From 7aab24e8bff9f9d7f0ab4247bc4cb727a33aa2a5 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Tue, 18 Jun 2024 16:09:00 -0400 Subject: [PATCH v1 1/2] Repro for vacuum infinite loop This repro is not stable enough to be added as a test to the regression suite. It is for demonstration purposes on the thread. --- src/test/recovery/t/099_vacuum_hang.pl | 286 +++++++++++++++++++++++++ 1 file changed, 286 insertions(+) create mode 100644 src/test/recovery/t/099_vacuum_hang.pl diff --git a/src/test/recovery/t/099_vacuum_hang.pl b/src/test/recovery/t/099_vacuum_hang.pl new file mode 100644 index 00000000000..55272c39b23 --- /dev/null +++ b/src/test/recovery/t/099_vacuum_hang.pl @@ -0,0 +1,286 @@ +use strict; +use warnings; +use PostgreSQL::Test::Cluster; +use PostgreSQL::Test::Utils; +use Test::More; +use IPC::Run qw(pump); + +# Set up nodes +my $node_primary = PostgreSQL::Test::Cluster->new('primary'); +$node_primary->init(allows_streaming => 'physical'); + +my $tablespace1 = "test_vacuum_hang_tblspc"; + +$node_primary->append_conf( + 'postgresql.conf', qq[ +allow_in_place_tablespaces = on +hot_standby_feedback = on +log_recovery_conflict_waits = true +log_statement='all' +log_connections=true +log_lock_waits = true +autovacuum = off +]); +$node_primary->start; + +my $backup_name = 'my_backup'; + +# Make a tablespace for use with our later ALTER INDEX ... SET TABLESPACE +$node_primary->safe_psql('postgres', + qq[CREATE TABLESPACE $tablespace1 LOCATION '']); + +$node_primary->backup($backup_name); +my $node_replica = PostgreSQL::Test::Cluster->new('standby'); +$node_replica->init_from_backup($node_primary, $backup_name, + has_streaming => 1); + +$node_replica->start; + +my $test_db = "test_db"; +$node_primary->safe_psql('postgres', "CREATE DATABASE $test_db"); + +my $orig_conninfo = $node_primary->connstr(); + +# test schema / data +my $table1 = "test_vacuum_hang_table"; +my $index1 = "test_vacuum_hang_index"; +my $col1 = "col1"; + +my $psql_timeout = IPC::Run::timer(10); + +# Long-running Primary Session A +my %psql_primaryA = ('stdin' => '', 'stdout' => ''); +$psql_primaryA{run} = + $node_primary->background_psql($test_db, \$psql_primaryA{stdin}, + \$psql_primaryA{stdout}, + $psql_timeout); +$psql_primaryA{stdout} = ''; +$psql_primaryA{stdin} = "set application_name=A;\n"; + +# Long-running Primary Session B +my %psql_primaryB = ('stdin' => '', 'stdout' => ''); +$psql_primaryB{run} = + $node_primary->background_psql($test_db, \$psql_primaryB{stdin}, + \$psql_primaryB{stdout}, + $psql_timeout); +$psql_primaryB{stdout} = ''; +$psql_primaryB{stdin} = "set application_name=B;\n"; + +# Long-running Primary Session C +my %psql_primaryC = ('stdin' => '', 'stdout' => ''); +$psql_primaryC{run} = + $node_primary->background_psql($test_db, \$psql_primaryC{stdin}, + \$psql_primaryC{stdout}, + $psql_timeout); +$psql_primaryC{stdout} = ''; +$psql_primaryC{stdin} = "set application_name=C;\n"; + +# Long-running Replica Session A +my %psql_replicaA = ('stdin' => '', 'stdout' => ''); +$psql_replicaA{run} = + $node_replica->background_psql($test_db, \$psql_replicaA{stdin}, + \$psql_replicaA{stdout}, + $psql_timeout); +$psql_replicaA{stdout} = ''; + +# Insert one tuple with value 1 which we can use to make sure the cursor has +# successfully pinned and locked the buffer. +$node_primary->safe_psql($test_db, qq[ + CREATE TABLE ${table1}(${col1} int) with (autovacuum_enabled=false); + CREATE INDEX ${index1} on ${table1}(${col1}); + INSERT INTO $table1 VALUES(1); +]); + +my $primary_lsn = $node_primary->lsn('flush'); +$node_primary->wait_for_catchup($node_replica, 'replay', $primary_lsn); + +my $walreceiver_pid = $node_replica->safe_psql($test_db, qq[ + select pid from pg_stat_activity where backend_type = 'walreceiver';]); + +# Set primary_conninfo to something invalid on the replica and reload the config. +# This will prevent the standby from reconnecting once the connection is terminated. +# Then terminate the wal receiver. When a new WAL receiver process starts up, +# it will have to use the primary_conninfo to connect to the primary and be +# unable to do so. +$node_replica->safe_psql($test_db, qq[ + ALTER SYSTEM SET primary_conninfo = ''; + SELECT pg_reload_conf(); + SELECT pg_terminate_backend($walreceiver_pid)]); + +# Ensure the WAL receiver is no longer active on replica. +$node_replica->poll_query_until($test_db, qq[ + select exists (select * from pg_stat_activity where pid = $walreceiver_pid);] , 'f'); + +# DECLARE and use a cursor on standby, causing the block of the relation to be +# pinned and locked in a buffer on the replica. It is important that this is +# after termination of the WAL receiver so that the primary does not know about +# the cursor and it can't hold back the horizon on the primary. +my $replica_cursor1 = "test_vacuum_hang_cursor_replica1"; +$psql_replicaA{stdin} .= qq[ + BEGIN; + DECLARE $replica_cursor1 CURSOR FOR SELECT * FROM $table1; + FETCH FORWARD FROM $replica_cursor1; + ]; + +# FETCH FORWARD should have returned a 1. That's how we know the cursor has a +# pin and lock. +ok(pump_until($psql_replicaA{run}, $psql_timeout, + \$psql_replicaA{stdout}, qr/^1$/m), "got first value from replica cursor"); + +# Insert a new tuple and update it. Now there are two live tuples and one dead +# tuple on the page on the primary. The connection to the replica was +# terminated, so the replica will only have the single live tuple. +$psql_primaryA{stdin} .= qq[ + INSERT INTO $table1 VALUES (99); + UPDATE $table1 SET $col1 = 100 WHERE $col1 = 99; + SELECT 'after_update'; + ]; + +# Make sure the UPDATE finished +ok(pump_until($psql_primaryA{run}, $psql_timeout, + \$psql_primaryA{stdout}, qr/^after_update$/m), "SELECT output from primary session A"); + +# Open a cursor on the primary whose lock will keep a subsequent ALTER INDEX +# from executing. We want VACUUM to be able to start, calculate initial values +# for OldestXmin and GlobalVisState and then pause before pruning our dead +# tuple. To accomplish this, we will run an ALTER INDEX which starts before +# VACUUM but cannot proceed (because of the cursor's lock on the index) until +# after VACUUM gets initial values for OldestXmin and GlobalVisState. When the +# cursor is closed, the ALTER INDEX will proceed and modify the index, causing +# a relcache invalidation and forcing vacuum to rebuild the catalog snapshot +# after the ALTER INDEX commits before pruning the dead tuple. +# +my $primary_cursor1 = "test_vacuum_hang_cursor_primary1"; +$psql_primaryB{stdin} .= qq[ + BEGIN; + DECLARE $primary_cursor1 CURSOR FOR SELECT * FROM $table1; + FETCH FORWARD FROM $primary_cursor1; + ]; + +# There is one live tuple on the primary with value 100 and one live tuple with +# value 1. +ok(pump_until($psql_primaryB{run}, $psql_timeout, + \$psql_primaryB{stdout}, qr/^1$/m), "got first value from primary cursor"); + +# the ALTER INDEX won't proceed until the cursor has been closed because it +# needs an exclusive lock and the cursor has an access share lock. +$psql_primaryC{stdin} .= qq[ + BEGIN; + ALTER INDEX $index1 SET TABLESPACE $tablespace1; + SELECT 'after_alter_index'; + ]; + +$psql_primaryC{run}->pump_nb(); + +# Wait until we know the access exclusive lock has been requested but not granted +$node_primary->poll_query_until($test_db, qq[ + select granted from pg_locks + where mode = 'AccessExclusiveLock' and relation = '$index1'::regclass;], 'f'); + +# ALTER INDEX has a row exclusive lock on the index and share update exclusive +# lock on the table, so VACUUM will have to wait while attempting to open the +# indexes. +# +# Note that all transactions on the primary see the dead tuple on the primary +# as committed, so before the new snapshot is taken and GlobalVisState is +# updated, VACUUM's GlobalVisState->maybe_needed will be newer than the dead +# tuple's xmax, so the tuple would have been considered removable when compared +# to GlobalVisState. +$psql_primaryA{stdin} .= qq[ + VACUUM $table1; + \\echo VACUUM + ]; + +# Try and make sure our vacuum command has reached the server before we commit +# the cursor. +$psql_primaryA{run}->pump_nb(); + +# After committing the cursor, the ALTER INDEX should proceed. We don't commit +# its outer transaction, however, so VACUUM will still be waiting. +$psql_primaryB{stdin} .= qq[ + COMMIT; + \\echo commit + ]; + +ok(pump_until($psql_primaryB{run}, $psql_timeout, + \$psql_primaryB{stdout}, qr/^commit$/m), "CURSOR committing"); + +ok(pump_until($psql_primaryC{run}, $psql_timeout, + \$psql_primaryC{stdout}, qr/^after_alter_index$/m), "ALTER INDEX ran"); + +# Allow the WAL receiver connection to re-establish. VACUUM is still +# waiting for the ALTER INDEX to commit. +$node_replica->safe_psql( + $test_db, qq[ + ALTER SYSTEM SET primary_conninfo = '$orig_conninfo'; + SELECT pg_reload_conf(); + ]); + +$node_replica->poll_query_until($test_db, qq[ + select exists (select * from pg_stat_wal_receiver);] , 't'); + +# Once the WAL sender is shown on the primary, the replica should have +# connected with the primary and pushed the horizon backward. Primary Session A +# won't see that until the GlobalVisUpdate() though. +$node_primary->poll_query_until($test_db, qq[ + select exists (select * from pg_stat_replication);] , 't'); + +# Commit the transaction surrounding the ALTER INDEX +$psql_primaryC{stdin} .= qq[ + COMMIT; + \\echo postcommit + ]; + +# VACUUM will take a new snapshot since the index modification caused a +# relcache invalidation. The new value of RecentXmin should reflect the +# older horizon from the standby and it will differ with +# ComputeXidHorizonsResultLastXmin, causing us to update +# GlobalVisState->maybe_needed to an older value. +ok(pump_until($psql_primaryC{run}, $psql_timeout, + \$psql_primaryC{stdout}, qr/^postcommit$/m), "FINISH ALTER INDEX"); + +$psql_primaryC{run}->pump_nb(); + +$psql_primaryA{run}->pump_nb(); + +# VACUUM proceeds to pruning and does a visibility check on each tuple. It will +# find our dead tuple non-removable (HEAPTUPLE_RECENTLY_DEAD) since its xmax is +# after the new value of maybe_needed. Once vacuum finishes the first pruning +# pass, it will, in lazy_scan_prune(), do another visibility check, this time +# with HeapTupleSatisfiesVacuum() which compares dead_after to OldestXmin. It +# will find the tuple HEAPTUPLE_DEAD since its xmax precedes OldestXmin. This +# will cause the infinite loop. +pump $psql_primaryA{run} until ($psql_primaryA{stdout} =~ /VACUUM/ || $psql_timeout->is_expired); + +ok(!$psql_timeout->is_expired); + +# Commit the original cursor transaction on the replica so it can catch up. it +# will end up replaying the vacuum and not removing the tuple too. +$psql_replicaA{stdin} .= qq[ + COMMIT; + ]; + +$psql_replicaA{run}->pump_nb(); + +$primary_lsn = $node_primary->lsn('flush'); +# Make sure something causes us to flush +$node_primary->safe_psql($test_db, "insert into $table1 values (1);"); +$node_primary->wait_for_catchup($node_replica, 'replay', $primary_lsn); + +# Shut down psqls +$psql_primaryA{stdin} .= "\\q\n"; +$psql_primaryA{run}->finish; + +$psql_primaryB{stdin} .= "\\q\n"; +$psql_primaryB{run}->finish; + +$psql_primaryC{stdin} .= "\\q\n"; +$psql_primaryC{run}->finish; + +$psql_replicaA{stdin} .= "\\q\n"; +$psql_replicaA{run}->finish; + +$node_replica->stop(); +$node_primary->stop(); + +done_testing(); -- 2.34.1