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https://issues.apache.org/jira/browse/HBASE-1084?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12746359#action_12746359
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stack commented on HBASE-1084:
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There is a pregnant suggestion over in hbase-4739 where dfsclient passes nn
datanodes it knows are bad so nn won't use these when allocating blocks for new
files. Client side of code is up but not the server-side.
> 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
>
> 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 socketWrite
> 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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