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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1084) Reinitializable DFS client
Date Sat, 23 May 2009 20:05:46 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1084?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12712457#action_12712457

stack commented on HBASE-1084:

dfs.client.max.block.acquire.failures looks like it might be useful.  Could double this rather
than mess with the timer.

Root problem though seems to be https://issues.apache.org/jira/browse/HADOOP-5903  Lets figure
out a patch for it and recommend backporting it in hbase installs on hadoop 0.19.x and 0.20.x.

> 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
> 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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