Hi John,
I am trying again :)
The way I understand it is that compression gives you the advantage of
having to use way less IO and rather use CPU. The bottleneck of reads is
usually the IO time you need to read the data from disk. As a figure, we
had about 25 reads/s reading from disk, while we get up to 3000 reads/s
when we have all of it in cache. So having good compression reduces the
amount you have to read from disk. Rather you may spend a little bit
more time decompressing data, but this data will be in cache anyways so
it won't matter.
Cheers
On 29/11/13 01:09, John Sanda wrote:
This article[1] cites gains in read performance can be achieved when
compression is enabled. The more I thought about it, even after
reading the DataStax docs about reads[2], I realized I do not
understand how compression improves read performance. Can someone
provide some details on this?
Is the compression offsets map still used if compression is disabled
for a table? If so what is its rate of growth like as compared to the
growth of the map when compression is enabled?
[1] whats-new-in-cassandra-1-0-compression
<http://www.datastax.com/dev/blog/whats-new-in-cassandra-1-0-compression>
[2] about reads
<http://www.datastax.com/documentation/cassandra/1.2/webhelp/index.html?pagename=docs&version=1.2&file=index#cassandra/dml/dml_about_reads_c.html>
Thanks
- John
