[
https://issues.apache.org/jira/browse/CASSANDRA-13241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15888189#comment-15888189
]
Ariel Weisberg commented on CASSANDRA-13241:
--------------------------------------------
I was saying that the chunk offsets don't need to take up as much space as they
do now. A simple relative offset encoding scheme could make it 3 bytes per
offset instead of 8. There is also
http://www.javadoc.io/doc/me.lemire.integercompression/JavaFastPFOR/0.1.10
which doesn't have an off heap implementation near as I can tell, but does
demonstrate how you can have an even more compact encoding that supports random
access. The performance/space efficiency may not be what we want I can't really
tell.
You could decrease the chunk size by 1/4 with no impact on memory utilization.
My question is with density like this how do the bloom filters fit in memory?
How are the chunk offsets the high pole in the tent?
> 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
>
> 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
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
