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https://issues.apache.org/jira/browse/CASSANDRA-13241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16653988#comment-16653988
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Ariel Weisberg commented on CASSANDRA-13241:
--------------------------------------------
Performance comparison of summing vs the larger compact sequence vs just
fetching a long from memory. These numbers are low enough that I don't think it
matters which we pick. For every lookup we do here we are going to do several
microseconds of decompression and that is going to get much faster by virtue of
decompressing less data. Decompression may also get faster due to being a
better fit for cache.
{noformat}
[java] Benchmark
Mode Cnt Score Error Units
[java] CompactIntegerSequenceBench.benchCompactIntegerSequence
sample 2 59.500 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.00
sample 57.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.50
sample 59.500 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.90
sample 62.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.95
sample 62.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.99
sample 62.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.999
sample 62.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p0.9999
sample 62.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactIntegerSequence:benchCompactIntegerSequence·p1.00
sample 62.000 ns/op
[java] CompactIntegerSequenceBench.benchCompactSummingntegerSequence
sample 2 147.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.00
sample 146.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.50
sample 147.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.90
sample 148.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.95
sample 148.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.99
sample 148.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.999
sample 148.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p0.9999
sample 148.000 ns/op
[java]
CompactIntegerSequenceBench.benchCompactSummingntegerSequence:benchCompactSummingntegerSequence·p1.00
sample 148.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory
sample 2 49.500 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.00
sample 44.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.50
sample 49.500 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.90
sample 55.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.95
sample 55.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.99
sample 55.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.999
sample 55.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p0.9999
sample 55.000 ns/op
[java] CompactIntegerSequenceBench.benchMemory:benchMemory·p1.00
sample 55.000 ns/op
{noformat}
> Lower default chunk_length_in_kb from 64kb to 4kb
> -------------------------------------------------
>
> Key: CASSANDRA-13241
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13241
> Project: Cassandra
> Issue Type: Wish
> Components: Core
> Reporter: Benjamin Roth
> Assignee: Ariel Weisberg
> Priority: Major
> Attachments: CompactIntegerSequence.java,
> CompactIntegerSequenceBench.java, CompactSummingIntegerSequence.java
>
>
> Having a too low chunk size may result in some wasted disk space. A too high
> chunk size may lead to massive overreads and may have a critical impact on
> overall system performance.
> In my case, the default chunk size lead to peak read IOs of up to 1GB/s and
> avg reads of 200MB/s. After lowering chunksize (of course aligned with read
> ahead), the avg read IO went below 20 MB/s, rather 10-15MB/s.
> The risk of (physical) overreads is increasing with lower (page cache size) /
> (total data size) ratio.
> High chunk sizes are mostly appropriate for bigger payloads pre request but
> if the model consists rather of small rows or small resultsets, the read
> overhead with 64kb chunk size is insanely high. This applies for example for
> (small) skinny rows.
> Please also see here:
> https://groups.google.com/forum/#!topic/scylladb-dev/j_qXSP-6-gY
> To give you some insights what a difference it can make (460GB data, 128GB
> RAM):
> - Latency of a quite large CF: https://cl.ly/1r3e0W0S393L
> - Disk throughput: https://cl.ly/2a0Z250S1M3c
> - This shows, that the request distribution remained the same, so no "dynamic
> snitch magic": https://cl.ly/3E0t1T1z2c0J
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