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

["Berenguer Blasi (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-15880?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17191949#comment-17191949 ] 

Berenguer Blasi commented on CASSANDRA-15880:
---------------------------------------------

Note for the reviewer: {{CompressedChunkReader.Standard}} is a {{RebuffererFactory}} where the main method at use is {{CompressedChunkReader.instantiateRebufferer()}}. That one wraps the reader in a {{BufferManagingRebufferer}} which will call {{close()}} and also is {{AutoClosable}}. I have checked for uses of the reader in the code and as expected it is being closed/auto closed so I expect the {{ThreadLocal}} to be properly removed and not leak now.

> 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
>            Assignee: Berenguer Blasi
>            Priority: Normal
>             Fix For: 4.0, 3.11.x
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> 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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