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https://issues.apache.org/jira/browse/HBASE-3855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13029241#comment-13029241
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mikhail commented on HBASE-3855:
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When writing the scanner code for the new HFile format I thought about getting
rid of linear scans by adding an array of key/value pair offsets at the
beginning of each data block, so that seek/reseek can be implemented as a
binary search. If we do have cases when the seek operation has to scan
thousands of kvs, then I will certainly implement the binary search seek in the
HFile V2 format.
> Performance degradation of memstore because reseek is linear
> ------------------------------------------------------------
>
> Key: HBASE-3855
> URL: https://issues.apache.org/jira/browse/HBASE-3855
> Project: HBase
> Issue Type: Improvement
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
>
> The scanner use reseek to find the next row (or next column) as part of a
> scan. The reseek code iterates over a Set to position itself at the right
> place. If there are many thousands of kvs that need to be skipped over, then
> the time-cost is very high. In this case, a seek would be far lesser in cost
> than a reseek.
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