pgsql: Add logging for excessive ProcSignalBarrier waits.

Add logging for excessive ProcSignalBarrier waits.

To enable diagnosis of systems that are not processing ProcSignalBarrier
requests promptly, add a LOG message every 5 seconds if we seem to be
wedged. Although you could already see this state as a wait event in
pg_stat_activity, the log message also shows the PID of the process that
is preventing progress.

Also add DEBUG1 logging around the whole wait loop.

Reviewed-by: Robert Haas <robertmhaas(at)gmail(dot)com>
Discussion: https://postgr.es/m/CA%2BTgmoYJ03r5359gQutRGP9BtigYCg3_UskcmnVjBf-QO3-0pQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0d3431497dbe91ba1e428ace4e9537c109eaff07

Modified Files
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src/backend/storage/ipc/procsignal.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)