[
https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13922619#comment-13922619
]
Benedict commented on CASSANDRA-5863:
-------------------------------------
I wonder if storing decompressed chunks on SSD really makes much sense? It's
likely the decompression is still faster than IO to even a fast flash drive.
Moving hot compressed chunks onto an SSD makes a lot of sense, but think that
maybe these are two different tickets? One to bring the page/buffer cache in
process, and store it uncompressed, the other to track hot file regions and
store them on a cache drive.
One possible neat thing to try doing as well might be to have a mixed
compressed/uncompressed in-memory page cache. i.e. have a smaller uncompressed
page cache, into which pages are moved from a larger compressed page cache, at
which point it's removed from the compressed page cache, and when evicted from
the uncompressed page cache the data is recompressed and placed in the
compressed page cache. This is probably only helpful for non-SSD boxes, though,
as reading may be faster than recompressing.
> Create a Decompressed Chunk [block] Cache
> -----------------------------------------
>
> Key: CASSANDRA-5863
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5863
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: T Jake Luciani
> Assignee: Pavel Yaskevich
> Labels: performance
> Fix For: 2.1 beta2
>
>
> Currently, for every read, the CRAR reads each compressed chunk into a
> byte[], sends it to ICompressor, gets back another byte[] and verifies a
> checksum.
> This process is where the majority of time is spent in a read request.
> Before compression, we would have zero-copy of data and could respond
> directly from the page-cache.
> It would be useful to have some kind of Chunk cache that could speed up this
> process for hot data. Initially this could be a off heap cache but it would
> be great to put these decompressed chunks onto a SSD so the hot data lives on
> a fast disk similar to https://github.com/facebook/flashcache.
--
This message was sent by Atlassian JIRA
(v6.2#6252)
