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From "Billie Rinaldi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-759) remove priority setting for scan-time iterators
Date Tue, 11 Sep 2012 12:20:07 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452966#comment-13452966
] 

Billie Rinaldi commented on ACCUMULO-759:
-----------------------------------------

> However, the boolean is more restrictive than this, because it prevents insertion of
an iterator at other points in the scan.

No, the boolean method could be used along with two Scanner methods:

{code:java}
  something(IteratorSetting) // user handles priority, boolean set to false
  something(ScanIteratorSetting) // priority is handled automatically, boolean set to true
{code}

which is not to say that I'm convinced this is the way to do it.  I kind of like the port-like
method you suggest, but it does break some things people were doing before (mainly setting
an iterator at priority Integer.MAX_VALUE), so I wanted to suggest a method that would not.
                
> 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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