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

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

     [ https://issues.apache.org/jira/browse/CASSANDRA-15880?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jaroslaw Grabowski updated CASSANDRA-15880:
-------------------------------------------
    Since Version: 3.6

> 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
>            Priority: Normal
>
> 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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