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From "chunhui shen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6065) Log for flush would append a non-sequential edit in the hlog, may cause data loss
Date Tue, 22 May 2012 05:21:41 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13280734#comment-13280734
] 

chunhui shen commented on HBASE-6065:
-------------------------------------

I have tried to write a test, but it is a little hard.

We also could fix the issue using another solution (patchv2):
In current logic, we consider the last edit's seq id as the maximal seq id in the recoverd.edits
file, however it is wrong because we can't ensure the sequentia edit in the hlog.
So we should changed the logic of find the maximal seq id for the recoverd.edits file, 
We only need do a little for the method HLogSplitter#updateRegionMaximumEditLogSeqNum.
                
> Log for flush would append a non-sequential edit in the hlog, may cause data loss
> ---------------------------------------------------------------------------------
>
>                 Key: HBASE-6065
>                 URL: https://issues.apache.org/jira/browse/HBASE-6065
>             Project: HBase
>          Issue Type: Bug
>          Components: wal
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>         Attachments: HBASE-6065.patch, HBASE-6065v2.patch
>
>
> After completing flush region, we will append a log edit in the hlog file through HLog#completeCacheFlush.
> {code}
> public void completeCacheFlush(final byte [] encodedRegionName,
>       final byte [] tableName, final long logSeqId, final boolean isMetaRegion)
> {
> ...
> HLogKey key = makeKey(encodedRegionName, tableName, logSeqId,
>             System.currentTimeMillis(), HConstants.DEFAULT_CLUSTER_ID);
> ...
> }
> {code}
> when we make the hlog key, we use the seqId from the parameter, and it is generated by
HLog#startCacheFlush,
> Here, we may append a lower seq id edit than the last edit in the hlog file.
> If it is the last edit log in the file, it may cause data loss.
> because 
> {code}
> HRegion#replayRecoveredEditsIfAny{
> ...
> maxSeqId = Math.abs(Long.parseLong(fileName));
>       if (maxSeqId <= minSeqId) {
>         String msg = "Maximum sequenceid for this log is " + maxSeqId
>             + " and minimum sequenceid for the region is " + minSeqId
>             + ", skipped the whole file, path=" + edits;
>         LOG.debug(msg);
>         continue;
>       }
> ...
> }
> {code}
> We may skip the splitted log file, because we use the lase edit's seq id as its file
name, and consider this seqId as the max seq id in this log file.

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