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From "chunhui shen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6311) Data error after majorCompaction caused by keeping MVCC for opened scanners
Date Fri, 06 Jul 2012 04:37:36 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13407698#comment-13407698
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chunhui shen commented on HBASE-6311:
-------------------------------------

bq.When will the delete markers now be collected?
Do you mean collected to compacted file or to DeleteTracker in ScanQueryMatcher?
We won't collected delete markers to compacted file in majorCompaction except deleted KV is
also collectd to compacted file.

For example through the code

If a delete marker is not collected to deleteTracker because  
kv.getMemstoreTS()<=maxReadPointToTrackVersions, it must will be collected to compacted
file
                
> Data error after majorCompaction caused by keeping MVCC for opened scanners
> ---------------------------------------------------------------------------
>
>                 Key: HBASE-6311
>                 URL: https://issues.apache.org/jira/browse/HBASE-6311
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.94.0
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>            Priority: Blocker
>             Fix For: 0.96.0, 0.94.1
>
>         Attachments: HBASE-6311-test.patch, HBASE-6311v1.patch, HBASE-6311v2.patch
>
>
> It is a big problem we found in 0.94, and you could reproduce the problem in Trunk using
the test case I uploaded.
> When we do compaction, we will use region.getSmallestReadPoint() to keep MVCC for opened
scanners;
> However,It will make data mistake after majorCompaction because we will skip delete type
KV but keep the put type kv in the compacted storefile.
> The following is the reason from code:
> In StoreFileScanner, enforceMVCC is false when compaction, so we could read the delete
type KV,
> However, we will skip this delete type KV in ScanQueryMatcher because following code
> {code}
> if (kv.isDelete())
> {
> ...
>  if (includeDeleteMarker
>             && kv.getMemstoreTS() <= maxReadPointToTrackVersions) {
>           System.out.println("add deletes,maxReadPointToTrackVersions="
>               + maxReadPointToTrackVersions);
>           this.deletes.add(bytes, offset, qualLength, timestamp, type);
>         }
> ...
> }
> {code}
> Here maxReadPointToTrackVersions = region.getSmallestReadPoint();
> and kv.getMemstoreTS() > maxReadPointToTrackVersions 
> So we won't add this to DeleteTracker.
> Why test case passed if remove the line MultiVersionConsistencyControl.setThreadReadPoint(smallestReadPoint);
> Because in the StoreFileScanner#skipKVsNewerThanReadpoint
> {code}
> if (cur.getMemstoreTS() <= readPoint) {
>       cur.setMemstoreTS(0);
>     }
> {code}
> So if we remove the line MultiVersionConsistencyControl.setThreadReadPoint(smallestReadPoint);
> Here readPoint is LONG.MAX_VALUE, we will set memStore ts as 0, so we will add it to
DeleteTracker in ScanQueryMatcher 
> Solution:
> We use smallestReadPoint of region when compaction to keep MVCC for OPENED scanner, So
we should retain delete type kv in output in the case(Already deleted KV is retained in output
to make old opened scanner could read this KV) even if it is a majorcompaction.

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