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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2467) Concurrent flushers in HLog sync using HDFS-895
Date Tue, 17 Aug 2010 14:49:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2467?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12899426#action_12899426

stack commented on HBASE-2467:

What did you do to the patch J-D?  In the hadoop we ship, we should include hdfs-895? (Its
a dfsclient-only fix, right?).  What should we do about group commit.  Open a new issue? 
If hdfs-895 is not in place, we just run slower, is that right?

On the patch:

If concurrency, should 'private boolean logRollRequested' be volatile?  (Maybe not necessary
-- I see check is done in a synchronized method?)

I don't get this bit:

+      synchronized (this) {
+        this.syncTime += System.currentTimeMillis() - now;
+        this.syncOps++;
+      }
+      synchronized (this.updateLock) {

Why not do the syncTime and syncOps under the updateLock rather than do a synchronize on 'this'?
 Wouldn't it have same effect but be less obnoxious? (Haven't looked at rest of this class
to check if syncops and synctime updates are done under a synchronize(this)).

> Concurrent flushers in HLog sync using HDFS-895
> -----------------------------------------------
>                 Key: HBASE-2467
>                 URL: https://issues.apache.org/jira/browse/HBASE-2467
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.90.0
>         Attachments: HBASE-2467-v2.patch, hbase-2467.txt
> HDFS-895 changes hflush() to be able to run concurrently from multiple threads, where
flushes can be concurrent with further writes to the same file.
> We need to rip out/amend the group commit code a bit to take advantage of this.

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