Fix NPE in ShardReplicationTask under high shard concurrency (#1660)#1663
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…rch-project#1660) FollowerClusterStats.stats was backed by a non-thread-safe LinkedHashMap (mutableMapOf()). The singleton is shared across all ShardReplicationTasks (one per shard), and under concurrent puts from ~1024 shards, internal rehashing caused stats[shardId] to return a transient null, which the '!!' assertion in ShardReplicationTask.replicate() and TranslogSequencer turned into a NullPointerException, auto-pausing replication. Replace mutableMapOf() with ConcurrentHashMap() so concurrent put/get/remove never observe a spurious null. Change var to val since the reference is never reassigned. Add FollowerClusterStatsTests with a regression test that stresses the shared map under concurrent put/get/remove patterns mirroring the production call sites. Signed-off-by: Monu Singh <msnghgw@amazon.com>
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It should have been mentioned in the issue but it seems like RemoteClusterStats has the same issue. |
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Description
FollowerClusterStats.stats was backed by a non-thread-safe LinkedHashMap (mutableMapOf()). The singleton is shared across all ShardReplicationTasks (one per shard), and under concurrent puts from ~1024 shards, internal rehashing caused stats[shardId] to return a transient null, which the '!!' assertion in ShardReplicationTask.replicate() and TranslogSequencer turned into a NullPointerException, auto-pausing replication.
Replace mutableMapOf() with ConcurrentHashMap() so concurrent put/get/remove never observe a spurious null. Change var to val since the reference is never reassigned.
Related Issues
Resolves #1660
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