I've attached a minimally-updated patch that doesn't yet address the bigger
topics under discussion.
On Thu, Mar 16, 2023 at 03:30:37PM +0530, Amit Kapila wrote:
> On Wed, Feb 1, 2023 at 5:35 AM Nathan Bossart <nathandboss...@gmail.com>
> wrote:
>> On Sat, Jan 28, 2023 at 10:26:25AM +0530, Amit Kapila wrote:
>> > BTW, do we need to do something about wakeups in
>> > wait_for_relation_state_change()?
>>
>> ... and wait_for_worker_state_change(), and copy_read_data(). From a quick
>> glance, it looks like fixing these would be a more invasive change.
>
> What kind of logic do you have in mind to avoid waking up once per
> second in those cases?
I haven't looked into this too much yet. I'd probably try out Tom's
suggestions from upthread [0] next and see if those can be applied here,
too.
>> TBH
>> I'm beginning to wonder whether all this is really worth it to prevent
>> waking up once per second.
>
> If we can't do it for all cases, do you see any harm in doing it for
> cases where we can achieve it without adding much complexity? We can
> probably add comments for others so that if someone else has better
> ideas in the future we can deal with those as well.
I don't think there's any harm, but I'm also not sure it does a whole lot
of good. At the very least, I think we should figure out something better
than the process_syncing_tables() hacks before taking this patch seriously.
[0] https://postgr.es/m/3220831.1674772625%40sss.pgh.pa.us
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From d76710d4b79e173e2d1baf1af228fe7dd8927e72 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathandboss...@gmail.com>
Date: Tue, 24 Jan 2023 21:12:28 -0800
Subject: [PATCH v4 1/1] suppress useless wakeups in logical/worker.c
---
src/backend/replication/logical/tablesync.c | 28 +++
src/backend/replication/logical/worker.c | 189 ++++++++++++++++----
src/include/replication/worker_internal.h | 4 +
src/tools/pgindent/typedefs.list | 1 +
4 files changed, 186 insertions(+), 36 deletions(-)
diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 07eea504ba..573b46b5a2 100644
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -419,6 +419,13 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
Assert(!IsTransactionState());
+ /*
+ * If we've made it past our previously-stored special wakeup time, reset
+ * it so that it can be recalculated as needed.
+ */
+ if (LogRepWorkerGetSyncStartWakeup() <= GetCurrentTimestamp())
+ LogRepWorkerClearSyncStartWakeup();
+
/* We need up-to-date sync state info for subscription tables here. */
FetchTableStates(&started_tx);
@@ -592,6 +599,27 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
DSM_HANDLE_INVALID);
hentry->last_start_time = now;
}
+ else
+ {
+ TimestampTz retry_time;
+
+ /*
+ * Store when we can start the sync worker so that we
+ * know how long to sleep.
+ */
+ retry_time = TimestampTzPlusMilliseconds(hentry->last_start_time,
+ wal_retrieve_retry_interval);
+ LogRepWorkerUpdateSyncStartWakeup(retry_time);
+ }
+ }
+ else
+ {
+ TimestampTz now = GetCurrentTimestamp();
+ TimestampTz retry_time;
+
+ /* Maybe there will be a free slot in a second... */
+ retry_time = TimestampTzPlusSeconds(now, 1);
+ LogRepWorkerUpdateSyncStartWakeup(retry_time);
}
}
}
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 10f9711972..8e68540b6f 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -208,8 +208,6 @@
#include "utils/syscache.h"
#include "utils/timeout.h"
-#define NAPTIME_PER_CYCLE 1000 /* max sleep time between cycles (1s) */
-
typedef struct FlushPosition
{
dlist_node node;
@@ -351,6 +349,26 @@ static XLogRecPtr skip_xact_finish_lsn = InvalidXLogRecPtr;
/* BufFile handle of the current streaming file */
static BufFile *stream_fd = NULL;
+/*
+ * Reasons to wake up and perform periodic tasks.
+ */
+typedef enum LogRepWorkerWakeupReason
+{
+ LRW_WAKEUP_TERMINATE,
+ LRW_WAKEUP_PING,
+ LRW_WAKEUP_STATUS,
+ LRW_WAKEUP_SYNC_START
+#define NUM_LRW_WAKEUPS (LRW_WAKEUP_SYNC_START + 1)
+} LogRepWorkerWakeupReason;
+
+/*
+ * Wake up times for periodic tasks.
+ */
+static TimestampTz wakeup[NUM_LRW_WAKEUPS];
+
+static void LogRepWorkerComputeNextWakeup(LogRepWorkerWakeupReason reason,
+ TimestampTz now);
+
typedef struct SubXactInfo
{
TransactionId xid; /* XID of the subxact */
@@ -3441,10 +3459,9 @@ UpdateWorkerStats(XLogRecPtr last_lsn, TimestampTz send_time, bool reply)
static void
LogicalRepApplyLoop(XLogRecPtr last_received)
{
- TimestampTz last_recv_timestamp = GetCurrentTimestamp();
- bool ping_sent = false;
TimeLineID tli;
ErrorContextCallback errcallback;
+ TimestampTz now;
/*
* Init the ApplyMessageContext which we clean up after each replication
@@ -3474,6 +3491,11 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
error_context_stack = &errcallback;
apply_error_context_stack = error_context_stack;
+ /* Initialize nap wakeup times. */
+ now = GetCurrentTimestamp();
+ for (int i = 0; i < NUM_LRW_WAKEUPS; i++)
+ LogRepWorkerComputeNextWakeup(i, now);
+
/* This outer loop iterates once per wait. */
for (;;)
{
@@ -3513,9 +3535,10 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
int c;
StringInfoData s;
- /* Reset timeout. */
- last_recv_timestamp = GetCurrentTimestamp();
- ping_sent = false;
+ /* Adjust the ping and terminate wakeup times. */
+ now = GetCurrentTimestamp();
+ LogRepWorkerComputeNextWakeup(LRW_WAKEUP_TERMINATE, now);
+ LogRepWorkerComputeNextWakeup(LRW_WAKEUP_PING, now);
/* Ensure we are reading the data into our memory context. */
MemoryContextSwitchTo(ApplyMessageContext);
@@ -3607,7 +3630,29 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
if (!dlist_is_empty(&lsn_mapping))
wait_time = WalWriterDelay;
else
- wait_time = NAPTIME_PER_CYCLE;
+ {
+ TimestampTz nextWakeup = TIMESTAMP_INFINITY;
+
+ /*
+ * Since process_syncing_tables() is called conditionally, the
+ * tablesync worker start wakeup time might be in the past, and we
+ * can't know for sure when it will be updated again. Rather than
+ * spinning in a tight loop in this case, bump this wakeup time by
+ * a second.
+ */
+ now = GetCurrentTimestamp();
+ if (wakeup[LRW_WAKEUP_SYNC_START] < now)
+ wakeup[LRW_WAKEUP_SYNC_START] = TimestampTzPlusSeconds(wakeup[LRW_WAKEUP_SYNC_START], 1);
+
+ /* Find soonest wakeup time, to limit our nap. */
+ for (int i = 0; i < NUM_LRW_WAKEUPS; i++)
+ nextWakeup = Min(wakeup[i], nextWakeup);
+
+ /*
+ * Calculate the nap time, clamping as necessary.
+ */
+ wait_time = TimestampDifferenceMilliseconds(now, nextWakeup);
+ }
rc = WaitLatchOrSocket(MyLatch,
WL_SOCKET_READABLE | WL_LATCH_SET |
@@ -3625,6 +3670,21 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
{
ConfigReloadPending = false;
ProcessConfigFile(PGC_SIGHUP);
+ /* recompute wakeup times */
+ now = GetCurrentTimestamp();
+ for (int i = 0; i < NUM_LRW_WAKEUPS; i++)
+ LogRepWorkerComputeNextWakeup(i, now);
+
+ /*
+ * LogRepWorkerComputeNextWakeup() will have cleared the tablesync
+ * worker start wakeup time, so we might not wake up to start a new
+ * worker at the appropriate time. To deal with this, we set the
+ * wakeup time to right now so that
+ * process_syncing_tables_for_apply() recalculates it as soon as
+ * possible.
+ */
+ if (!am_tablesync_worker())
+ LogRepWorkerUpdateSyncStartWakeup(now);
}
if (rc & WL_TIMEOUT)
@@ -3643,31 +3703,17 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
* Check if time since last receive from primary has reached the
* configured limit.
*/
- if (wal_receiver_timeout > 0)
+ now = GetCurrentTimestamp();
+ if (now >= wakeup[LRW_WAKEUP_TERMINATE])
+ ereport(ERROR,
+ (errcode(ERRCODE_CONNECTION_FAILURE),
+ errmsg("terminating logical replication worker due to timeout")));
+
+ /* Check to see if it's time for a ping. */
+ if (now >= wakeup[LRW_WAKEUP_PING])
{
- TimestampTz now = GetCurrentTimestamp();
- TimestampTz timeout;
-
- timeout =
- TimestampTzPlusMilliseconds(last_recv_timestamp,
- wal_receiver_timeout);
-
- if (now >= timeout)
- ereport(ERROR,
- (errcode(ERRCODE_CONNECTION_FAILURE),
- errmsg("terminating logical replication worker due to timeout")));
-
- /* Check to see if it's time for a ping. */
- if (!ping_sent)
- {
- timeout = TimestampTzPlusMilliseconds(last_recv_timestamp,
- (wal_receiver_timeout / 2));
- if (now >= timeout)
- {
- requestReply = true;
- ping_sent = true;
- }
- }
+ requestReply = true;
+ wakeup[LRW_WAKEUP_PING] = TIMESTAMP_INFINITY;
}
send_feedback(last_received, requestReply, requestReply);
@@ -3703,7 +3749,6 @@ static void
send_feedback(XLogRecPtr recvpos, bool force, bool requestReply)
{
static StringInfo reply_message = NULL;
- static TimestampTz send_time = 0;
static XLogRecPtr last_recvpos = InvalidXLogRecPtr;
static XLogRecPtr last_writepos = InvalidXLogRecPtr;
@@ -3746,10 +3791,11 @@ send_feedback(XLogRecPtr recvpos, bool force, bool requestReply)
if (!force &&
writepos == last_writepos &&
flushpos == last_flushpos &&
- !TimestampDifferenceExceeds(send_time, now,
- wal_receiver_status_interval * 1000))
+ now < wakeup[LRW_WAKEUP_STATUS])
return;
- send_time = now;
+
+ /* Make sure we wake up when it's time to send another status update. */
+ LogRepWorkerComputeNextWakeup(LRW_WAKEUP_STATUS, now);
if (!reply_message)
{
@@ -5048,3 +5094,74 @@ get_transaction_apply_action(TransactionId xid, ParallelApplyWorkerInfo **winfo)
return TRANS_LEADER_APPLY;
}
}
+
+/*
+ * Compute the next wakeup time for a given wakeup reason. Can be called to
+ * initialize a wakeup time, to adjust it for the next wakeup, or to
+ * reinitialize it when GUCs have changed. We ask the caller to pass in the
+ * value of "now" because this frequently avoids multiple calls of
+ * GetCurrentTimestamp(). It had better be a reasonably up-to-date value
+ * though.
+ */
+static void
+LogRepWorkerComputeNextWakeup(LogRepWorkerWakeupReason reason, TimestampTz now)
+{
+ switch (reason)
+ {
+ case LRW_WAKEUP_TERMINATE:
+ if (wal_receiver_timeout <= 0)
+ wakeup[reason] = TIMESTAMP_INFINITY;
+ else
+ wakeup[reason] = TimestampTzPlusMilliseconds(now, wal_receiver_timeout);
+ break;
+ case LRW_WAKEUP_PING:
+ if (wal_receiver_timeout <= 0)
+ wakeup[reason] = TIMESTAMP_INFINITY;
+ else
+ wakeup[reason] = TimestampTzPlusMilliseconds(now, wal_receiver_timeout / 2);
+ break;
+ case LRW_WAKEUP_STATUS:
+ if (wal_receiver_status_interval <= 0)
+ wakeup[reason] = TIMESTAMP_INFINITY;
+ else
+ wakeup[reason] = TimestampTzPlusSeconds(now, wal_receiver_status_interval);
+ break;
+ case LRW_WAKEUP_SYNC_START:
+ /*
+ * This wakeup time is manually set as needed. This function can
+ * only be used to initialize its value.
+ */
+ wakeup[reason] = TIMESTAMP_INFINITY;
+ break;
+ /* there's intentionally no default: here */
+ }
+}
+
+/*
+ * Retrieve the current wakeup time for starting tablesync workers.
+ */
+TimestampTz
+LogRepWorkerGetSyncStartWakeup(void)
+{
+ return wakeup[LRW_WAKEUP_SYNC_START];
+}
+
+/*
+ * Update the current wakeup time for starting tablesync workers. If the
+ * current wakeup time is <= next_sync_start, no action is taken.
+ */
+void
+LogRepWorkerUpdateSyncStartWakeup(TimestampTz next_sync_start)
+{
+ if (next_sync_start < wakeup[LRW_WAKEUP_SYNC_START])
+ wakeup[LRW_WAKEUP_SYNC_START] = next_sync_start;
+}
+
+/*
+ * Clear the current wakeup time for starting tablesync workers.
+ */
+void
+LogRepWorkerClearSyncStartWakeup(void)
+{
+ wakeup[LRW_WAKEUP_SYNC_START] = TIMESTAMP_INFINITY;
+}
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index dc87a4edd1..ae44717588 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -225,6 +225,10 @@ extern PGDLLIMPORT LogicalRepWorker *MyLogicalRepWorker;
extern PGDLLIMPORT bool in_remote_transaction;
+extern TimestampTz LogRepWorkerGetSyncStartWakeup(void);
+extern void LogRepWorkerUpdateSyncStartWakeup(TimestampTz next_sync_start);
+extern void LogRepWorkerClearSyncStartWakeup(void);
+
extern void logicalrep_worker_attach(int slot);
extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
bool only_running);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 097f42e1b3..66b699852a 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1443,6 +1443,7 @@ LockViewRecurse_context
LockWaitPolicy
LockingClause
LogOpts
+LogRepWorkerWakeupReason
LogStmtLevel
LogicalDecodeBeginCB
LogicalDecodeBeginPrepareCB
--
2.25.1
