[jira] [Commented] (CASSANDRA-5863) In process (uncompressed) page cache

["Branimir Lambov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15191284#comment-15191284 ] 

Branimir Lambov commented on CASSANDRA-5863:
--------------------------------------------

Work-in-progress patch here:
|[code|https://github.com/blambov/cassandra/tree/5863-page-cache]|[utest|http://cassci.datastax.com/job/blambov-5863-page-cache-testall/]|[dtest|http://cassci.datastax.com/job/blambov-5863-page-cache-dtest/]|[cstar_perf|http://cstar.datastax.com/tests/id/aff1cbdc-e6bf-11e5-9473-0256e416528f]|

The patch mainly refactors things around {{\[Compressed\]RandomAccessReader}} to allow caching to be inserted between the RAR and decompressor, and adds a basic cache built around guava's {{LoadingCache}}. Perf results show this to be viable even in this basic form, as there's a clear performance benefit. It is more pronounced looking at the local read latency (taken from {{nodetool tablestats}}):
Work-in-progress patch here:
|[code|https://github.com/blambov/cassandra/tree/5863-page-cache]|[utest|http://cassci.datastax.com/job/blambov-5863-page-cache-testall/]|[dtest|http://cassci.datastax.com/job/blambov-5863-page-cache-dtest/]|[cstar_perf|http://cstar.datastax.com/tests/id/aff1cbdc-e6bf-11e5-9473-0256e416528f]|

The patch mainly refactors things around {{\[Compressed\]RandomAccessReader}} to allow caching to be inserted between the RAR and decompressor, and adds a basic cache built around guava's {{LoadingCache}}. Perf results show this to be viable even in this basic form, as there's a clear performance benefit. It is more pronounced looking at the local read latency (taken from {{nodetool tablestats}}):
| |node 1|node2|node3||
|baseline|0.197 ms|0.194 ms|0.196 ms|
|with uncompressed chunk cache|0.172 ms|0.170 ms|0.158 ms|
|chunk cache and buffer pool off|0.217 ms|0.210 ms|0.206 ms|
as well as in single-node runs on my local machine where cache on takes reads 

> 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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