[jira] [Commented] (CASSANDRA-16717) The fetching strategy can be optimized for CL.ONE and CL.LOCAL_ONE

["Alex Petrov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-16717?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17567948#comment-17567948 ] 

Alex Petrov commented on CASSANDRA-16717:
-----------------------------------------

Unless we add a significant amount of fuzz tests for column filter, I would not be very keen to include new optimisations, since some of them have led to significant issues in the past. Allowing for a difference between different consistency levels may make it even more likely to introduce a hard-to-see issues.

> The fetching strategy can be optimized for CL.ONE and CL.LOCAL_ONE
> ------------------------------------------------------------------
>
>                 Key: CASSANDRA-16717
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16717
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benjamin Lerer
>            Assignee: Benjamin Lerer
>            Priority: Normal
>
> The current {{ColumnFilter}} fetching strategy has been implemented in order to guaranty the CQL semantics around empty vs non-existing rows. It has also some importance regarding read-repair (CASSANDRA-16710). Nevertheless, reads at {{CL.ONE}} and at {{CL.LOCAL_ONE}} do not use read-repair and do not require more columns than the queried ones as those cannot be deleted by column deletions present on other nodes. By consequence, having {{ColumnFilter}} fetching only the queried columns should improve query speed, by reducing the number of SSTable reads for queries fetching specific rows and reducing the amound of data serialized and transfered between nodes (if the data is not local). 



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