Track conflict_reason in pg_replication_slots.

This patch changes the existing 'conflicting' field to 'conflict_reason'
in pg_replication_slots. This new field indicates the reason for the
logical slot's conflict with recovery. It is always NULL for physical
slots, as well as for logical slots which are not invalidated. The
non-NULL values indicate that the slot is marked as invalidated. Possible
values are:

wal_removed = required WAL has been removed.
rows_removed = required rows have been removed.
wal_level_insufficient = the primary doesn't have a wal_level sufficient
to perform logical decoding.

The existing users of 'conflicting' column can get the same answer by
using 'conflict_reason' IS NOT NULL.

Author: Shveta Malik
Reviewed-by: Amit Kapila, Bertrand Drouvot, Michael Paquier
Discussion: https://postgr.es/m/ZYOE8IguqTbp-seF@paquier.xyz

2 files changed, 40 insertions, 36 deletions

diff --git a/src/test/recovery/t/035_standby_logical_decoding.pl b/src/test/recovery/t/035_standby_logical_decoding.pl
index 3231538418b..8bc39a5f033 100644
--- a/src/test/recovery/t/035_standby_logical_decoding.pl
+++ b/src/test/recovery/t/035_standby_logical_decoding.pl
@@ -168,27 +168,25 @@ sub change_hot_standby_feedback_and_wait_for_xmins
 	}
 }
 
-# Check conflicting status in pg_replication_slots.
-sub check_slots_conflicting_status
+# Check conflict_reason in pg_replication_slots.
+sub check_slots_conflict_reason
 {
-	my ($conflicting) = @_;
+	my ($slot_prefix, $reason) = @_;
 
-	if ($conflicting)
-	{
-		$res = $node_standby->safe_psql(
-			'postgres', qq(
-				 select bool_and(conflicting) from pg_replication_slots;));
+	my $active_slot = $slot_prefix . 'activeslot';
+	my $inactive_slot = $slot_prefix . 'inactiveslot';
 
-		is($res, 't', "Logical slots are reported as conflicting");
-	}
-	else
-	{
-		$res = $node_standby->safe_psql(
-			'postgres', qq(
-				select bool_or(conflicting) from pg_replication_slots;));
+	$res = $node_standby->safe_psql(
+		'postgres', qq(
+			 select conflict_reason from pg_replication_slots where slot_name = '$active_slot';));
 
-		is($res, 'f', "Logical slots are reported as non conflicting");
-	}
+	is($res, "$reason", "$active_slot conflict_reason is $reason");
+
+	$res = $node_standby->safe_psql(
+		'postgres', qq(
+			 select conflict_reason from pg_replication_slots where slot_name = '$inactive_slot';));
+
+	is($res, "$reason", "$inactive_slot conflict_reason is $reason");
 }
 
 # Drop the slots, re-create them, change hot_standby_feedback,
@@ -260,13 +258,13 @@ $node_primary->safe_psql('testdb',
 	qq[SELECT * FROM pg_create_physical_replication_slot('$primary_slotname');]
 );
 
-# Check conflicting is NULL for physical slot
+# Check conflict_reason is NULL for physical slot
 $res = $node_primary->safe_psql(
 	'postgres', qq[
-		 SELECT conflicting is null FROM pg_replication_slots where slot_name = '$primary_slotname';]
+		 SELECT conflict_reason is null FROM pg_replication_slots where slot_name = '$primary_slotname';]
 );
 
-is($res, 't', "Physical slot reports conflicting as NULL");
+is($res, 't', "Physical slot reports conflict_reason as NULL");
 
 my $backup_name = 'b1';
 $node_primary->backup($backup_name);
@@ -483,8 +481,8 @@ $node_primary->wait_for_replay_catchup($node_standby);
 # Check invalidation in the logfile and in pg_stat_database_conflicts
 check_for_invalidation('vacuum_full_', 1, 'with vacuum FULL on pg_class');
 
-# Verify slots are reported as conflicting in pg_replication_slots
-check_slots_conflicting_status(1);
+# Verify conflict_reason is 'rows_removed' in pg_replication_slots
+check_slots_conflict_reason('vacuum_full_', 'rows_removed');
 
 $handle =
   make_slot_active($node_standby, 'vacuum_full_', 0, \$stdout, \$stderr);
@@ -502,8 +500,8 @@ change_hot_standby_feedback_and_wait_for_xmins(1, 1);
 ##################################################
 $node_standby->restart;
 
-# Verify slots are reported as conflicting in pg_replication_slots
-check_slots_conflicting_status(1);
+# Verify conflict_reason is retained across a restart.
+check_slots_conflict_reason('vacuum_full_', 'rows_removed');
 
 ##################################################
 # Verify that invalidated logical slots do not lead to retaining WAL.
@@ -511,7 +509,7 @@ check_slots_conflicting_status(1);
 
 # Get the restart_lsn from an invalidated slot
 my $restart_lsn = $node_standby->safe_psql('postgres',
-	"SELECT restart_lsn from pg_replication_slots WHERE slot_name = 'vacuum_full_activeslot' and conflicting is true;"
+	"SELECT restart_lsn from pg_replication_slots WHERE slot_name = 'vacuum_full_activeslot' and conflict_reason is not null;"
 );
 
 chomp($restart_lsn);
@@ -565,8 +563,8 @@ $node_primary->wait_for_replay_catchup($node_standby);
 # Check invalidation in the logfile and in pg_stat_database_conflicts
 check_for_invalidation('row_removal_', $logstart, 'with vacuum on pg_class');
 
-# Verify slots are reported as conflicting in pg_replication_slots
-check_slots_conflicting_status(1);
+# Verify conflict_reason is 'rows_removed' in pg_replication_slots
+check_slots_conflict_reason('row_removal_', 'rows_removed');
 
 $handle =
   make_slot_active($node_standby, 'row_removal_', 0, \$stdout, \$stderr);
@@ -604,8 +602,8 @@ $node_primary->wait_for_replay_catchup($node_standby);
 check_for_invalidation('shared_row_removal_', $logstart,
 	'with vacuum on pg_authid');
 
-# Verify slots are reported as conflicting in pg_replication_slots
-check_slots_conflicting_status(1);
+# Verify conflict_reason is 'rows_removed' in pg_replication_slots
+check_slots_conflict_reason('shared_row_removal_', 'rows_removed');
 
 $handle = make_slot_active($node_standby, 'shared_row_removal_', 0, \$stdout,
 	\$stderr);
@@ -657,7 +655,13 @@ ok( $node_standby->poll_query_until(
 ) or die "Timed out waiting confl_active_logicalslot to be updated";
 
 # Verify slots are reported as non conflicting in pg_replication_slots
-check_slots_conflicting_status(0);
+is( $node_standby->safe_psql(
+		'postgres',
+		q[select bool_or(conflicting) from
+		  (select conflict_reason is not NULL as conflicting
+		   from pg_replication_slots WHERE slot_type = 'logical')]),
+	'f',
+	'Logical slots are reported as non conflicting');
 
 # Turn hot_standby_feedback back on
 change_hot_standby_feedback_and_wait_for_xmins(1, 0);
@@ -693,8 +697,8 @@ $node_primary->wait_for_replay_catchup($node_standby);
 # Check invalidation in the logfile and in pg_stat_database_conflicts
 check_for_invalidation('pruning_', $logstart, 'with on-access pruning');
 
-# Verify slots are reported as conflicting in pg_replication_slots
-check_slots_conflicting_status(1);
+# Verify conflict_reason is 'rows_removed' in pg_replication_slots
+check_slots_conflict_reason('pruning_', 'rows_removed');
 
 $handle = make_slot_active($node_standby, 'pruning_', 0, \$stdout, \$stderr);
 
@@ -737,8 +741,8 @@ $node_primary->wait_for_replay_catchup($node_standby);
 # Check invalidation in the logfile and in pg_stat_database_conflicts
 check_for_invalidation('wal_level_', $logstart, 'due to wal_level');
 
-# Verify slots are reported as conflicting in pg_replication_slots
-check_slots_conflicting_status(1);
+# Verify conflict_reason is 'wal_level_insufficient' in pg_replication_slots
+check_slots_conflict_reason('wal_level_', 'wal_level_insufficient');
 
 $handle =
   make_slot_active($node_standby, 'wal_level_', 0, \$stdout, \$stderr);
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index f645e8486bf..d878a971df9 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1473,8 +1473,8 @@ pg_replication_slots| SELECT l.slot_name,
     l.wal_status,
     l.safe_wal_size,
     l.two_phase,
-    l.conflicting
-   FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size, two_phase, conflicting)
+    l.conflict_reason
+   FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size, two_phase, conflict_reason)
      LEFT JOIN pg_database d ON ((l.datoid = d.oid)));
 pg_roles| SELECT pg_authid.rolname,
     pg_authid.rolsuper,