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From "Melvin Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-2988) Improve SSTableReader.load() when loading index files
Date Wed, 10 Aug 2011 00:05:27 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13082008#comment-13082008
] 

Melvin Wang commented on CASSANDRA-2988:
----------------------------------------

bq. First of all I would like to point you to http://wiki.apache.org/cassandra/CodeStyle,
please modify your code according to conventions listed in there.
Sure. This boils down to where to put the curly braces

bq. please encapsulate your modifications because if you compare how it was and how it is
in your patch it's hard to undertand and just looks like a mess, I would like to suggest moving
those modifications to separate inner class (IndexReader maybe?) and replace only RandomAccessReader
initialization in the SSTableReader.load(...) method...
This patch is about changing the most part of the load() method. I am not clear how we could
only change the initialization of RandomAcessReader.

bq. Also I don't quiet understand logic behind "while (buffer.remaining() > 10) {" in SSTableReader.loadByteBuffer,
let's avoid any hardcoding or at least comment why you did that.
Sorry for lacking comments. I will add it. However, this is not a hard coding in the sense
that, Short consists of 2 bytes and Long consists of 8 bytes, the sum is 10 bytes. It is just
a quick checking if we reach the end.

bq. I'm going to take a closer look at patch for parallel index file loading after we will
be done with index reader patch (c2988-modified-buffer.patch).
FYI, these two patches are completely independent with each other.

> Improve SSTableReader.load() when loading index files
> -----------------------------------------------------
>
>                 Key: CASSANDRA-2988
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2988
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Melvin Wang
>            Assignee: Melvin Wang
>            Priority: Minor
>             Fix For: 1.0
>
>         Attachments: c2988-modified-buffer.patch, c2988-parallel-load-sstables.patch
>
>
> * when we create BufferredRandomAccessFile, we pass skipCache=true. This hurts the read
performance because we always process the index files sequentially. Simple fix would be set
it to false.
> * multiple index files of a single column family can be loaded in parallel. This buys
a lot when you have multiple super large index files.
> * we may also change how we buffer. By using BufferredRandomAccessFile, for every read,
we need bunch of checking like
>   - do we need to rebuffer?
>   - isEOF()?
>   - assertions
>   These can be simplified to some extent.  We can blindly buffer the index file by chunks
and process the buffer until a key lies across boundary of a chunk. Then we rebuffer and start
from the beginning of the partially read key. Conceptually, this is same as what BRAF does
but w/o the overhead in the read**() methods in BRAF.

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