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From "Chris Goffinet (JIRA)" <>
Subject [jira] Created: (CASSANDRA-1825) Separation of Data (Cached/Non-Cached)
Date Mon, 06 Dec 2010 20:09:10 GMT
Separation of Data (Cached/Non-Cached)

                 Key: CASSANDRA-1825
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Chris Goffinet
             Fix For: 0.8

At the moment Cassandra goes through the ROW-READ stage to fetch data from the page cache,
and if it's not in the page cache, it goes to disk.

Data that is currently hot (in page cache) will block if all I/O threads are busy reading
from disk. We should seriously look at implementing a buffer pool similar to MySQL for storing
data in-memory, and our I/O threads be dedicated to just going to disk.  I suggest studying
how InnoDB does scheduling as well, they have good lessons to learn from.

Scaling I/O by thread's isn't going to be a good solution here either. I would argue that
going past 64 threads for I/O is just going to hurt overall performance based on context switching.

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