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https://issues.apache.org/jira/browse/ACCUMULO-3633?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14354999#comment-14354999
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Keith Turner commented on ACCUMULO-3633:
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[~elserj] some thoughts as I read over it. If you make a 2nd revision, would
you mind putting it on RB?
* init section : iterator config can come from other places than table config
* Instantiation section : Could also mention per table classpath. Also could
mention that one should not seek source in init()
* Iterator design section : List is mentioned, could also mention Tree of
iterators. Also could use Tree terminology in deepCopy section. Could mention
deepCopy() should be called in init()
* explain isolation, data sources do not change until top iterator returns
key/value, could move [html isolation iterater
documation|https://github.com/apache/accumulo/blob/1.6.2/docs/src/main/resources/isolation.html]
to this new section in user manual
* in addition to combiner and filter, could mention transforming iterator
* next section : does it have to be a cached key value?
* could explain why cross row operations are not recommended
* hasTop section : java iterators have nothing similar to hasTop
Some code like the following showing how tserver will call iterators for a scan
may be useful.
{code:java}
List<KeyValue> batch;
Range range = //range from client
while(!overSizeLimit(batch)){
source = systemIterator()
for(SKVI iter : iterators){
iter.init(source, opts, env)
source = iter
}
//read a batch of data to return to client
topIter = iterators.last()
topIter.seek(range, ...)
while(topIter.hasTop() && !overSizeLimit(batch)){
key = topIter.getTopKey()
val = topIter.getTopValue()
batch.add(new KeyValue(key, val)
if(systemDataSourcesChanged()){
//code does not show isolation case, which will keep using same data
sources until a row boundry is hit
range = new Range(key, false, range.endKey(), range.endKeyInclusive());
break;
}
}
}
//return batch of key values to client
{code}
> Please provide information on implementing custom iterators in the
> documentation
> --------------------------------------------------------------------------------
>
> Key: ACCUMULO-3633
> URL: https://issues.apache.org/jira/browse/ACCUMULO-3633
> 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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