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https://issues.apache.org/jira/browse/HBASE-2312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12845531#action_12845531
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Todd Lipcon commented on HBASE-2312:
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Yea, like I said I think it's really unlikely. What I'm thinking is something
like:
|*RS*|*Master*|
|Writes "intent to roll to hlog.2"|-|
|enters GC pause|-|
|-|detects RS dead, lists files, sees only up to hlog.1|
|comes back to life|-|
|opens hlog.2 for append|-|
|writes log.1 rolled, closes|-|
|-|sees intent to roll at end of hlog.1|
|writes some edits to hlog.2|-|
|writes "intent to roll to hlog.3"|-|
|opens hlog.3 for append|-|
|writes "rolled" to hlog.2, closes|-|
|-|opens hlog.2 for append|
|-|*needs to check for intent to roll at end of hlog.2*|
Like I said this is very unlikely :)
> Possible data loss when RS goes into GC pause while rolling HLog
> ----------------------------------------------------------------
>
> Key: HBASE-2312
> URL: https://issues.apache.org/jira/browse/HBASE-2312
> Project: Hadoop HBase
> Issue Type: Bug
> Components: master, regionserver
> Affects Versions: 0.20.3
> Reporter: Karthik Ranganathan
>
> There is a very corner case when bad things could happen(ie data loss):
> 1) RS #1 is going to roll its HLog - not yet created the new one, old one
> will get no more writes
> 2) RS #1 enters GC Pause of Death
> 3) Master lists HLog files of RS#1 that is has to split as RS#1 is dead,
> starts splitting
> 4) RS #1 wakes up, created the new HLog (previous one was rolled) and
> appends an edit - which is lost
> The following seems like a possible solution:
> 1) Master detects RS#1 is dead
> 2) The master renames the /hbase/.logs/<regionserver name> directory to
> something else (say /hbase/.logs/<regionserver name>-dead)
> 3) Add mkdir support (as opposed to mkdirs) to HDFS - so that a file
> create fails if the directory doesn't exist. Dhruba tells me this is very
> doable.
> 4) RS#1 comes back up and is not able create the new hlog. It restarts
> itself.
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