On Wed, Oct 05, 2016 at 04:39:39PM +0200, Michael Banck wrote: > if pg_rewind is told to fetch data via a libpq connection > (--source-server), synchronous replication is enabled and there is only > one sync standby (pilot error, but sill); pg_rewinding the old master > hangs at the CREATE TEMPORARY TABLE step (CREATE TABLE waiting for > X/XXXXXXXX). At least this happened to one of our clients while > evaluating pg_rewind. > > To the user, the last thing printed is "need to copy XXXX MB [...]". If > the user cancels the pg_rewind command with ^C, the backend keeps > hanging around even in --dry-run mode. That won't hurt too much as it > does not seem to block future pg_rewind runs after synchronous_commit > has been set to a different value, but looks surprising to me. > > Not sure whether pg_rewind could error out gracefully without hanging in > this case,
My colleague Christoph Berg pointed out that pg_rewind could just set synchronous_commit = local before creating the temporary table, which indeed works, proof-of-concept patch attached Michael -- Michael Banck Projektleiter / Senior Berater Tel.: +49 2166 9901-171 Fax: +49 2166 9901-100 Email: michael.ba...@credativ.de credativ GmbH, HRB Mönchengladbach 12080 USt-ID-Nummer: DE204566209 Trompeterallee 108, 41189 Mönchengladbach Geschäftsführung: Dr. Michael Meskes, Jörg Folz, Sascha Heuer
diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c index 9239009..a5cb426 100644 --- a/src/bin/pg_rewind/libpq_fetch.c +++ b/src/bin/pg_rewind/libpq_fetch.c @@ -406,7 +406,7 @@ libpq_executeFileMap(filemap_t *map) * First create a temporary table, and load it with the blocks that we * need to fetch. */ - sql = "CREATE TEMPORARY TABLE fetchchunks(path text, begin int4, len int4);"; + sql = "SET synchronous_commit = local; CREATE TEMPORARY TABLE fetchchunks(path text, begin int4, len int4);"; res = PQexec(conn, sql); if (PQresultStatus(res) != PGRES_COMMAND_OK)
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