[jira] Resolved: (HBASE-2925) LRU of HConnectionManager.HBASE_INSTANCES breaks if HBaseConfiguration is changed

["stack (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-2925?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

stack resolved HBASE-2925.
--------------------------

     Hadoop Flags: [Reviewed]
    Fix Version/s: 0.90.0
       Resolution: Fixed

@Robert Yeah I removed some, left others but also added asserts so tests should fail is regression.  Thanks for doing up the test.  I just committed v2.

> LRU of HConnectionManager.HBASE_INSTANCES breaks if HBaseConfiguration is changed
> ---------------------------------------------------------------------------------
>
>                 Key: HBASE-2925
>                 URL: https://issues.apache.org/jira/browse/HBASE-2925
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.20.3, 0.90.0
>            Reporter: Robert Mahfoud
>             Fix For: 0.90.0
>
>         Attachments: 2925-v2.txt, 2925.txt, SimpleHConnectionManagerLeakReplicator.java
>
>
> {{HConnectionManager.getConnection(config)}} caches the created {{TableServer}} in {{HBASE_INSTANCES}} (a {{LinkedHashMap}} ) which is keyed by the configuration instance itself.
> Given the current implementation of {{hashCode()}} (and {{equals()}}) of {{HBaseConfiguration}}, the hash code of the configuration is changed if any of its properties are changed, which will cause the keys of {{HBASE_INSTANCES}} to be inconsistent with the hashtable that contains them, making some entries unreachable.
> In this case, when the map's LRU strategy needs to remove the oldest entry, it tries to remove it based on the oldest key, which no longer gives the original hash code, therefore the lookup in {{HBASE_INSTANCES.remove(oldest)}} doesn't actually remove anything.
> This has been observed to lead to OOM errors in long running clients.

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