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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1394) Uploads sometimes fall to 0 requests/second (Binding up on HLog#append?)
Date Tue, 12 May 2009 20:46:45 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708616#action_12708616

stack commented on HBASE-1394:

Thinking yet more -- with an idea from Ryan -- then I think we can do pooled commit log writing
AND have the split run multithreaded.  Here's how:

Put up pools of HLog commit log writers.  Say 3 as default.  Round-robin edits.  ADD to the
HLogKey a timestamp.  The timestamp will be the time at which we added the edit to the log.
 Logs are rotated off as they fill.

On crash, master starts up as many threads as there are log files up to some limit.  Each
thread splits its log writing a new one per Region (though looks like it should do per Store
given how stuff is currently processed).  Being multithreaded, the split should run faster.

When the region comes on line, it'll have a bunch of files to process -- as many as there
were pool writers.  It opens all of them and then applies them to the memcache respecting
adding that with the lowest HLogKey timestamp first (Ryan's idea).

This should speed our writing and speed recovery on crash.

> Uploads sometimes fall to 0 requests/second (Binding up on HLog#append?)
> ------------------------------------------------------------------------
>                 Key: HBASE-1394
>                 URL: https://issues.apache.org/jira/browse/HBASE-1394
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: stack
>            Priority: Critical
>             Fix For: 0.20.0
>         Attachments: loghowlongittookappendinghlog.patch
> Trying to figure why rate sometimes goes to zero.
> Studying the reginoserver, HLog#append looks like a possible culprit.
> {code}
> "IPC Server handler 7 on 60021" daemon prio=10 tid=0x000000004057dc00 nid=0x1bc4 in Object.wait()
>    java.lang.Thread.State: WAITING (on object monitor)
>         at java.lang.Object.wait(Native Method)
>         at java.lang.Object.wait(Object.java:485)
>         at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.writeChunk(DFSClient.java:2964)
>         - locked <0x00007f9e3e449ff0> (a java.util.LinkedList)
>         - locked <0x00007f9e3e449e18> (a org.apache.hadoop.hdfs.DFSClient$DFSOutputStream)
>         at org.apache.hadoop.fs.FSOutputSummer.writeChecksumChunk(FSOutputSummer.java:150)
>         at org.apache.hadoop.fs.FSOutputSummer.write1(FSOutputSummer.java:100)
>         at org.apache.hadoop.fs.FSOutputSummer.write(FSOutputSummer.java:86)
>         - locked <0x00007f9e3e449e18> (a org.apache.hadoop.hdfs.DFSClient$DFSOutputStream)
>         at org.apache.hadoop.fs.FSDataOutputStream$PositionCache.write(FSDataOutputStream.java:49)
>         at java.io.DataOutputStream.write(DataOutputStream.java:90)
>         - locked <0x00007f9e434e5588> (a org.apache.hadoop.fs.FSDataOutputStream)
>         at org.apache.hadoop.io.SequenceFile$Writer.append(SequenceFile.java:1020)
>         - locked <0x00007f9e434e55c0> (a org.apache.hadoop.io.SequenceFile$Writer)
>         at org.apache.hadoop.io.SequenceFile$Writer.append(SequenceFile.java:984)
>         - locked <0x00007f9e434e55c0> (a org.apache.hadoop.io.SequenceFile$Writer)
>         at org.apache.hadoop.hbase.regionserver.HLog.doWrite(HLog.java:565)
>         at org.apache.hadoop.hbase.regionserver.HLog.append(HLog.java:521)
>         - locked <0x00007f9dfa376f70> (a java.lang.Object)
>         at org.apache.hadoop.hbase.regionserver.HRegion.update(HRegion.java:1777)
>         at org.apache.hadoop.hbase.regionserver.HRegion.batchUpdate(HRegion.java:1348)
>         at org.apache.hadoop.hbase.regionserver.HRegion.batchUpdate(HRegion.java:1289)
>         at org.apache.hadoop.hbase.regionserver.HRegionServer.batchUpdates(HRegionServer.java:1727)
>         at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>         at java.lang.reflect.Method.invoke(Method.java:597)
>         at org.apache.hadoop.hbase.ipc.HBaseRPC$Server.call(HBaseRPC.java:642)
>         at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:911)
> {code}

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