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https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Branimir Lambov updated CASSANDRA-5863:
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Status: Patch Available (was: In Progress)
Marking patch ready for review, as I believe it is worth adding to the codebase
in its current form while I continue working on replacing and improving the
actual cache implementation.
The main changes the patch does are to extract rebuffering from
{{\[Compressed\]RandomAccessReader}} into a separate interface {{Rebufferer}},
and provide different rebuffering implementations that build upon each other to
provide functionality.
The simplest one is {{SimpleReadRebufferer}} which just reads from a channel,
and does not own a buffer. When cache is not enabled, a
{{BufferManagingRebufferer}} is used to provide it with a buffer only used by
the specific {{RandomAccessReader}}. If cache is enabled, it is used in
combination with a shared {{ReaderCache.CachingRebufferer}} which operates
cached buffers and gives them as required to (multiple) readers, without any
data copying. If rate limitation is required, a {{LimitingRebufferer}} wrapper
(specific to the reader) is applied.
In the case of compressed data, the {{SimpleReadRebufferer}} is replaced by
{{CompressedRandomAccessReader.StandardRebufferer}} or
{{CompressedRandomAccessReader.MmapRebufferer}}; the stack on top of it stays
the same.
Separately, uncompressed memory-mapped access is implemented in one step by
{{MmapRebufferer}} which can directly provide the mapped buffers (+ a
{{LimitingRebufferer}} if required).
Most of the rebufferer stack is thread-safe and is placed in {{SegmentedFile}}
to be shared among readers.
The patch also changes {{ChecksummedDataInput}} and the other hinting-related
readers to be based on {{RebufferingInputStream}} instead of
{{RandomAccessReader}} as they don't need random access (or caching).
> 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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