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From "ramkrishna.s.vasudevan (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 Wed, 23 May 2012 05:06:42 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13281406#comment-13281406
] 

ramkrishna.s.vasudevan commented on HBASE-6065:
-----------------------------------------------

@Chunhui
Again thinking on this patch
HBASE-5782 ensures that the seqid should be in sequence.  It is only the CACHEFLUSH entry
that deviates from the fact that the seq id can be ordered.
I feel that instead of checking the real max seq id we can just avoid this entry from adding
to regionMaximumEditLogSeqNum.
This will ensure that finally when we create the recovered.edits file we will have only the
max entry.  What do you feel?  It should be simple also.
                
> 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
>            Priority: Critical
>             Fix For: 0.96.0, 0.94.1
>
>         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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