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From: Nathan Bossart <[email protected]>
To: Tom Lane <[email protected]>
Cc: Kumar, Sachin <[email protected]>
Cc: Robins Tharakan <[email protected]>
Cc: Jan Wieck <[email protected]>
Cc: Bruce Momjian <[email protected]>
Cc: Zhihong Yu <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Magnus Hagander <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: pg_upgrade failing for 200+ million Large Objects
Date: Fri, 12 Jan 2024 16:48:20 -0600
Message-ID: <20240112224820.GB3857154@nathanxps13> (raw)
In-Reply-To: <[email protected]>
References: <CAAWbhmgUb8p7ff_ZX5jCvqM=ipPxbbDJTXMNVzH-Ho_CXVkRHA@mail.gmail.com>
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On Fri, Jan 05, 2024 at 03:02:34PM -0500, Tom Lane wrote:
> On further reflection, there is a very good reason why it's done like
> that.  Because pg_upgrade is doing schema-only dump and restore,
> there's next to no opportunity for parallelism within either pg_dump
> or pg_restore.  There's no data-loading steps, and there's no
> index-building either, so the time-consuming stuff that could be
> parallelized just isn't happening in pg_upgrade's usage.
> 
> Now it's true that my 0003 patch moves the needle a little bit:
> since it makes BLOB creation (as opposed to loading) parallelizable,
> there'd be some hope for parallel pg_restore doing something useful in
> a database with very many blobs.  But it makes no sense to remove the
> existing cross-database parallelism in pursuit of that; you'd make
> many more people unhappy than happy.

I assume the concern is that we'd end up multiplying the effective number
of workers if we parallelized both in-database and cross-database?  Would
it be sufficient to make those separately configurable with a note about
the multiplicative effects of setting both?  I think it'd be unfortunate if
pg_upgrade completely missed out on this improvement.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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