Date: Tue, 2 Aug 2016 18:21:03 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Subject: Re: Increasing timeout of poll_query_until for TAP tests
Message-ID: <20160802222103.GA602448@alvherre.pgsql>
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Michael Paquier wrote:

> Here using pg_xlog_replay_resume() is not the correct solution because
> this would cause the node to finish recovery before we want it to, and
> so is recovery_target_action = 'promote'. If we look at the test, it
> is doing the following when getting the TXID that is used as recovery
> target:
> $node_master->safe_psql('postgres',
>         "INSERT INTO tab_int VALUES (generate_series(1001,2000))");
> my $recovery_txid =
>   $node_master->safe_psql('postgres', "SELECT txid_current()");
> my $lsn2 =
>   $node_master->safe_psql('postgres', "SELECT pg_current_xlog_location();");
> What I think we had better do is reverse the calls
> pg_current_xlog_location() and txid_current() so as we are sure that
> the LSN we track for replay is lower than the real target LSN. The
> same problem exists when defining the timestamp target.
> 
> The patch attached does that,

Why not capture both items in a single select, such as in the attached
patch?

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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diff --git a/src/test/recovery/t/003_recovery_targets.pl b/src/test/recovery/t/003_recovery_targets.pl
index 20b878e..3864e60 100644
--- a/src/test/recovery/t/003_recovery_targets.pl
+++ b/src/test/recovery/t/003_recovery_targets.pl
@@ -66,17 +66,16 @@ $node_master->backup('my_backup');
 # target TXID.
 $node_master->safe_psql('postgres',
 	"INSERT INTO tab_int VALUES (generate_series(1001,2000))");
-my $recovery_txid =
-  $node_master->safe_psql('postgres', "SELECT txid_current()");
-my $lsn2 =
-  $node_master->safe_psql('postgres', "SELECT pg_current_xlog_location();");
+my $ret =
+  $node_master->safe_psql('postgres', "SELECT pg_current_xlog_location(), txid_current();");
+my ($lsn2, $recovery_txid) = split /\|/, $ret;
 
 # More data, with recovery target timestamp
 $node_master->safe_psql('postgres',
 	"INSERT INTO tab_int VALUES (generate_series(2001,3000))");
-my $recovery_time = $node_master->safe_psql('postgres', "SELECT now()");
-my $lsn3 =
-  $node_master->safe_psql('postgres', "SELECT pg_current_xlog_location();");
+$ret =
+  $node_master->safe_psql('postgres', "SELECT pg_current_xlog_location(), now();");
+my ($lsn3, $recovery_time) = split /\|/, $ret;
 
 # Even more data, this time with a recovery target name
 $node_master->safe_psql('postgres',

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