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From "Adam Fuchs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-803) Add Reverse Logical Time as a Time Type
Date Tue, 16 Oct 2012 15:39:03 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13477087#comment-13477087
] 

Adam Fuchs commented on ACCUMULO-803:
-------------------------------------

You could do both count up and count down logical time on many different groups of keys in
the same tablet with only persisting one timestamp. If the plugin framework supports a one-up
counter, a plugin can then subtract that from max long or transform it otherwise as necessary
for each timestamp group. This would maintain the monotonicity property of logical time on
any of the groups of entries at the cost of introducing sparcity (which doesn't really matter).
                
> Add Reverse Logical Time as a Time Type
> ---------------------------------------
>
>                 Key: ACCUMULO-803
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-803
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>    Affects Versions: 1.4.2
>            Reporter: Drew Farris
>            Assignee: Drew Farris
>            Priority: Minor
>         Attachments: ACCUMULO-803.patch
>
>
> In a context where we are doing aggregation/combination of multiple values for a given
key it may be useful to iterate over the values associated with that key in the order in which
the mutations were applied (FIFO), instead of the FILO order that seems to occur when using
{{TimeType.LOGICAL}}. 
> I encountered when implemeting a checkAndPut operation that would ensure that the previous
value was expected before putting a new value. In this case, if the previous value was not
as expected, the mutation would be ignored. 
> Perhaps it is useful in a general case?

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