[jira] [Created] (CASSANDRA-15880) Memory leak in CompressedChunkReader

["Jaroslaw Grabowski (Jira)" <ji...@apache.org>]

Jaroslaw Grabowski created CASSANDRA-15880:
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             Summary: Memory leak in CompressedChunkReader
                 Key: CASSANDRA-15880
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15880
             Project: Cassandra
          Issue Type: Bug
          Components: Feature/Compression
            Reporter: Jaroslaw Grabowski


CompressedChunkReader uses java.lang.ThreadLocal to reuse ByteBuffer for compressed data. ByteBuffers leak due to peculiar ThreadLocal quality.
ThreadLocals are stored in a map, where the key is a weak reference to a ThreadLocal and the value is the user's object (ByteBuffer in this case). When a last strong reference to a ThreadLocal is lost, weak reference to ThreadLocal (key) is removed but the value (ByteBuffer) is kept until cleaned by ThreadLocal heuristic expunge mechanism. See ThreadLocal's "stale entries" for details.

When a number of long-living threads is high enough this results in thousands of ByteBuffers stored as stale entries in ThreadLocals. In a not-so-lucky scenario we get OutOfMemoryException.



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