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https://issues.apache.org/jira/browse/CASSANDRA-19564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17838249#comment-17838249
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Benedict Elliott Smith commented on CASSANDRA-19564:
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Is the Flush that is blocked the one that the postFlush is waiting on? You can
check this from a heap dump.
If it is, the question is why the writeBarrier it has issued doesn't complete -
any write that is behind such an issued barrier should be clear to complete
without blocking. In which case we have perhaps introduced some new blocking
mechanism that sits behind the completion of the barrier that depends on the
barrier itself finishing. This should also be apparent from a heap dump, from
which you can find the OpOrder that haven't completed, and which threads are
holding a reference to it and what they are blocking on.
> MemtablePostFlush deadlock leads to stuck nodes and crashes
> -----------------------------------------------------------
>
> Key: CASSANDRA-19564
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19564
> Project: Cassandra
> Issue Type: Bug
> Components: Local/Compaction, Local/Memtable
> Reporter: Jon Haddad
> Priority: Urgent
> Fix For: 4.1.x
>
> Attachments: image-2024-04-16-11-55-54-750.png,
> image-2024-04-16-12-29-15-386.png, image-2024-04-16-13-43-11-064.png,
> image-2024-04-16-13-53-24-455.png
>
>
> I've run into an issue on a 4.1.4 cluster where an entire node has locked up
> due to what I believe is a deadlock in memtable flushing. Here's what I know
> so far. I've stitched together what happened based on conversations, logs,
> and some flame graphs.
> *Log reports memtable flushing*
> The last successful flush happens at 12:19.
> {noformat}
> INFO [NativePoolCleaner] 2024-04-16 12:19:53,634
> AbstractAllocatorMemtable.java:286 - Flushing largest CFS(Keyspace='ks',
> ColumnFamily='version') to free up room. Used total: 0.24/0.33, live:
> 0.16/0.20, flushing: 0.09/0.13, this: 0.13/0.15
> INFO [NativePoolCleaner] 2024-04-16 12:19:53,634 ColumnFamilyStore.java:1012
> - Enqueuing flush of ks.version, Reason: MEMTABLE_LIMIT, Usage: 660.521MiB
> (13%) on-heap, 790.606MiB (15%) off-heap
> {noformat}
> *MemtablePostFlush appears to be blocked*
> At this point, MemtablePostFlush completed tasks stops incrementing, active
> stays at 1 and pending starts to rise.
> {noformat}
> MemtablePostFlush 1 1 3446 0 0
> {noformat}
>
> The flame graph reveals that PostFlush.call is stuck. I don't have the line
> number, but I know we're stuck in
> {{org.apache.cassandra.db.ColumnFamilyStore.PostFlush#call}} given the visual
> below:
> *!image-2024-04-16-13-43-11-064.png!*
> *Memtable flushing is now blocked.*
> All MemtableFlushWriter threads are Parked waiting on
> {{{}OpOrder.Barrier.await{}}}. A wall clock profile of 30s reveals all time
> is spent here. Presumably we're waiting on the single threaded Post Flush.
> !image-2024-04-16-12-29-15-386.png!
> *Memtable allocations start to block*
> Eventually it looks like the NativeAllocator stops successfully allocating
> memory. I assume it's waiting on memory to be freed, but since memtable
> flushes are blocked, we wait indefinitely.
> Looking at a wall clock flame graph, all writer threads have reached the
> allocation failure path of {{MemtableAllocator.allocate()}}. I believe we're
> waiting on {{signal.awaitThrowUncheckedOnInterrupt()}}
> {noformat}
> MutationStage 48 828425 980253369 0 0{noformat}
> !image-2024-04-16-11-55-54-750.png!
>
> *Compaction Stops*
> Since we write to the compaction history table, and that requires memtables,
> compactions are now blocked as well.
>
> !image-2024-04-16-13-53-24-455.png!
>
> The node is now doing basically nothing and must be restarted.
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