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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5863) In process (uncompressed) page cache
Date Sun, 24 Apr 2016 08:53:13 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15255538#comment-15255538
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Benedict commented on CASSANDRA-5863:
-------------------------------------

bq. I've double checked with multiple familiar people that most of the modern/popular filesystems
(NTFS, ext*, xfs etc.) already have support for that

It's worth double checking what that support entails - in XFS (since I happen to have recently
read the spec), such a gap would be represented by introducing a b+-tree, rather than a single-continuous
allocation (on the assumption contiguous space was available on disk in the location of the
first inode).  This could result in multiple levels of inode, such that a random seek into
the file (our usual modus operandi) could incur many more disk accesses than previously was
the case.

> In process (uncompressed) page cache
> ------------------------------------
>
>                 Key: CASSANDRA-5863
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5863
>             Project: Cassandra
>          Issue Type: Sub-task
>            Reporter: T Jake Luciani
>            Assignee: Branimir Lambov
>              Labels: performance
>             Fix For: 3.x
>
>
> 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, possibly off heap.



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