Message-ID: <8e24a470-b092-3c9f-0614-acd9df3f724f@enterprisedb.com>
Date: Sat, 18 Dec 2021 22:48:11 +0100
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Subject: Re: sequences vs. synchronous replication
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
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On 12/18/21 22:27, Tom Lane wrote:
> Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
>> Here's a PoC demonstrating this idea. I'm not convinced it's the right
>> way to deal with this - it surely seems more like a duct tape fix than a
>> clean solution. But it does the trick.
> 
> I was imagining something a whole lot simpler, like "don't try to
> cache unused sequence numbers when wal_level > minimal".  We've
> accepted worse performance hits in that operating mode, and it'd
> fix a number of user complaints we've seen about weird sequence
> behavior on standbys.
> 

What do you mean by "not caching unused sequence numbers"? Reducing 
SEQ_LOG_VALS to 1, i.e. WAL-logging every sequence increment?

That'd work, but I wonder how significant the impact will be. It'd bet 
it hurts the patch adding logical decoding of sequences quite a bit.

regards

-- 
Tomas Vondra
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