From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Mark Dilger <hornschnorter(at)gmail(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Do XID sequences need to be contiguous? |
Date: | 2019-11-28 21:25:54 |
Message-ID: | 32485.1574976354@sss.pgh.pa.us |
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Mark Dilger <hornschnorter(at)gmail(dot)com> writes:
> While working on the problem of XID wraparound within the LISTEN/NOTIFY
> system, I tried to increment XIDs by more than one per transaction.
> This leads to a number of test failures, many which look like:
IIRC, the XID-creation logic is designed to initialize the next clog
page whenever it allocates an exact-multiple-of-BLCKSZ*4 transaction
number. Skipping over such numbers would create trouble.
> First, I'd like a good method of burning through transaction ids in
> tests designed to check for problems in XID wrap-around.
Don't "burn through them". Stop the cluster and use pg_resetwal to
set the XID counter wherever you want it. (You might need to set it
just before a page or segment boundary; I'm not sure if pg_resetwal
has any logic of its own to initialize a new CLOG page/file when you
move the counter this way. Perhaps it's worth improving that.)
> Second, I'd like to add Asserts where appropriate regarding this
> assumption.
I'm not excited about that, and it's *certainly* not a problem that
justifies additional configure infrastructure.
regards, tom lane
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