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https://issues.apache.org/jira/browse/ACCUMULO-803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13485136#comment-13485136
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Drew Farris commented on ACCUMULO-803:
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I agree, I don't feel comfortable allowing users to set column family ordering
on a per mutation basis.
With the API you propose, do you feel that fifo ordering would be best achieved
by manipulating timestamps as is done the original patch? If so, does this
introduce any strangeness in the relationship between typeType and
fifoColumnFamilies? Could it make sense to use TimeType.MILLIS and a fifo
column family? Perhaps yes.
I feel a little uncomfortable with the fact that column families are dynamic
but we would require the user to specify a set of column families at creation
time if they want fifo behavior. This seems to run counter to the spirit of
column families (and how they're used) in Accumulo.
One way to solve this problem would be to add setColumnFamilyOrdering(String
cf, boolean fifo) (or something like it) to TableOperations. This might not be
a good idea because we run into the same problem we have with Mutations: the
user could shoot themselves in the foot if they set the ordering on a column
family to be different than the default for a table that already contains data.
So, I have to admit that I lean closest to the original mechanism, but I could
be biased because I'm the patch author :)
Thoughts?
> 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: 1.5.0
> Reporter: Drew Farris
> Assignee: Drew Farris
> Priority: Minor
> Attachments: ACCUMULO-803.patch, 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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