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From "sankalp kohli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4784) Create separate sstables for each token range handled by a node
Date Fri, 19 Oct 2012 19:05:11 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13480267#comment-13480267
] 

sankalp kohli commented on CASSANDRA-4784:
------------------------------------------

vnodes will improve the performance, but still we need to go through application layer to
filter out data from each sstable that needs to be transferred. This will affect the CPU and
page cache and create short lived java objects. I have another JIRA which states how a new
connection is created for each sstable transferred. 

My point is that this change will make the bootstrap of a node theoretically faster than you
can get. This is the reason many people restore the data from backup and then run a repair
instead of bootstrapping a node and streaming the data. 
                
> Create separate sstables for each token range handled by a node
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-4784
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4784
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: sankalp kohli
>            Priority: Minor
>              Labels: perfomance
>
> Currently, each sstable has data for all the ranges that node is handling. If we change
that and rather have separate sstables for each range that node is handling, it can lead to
some improvements.
> Improvements
> 1) Node rebuild will be very fast as sstables can be directly copied over to the bootstrapping
node. It will minimize any application level logic. We can directly use Linux native methods
to transfer sstables without using CPU and putting less pressure on the serving node. I think
in theory it will be the fastest way to transfer data. 
> 2) Backup can only transfer sstables for a node which belong to its primary keyrange.

> 3) ETL process can only copy one replica of data and will be much faster. 
> Changes:
> We can split the writes into multiple memtables for each range it is handling. The sstables
being flushed from these can have details of which range of data it is handling.
> There will be no change I think for any reads as they work with interleaved data anyway.
But may be we can improve there as well? 
> Complexities:
> The change does not look very complicated. I am not taking into account how it will work
when ranges are being changed for nodes. 
> Vnodes might make this work more complicated. We can also have a bit on each sstable
which says whether it is primary data or not. 

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