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Posted to commits@cassandra.apache.org by "Benedict Elliott Smith (Jira)" <ji...@apache.org> on 2019/10/31 12:39:00 UTC
[jira] [Comment Edited] (CASSANDRA-15394) Remove list iterators
[ https://issues.apache.org/jira/browse/CASSANDRA-15394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16963859#comment-16963859 ]
Benedict Elliott Smith edited comment on CASSANDRA-15394 at 10/31/19 12:38 PM:
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LGTM.
_Very optional suggestion_:
If we're doing an optimisation pass, it might be worth extracting the call to {{.size()}}? Since, at least in cases where the concrete type of the {{List}} is opaque to the JVM, it will be unable to understand that it is constant. This includes at least {{EncodingStats.merge}} and {{MergeIterator.close}}, as these are megamorphic, given the wide variety of {{List}} type we use.
e.g., {{for (int i=0,mi=list.size(); i<mi; i++)}}
It would be nice to start a pattern for this in the codebase, so that it becomes a norm, at least until we clean up our megamorphic list usages, and this is as good a place as any given performance is the sole purpose. It also gives us a chance to discuss what a good standard variable name for this is.
As I say, entirely optional, but also a pretty low cost kind of hygiene to introduce.
was (Author: benedict):
LGTM.
_Very optional suggestion_:
If we're doing an optimisation pass, it might be worth extracting the call to {{.size()}}? Since, at least in cases where the concrete type of the {{List}} is opaque to the JVM, it will be unable to understand that it is constant. This includes at least {{EncodingStats.merge}} and {{MergeIterator.close}}, as these are megamorphic, given the wide variety of {{List}} type we use.
e.g., \{{ for (int i=0,mi=list.size(); i<mi; i++) }}
It would be nice to start a pattern for this in the codebase, so that it becomes a norm, at least until we clean up our megamorphic list usages, and this is as good a place as any given performance is the sole purpose. It also gives us a chance to discuss what a good standard variable name for this is.
As I say, entirely optional, but also a pretty low cost kind of hygiene to introduce.
> Remove list iterators
> ---------------------
>
> Key: CASSANDRA-15394
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15394
> Project: Cassandra
> Issue Type: Sub-task
> Components: Local/Compaction
> Reporter: Blake Eggleston
> Assignee: Blake Eggleston
> Priority: Normal
> Fix For: 4.0
>
>
> We allocate list iterators in several places in hot paths. This converts them to get by index. This provides a ~4% improvement in relvant workloads.
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