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From "Stefania (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-10520) Compressed writer and reader should support non-compressed data.
Date Mon, 27 Feb 2017 03:03:45 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10520?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15885063#comment-15885063
] 

Stefania commented on CASSANDRA-10520:
--------------------------------------

If the default value of {{min_compress_ratio}} is changed in the follow-up commit, the cqlshlib
tests should also be updated, see [8bfa82769|https://github.com/apache/cassandra/commit/8bfa8276968db3d25d3e305a0fad156eeb904c34].


[{{test_describe}}|http://cassci.datastax.com/view/trunk/job/trunk_dtest/lastCompletedBuild/testReport/cqlsh_tests.cqlsh_tests/TestCqlsh/test_describe/]
and [{{test_describe_mv}}|http://cassci.datastax.com/view/trunk/job/trunk_dtest/lastCompletedBuild/testReport/cqlsh_tests.cqlsh_tests/TestCqlsh/test_describe_mv/]
need fixing if not already done, thanks.

> Compressed writer and reader should support non-compressed data.
> ----------------------------------------------------------------
>
>                 Key: CASSANDRA-10520
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10520
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local Write-Read Paths
>            Reporter: Branimir Lambov
>            Assignee: Branimir Lambov
>              Labels: messaging-service-bump-required
>             Fix For: 4.x
>
>         Attachments: ReadWriteTestCompression.java
>
>
> Compressing uncompressible data, as done, for instance, to write SSTables during stress-tests,
results in chunks larger than 64k which are a problem for the buffer pooling mechanisms employed
by the {{CompressedRandomAccessReader}}. This results in non-negligible performance issues
due to excessive memory allocation.
> To solve this problem and avoid decompression delays in the cases where it does not provide
benefits, I think we should allow compressed files to store uncompressed chunks as alternative
to compressed data. Such a chunk could be written after compression returns a buffer larger
than, for example, 90% of the input, and would not result in additional delays in writing.
On reads it could be recognized by size (using a single global threshold constant in the compression
metadata) and data could be directly transferred into the decompressed buffer, skipping the
decompression step and ensuring a 64k buffer for compressed data always suffices.



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