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Relax overly strict assertion

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Ever since its birth, ReorderBufferBuildTupleCidHash() has contained an
assertion that a catalog tuple cannot change Cmax after acquiring one.  But
that's wrong: if a subtransaction executes DDL that affects that catalog
tuple, and later aborts and another DDL affects the same tuple, it will
change Cmax.  Relax the assertion to merely verify that the Cmax remains
valid and monotonically increasing, instead.

Add a test that tickles the relevant code.

Diagnosed by, and initial patch submitted by: Arseny Sher
Co-authored-by: Arseny Sher
Discussion: https://postgr.es/m/874l9p8hyw.fsf@ars-thinkpad
This commit is contained in:
Alvaro Herrera
2019-02-12 18:42:37 -03:00
parent 2a0edae47a
commit f5f9a760a3
3 changed files with 40 additions and 5 deletions
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14
src/backend/replication/logical/reorderbuffer.c
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@ -1334,15 +1334,19 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
}
else
{
/*
* Maybe we already saw this tuple before in this transaction,
* but if so it must have the same cmin.
*/
Assert(ent->cmin == change->data.tuplecid.cmin);
Assert(ent->cmax == InvalidCommandId ||
ent->cmax == change->data.tuplecid.cmax);
/*
* if the tuple got valid in this transaction and now got deleted
* we already have a valid cmin stored. The cmax will be
* InvalidCommandId though.
* cmax may be initially invalid, but once set it can only grow,
* and never become invalid again.
*/
Assert((ent->cmax == InvalidCommandId) ||
((change->data.tuplecid.cmax != InvalidCommandId) &&
(change->data.tuplecid.cmax > ent->cmax)));
ent->cmax = change->data.tuplecid.cmax;
}
}