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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4222) Make HLog more resilient to write pipeline failures
Date Fri, 19 Aug 2011 18:58:32 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4222?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13087894#comment-13087894

Ted Yu commented on HBASE-4222:

In point 2 of description on review board:
bq. This would prevent the log from being recovered in a timely manner.
Is the above description accurate.

Nice work Gary.

> Make HLog more resilient to write pipeline failures
> ---------------------------------------------------
>                 Key: HBASE-4222
>                 URL: https://issues.apache.org/jira/browse/HBASE-4222
>             Project: HBase
>          Issue Type: Improvement
>          Components: wal
>            Reporter: Gary Helmling
>            Assignee: Gary Helmling
>             Fix For: 0.92.0
> The current implementation of HLog rolling to recover from transient errors in the write
pipeline seems to have two problems:
> # When {{HLog.LogSyncer}} triggers an {{IOException}} during time-based sync operations,
it triggers a log rolling request in the corresponding catch block, but only after escaping
from the internal while loop.  As a result, the {{LogSyncer}} thread will exit and never be
restarted from what I can tell, even if the log rolling was successful.
> # Log rolling requests triggered by an {{IOException}} in {{sync()}} or {{append()}}
never happen if no entries have yet been written to the log.  This means that write errors
are not immediately recovered, which extends the exposure to more errors occurring in the
> In addition, it seems like we should be able to better handle transient problems, like
a rolling restart of DataNodes while the HBase RegionServers are running.  Currently this
will reliably cause RegionServer aborts during log rolling: either an append or time-based
sync triggers an initial {{IOException}}, initiating a log rolling request.  However the log
rolling then fails in closing the current writer ("All datanodes are bad"), causing a RegionServer
abort.  In this case, it seems like we should at least allow you an option to continue with
the new writer and only abort on subsequent errors.

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