Of cause, let me explain the situation. I have a common question without direct
relation the problem with “Unexplained stuck memtable flush”. I would like to
know, how can I identify situation that all nodes cross all data centers will
be synch.
* It is little tricky to wait e.g. 1 day, 2 days or longer time for the
synchronization
My question is. Do you see easy way, how can I check that expected huge
synchronization (e.g. after extension cluster – add new data center or add half
of new nodes) fill be finish from perspective of data synch? Thx for sharing
you best practices, regards
Jiri
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From: Bowen Song via user <user@cassandra.apache.org>
Sent: Tuesday, November 5, 2024 1:39 PM
To: user@cassandra.apache.org
Cc: Bowen Song <bo...@bso.ng>
Subject: Re: [External]Unexplained stuck memtable flush
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________________________________
Hi Jiri,
Thank you for taking a look at this issue. But I'm sorry, I don't really
understand your message. Can you please elaborate?
Cheers,
Bowen
On 05/11/2024 12:34, Jiri Steuer (EIT) wrote:
Hi all,
It is possible easy to check the moment/milestone, when the data cross more
data centers will by synch (in case that other applications and user access
will be disabled)? I think about monitoring of throughput or …? Thx for feedback
J. Steuer
This item's classification is Internal. It was created by and is in property of
the EmbedIT. Do not distribute outside of the organization.
From: Bowen Song via user
<user@cassandra.apache.org><mailto:user@cassandra.apache.org>
Sent: Tuesday, November 5, 2024 1:12 PM
To: d...@cassandra.apache.org<mailto:d...@cassandra.apache.org>;
user@cassandra.apache.org<mailto:user@cassandra.apache.org>
Cc: Bowen Song <bo...@bso.ng><mailto:bo...@bso.ng>
Subject: [External]Unexplained stuck memtable flush
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________________________________
Hi all,
We have a cluster running Cassandra 4.1.1. We are seeing the memtable flush
randomly getting stuck. This has happened twice in the last 10 days, to two
different nodes in the same cluster. This started to happen after we enabled
CDC, and each time it got stuck, there was at least one repair running
involving the affected node.
The signs of the stuck memtable flush is most obvious from the "StatusLogger"
logs.
At the beginning, the MemtablePostFlush and MemtableFlushWriter got stuck, they
have 1 and 2 active tasks each, and a small number of pending tasks.
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:65 - Pool
Name Active Pending Completed Blocked All Time
Blocked
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
ReadStage 0 0 34052333 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
CompactionExecutor 0 0 1019777 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
MutationStage 0 0 14930764 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
MemtableReclaimMemory 0 0 21877 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
PendingRangeCalculator 0 0 177 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
Repair#61 0 0 1344 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
GossipStage 0 0 889452 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
SecondaryIndexManagement 0 0 1 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
HintsDispatcher 0 0 19 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
Repair-Task 0 0 65 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
RequestResponseStage 0 0 44447834 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
Native-Transport-Requests 0 0 8967921 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
MigrationStage 0 0 5 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
MemtableFlushWriter 2 10 21781 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
MemtablePostFlush 1 11 47856 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
PerDiskMemtableFlushWriter_0 0 0 21769 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 - Sampler
0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
ValidationExecutor 0 0 36651 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
ViewBuildExecutor 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
InternalResponseStage 0 0 240 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
AntiEntropyStage 1 1773 120067 0
0
INFO [ScheduledTasks:1] 2024-11-03 03:50:15,224 StatusLogger.java:69 -
CacheCleanupExecutor 0 0 0 0
0
The number of pending tasks slowly grows larger over time, and the number of
completed tasks do not increase at all.
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:65 - Pool
Name Active Pending Completed Blocked All Time
Blocked
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
ReadStage 0 0 39905462 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
CompactionExecutor 0 0 1170100 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
MutationStage 0 0 16976992 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair#76 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair#74 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair#72 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
GossipStage 0 0 1026877 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair-Task 0 0 83 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
RequestResponseStage 0 0 51122191 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
ValidationExecutor 0 0 36651 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
MemtablePostFlush 1 54 47856 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
MemtableFlushWriter 2 53 21781 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
CacheCleanupExecutor 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair#67 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
MemtableReclaimMemory 0 0 21877 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
PendingRangeCalculator 0 0 177 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair#82 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Repair#61 0 0 1344 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
SecondaryIndexManagement 0 0 1 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
HintsDispatcher 0 0 20 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
Native-Transport-Requests 0 0 10145020 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
MigrationStage 0 0 5 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 - Sampler
0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,941 StatusLogger.java:69 -
PerDiskMemtableFlushWriter_0 0 0 21769 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,942 StatusLogger.java:69 -
ViewBuildExecutor 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,942 StatusLogger.java:69 -
InternalResponseStage 0 0 996 0
0
INFO [ScheduledTasks:1] 2024-11-03 16:33:05,942 StatusLogger.java:69 -
AntiEntropyStage 1 9694 120067 0
0
Then, things start to get worse, the MutationStage also got stuck.
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:65 - Pool
Name Active Pending Completed Blocked All Time
Blocked
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
ReadStage 0 0 40186426 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
CompactionExecutor 0 0 1171479 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
MutationStage 128 201414 16988212 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#76 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#74 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#72 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
GossipStage 0 0 1032988 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair-Task 0 0 85 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
RequestResponseStage 0 0 51307497 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
ValidationExecutor 0 0 36651 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
MemtablePostFlush 1 54 47856 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
MemtableFlushWriter 2 53 21781 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
CacheCleanupExecutor 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#67 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
MemtableReclaimMemory 0 0 21877 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#84 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
PendingRangeCalculator 0 0 177 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#82 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Repair#61 0 0 1344 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
SecondaryIndexManagement 0 0 1 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
HintsDispatcher 0 0 20 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
Native-Transport-Requests 0 0 10194549 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
MigrationStage 0 0 5 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 - Sampler
0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
PerDiskMemtableFlushWriter_0 0 0 21769 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
ViewBuildExecutor 0 0 0 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
InternalResponseStage 0 0 1087 0
0
INFO [ScheduledTasks:1] 2024-11-03 17:05:40,974 StatusLogger.java:69 -
AntiEntropyStage 1 10364 120067 0
0
Writes on this node starts to timeout and fail. But if left untouched, it's
only gonna get worse, and eventually lead to JVM OOM and crash.
By inspecting the heap dump created at OOM, we can see that both of the
MemtableFlushWriter threads are stuck on line
1190<https://github.com/apache/cassandra/blob/8d91b469afd3fcafef7ef85c10c8acc11703ba2d/src/java/org/apache/cassandra/db/ColumnFamilyStore.java#L1190>
in the ColumnFamilyStore.java:
// mark writes older than the barrier as blocking progress,
permitting them to exceed our memory limit
// if they are stuck waiting on it, then wait for them all to
complete
writeBarrier.markBlocking();
writeBarrier.await(); // <----------- stuck here
And the MemtablePostFlush thread is stuck on line
1094<https://github.com/apache/cassandra/blob/8d91b469afd3fcafef7ef85c10c8acc11703ba2d/src/java/org/apache/cassandra/db/ColumnFamilyStore.java#L1094>
in the same file.
try
{
// we wait on the latch for the commitLogUpperBound to be set,
and so that waiters
// on this task can rely on all prior flushes being complete
latch.await(); // <----------- stuck here
}
Our top suspect is CDC interacting with repair, since this started to happen
shortly after we enabled CDC on the nodes, and each time repair was running.
But we have not been able to reproduce this in a testing cluster, and don't
know what's the next step to troubleshoot this issue. So I'm posting it in the
mailing lists and hoping someone may know something about it or point me to the
right direction.
p.s.: sorry about posting this to both the user & dev mailing lists. It's an
end-user related issue but involves Cassandra internals, so I can't decide
which one is best suited.
Cheers,
Bowen
