From 70496bd3d16a71b06c38bb7dac528436a3c459cf Mon Sep 17 00:00:00 2001 From: Julien Rouhaud Date: Fri, 14 Apr 2023 13:49:09 +0800 Subject: [PATCH v10] Persist logical slots to disk during a shutdown checkpoint if required. It's entirely possible for a logical slot to have a confirmed_flush LSN higher than the last value saved on disk while not being marked as dirty. Currently, it is not a major problem but a later patch adding support for the upgrade of slots relies on that value being properly persisted to disk. It can also help avoid processing the same transactions again in some boundary cases after the clean shutdown and restart. Say, we process some transactions for which we didn't send anything downstream (the changes got filtered) but the confirm_flush LSN is updated due to keepalives. As we don't flush the latest value of confirm_flush LSN, it may lead to processing the same changes again without this patch. Author: Vignesh C, Julien Rouhaud, Kuroda Hayato based on suggestions by Ashutosh Bapat Reviewed-by: Amit Kapila, Dilip Kumar, Ashutosh Bapat, Peter Smith Discussion: http://postgr.es/m/CAA4eK1JzJagMmb_E8D4au=GYQkxox0AfNBm1FbP7sy7t4YWXPQ@mail.gmail.com Discussion: http://postgr.es/m/TYAPR01MB58664C81887B3AF2EB6B16E3F5939@TYAPR01MB5866.jpnprd01.prod.outlook.com --- src/backend/access/transam/xlog.c | 2 +- src/backend/replication/slot.c | 38 ++++++- src/include/replication/slot.h | 8 +- src/test/recovery/meson.build | 1 + .../t/038_save_logical_slots_shutdown.pl | 102 ++++++++++++++++++ 5 files changed, 145 insertions(+), 6 deletions(-) create mode 100644 src/test/recovery/t/038_save_logical_slots_shutdown.pl diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f6f8adc72a..f26c8d18a6 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -7039,7 +7039,7 @@ static void CheckPointGuts(XLogRecPtr checkPointRedo, int flags) { CheckPointRelationMap(); - CheckPointReplicationSlots(); + CheckPointReplicationSlots(flags & CHECKPOINT_IS_SHUTDOWN); CheckPointSnapBuild(); CheckPointLogicalRewriteHeap(); CheckPointReplicationOrigin(); diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c index bb09c4010f..5a6d376cfa 100644 --- a/src/backend/replication/slot.c +++ b/src/backend/replication/slot.c @@ -321,6 +321,7 @@ ReplicationSlotCreate(const char *name, bool db_specific, slot->candidate_xmin_lsn = InvalidXLogRecPtr; slot->candidate_restart_valid = InvalidXLogRecPtr; slot->candidate_restart_lsn = InvalidXLogRecPtr; + slot->last_saved_confirmed_flush = InvalidXLogRecPtr; /* * Create the slot on disk. We haven't actually marked the slot allocated @@ -1572,11 +1573,14 @@ restart: /* * Flush all replication slots to disk. * - * This needn't actually be part of a checkpoint, but it's a convenient - * location. + * We can flush dirty replication slots at regular intervals by any + * background process like bgwriter but checkpoint is a convenient location. + * Additionally, in case of a shutdown checkpoint, we also identify the + * slots for which confirmed_flush LSN has been updated since the last time + * it persisted and flush them. */ void -CheckPointReplicationSlots(void) +CheckPointReplicationSlots(bool is_shutdown) { int i; @@ -1601,6 +1605,30 @@ CheckPointReplicationSlots(void) /* save the slot to disk, locking is handled in SaveSlotToPath() */ sprintf(path, "pg_replslot/%s", NameStr(s->data.name)); + + /* + * We won't ensure that the slot is persisted after the + * confirmed_flush LSN is updated as that could lead to frequent + * writes. However, we need to ensure that we do persist the slots at + * the time of shutdown whose confirmed_flush LSN is changed since we + * last saved the slot to disk. This will help in avoiding retreat of + * the confirmed_flush LSN after restart. At other times, the + * walsender keeps saving the slot from time to time as the + * replication progresses, so there is no clear advantage of flushing + * additional slots at the time of checkpoint. + */ + if (is_shutdown && SlotIsLogical(s)) + { + SpinLockAcquire(&s->mutex); + if (s->data.invalidated == RS_INVAL_NONE && + s->data.confirmed_flush != s->last_saved_confirmed_flush) + { + s->just_dirtied = true; + s->dirty = true; + } + SpinLockRelease(&s->mutex); + } + SaveSlotToPath(s, path, LOG); } LWLockRelease(ReplicationSlotAllocationLock); @@ -1873,11 +1901,12 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel) /* * Successfully wrote, unset dirty bit, unless somebody dirtied again - * already. + * already and remember the confirmed_flush LSN value. */ SpinLockAcquire(&slot->mutex); if (!slot->just_dirtied) slot->dirty = false; + slot->last_saved_confirmed_flush = cp.slotdata.confirmed_flush; SpinLockRelease(&slot->mutex); LWLockRelease(&slot->io_in_progress_lock); @@ -2074,6 +2103,7 @@ RestoreSlotFromDisk(const char *name) /* initialize in memory state */ slot->effective_xmin = cp.slotdata.xmin; slot->effective_catalog_xmin = cp.slotdata.catalog_xmin; + slot->last_saved_confirmed_flush = cp.slotdata.confirmed_flush; slot->candidate_catalog_xmin = InvalidTransactionId; slot->candidate_xmin_lsn = InvalidXLogRecPtr; diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h index a8a89dc784..4c4fe10e57 100644 --- a/src/include/replication/slot.h +++ b/src/include/replication/slot.h @@ -178,6 +178,12 @@ typedef struct ReplicationSlot XLogRecPtr candidate_xmin_lsn; XLogRecPtr candidate_restart_valid; XLogRecPtr candidate_restart_lsn; + + /* + * This is used to track the last persisted confirmed_flush LSN value to + * detect any divergence in the in-memory and on-disk values for the same. + */ + XLogRecPtr last_saved_confirmed_flush; } ReplicationSlot; #define SlotIsPhysical(slot) ((slot)->data.database == InvalidOid) @@ -241,7 +247,7 @@ extern void ReplicationSlotNameForTablesync(Oid suboid, Oid relid, char *syncslo extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname, bool missing_ok); extern void StartupReplicationSlots(void); -extern void CheckPointReplicationSlots(void); +extern void CheckPointReplicationSlots(bool is_shutdown); extern void CheckSlotRequirements(void); extern void CheckSlotPermissions(void); diff --git a/src/test/recovery/meson.build b/src/test/recovery/meson.build index e7328e4894..646d6ffde4 100644 --- a/src/test/recovery/meson.build +++ b/src/test/recovery/meson.build @@ -43,6 +43,7 @@ tests += { 't/035_standby_logical_decoding.pl', 't/036_truncated_dropped.pl', 't/037_invalid_database.pl', + 't/038_save_logical_slots_shutdown.pl', ], }, } diff --git a/src/test/recovery/t/038_save_logical_slots_shutdown.pl b/src/test/recovery/t/038_save_logical_slots_shutdown.pl new file mode 100644 index 0000000000..224a840a61 --- /dev/null +++ b/src/test/recovery/t/038_save_logical_slots_shutdown.pl @@ -0,0 +1,102 @@ + +# Copyright (c) 2023, PostgreSQL Global Development Group + +# Test logical replication slots are always persisted to disk during a shutdown +# checkpoint. + +use strict; +use warnings; + +use PostgreSQL::Test::Cluster; +use PostgreSQL::Test::Utils; +use Test::More; + +sub compare_confirmed_flush +{ + my ($node, $confirmed_flush_from_log) = @_; + + # Fetch Latest checkpoint location from the control file + my ($stdout, $stderr) = + run_command([ 'pg_controldata', $node->data_dir ]); + my @control_data = split("\n", $stdout); + my $latest_checkpoint = undef; + foreach (@control_data) + { + if ($_ =~ /^Latest checkpoint location:\s*(.*)$/mg) + { + $latest_checkpoint = $1; + last; + } + } + die "Latest checkpoint location not found in control file\n" + unless defined($latest_checkpoint); + + # Is it same as the value read from log? + ok( $latest_checkpoint eq $confirmed_flush_from_log, + "Check that the slot's confirmed_flush LSN is the same as the latest_checkpoint location" + ); + + return; +} + +# Initialize publisher node +my $node_publisher = PostgreSQL::Test::Cluster->new('pub'); +$node_publisher->init(allows_streaming => 'logical'); +# Avoid checkpoint during the test, otherwise, the latest checkpoint location +# will change. +$node_publisher->append_conf( + 'postgresql.conf', q{ +checkpoint_timeout = 1h +autovacuum = off +}); +$node_publisher->start; + +# Create subscriber node +my $node_subscriber = PostgreSQL::Test::Cluster->new('sub'); +$node_subscriber->init(allows_streaming => 'logical'); +$node_subscriber->start; + +# Create tables +$node_publisher->safe_psql('postgres', "CREATE TABLE test_tbl (id int)"); +$node_subscriber->safe_psql('postgres', "CREATE TABLE test_tbl (id int)"); + +# Insert some data +$node_publisher->safe_psql('postgres', + "INSERT INTO test_tbl VALUES (generate_series(1, 5));"); + +# Setup logical replication +my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres'; +$node_publisher->safe_psql('postgres', + "CREATE PUBLICATION pub FOR ALL TABLES"); +$node_subscriber->safe_psql('postgres', + "CREATE SUBSCRIPTION sub CONNECTION '$publisher_connstr' PUBLICATION pub" +); + +$node_subscriber->wait_for_subscription_sync($node_publisher, 'sub'); + +my $result = + $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM test_tbl"); + +is($result, qq(5), "check initial copy was done"); + +my $offset = -s $node_publisher->logfile; + +# Restart the publisher to ensure that the slot will be persisted if required +$node_publisher->restart(); + +# Wait until the walsender creates decoding context +$node_publisher->wait_for_log( + qr/Streaming transactions committing after ([A-F0-9]+\/[A-F0-9]+), reading WAL from ([A-F0-9]+\/[A-F0-9]+)./, + $offset); + +# Extract confirmed_flush from the logfile +my $log_contents = slurp_file($node_publisher->logfile, $offset); +$log_contents =~ + qr/Streaming transactions committing after ([A-F0-9]+\/[A-F0-9]+), reading WAL from ([A-F0-9]+\/[A-F0-9]+)./ + or die "could not get confirmed_flush_lsn"; + +# Ensure that the slot's confirmed_flush LSN is the same as the +# latest_checkpoint location. +compare_confirmed_flush($node_publisher, $1); + +done_testing(); -- 2.28.0.windows.1