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From "Eric Newton (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3633) Please provide information on implementing custom iterators in the documentation
Date Tue, 10 Mar 2015 16:50:38 GMT


Eric Newton commented on ACCUMULO-3633:

Gotchas I've learned about over the years:

* {{init}} is/should always called before {{seek}}
* {{seek}} is/should always called before {{hasTop}}
* any time an Iterator returns, it may be torn down and thrown away
* the last returned value from {{getTopKey}} will be provided to {{seek}} after an iterator
stack is re-instantiated
* iterators run at compaction time need to deal with delete entries
* (security) iterators run at compaction time see all Key/Values
* (security) iterators run at scan time may not see all Key/Values based on visibility

> Please provide information on implementing custom iterators in the documentation
> --------------------------------------------------------------------------------
>                 Key: ACCUMULO-3633
>                 URL:
>             Project: Accumulo
>          Issue Type: Wish
>          Components: docs
>    Affects Versions: 1.6.0
>         Environment: Centos 6.5, Accumulo 1.6.0, CDH 5. 
>            Reporter: Vaibhav Thapliyal
>            Assignee: Josh Elser
>              Labels: documentation
>             Fix For: 1.7.0
>         Attachments: 0001-ACCUMULO-3633-User-manual-chapter-on-custom-iterator.patch
> Dear all,
> Can you please provide a documentation regarding creating custom Iterators. For example,
explain the functionality  of the functions inside SortedKeyValueIterator and how to override
those functions.
> Please explain how these functions are executed (which class calls these functions when
the iterator executes).
> I would appreciate if these changes are made in your future documentations as this would
help developers who are new to accumulo to quickly get started on writing their own custom
iterators which is an essential part of accumulo. 

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