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https://issues.apache.org/jira/browse/ACCUMULO-759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452117#comment-13452117
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Keith Turner commented on ACCUMULO-759:
---------------------------------------
We do need to make this easier for users. Currently if the user wants scan
time iterators to come after iterators configured for the table, they must
guess and choose some "large" priority that should make this happen. I think
we should try to make achieving this goal easier while preserving the current
API. One possible way to achieve is to add a getMaxIteratorPriority() method
to table operations. So a user could then do something like the following.
{code:java}
//assume conn and scanner are initialized somewhow, just want to show their type
Connector conn;
Scanner scanner;
int tableMax = conn.tableOperations().getMaxIteratorPriority();
scanner.addScanIterator(new IteratorSetting(tableMax++, "foo1",
".org.bar.FooIter));
scanner.addScanIterator(new IteratorSetting(tableMax++, "foo2",
".org.bar.BarIter));
{code}
If tableMax overflows, I think the code above will throw an exception because
IteratorSetting's constructor ensure the prio is positive.
> 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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