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From "Branimir Lambov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9975) Flatten Iterator call hierarchy with a shared Transformer
Date Thu, 22 Oct 2015 15:03:27 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14969268#comment-14969268
] 

Branimir Lambov commented on CASSANDRA-9975:
--------------------------------------------

The code is complicated, but looks correct and is well documented. I think it's practically
ready to commit once CI is clean.

Wondering if {{BasePartitions.hasNext/applyOne}} shouldn't take responsibility of closing
{{next}} if {{applyToPartitions}} returned {{null}} since other aspects of the transformer
do close automatically?

[toQuery in checkForShortRead|https://github.com/apache/cassandra/compare/trunk...belliottsmith:9975#diff-8781f9483cca1cfc87145c767295cc79R358]
no longer has division-by-zero protection. Is it no longer necessary?

You should run the {{eclipse-warnings}} ant target and suppress any new warnings.


> Flatten Iterator call hierarchy with a shared Transformer
> ---------------------------------------------------------
>
>                 Key: CASSANDRA-9975
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9975
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>             Fix For: 3.0.0
>
>
> Stepping through a read response is made exceedingly difficult by the sheer depth of
the call hierarchy, and how rapidly your context jumps around. This ticket intend to partially
address that, by flattening one of the main causes of this: iterator transformations.
> I have a patch that attempts to mitigate (but not entirely eliminate) this, through the
introduction of a {{RowTransformer}} class that all transformations are applied through. If
a transformation has already been applied, the {{RowTransformer}} class does not wrap a new
iterator, but instead returns a new {{RowTransformer}} that wraps the original underlying
(untransformed) iterator and both transformations. This can accumulate an arbitrary number
of transformations and, quite importantly, can apply the filtration step {{Unfiltered ->
Row}}  in the same instance as well. The intention being that a majority of control flow happens
inside this {{RowTransformer}}, so there is far less context jumping to cope with.



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