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From "Feng Honghua (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8721) Deletes can mask puts that happen after the delete
Date Fri, 21 Jun 2013 02:23:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13689975#comment-13689975
] 

Feng Honghua commented on HBASE-8721:
-------------------------------------

[~sershe] :

It still need 10+ms, at best, for checkAndPut / increment when the KV read isn't in RS's block-cache
and need access to HDFS, though this read in RS can save 2 rpcs. 

Actually two months ago one of our Xiaomi's internal customers gave up using checkAndPut since
they can't afford the poor performance, though they did admit they love the atomicity checkAndPut
provides.
                
> Deletes can mask puts that happen after the delete
> --------------------------------------------------
>
>                 Key: HBASE-8721
>                 URL: https://issues.apache.org/jira/browse/HBASE-8721
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Feng Honghua
>         Attachments: HBASE-8721-0.94-V0.patch
>
>
> this fix aims for bug mentioned in http://hbase.apache.org/book.html 5.8.2.1:
> "Deletes mask puts, even puts that happened after the delete was entered. Remember that
a delete writes a tombstone, which only disappears after then next major compaction has run.
Suppose you do a delete of everything <= T. After this you do a new put with a timestamp
<= T. This put, even if it happened after the delete, will be masked by the delete tombstone.
Performing the put will not fail, but when you do a get you will notice the put did have no
effect. It will start working again after the major compaction has run. These issues should
not be a problem if you use always-increasing versions for new puts to a row. But they can
occur even if you do not care about time: just do delete and put immediately after each other,
and there is some chance they happen within the same millisecond."

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