[jira] Updated: (CASSANDRA-270) Reduce copies in data write path

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-270?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jonathan Ellis updated CASSANDRA-270:
-------------------------------------

    Attachment: 270.txt

The root of the problem is that writing a ColumnFamily [row data] object has been

 1. serialize the row to a DataOutput
 2. write the DataOutput's length, followed by the DataOutput's content, to the sstable file

Thus, there is an extra copy to the intermediate DataOutput before getting to the file.

This patch takes a different approach than Todd's: instead of using a clever DataOutput to avoid copying the byte[] inside Column objects, we change the algorithm to

 1. write a placeholder length value
 2. serialize the row directly to the sstable
 3. seek back and write the correct length now that we know it

If we seek within our BufferedRandomAccessFile buffer, we're not actually generating seek system calls, so there's basically no penalty for doing this, and we can guarantee that this is our situation by setting the buffer size to the InMemoryCompactionLimit (past which we do two passes already as explained in CASSANDRA-16).

(This did require a small modification to BRAF, which would flush whenever seeking backwards, which is unnecessarily pessimistic.)

> Reduce copies in data write path
> --------------------------------
>
>                 Key: CASSANDRA-270
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-270
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Todd Lipcon
>             Fix For: 0.7
>
>         Attachments: 270.txt, patches.tar
>
>
> This is a series of patches against a very old version of Cassandra - they certainly won't apply, but Jonathan asked me to upload the patches here to do the ASF grant.

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