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From "Jeffrey Zhong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11591) Scanner fails to retrieve KV from bulk loaded file with highest sequence id than the cell's mvcc in a non-bulk loaded file
Date Tue, 29 Jul 2014 02:16:38 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14077290#comment-14077290

Jeffrey Zhong commented on HBASE-11591:

I think this can be solved when reading bulk load hfiles, we can use current hfile sequenceId
as its KVs' mvcc values.  The other option is to add a new metadata into hfile as default
mvcc value for situations like bulk loaded hfiles. Thanks.

> 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: TestBulkload.java
> 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
> 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
> 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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