--- /dev/null
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+# Test that vacuum prunes away all dead tuples killed before OldestXmin
+#
+# This test creates a table on a primary, updates the table to generate dead
+# tuples for vacuum, and then, during the vacuum, uses the replica to force
+# GlobalVisState->maybe_needed on the primary to move backwards and precede
+# the value of OldestXmin set at the beginning of vacuuming the table.
+
+# Set up nodes
+my $node_primary = PostgreSQL::Test::Cluster->new('primary');
+$node_primary->init(allows_streaming => 'physical');
+
+$node_primary->append_conf(
+ 'postgresql.conf', qq[
+hot_standby_feedback = on
+log_recovery_conflict_waits = true
+autovacuum = off
+log_min_messages = INFO
+maintenance_work_mem = 1024
+]);
+$node_primary->start;
+
+my $node_replica = PostgreSQL::Test::Cluster->new('standby');
+
+$node_primary->backup('my_backup');
+$node_replica->init_from_backup($node_primary, 'my_backup',
+ has_streaming => 1);
+
+$node_replica->start;
+
+my $test_db = "test_db";
+$node_primary->safe_psql('postgres', "CREATE DATABASE $test_db");
+
+# Save the original connection info for later use
+my $orig_conninfo = $node_primary->connstr();
+
+my $table1 = "vac_horizon_floor_table";
+
+# Long-running Primary Session A
+my $psql_primaryA =
+ $node_primary->background_psql($test_db, on_error_stop => 1);
+
+# Long-running Primary Session B
+my $psql_primaryB =
+ $node_primary->background_psql($test_db, on_error_stop => 1);
+
+# The TIDStore vacuum uses to store dead items is optimized for its target
+# system. On a 32-bit system, our example requires twice as many pages with
+# the same number of dead items per page to fill the TIDStore and trigger a
+# second round of index vacuuming.
+my $is_64bit = $node_primary->safe_psql($test_db,
+ qq[SELECT typbyval FROM pg_type WHERE typname = 'int8';]);
+
+my $nrows = $is_64bit eq 't' ? 400000 : 800000;
+
+# Because vacuum's first pass, pruning, is where we use the GlobalVisState to
+# check tuple visibility, GlobalVisState->maybe_needed must move backwards
+# during pruning before checking the visibility for a tuple which would have
+# been considered HEAPTUPLE_DEAD prior to maybe_needed moving backwards but
+# HEAPTUPLE_RECENTLY_DEAD compared to the new, older value of maybe_needed.
+#
+# We must not only force the horizon on the primary to move backwards but also
+# force the vacuuming backend's GlobalVisState to be updated. GlobalVisState
+# is forced to update during index vacuuming.
+#
+# _bt_pendingfsm_finalize() calls GetOldestNonRemovableTransactionId() at the
+# end of a round of index vacuuming, updating the backend's GlobalVisState
+# and, in our case, moving maybe_needed backwards.
+#
+# Then vacuum's first (pruning) pass will continue and pruning will find our
+# later inserted and updated tuple HEAPTUPLE_RECENTLY_DEAD when compared to
+# maybe_needed but HEAPTUPLE_DEAD when compared to OldestXmin.
+#
+# Thus, we must force at least two rounds of index vacuuming to ensure that
+# some tuple visibility checks will happen after a round of index vacuuming.
+# To accomplish this, we set maintenance_work_mem to its minimum value and
+# insert and update enough rows that we force at least one round of index
+# vacuuming before getting to a dead tuple which was killed after the standby
+# is disconnected.
+$node_primary->safe_psql($test_db, qq[
+ CREATE TABLE ${table1}(col1 int)
+ WITH (autovacuum_enabled=false, fillfactor=10);
+ INSERT INTO $table1 VALUES(7);
+ INSERT INTO $table1 SELECT generate_series(1, $nrows) % 3;
+ CREATE INDEX on ${table1}(col1);
+ UPDATE $table1 SET col1 = 3 WHERE col1 = 0;
+ INSERT INTO $table1 VALUES(7);
+]);
+
+# We will later move the primary forward while the standby is disconnected.
+# For now, however, there is no reason not to wait for the standby to catch
+# up.
+my $primary_lsn = $node_primary->lsn('flush');
+$node_primary->wait_for_catchup($node_replica, 'replay', $primary_lsn);
+
+# Test that the WAL receiver is up and running.
+$node_replica->poll_query_until($test_db, qq[
+ select exists (select * from pg_stat_wal_receiver);] , 't');
+
+# Set primary_conninfo to something invalid on the replica and reload the
+# config. Once the config is reloaded, the startup process will force the WAL
+# receiver to restart and it will be unable to reconnect because of the
+# invalid connection information.
+$node_replica->safe_psql($test_db, qq[
+ ALTER SYSTEM SET primary_conninfo = '';
+ SELECT pg_reload_conf();
+ ]);
+
+# Wait until the WAL receiver has shut down and been unable to start up again.
+$node_replica->poll_query_until($test_db, qq[
+ select exists (select * from pg_stat_wal_receiver);] , 'f');
+
+# Now insert and update a tuple which will be visible to the vacuum on the
+# primary but which will have xmax newer than the oldest xmin on the standby
+# that was recently disconnected.
+my $res = $psql_primaryA->query_safe(
+ qq[
+ INSERT INTO $table1 VALUES (99);
+ UPDATE $table1 SET col1 = 100 WHERE col1 = 99;
+ SELECT 'after_update';
+ ]
+ );
+
+# Make sure the UPDATE finished
+like($res, qr/^after_update$/m, "UPDATE occurred on primary session A");
+
+# Open a cursor on the primary whose pin will keep VACUUM from getting a
+# cleanup lock on the first page of the relation. We want VACUUM to be able to
+# start, calculate initial values for OldestXmin and GlobalVisState and then
+# be unable to proceed with pruning our dead tuples. This will allow us to
+# reconnect the standby and push the horizon back before we start actual
+# pruning and vacuuming.
+my $primary_cursor1 = "vac_horizon_floor_cursor1";
+
+# The first value inserted into the table was a 7, so FETCH FORWARD should
+# return a 7. That's how we know the cursor has a pin.
+$res = $psql_primaryB->query_safe(
+ qq[
+ BEGIN;
+ DECLARE $primary_cursor1 CURSOR FOR SELECT * FROM $table1 WHERE col1 = 7;
+ FETCH $primary_cursor1;
+ ]
+ );
+
+is($res, 7, qq[Cursor query returned $res. Expected value 7.]);
+
+# Get the PID of the session which will run the VACUUM FREEZE so that we can
+# use it to filter pg_stat_activity later.
+my $vacuum_pid = $psql_primaryA->query_safe("SELECT pg_backend_pid();");
+
+# Now start a VACUUM FREEZE on the primary. It will call vacuum_get_cutoffs()
+# and establish values of OldestXmin and GlobalVisState which are newer than
+# all of our dead tuples. Then it will be unable to get a cleanup lock to
+# start pruning, so it will hang.
+#
+# We use VACUUM FREEZE because it will wait for a cleanup lock instead of
+# skipping the page pinned by the cursor. Note that works because the target
+# tuple's xmax precedes OldestXmin which ensures that lazy_scan_noprune() will
+# return false and we will wait for the cleanup lock.
+$psql_primaryA->{stdin} .= qq[
+ VACUUM (VERBOSE, FREEZE) $table1;
+ \\echo VACUUM
+ ];
+
+# Make sure the VACUUM command makes it to the server.
+$psql_primaryA->{run}->pump_nb();
+
+# Make sure that the VACUUM has already called vacuum_get_cutoffs() and is
+# just waiting on the lock to start vacuuming. We don't want the standby to
+# re-establish a connection to the primary and push the horizon back until
+# we've saved initial values in GlobalVisState and calculated OldestXmin.
+$node_primary->poll_query_until($test_db,
+ qq[
+ SELECT count(*) >= 1 FROM pg_stat_activity
+ WHERE pid = $vacuum_pid
+ AND wait_event = 'BufferPin';
+ ],
+ 't');
+
+# Ensure the WAL receiver is still not active on the replica.
+$node_replica->poll_query_until($test_db, qq[
+ SELECT EXISTS (SELECT * FROM pg_stat_wal_receiver);] , 'f');
+
+# Allow the WAL receiver connection to re-establish.
+$node_replica->safe_psql(
+ $test_db, qq[
+ ALTER SYSTEM SET primary_conninfo = '$orig_conninfo';
+ SELECT pg_reload_conf();
+ ]);
+
+# Ensure the new WAL receiver has connected.
+$node_replica->poll_query_until($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 VACUUM FREEZE proceeds and does its first round
+# of index vacuuming.
+$node_primary->poll_query_until($test_db, qq[
+ SELECT EXISTS (SELECT * FROm pg_stat_replication);] , 't');
+
+# Move the cursor forward to the next 7. We inserted the 7 much later, so
+# advancing the cursor should allow vacuum to proceed vacuuming most pages of
+# the relation. Because we set maintanence_work_mem sufficiently low, we
+# expect that a round of index vacuuming has happened and that the vacuum is
+# now waiting for the cursor to release its pin on the last page of the
+# relation.
+$res = $psql_primaryB->query_safe("FETCH $primary_cursor1");
+is($res, 7,
+ qq[Cursor query returned $res from second fetch. Expected value 7.]);
+
+# Prevent the test from incorrectly passing by confirming that we did indeed
+# do a pass of index vacuuming.
+$node_primary->poll_query_until($test_db, qq[
+ SELECT index_vacuum_count > 0
+ FROM pg_stat_progress_vacuum
+ WHERE datname='$test_db' AND relid::regclass = '$table1'::regclass;
+ ] , 't');
+
+# Commit the transaction with the open cursor so that the VACUUM can finish.
+$psql_primaryB->query_until(
+ qr/^commit$/m,
+ qq[
+ COMMIT;
+ \\echo commit
+ ]
+ );
+
+# VACUUM proceeds with pruning and does a visibility check on each tuple. In
+# older versions of Postgres, pruning found our final dead tuple
+# non-removable (HEAPTUPLE_RECENTLY_DEAD) since its xmax is after the new
+# value of maybe_needed. Then heap_prepare_freeze_tuple() would decide the
+# tuple xmax should be frozen because it precedes OldestXmin. Vacuum would
+# then error out in heap_pre_freeze_checks() with "cannot freeze committed
+# xmax". This was fixed by changing pruning to find all
+# HEAPTUPLE_RECENTLY_DEAD tuples with xmaxes preceding OldestXmin
+# HEAPTUPLE_DEAD and removing them.
+
+# With the fix, VACUUM should finish successfully, incrementing the table
+# vacuum_count.
+$node_primary->poll_query_until($test_db,
+ qq[
+ SELECT vacuum_count > 0
+ FROM pg_stat_all_tables WHERE relname = '${table1}';
+ ]
+ , 't');
+
+$primary_lsn = $node_primary->lsn('flush');
+
+# Make sure something causes us to flush
+$node_primary->safe_psql($test_db, "INSERT INTO $table1 VALUES (1);");
+
+# Nothing on the replica should cause a recovery conflict, so this should
+# finish successfully.
+$node_primary->wait_for_catchup($node_replica, 'replay', $primary_lsn);
+
+## Shut down psqls
+$psql_primaryA->quit;
+$psql_primaryB->quit;
+
+$node_replica->stop();
+$node_primary->stop();
+
+done_testing();
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