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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1084) Reinitializable DFS client
Date Mon, 22 Dec 2008 19:02:44 GMT
Reinitializable DFS client

                 Key: HBASE-1084
                 URL: https://issues.apache.org/jira/browse/HBASE-1084
             Project: Hadoop HBase
          Issue Type: Improvement
          Components: io, master, regionserver
            Reporter: Andrew Purtell
             Fix For: 0.20.0

HBase is the only long lived DFS client. Tasks handle DFS errors by dying. HBase daemons do
not and instead depend on dfsclient error recovery capability, but that is not sufficiently
developed or tested. Several issues are a result:
* HBASE-846: hbase looses its mind when hdfs fills
* HBASE-879: When dfs restarts or moves blocks around, hbase regionservers don't notice
* HBASE-932: Regionserver restart
* HBASE-1078: "java.io.IOException: Could not obtain block": allthough file is there and accessible
through the dfs client
* hlog indefinitely hung on getting new blocks from dfs on apurtell cluster
* regions closed due to transient DFS problems during loaded cluster restart

These issues might also be related:
* HBASE-15: Could not complete hdfs write out to flush file forcing regionserver restart
* HBASE-667: Hung regionserver; hung on hdfs: writeChunk, DFSClient.java:2126, DataStreamer

HBase should reinitialize the fs a few times upon catching fs exceptions, with backoff, to
compensate. This can be done by making a wrapper around all fs operations that releases references
to the old fs instance and makes and initializes a new instance to retry. All fs users would
need to be fixed up to handle loss of state around fs wrapper invocations: hlog, memcache
flusher, hstore, etc. 

Cases of clear unrecoverable failure (are there any?) should be excepted.

Once the fs wrapper is in place, error recovery scenarios can be tested by forcing reinitialization
of the fs during PE or other test cases.

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