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From "Daniel Meyer (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-5727) Evaluate default LCS sstable size
Date Mon, 29 Jul 2013 16:07:49 GMT


Daniel Meyer updated CASSANDRA-5727:

    Attachment: UpdateLatency_vs_LCS.png

I have conducted an investigation into the default LCS file size.  YCSB was used to perform
all tests.  The system under test consisted of a single rackspace node with 2GB of ram.  YCSB
workloada was used for all tests, which consists of 50/50 read/update workload with the total
number of operations set to 900K.  The amount of data was varied from 4GB to 40GB.
LCS file size was varied for the 4GB tests as 5MB, 10MB, 20MB, 160MB, 320MB, 475MB, 640MB,
1280MB.  LCS file size for the 40GB tests was varied as 5MB, 40MB, 80MB, 160MB, 320MB, 640MB.

It is important to note that the 40GB test was not runnable with the current default LCS file
size of 5MB due to consistent OOM errors.  Those OOM issues go away with increased LCS file

Based upon the data from this experiment an LCS file size of 160MB would be an optimal default
value. Please see attached graphs.
> Evaluate default LCS sstable size
> ---------------------------------
>                 Key: CASSANDRA-5727
>                 URL:
>             Project: Cassandra
>          Issue Type: Task
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Daniel Meyer
>         Attachments: BytesRead_vs_LCS.png, ReadLatency_vs_LCS.png, Throughtput_vs_LCS.png,
> What we're not sure about is the effect on compaction efficiency --
> larger files mean that each level contains more data, so reads will
> have to touch less sstables, but we're also compacting less unchanged
> data when we merge forward.
> So the question is, how big can we make the sstables to get the benefits of the
> first effect, before the second effect starts to dominate?

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