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From "Dave Marion (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-759) remove priority setting for scan-time iterators
Date Wed, 12 Sep 2012 00:44:07 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13453584#comment-13453584
] 

Dave Marion commented on ACCUMULO-759:
--------------------------------------

When you say IteratorChain, do you mean the one from Apache Commons Collections? If not, I
would look at this package. There are some pretty cool features.
                
> remove priority setting for scan-time iterators
> -----------------------------------------------
>
>                 Key: ACCUMULO-759
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-759
>             Project: Accumulo
>          Issue Type: Improvement
>            Reporter: Adam Fuchs
>              Labels: newbie
>
> Iterators have a priority setting that allows a user to order iterators arbitrarily.
However that priority is an integer that doesn't directly convey the iterator's relationship
to other iterators. I would postulate that nobody has ever needed to sneak in a scan-time
iterator underneath a configured table iterator (please let me know if I'm wrong about this),
and the effect of doing so is not easy to calculate. Many people have chosen a bad iterator
priority and seen commutativity problems with previously configured iterators.
> I propose that we use more of an agglomerative approach to configuring scan-time iterators,
in which the order of the iterator tree is the same order in which the addScanIterator method
is called, and all scan-time iterators apply after the configured iterators apply. The change
to the API should just be to remove the priority number, and the existing IteratorSetting
constructor and accessors should be deprecated.
> With this change, we can think of an iterator as more of a functional modification to
a data set, as in T' = f(T) or T'' = g(f(T)). This should make it easier for developers to
use iterators correctly.

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