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https://issues.apache.org/jira/browse/HBASE-6311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13405804#comment-13405804
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ramkrishna.s.vasudevan commented on HBASE-6311:
-----------------------------------------------
As per MVCC the behaviour like the firstscanner should read is correct. But
when the compaction is done and the in this case the put and delete is removed,
we have a new set of store files.. Now already when starting a scan we have
logic
{code}
public synchronized boolean next(List<KeyValue> outResult, int limit) throws
IOException {
if (checkReseek()) {
return true;
}
{code}
So now i have doubt on this behaviour. Pls correct me if am wrong.
> 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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