Re: Refactor pg_rewind code and make it work against a standby

Hi,

On 2020-11-15 17:10:53 +0200, Heikki Linnakangas wrote:
> Yep, quite right. Fixed that way, thanks for the debugging!

I locally, on a heavily modified branch (AIO support), started to get
consistent failures in this test. I *suspect*, but am not sure, that
it's the test's fault, not the fault of modifications.

As far as I can tell, after the pg_rewind call, there's no guarantee
that node_c has fully caught up to the 'in A, after C was promoted'
insertion on node a. Thus at the check_query() I sometimes get just 'in
A, before promotion' back.

After adding a wait that problem seems to be fixed. Here's what I did

diff --git i/src/bin/pg_rewind/t/007_standby_source.pl w/src/bin/pg_rewind/t/007_standby_source.pl
index f6abcc2d987..48898bef2f5 100644
--- i/src/bin/pg_rewind/t/007_standby_source.pl
+++ w/src/bin/pg_rewind/t/007_standby_source.pl
@@ -88,6 +88,7 @@ $node_c->safe_psql('postgres', "checkpoint");
# - you need to rewind.
$node_a->safe_psql('postgres',
"INSERT INTO tbl1 VALUES ('in A, after C was promoted')");
+$lsn = $node_a->lsn('insert');

# Also insert a new row in the standby, which won't be present in the
# old primary.
@@ -142,6 +143,8 @@ $node_primary = $node_c;
# Run some checks to verify that C has been successfully rewound,
# and connected back to follow B.

+$node_b->wait_for_catchup('node_c', 'replay', $lsn);
+
check_query(
'SELECT * FROM tbl1',
qq(in A

- Andres