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https://issues.apache.org/jira/browse/HBASE-6311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13405647#comment-13405647
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chunhui shen commented on HBASE-6311:
-------------------------------------
@ram
bq.But this patch will now write the delete marker also even during Major
compaction?
Yes, we write the delete marker only if kv.getMemstoreTS() >
maxReadPointToTrackVersions, because in that case, the already deleted put KV
will be retained in output.
bq.Ideally the expected behaviour is the put and deleted both should not be
written while major compaction.
Assume that one scanner could read put type KV first, and then we delete this
KV, but this scanner should also could read this scannner as the MVCC , If we
don't write put and delete KV in majorCompaction, this scanner couldn't read
the put type KV and break the MVCC, is it right?
> 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
> Attachments: HBASE-6311-test.patch, HBASE-6311v1.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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