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From "Elliott Clark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8927) Use nano time instead of mili time everywhere
Date Thu, 11 Jul 2013 21:37:48 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13706274#comment-13706274
] 

Elliott Clark commented on HBASE-8927:
--------------------------------------

bq.The hardware clocks themselves do not go back, but if two updates come with seq_num X and
seq_num X+1, then X+1 might get a smaller ns because the hardware thread might observe a different
clock than the other thread.

That can happen now if the mutations are not on the same row:

* [Thread 1] Mutation A comes in to thread
* [Thread 1] Wal edit A gets seq id.
* [Thread 1] Thread Context Switches
* [Thread 2] Mutation B comes in
* [Thread 2] Wal edit B gets seq id.
* [Thread 2] Mutation B gets timestamp.
* [Thread 1] Wakes up
* [Thread 1] Mutation A gets time stamp.

A.id < B.id && A.ts > B.ts

Locks ensure this isn't an issue on the same row.
                
> Use nano time instead of mili time everywhere
> ---------------------------------------------
>
>                 Key: HBASE-8927
>                 URL: https://issues.apache.org/jira/browse/HBASE-8927
>             Project: HBase
>          Issue Type: Bug
>            Reporter: stack
>         Attachments: 8927.txt
>
>
> Less collisions and we are paying the price of a long anyways so might as well fill it.

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