Allan Yang created HBASE-21228:
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Summary: Memory leak since AbstractFSWAL caches Thread object and
never clean later
Key: HBASE-21228
URL: https://issues.apache.org/jira/browse/HBASE-21228
Project: HBase
Issue Type: Bug
Affects Versions: 1.4.7, 2.0.2, 2.1.0
Reporter: Allan Yang
Assignee: Allan Yang
In AbstractFSWAL(FSHLog in branch-1), we have a map caches thread and
SyncFutures.
{code}
/**
* Map of {@link SyncFuture}s keyed by Handler objects. Used so we reuse
SyncFutures.
* <p>
* TODO: Reuse FSWALEntry's rather than create them anew each time as we do
SyncFutures here.
* <p>
* TODO: Add a FSWalEntry and SyncFuture as thread locals on handlers rather
than have them get
* them from this Map?
*/
private final ConcurrentMap<Thread, SyncFuture> syncFuturesByHandler;
{code}
A colleague of mine find a memory leak case caused by this map.
Every thread who writes WAL will be cached in this map, And no one will clean
the threads in the map even after the thread is dead.
In one of our customer's cluster, we noticed that even though there is no
requests, the heap of the RS is almost full and CMS GC was triggered every
second.
We dumped the heap and then found out there were more than 30 thousands threads
with Terminated state. which are all cached in this map above. Everything
referenced in these threads were leaked. Most of the threads are:
1.PostOpenDeployTasksThread, which will write Open Region mark in WAL
2. hconnection-0x1f838e31-shared--pool, which are used to write index short
circuit(Phoenix), and WAL will be write and sync in these threads.
3. Index writer thread(Phoenix), which referenced by RegionEnvironment then
by HRegion and finally been referenced by PostOpenDeployTasksThread.
We should turn this map into a thread local one, let JVM GC the terminated
thread for us.
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