Adam Fuchs created ACCUMULO-759:
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Summary: 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
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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