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https://issues.apache.org/jira/browse/CASSANDRA-21390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18082607#comment-18082607
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Praveen Reddy Arra commented on CASSANDRA-21390:
------------------------------------------------
We are seeing this when repairs are running and the flush of Reaper's *cluster*
table.
After switching out 500+ clusters to use Trie Memtables we started seeing this
issue on 13 clusters.
Our Reaper version is *3.8.0*
And we are seeing this unusual spikes in Old Gen.
!image-2026-05-21-09-17-49-716.png|width=820,height=354!
{{CREATE TABLE caas_repair.cluster (
name text,
last_contact timestamp,
partitioner text,
properties text,
seed_hosts set<text>,
state text,
PRIMARY KEY (name)
) WITH bloom_filter_fp_chance = 0.01
AND caching = \{'keys':'ALL','rows_per_partition':'ALL'}
AND comment = ''
AND compaction =
\{'class':'org.apache.cassandra.db.compaction.LeveledCompactionStrategy'}
AND compression =
\{'chunk_length_in_kb':'64','class':'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND default_time_to_live = 0
AND extensions = {}
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND speculative_retry = '99PERCENTILE';}}
> TrieMemtable MemtableReclaimMemory AssertionError: Negative released in
> MemtablePool$SubPool
> --------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21390
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21390
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Local/Memtable
> Reporter: Praveen Reddy Arra
> Priority: Normal
> Attachments: image-2026-05-21-09-17-49-716.png
>
>
> We have started seeing this fatal exception in Apache Cassandra 5.0.6 on one
> of our clusters.
> {code:java}
> [ERROR] [MemtableReclaimMemory:1] cluster_id=xxx ip_address=xxx.xxx.xxx.xxx
> JVMStabilityInspector.java:70 - Exception in thread
> Thread[MemtableReclaimMemory:1,5,MemtableReclaimMemory]
> java.lang.AssertionError: Negative released: -4332
> at
> org.apache.cassandra.utils.memory.MemtablePool$SubPool.released(MemtablePool.java:194)
> at
> org.apache.cassandra.utils.memory.MemtableAllocator$SubAllocator.releaseAll(MemtableAllocator.java:153)
> at
> org.apache.cassandra.utils.memory.MemtableAllocator$SubAllocator.setDiscarded(MemtableAllocator.java:144)
> at
> org.apache.cassandra.utils.memory.MemtableAllocator.setDiscarded(MemtableAllocator.java:95)
> at
> org.apache.cassandra.utils.memory.NativeAllocator.setDiscarded(NativeAllocator.java:205)
> at
> org.apache.cassandra.db.memtable.AbstractAllocatorMemtable.discard(AbstractAllocatorMemtable.java:171)
> at
> org.apache.cassandra.db.memtable.TrieMemtable.discard(TrieMemtable.java:163)
> at
> org.apache.cassandra.db.ColumnFamilyStore$Flush$1.runMayThrow(ColumnFamilyStore.java:1398)
> at org.apache.cassandra.utils.WrappedRunnable.run(WrappedRunnable.java:26)
> at
> org.apache.cassandra.concurrent.ExecutionFailure$1.run(ExecutionFailure.java:133)
> at
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
> at
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
> at
> io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
> at java.base/java.lang.Thread.run(Thread.java:842)
> {code}
> {code:yaml}
> memtable_allocation_type - heap_buffers
> file_cache_enabled: true
> file_cache_size: 2048MiB
> memtable:
> configurations:
> skiplist:
> class_name: SkipListMemtable
> trie:
> class_name: TrieMemtable
> default:
> inherits: trie
> {code}
> it looks similar to the open MemtableReclaimMemory assert issue in
> [CASSANDRA-18159|https://issues.apache.org/jira/browse/CASSANDRA-18159]
> Environment is RHEL 8.10 with OpenJDK 17 and 16GB heap, -ea enabled.
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