Jaime Casanova recently reported a situation where pglogical replicating
from 64 POS sites to a single central (64-core) node, each with two
replication sets, causes XLog's info_lck to become highly contended
because of frequently reading LogwrtResult. We tested the simple fix of
adding a new LWLock that protects LogwrtResult and LogwrtRqst; that
seems to solve the problem easily enough.
At first I wanted to make the new LWLock cover only LogwrtResult proper,
and leave LogwrtRqst alone. However on doing it, it seemed that that
might change the locking protocol in a nontrivial way. So I decided to
make it cover both and call it a day. We did verify that the patch
solves the reported problem, at any rate.
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Álvaro Herrera PostgreSQL Expert, https://www.2ndQuadrant.com/