Nikolai Grigoriev created HBASE-8336:
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Summary: PooledHTable may be returned multiple times to the same
pool
Key: HBASE-8336
URL: https://issues.apache.org/jira/browse/HBASE-8336
Project: HBase
Issue Type: Bug
Components: Client
Affects Versions: 0.95.0
Reporter: Nikolai Grigoriev
Priority: Minor
I have recently observed a very strange issue with an application using HBase
and HTablePool. After an investigation I have found that the root cause was the
piece of code that was calling close() twice on the same HTableInterface
instance retrieved from HTablePool (created with default policy).
A closer look at the code revealed that PooledHTable.close() calls
returnTable(), which, in turn, places the table back into the QUEUE of the
pooled tables. No checking of any kind is done so it is possible to call it
multiple times and place multiple references to the same HTable into the same
pool.
This creates a number of negative effects:
- pool grows on each close() call and eventually gets filled up with the
references to the same HTable. From this moment the pool stops working as pool.
- multiple callers will get the same instance of HTable while expecting to have
unique instances
- once the pool is full, next call to close() will result to the call to the
real close() method of HTable. This will make HTable unusable as close() call
may shutdown() the internal thread pool. From this moment other attempts to use
this HTable will fail with RejectedExecutionException. And since the HTablePool
will have additional references to that HTable, other users of the pool will
just start failing on any call that leads to flushCommits()
The problem was, obviously, triggered by bad code on our side. But I think the
pool has to be protected. Probably the best way to fix it would be to implement
a flag in PooledHTable that represent its state (leased/returned) and once
close() is called, it would be "returned". From this moment any operations on
this PooledHTable would result in something like IllegalStateException.
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