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https://issues.apache.org/jira/browse/ACCUMULO-759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13453457#comment-13453457
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Adam Fuchs commented on ACCUMULO-759:
-------------------------------------
What if we went with a more immutable form of Scanner, which was more
representative of the data set? This would allow things like:
{code:java}
Scanner allTheThings = connector.createScanner(...);
ScanIteratorSetting aggregateEverything = new
ScanIteratorSetting(MyAggregatingIterator.class,properties);
Scanner aggregatedThings = allTheThings.transform(aggregateEverything);
// scan over the table with the iterator
for(Entry<Key,Value> aggregate: aggregatedThings)
{
...
}
// scan over the table without extra scan-time iterators
for(Entry<Key,Value> thing: allTheThings)
{
...
}
{code}
I think this might be an easier way for users to conceptualize iterators.
> 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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