, that's why I was thinking about having
> > 2 pending lists for the variables stats and 2 flush callbacks for fixed stats.
> 
> Okay.  The first use case that comes into mind here is pgstat_io.c, to
> offer periodic reports on analytics (please extend that to the backend
> stats for WAL and I/O).  In this case, it seems that it would be good
> to know about all the stats fields, meaning that a single pending list
> is OK.  My feeling would be to reuse pgstat_report_stat() and plant a
> new argument for the transactional state (or just a bits32 that works
> along the force option) with the same threshold for reports, combined
> with a new option to allow non-transactional reports (don't see a
> point in forcing these and wait on locks, 1-min reports not happening
> would not matter if an analytical query takes a few hours).
> 
> It would be better to determine a list of the stats we'd be
> interesting in seeing updated without waiting for a query or a 
> transaction to finish, then design the needs around these
> requirements, with a new thread to discuss the matter.  The IO stats
> are just the first case coming into mind.

Yeah. Also for the relations stats we'd have a mix (for example there is no
need to wait for a transaction to finish to report it's related seq_scan if
any).

I'll work on a list and open a dedicated thread.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com





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