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Enhance slot synchronization API to respect promotion signal.

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Previously, during a promotion, only the slot synchronization worker was
signaled to shut down. The backend executing slot synchronization via the
pg_sync_replication_slots() SQL function was not signaled, allowing it to
complete its synchronization cycle before exiting.

An upcoming patch improves pg_sync_replication_slots() to wait until
replication slots are fully persisted before finishing. This behaviour
requires the backend to exit promptly if a promotion occurs.

This patch ensures that, during promotion, a signal is also sent to the
backend running pg_sync_replication_slots(), allowing it to be interrupted
and exit immediately.

Author: Ajin Cherian <itsajin@gmail.com>
Reviewed-by: Shveta Malik <shveta.malik@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CAFPTHDZAA%2BgWDntpa5ucqKKba41%3DtXmoXqN3q4rpjO9cdxgQrw%40mail.gmail.com
pull/256/head
Amit Kapila 6 days ago
parent e16c6f0247
commit 1362bc33e0
1 changed files with 99 additions and 58 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 125
      src/backend/replication/logical/slotsync.c

125
src/backend/replication/logical/slotsync.c
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@ -71,11 +71,14 @@
/*
* Struct for sharing information to control slot synchronization.
*
* The slot sync worker's pid is needed by the startup process to shut it
* down during promotion. The startup process shuts down the slot sync worker
* and also sets stopSignaled=true to handle the race condition when the
* The 'pid' is either the slot sync worker's pid or the backend's pid running
* the SQL function pg_sync_replication_slots(). When the startup process sets
* 'stopSignaled' during promotion, it uses this 'pid' to wake up the currently
* synchronizing process so that the process can immediately stop its
* synchronizing work on seeing 'stopSignaled' set.
* Setting 'stopSignaled' is also used to handle the race condition when the
* postmaster has not noticed the promotion yet and thus may end up restarting
* the slot sync worker. If stopSignaled is set, the worker will exit in such a
* the slot sync worker. If 'stopSignaled' is set, the worker will exit in such a
* case. The SQL function pg_sync_replication_slots() will also error out if
* this flag is set. Note that we don't need to reset this variable as after
* promotion the slot sync worker won't be restarted because the pmState
@ -1195,10 +1198,10 @@ ValidateSlotSyncParams(int elevel)
}
/*
* Re-read the config file.
* Re-read the config file for slot synchronization.
*
* Exit if any of the slot sync GUCs have changed. The postmaster will
* restart it.
* Exit or throw error if relevant GUCs have changed depending on whether
* called from slot sync worker or from the SQL function pg_sync_replication_slots()
*/
static void
slotsync_reread_config(void)
@ -1209,7 +1212,10 @@ slotsync_reread_config(void)
bool old_hot_standby_feedback = hot_standby_feedback;
bool conninfo_changed;
bool primary_slotname_changed;
bool is_slotsync_worker = AmLogicalSlotSyncWorkerProcess();
bool parameter_changed = false;
if (is_slotsync_worker)
Assert(sync_replication_slots);
ConfigReloadPending = false;
@ -1221,33 +1227,61 @@ slotsync_reread_config(void)
pfree(old_primary_slotname);
if (old_sync_replication_slots != sync_replication_slots)
{
if (is_slotsync_worker)
{
ereport(LOG,
/* translator: %s is a GUC variable name */
errmsg("replication slot synchronization worker will shut down because \"%s\" is disabled", "sync_replication_slots"));
errmsg("replication slot synchronization worker will stop because \"%s\" is disabled",
"sync_replication_slots"));
proc_exit(0);
}
parameter_changed = true;
}
else
{
if (conninfo_changed ||
primary_slotname_changed ||
(old_hot_standby_feedback != hot_standby_feedback))
{
if (is_slotsync_worker)
{
ereport(LOG,
errmsg("replication slot synchronization worker will restart because of a parameter change"));
/*
* Reset the last-start time for this worker so that the postmaster
* can restart it without waiting for SLOTSYNC_RESTART_INTERVAL_SEC.
* Reset the last-start time for this worker so that the
* postmaster can restart it without waiting for
* SLOTSYNC_RESTART_INTERVAL_SEC.
*/
SlotSyncCtx->last_start_time = 0;
proc_exit(0);
}
parameter_changed = true;
}
}
/*
* Interrupt handler for main loop of slot sync worker.
* If we have reached here with a parameter change, we must be running in
* SQL function, emit error in such a case.
*/
if (parameter_changed)
{
Assert(!is_slotsync_worker);
ereport(ERROR,
errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("replication slot synchronization will stop because of a parameter change"));
}
}
/*
* Interrupt handler for process performing slot synchronization.
*/
static void
ProcessSlotSyncInterrupts(void)
@ -1255,12 +1289,25 @@ ProcessSlotSyncInterrupts(void)
CHECK_FOR_INTERRUPTS();
if (SlotSyncCtx->stopSignaled)
{
if (AmLogicalSlotSyncWorkerProcess())
{
ereport(LOG,
errmsg("replication slot synchronization worker is shutting down because promotion is triggered"));
errmsg("replication slot synchronization worker will stop because promotion is triggered"));
proc_exit(0);
}
else
{
/*
* For the backend executing SQL function
* pg_sync_replication_slots().
*/
ereport(ERROR,
errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("replication slot synchronization will stop because promotion is triggered"));
}
}
if (ConfigReloadPending)
slotsync_reread_config();
@ -1362,29 +1409,14 @@ wait_for_slot_activity(bool some_slot_updated)
}
/*
* Emit an error if a promotion or a concurrent sync call is in progress.
* Emit an error if a concurrent sync call is in progress.
* Otherwise, advertise that a sync is in progress.
*/
static void
check_and_set_sync_info(pid_t worker_pid)
check_and_set_sync_info(pid_t sync_process_pid)
{
SpinLockAcquire(&SlotSyncCtx->mutex);
/* The worker pid must not be already assigned in SlotSyncCtx */
Assert(worker_pid == InvalidPid || SlotSyncCtx->pid == InvalidPid);
/*
* Emit an error if startup process signaled the slot sync machinery to
* stop. See comments atop SlotSyncCtxStruct.
*/
if (SlotSyncCtx->stopSignaled)
{
SpinLockRelease(&SlotSyncCtx->mutex);
ereport(ERROR,
errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("cannot synchronize replication slots when standby promotion is ongoing"));
}
if (SlotSyncCtx->syncing)
{
SpinLockRelease(&SlotSyncCtx->mutex);
@ -1393,13 +1425,16 @@ check_and_set_sync_info(pid_t worker_pid)
errmsg("cannot synchronize replication slots concurrently"));
}
/* The pid must not be already assigned in SlotSyncCtx */
Assert(SlotSyncCtx->pid == InvalidPid);
SlotSyncCtx->syncing = true;
/*
* Advertise the required PID so that the startup process can kill the
* slot sync worker on promotion.
* slot sync process on promotion.
*/
SlotSyncCtx->pid = worker_pid;
SlotSyncCtx->pid = sync_process_pid;
SpinLockRelease(&SlotSyncCtx->mutex);
@ -1414,6 +1449,7 @@ reset_syncing_flag(void)
{
SpinLockAcquire(&SlotSyncCtx->mutex);
SlotSyncCtx->syncing = false;
SlotSyncCtx->pid = InvalidPid;
SpinLockRelease(&SlotSyncCtx->mutex);
syncing_slots = false;
@ -1622,7 +1658,7 @@ update_synced_slots_inactive_since(void)
if (!StandbyMode)
return;
/* The slot sync worker or SQL function mustn't be running by now */
/* The slot sync worker or the SQL function mustn't be running by now */
Assert((SlotSyncCtx->pid == InvalidPid) && !SlotSyncCtx->syncing);
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
@ -1651,16 +1687,18 @@ update_synced_slots_inactive_since(void)
}
/*
* Shut down the slot sync worker.
* Shut down slot synchronization.
*
* This function sends signal to shutdown slot sync worker, if required. It
* also waits till the slot sync worker has exited or
* This function sets stopSignaled=true and wakes up the slot sync process
* (either worker or backend running the SQL function pg_sync_replication_slots())
* so that worker can exit or the SQL function pg_sync_replication_slots() can
* finish. It also waits till the slot sync worker has exited or
* pg_sync_replication_slots() has finished.
*/
void
ShutDownSlotSync(void)
{
pid_t worker_pid;
pid_t sync_process_pid;
SpinLockAcquire(&SlotSyncCtx->mutex);
@ -1677,16 +1715,16 @@ ShutDownSlotSync(void)
return;
}
worker_pid = SlotSyncCtx->pid;
sync_process_pid = SlotSyncCtx->pid;
SpinLockRelease(&SlotSyncCtx->mutex);
/*
* Signal slotsync worker if it was still running. The worker will stop
* upon detecting that the stopSignaled flag is set to true.
* Signal process doing slotsync, if any. The process will stop upon
* detecting that the stopSignaled flag is set to true.
*/
if (worker_pid != InvalidPid)
kill(worker_pid, SIGUSR1);
if (sync_process_pid != InvalidPid)
kill(sync_process_pid, SIGUSR1);
/* Wait for slot sync to end */
for (;;)
@ -1835,7 +1873,10 @@ SyncReplicationSlots(WalReceiverConn *wrconn)
{
PG_ENSURE_ERROR_CLEANUP(slotsync_failure_callback, PointerGetDatum(wrconn));
{
check_and_set_sync_info(InvalidPid);
check_and_set_sync_info(MyProcPid);
/* Check for interrupts and config changes */
ProcessSlotSyncInterrupts();
validate_remote_info(wrconn);

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