From f28b20706ea68e63d05029949a49f09e404e2751 Mon Sep 17 00:00:00 2001 From: Zhijie Hou Date: Tue, 9 Sep 2025 11:03:36 +0800 Subject: [PATCH v74] Allow conflict-relevant data retention to resume This commit enables automatic recovery of conflict-relevant data retention for a subscription. If the retention duration for a subscription previously exceeded the max_retention_duration and caused retention to stop, the retention can resume once the duration falls within the acceptable limits. --- doc/src/sgml/ref/create_subscription.sgml | 9 +- src/backend/replication/logical/launcher.c | 10 +- src/backend/replication/logical/worker.c | 217 ++++++++++++++++----- src/test/subscription/t/035_conflicts.pl | 27 +++ 4 files changed, 213 insertions(+), 50 deletions(-) diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml index fc314437311..ed82cf1809e 100644 --- a/doc/src/sgml/ref/create_subscription.sgml +++ b/doc/src/sgml/ref/create_subscription.sgml @@ -538,10 +538,11 @@ CREATE SUBSCRIPTION subscription_nameretain_dead_tuples is enabled, confirm that the retention duration has exceeded the max_retention_duration set within the corresponding - subscription. The retention will not be automatically resumed unless a - new subscription is created with retain_dead_tuples = - true, or the user manually re-enables - retain_dead_tuples. + subscription. The retention will automatically resume when at least one + apply worker confirms that the retention duration is within the + specified limit, or when a new subscription is created with + retain_dead_tuples = true. Alternatively, retention + can be manually resumed by re-enabling retain_dead_tuples. Note that overall retention will not stop if other subscriptions that diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c index add2e2e066c..1d42ca91ea3 100644 --- a/src/backend/replication/logical/launcher.c +++ b/src/backend/replication/logical/launcher.c @@ -1261,24 +1261,30 @@ ApplyLauncherMain(Datum main_arg) LWLockAcquire(LogicalRepWorkerLock, LW_SHARED); w = logicalrep_worker_find(sub->oid, InvalidOid, false); - LWLockRelease(LogicalRepWorkerLock); if (w != NULL) { /* * Compute the minimum xmin required to protect dead tuples * required for conflict detection among all running apply - * workers. + * workers. This computation is performed under + * LogicalRepWorkerLock to avoid accessing invalid worker + * information in scenarios where a worker may exit and reset + * data concurrently. */ if (sub->retaindeadtuples && sub->retentionactive && can_update_xmin) compute_min_nonremovable_xid(w, &xmin); + LWLockRelease(LogicalRepWorkerLock); + /* worker is running already */ continue; } + LWLockRelease(LogicalRepWorkerLock); + /* * Can't advance xmin of the slot unless all the workers * corresponding to subscriptions actively retaining dead tuples diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c index ee6ac22329f..6d9ff6828a4 100644 --- a/src/backend/replication/logical/worker.c +++ b/src/backend/replication/logical/worker.c @@ -181,6 +181,15 @@ * pg_subscription.subretentionactive is updated to false within a new * transaction, and oldest_nonremovable_xid is set to InvalidTransactionId. * + * - RDT_RESUME_CONFLICT_INFO_RETENTION: + * This phase is required only when max_retention_duration is defined. We + * enter this phase if the retention was previously stopped, and the time + * required to advance the non-removable transaction ID in the + * RDT_WAIT_FOR_LOCAL_FLUSH phase has decreased to within acceptable limits + * (or if max_retention_duration is set to 0). During this phase, + * pg_subscription.subretentionactive is updated to true within a new + * transaction, and the worker will be restarted. + * * The overall state progression is: GET_CANDIDATE_XID -> * REQUEST_PUBLISHER_STATUS -> WAIT_FOR_PUBLISHER_STATUS -> (loop to * REQUEST_PUBLISHER_STATUS till concurrent remote transactions end) -> @@ -381,7 +390,8 @@ typedef enum RDT_REQUEST_PUBLISHER_STATUS, RDT_WAIT_FOR_PUBLISHER_STATUS, RDT_WAIT_FOR_LOCAL_FLUSH, - RDT_STOP_CONFLICT_INFO_RETENTION + RDT_STOP_CONFLICT_INFO_RETENTION, + RDT_RESUME_CONFLICT_INFO_RETENTION, } RetainDeadTuplesPhase; /* @@ -568,10 +578,14 @@ static void wait_for_publisher_status(RetainDeadTuplesData *rdt_data, static void wait_for_local_flush(RetainDeadTuplesData *rdt_data); static bool should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data); static void stop_conflict_info_retention(RetainDeadTuplesData *rdt_data); +static void resume_conflict_info_retention(RetainDeadTuplesData *rdt_data); +static bool update_retention_status(bool active); static void reset_retention_data_fields(RetainDeadTuplesData *rdt_data); static void adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found); +static void apply_worker_exit(void); + static void apply_handle_commit_internal(LogicalRepCommitData *commit_data); static void apply_handle_insert_internal(ApplyExecutionData *edata, ResultRelInfo *relinfo, @@ -4367,10 +4381,6 @@ can_advance_nonremovable_xid(RetainDeadTuplesData *rdt_data) if (!MySubscription->retaindeadtuples) return false; - /* No need to advance if we have already stopped retaining */ - if (!MySubscription->retentionactive) - return false; - return true; } @@ -4399,6 +4409,9 @@ process_rdt_phase_transition(RetainDeadTuplesData *rdt_data, case RDT_STOP_CONFLICT_INFO_RETENTION: stop_conflict_info_retention(rdt_data); break; + case RDT_RESUME_CONFLICT_INFO_RETENTION: + resume_conflict_info_retention(rdt_data); + break; } } @@ -4522,7 +4535,25 @@ wait_for_publisher_status(RetainDeadTuplesData *rdt_data, * retaining conflict information for this worker. */ if (should_stop_conflict_info_retention(rdt_data)) + { + /* + * Stop retention if not yet. Otherwise, reset to the initial phase to + * retry resuming retention. This reset is required to recalculate the + * current wait time and resume retention if the time falls within + * max_retention_duration. + */ + if (MySubscription->retentionactive) + { + rdt_data->phase = RDT_STOP_CONFLICT_INFO_RETENTION; + } + else + { + Assert(!TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid)); + reset_retention_data_fields(rdt_data); + } + return; + } if (!FullTransactionIdIsValid(rdt_data->remote_wait_for)) rdt_data->remote_wait_for = rdt_data->remote_nextxid; @@ -4643,7 +4674,25 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data) * retaining conflict information for this worker. */ if (should_stop_conflict_info_retention(rdt_data)) + { + /* + * Stop retention if not yet. Otherwise, reset to the initial phase to + * retry resuming retention. This reset is required to recalculate the + * current wait time and resume retention if the time falls within + * max_retention_duration. + */ + if (MySubscription->retentionactive) + { + rdt_data->phase = RDT_STOP_CONFLICT_INFO_RETENTION; + } + else + { + Assert(!TransactionIdIsValid(MyLogicalRepWorker->oldest_nonremovable_xid)); + reset_retention_data_fields(rdt_data); + } + return; + } /* * Update and check the remote flush position if we are applying changes @@ -4672,6 +4721,21 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data) if (last_flushpos < rdt_data->remote_lsn) return; + /* + * Reaching this point implies should_stop_conflict_info_retention() + * returned false earlier, indicating that the most recent duration for + * advancing the non-removable transaction ID is within the + * max_retention_duration or max_retention_duration is set to 0. + * + * Therefore, if conflict info retention was previously stopped due to a + * timeout, proceed to resume retention now. + */ + if (!MySubscription->retentionactive) + { + rdt_data->phase = RDT_RESUME_CONFLICT_INFO_RETENTION; + return; + } + /* * Reaching here means the remote WAL position has been received, and all * transactions up to that position on the publisher have been applied and @@ -4698,13 +4762,7 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data) * Check whether conflict information retention should be stopped due to * exceeding the maximum wait time (max_retention_duration). * - * If retention should be stopped, transition to the - * RDT_STOP_CONFLICT_INFO_RETENTION phase and return true. Otherwise, return - * false. - * - * Note: Retention won't be resumed automatically. The user must manually - * disable retain_dead_tuples and re-enable it after confirming that the - * replication slot maintained by the launcher has been dropped. + * If retention should be stopped, return true. Otherwise, return false. */ static bool should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data) @@ -4735,11 +4793,6 @@ should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data) rdt_data->table_sync_wait_time)) return false; - rdt_data->phase = RDT_STOP_CONFLICT_INFO_RETENTION; - - /* process the next phase */ - process_rdt_phase_transition(rdt_data, false); - return true; } @@ -4748,6 +4801,73 @@ should_stop_conflict_info_retention(RetainDeadTuplesData *rdt_data) */ static void stop_conflict_info_retention(RetainDeadTuplesData *rdt_data) +{ + /* + * Return if unable to update subretentionactive (see + * update_retention_status). + */ + if (!update_retention_status(false)) + return; + + SpinLockAcquire(&MyLogicalRepWorker->relmutex); + MyLogicalRepWorker->oldest_nonremovable_xid = InvalidTransactionId; + SpinLockRelease(&MyLogicalRepWorker->relmutex); + + ereport(LOG, + errmsg("logical replication worker for subscription \"%s\" has stopped retaining the information for detecting conflicts", + MySubscription->name), + errdetail("Retention of information used for conflict detection has exceeded max_retention_duration of %u ms.", + MySubscription->maxretention)); + + reset_retention_data_fields(rdt_data); +} + +/* + * Workhorse for the RDT_RESUME_CONFLICT_INFO_RETENTION phase. + */ +static void +resume_conflict_info_retention(RetainDeadTuplesData *rdt_data) +{ + /* + * Return if unable to update subretentionactive (see + * update_retention_status). + */ + if (!update_retention_status(true)) + return; + + ereport(LOG, + errmsg("logical replication worker for subscription \"%s\" will resume retaining the information for detecting conflicts", + MySubscription->name), + MySubscription->maxretention + ? errdetail("Retention of information used for conflict detection is now within the max_retention_duration of %u ms.", + MySubscription->maxretention) + : errdetail("Retention of information used for conflict detection is now indefinite.")); + + /* + * Restart the worker to allow the launcher to initialize + * oldest_nonremovable_xid value at startup. + * + * An alternative approach is using the conflict detection slot.xmin to + * initialize the oldest_nonremovable_xid on-the-fly, without restarting + * the worker. However, this could create a race condition where the + * launcher invalidates slot.xmin immediately after the worker resumes + * retention, making oldest_nonremovable_xid unreliable if xid wraparound + * occurs. While implementing a heavy lock to prevent concurrent slot + * updates by the launcher is feasible, given that resuming is an + * infrequent operation, it may not be worthwhile to handle it. + */ + apply_worker_exit(); +} + +/* + * Update pg_subscription.subretentionactive to the given value within a new + * transaction. + * + * Returns true upon successful update; however, if currently within an active + * transaction, skip the update and return false. + */ +static bool +update_retention_status(bool active) { /* * Do not update the catalog during an active transaction. The transaction @@ -4755,7 +4875,7 @@ stop_conflict_info_retention(RetainDeadTuplesData *rdt_data) * rollback of catalog updates if the application fails subsequently. */ if (IsTransactionState()) - return; + return false; StartTransactionCommand(); @@ -4765,26 +4885,18 @@ stop_conflict_info_retention(RetainDeadTuplesData *rdt_data) */ PushActiveSnapshot(GetTransactionSnapshot()); - /* Set pg_subscription.subretentionactive to false */ - UpdateDeadTupleRetentionStatus(MySubscription->oid, false); + /* Update pg_subscription.subretentionactive */ + UpdateDeadTupleRetentionStatus(MySubscription->oid, active); PopActiveSnapshot(); CommitTransactionCommand(); - SpinLockAcquire(&MyLogicalRepWorker->relmutex); - MyLogicalRepWorker->oldest_nonremovable_xid = InvalidTransactionId; - SpinLockRelease(&MyLogicalRepWorker->relmutex); - - ereport(LOG, - errmsg("logical replication worker for subscription \"%s\" has stopped retaining the information for detecting conflicts", - MySubscription->name), - errdetail("Retention of information used for conflict detection has exceeded max_retention_duration of %u ms.", - MySubscription->maxretention)); - /* Notify launcher to update the conflict slot */ ApplyLauncherWakeup(); - reset_retention_data_fields(rdt_data); + MySubscription->retentionactive = active; + + return true; } /* @@ -4809,19 +4921,20 @@ reset_retention_data_fields(RetainDeadTuplesData *rdt_data) /* * Adjust the interval for advancing non-removable transaction IDs. * - * If there is no activity on the node, we progressively double the interval - * used to advance non-removable transaction ID. This helps conserve CPU - * and network resources when there's little benefit to frequent updates. + * If there is no activity on the node or retention has been stopped, we + * progressively double the interval used to advance non-removable transaction + * ID. This helps conserve CPU and network resources when there's little benefit + * to frequent updates. * * The interval is capped by the lowest of the following: - * - wal_receiver_status_interval (if set), + * - wal_receiver_status_interval (if set and retention is active), * - a default maximum of 3 minutes, - * - max_retention_duration. + * - max_retention_duration (if retention is active). * - * This ensures the interval never exceeds the retention boundary, even if - * other limits are higher. Once activity resumes on the node, the interval - * is reset to lesser of 100ms and max_retention_duration, allowing timely - * advancement of non-removable transaction ID. + * This ensures the interval never exceeds the retention boundary, even if other + * limits are higher. Once activity resumes on the node and the retention is + * active, the interval is reset to lesser of 100ms and max_retention_duration, + * allowing timely advancement of non-removable transaction ID. * * XXX The use of wal_receiver_status_interval is a bit arbitrary so we can * consider the other interval or a separate GUC if the need arises. @@ -4829,7 +4942,7 @@ reset_retention_data_fields(RetainDeadTuplesData *rdt_data) static void adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found) { - if (!new_xid_found && rdt_data->xid_advance_interval) + if (rdt_data->xid_advance_interval && !new_xid_found) { int max_interval = wal_receiver_status_interval ? wal_receiver_status_interval * 1000 @@ -4842,6 +4955,18 @@ adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found) rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval * 2, max_interval); } + else if (rdt_data->xid_advance_interval && + !MySubscription->retentionactive) + { + /* + * Retention has been stopped, so double the interval, but not beyond + * 3 minutes. The wal_receiver_status_interval is not considered as a + * maximum, since the chance of retention resuming is less than that + * of activity resuming. + */ + rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval * 2, + MAX_XID_ADVANCE_INTERVAL); + } else { /* @@ -4851,9 +4976,13 @@ adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found) rdt_data->xid_advance_interval = MIN_XID_ADVANCE_INTERVAL; } - /* Ensure the wait time remains within the maximum limit */ - rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval, - MySubscription->maxretention); + /* + * Ensure the wait time remains within the maximum limit when retention is + * active. + */ + if (MySubscription->retentionactive) + rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval, + MySubscription->maxretention); } /* diff --git a/src/test/subscription/t/035_conflicts.pl b/src/test/subscription/t/035_conflicts.pl index 880551fc69d..6f371b4b1f4 100644 --- a/src/test/subscription/t/035_conflicts.pl +++ b/src/test/subscription/t/035_conflicts.pl @@ -631,6 +631,33 @@ $node_B->safe_psql('postgres', $node_B->adjust_conf('postgresql.conf', 'synchronized_standby_slots', "''"); $node_B->reload; +############################################################################### +# Check that dead tuple retention resumes when the max_retention_duration is set +# 0. +############################################################################### + +$log_offset = -s $node_A->logfile; + +# Set max_retention_duration to 0 +$node_A->safe_psql('postgres', + "ALTER SUBSCRIPTION $subname_AB SET (max_retention_duration = 0);"); + +# Confirm that the retention resumes +$node_A->wait_for_log( + qr/logical replication worker for subscription "tap_sub_a_b" will resume retaining the information for detecting conflicts +.*DETAIL:.* Retention of information used for conflict detection is now indefinite.*/, + $log_offset); + +ok( $node_A->poll_query_until( + 'postgres', + "SELECT xmin IS NOT NULL from pg_replication_slots WHERE slot_name = 'pg_conflict_detection'" + ), + "the xmin value of slot 'pg_conflict_detection' is valid on Node A"); + +$result = $node_A->safe_psql('postgres', + "SELECT subretentionactive FROM pg_subscription WHERE subname='$subname_AB';"); +is($result, qq(t), 'retention is active'); + ############################################################################### # Check that the replication slot pg_conflict_detection is dropped after # removing all the subscriptions. -- 2.51.0.windows.1