[jira] [Commented] (CASSANDRA-4694) populate_io_cache_on_flush option should be configurable for each column family independently

["Robert Coli (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13723129#comment-13723129 ] 

Robert Coli commented on CASSANDRA-4694:
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populate_io_cache_on_flush seems misnamed for something which affects behavior both at flush time (_on_flush) and at compaction time (_on_compaction?).

With the current name, there is a risk of users becoming confused and thinking that the process of writing out a SSTable is a "flush", when in Cassandra 99.9% of the time a "flush" is in fact the process of turning a memtable into a SSTable. 

http://pastebin.com/GJMVZP9v

Shows that the overwhelming majority of uses of "flush" in user visible code paths refer only to the concept of "flush"ing a memtable.

I understand that the function in question is called "flushInternal," but submit that we are inviting confusion by conflating the specific "flush"ing of a memtable with generic "flush"ing data to disk. :)

"populate_io_cache_on_create" maybe? with "create" referring to the new file being "create"d on disk? I am willing to submit a patch if needed..
                
> populate_io_cache_on_flush option should be configurable for each column family independently
> ---------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-4694
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4694
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Alexey Zotov
>            Assignee: Alexey Zotov
>            Priority: Minor
>              Labels: cli, core, documentation
>             Fix For: 1.2.2
>
>         Attachments: cassandra-1.1.2-4694-populate_io_cache_v3.txt, cassandra-1.1-4694-populate_io_cache.txt, cassandra-1.2-4694-populate_io_cache.txt, cassandra-1.2-4694-populate_io_cache_v2.txt, cassandra-1.2-populate_io_cache_v4.txt
>
>
> I suggest to configure populate_io_cache_on_flush option for each column family. It should be configurable from cassandra-cli and should be stored in System keyspace. 
> That could be useful if you have a few column families inside single keyspace and you need to fit in memory only one of them.
> Patch has been attached. I've been testing it on pseudo-cluster using ccm. So I don't have fully confidence about lack of bugs. Please carefully review that code.

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