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https://issues.apache.org/jira/browse/HBASE-11591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14104559#comment-14104559
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Jeffrey Zhong commented on HBASE-11591:
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{quote}
it is possible that the cells in the original bulk load hfiles have seqId > 0.
{quote}
For bulk loaded files, this should not happen.
> Scanner fails to retrieve KV from bulk loaded file with highest sequence id
> than the cell's mvcc in a non-bulk loaded file
> ---------------------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-11591
> URL: https://issues.apache.org/jira/browse/HBASE-11591
> Project: HBase
> Issue Type: Bug
> Affects Versions: 0.99.0
> Reporter: ramkrishna.s.vasudevan
> Assignee: ramkrishna.s.vasudevan
> Priority: Critical
> Fix For: 0.99.0
>
> Attachments: HBASE-11591.patch, HBASE-11591_1.patch,
> HBASE-11591_2.patch, HBASE-11591_3.patch, TestBulkload.java,
> hbase-11591-03-02.patch, hbase-11591-03-jeff.patch
>
>
> See discussion in HBASE-11339.
> When we have a case where there are same KVs in two files one produced by
> flush/compaction and the other thro the bulk load.
> Both the files have some same kvs which matches even in timestamp.
> Steps:
> Add some rows with a specific timestamp and flush the same.
> Bulk load a file with the same data.. Enusre that "assign seqnum" property is
> set.
> The bulk load should use HFileOutputFormat2 (or ensure that we write the
> bulk_time_output key).
> This would ensure that the bulk loaded file has the highest seq num.
> Assume the cell in the flushed/compacted store file is
> row1,cf,cq,ts1, value1 and the cell in the bulk loaded file is
> row1,cf,cq,ts1,value2
> (There are no parallel scans).
> Issue a scan on the table in 0.96. The retrieved value is
> row1,cf1,cq,ts1,value2
> But the same in 0.98 will retrieve row1,cf1,cq,ts2,value1.
> This is a behaviour change. This is because of this code
> {code}
> public int compare(KeyValueScanner left, KeyValueScanner right) {
> int comparison = compare(left.peek(), right.peek());
> if (comparison != 0) {
> return comparison;
> } else {
> // Since both the keys are exactly the same, we break the tie in favor
> // of the key which came latest.
> long leftSequenceID = left.getSequenceID();
> long rightSequenceID = right.getSequenceID();
> if (leftSequenceID > rightSequenceID) {
> return -1;
> } else if (leftSequenceID < rightSequenceID) {
> return 1;
> } else {
> return 0;
> }
> }
> }
> {code}
> Here in 0.96 case the mvcc of the cell in both the files will have 0 and so
> the comparison will happen from the else condition . Where the seq id of the
> bulk loaded file is greater and would sort out first ensuring that the scan
> happens from that bulk loaded file.
> In case of 0.98+ as we are retaining the mvcc+seqid we are not making the
> mvcc as 0 (remains a non zero positive value). Hence the compare() sorts out
> the cell in the flushed/compacted file. Which means though we know the
> lateset file is the bulk loaded file we don't scan the data.
> Seems to be a behaviour change. Will check on other corner cases also but we
> are trying to know the behaviour of bulk load because we are evaluating if it
> can be used for MOB design.
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