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https://issues.apache.org/jira/browse/CASSANDRA-19429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17894606#comment-17894606
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Maxim Muzafarov commented on CASSANDRA-19429:
---------------------------------------------
> I think it just matter of taste if we ask if cache is enabled or not by
> asking it directly or deciding it via DD
[~smiklosovic] You're right, there's no difference between this and your
approach of relying on DD. The latter is more robust, I think because it binds
the configuration where it's needed.
What worries me is that in the release branch, we're trying to make some
configuration parameters runtime modifiable to fix the problem. The fix should
be straightforward for the 4.x and as simple as possible without changing
concepts.
My understanding is that "once a cache is enabled in the config we can amend
its capacity, but not disable it". This is based on the following observations:
- the corresponding configuration parameters are immutable;
- as far as I can see, there is no documentation for setting the capacity to
zero = disabling caching;
- there are no tests for it (there are a few of them that set the capacity to
zero at the end of the tests, but it seems that we are just resetting the
values before the next test run);
- some ICache implementations throw an exception when you try to change the
capacity e.g.
[OHCacheChunkedImpl.java#L416|https://github.com/snazy/ohc/blob/develop/ohc-core/src/main/java/org/caffinitas/ohc/chunked/OHCacheChunkedImpl.java#L416]
This all makes me feel that we can incorporate this attribute "whether cache is
enabled or not" into the InstrumentingCache and make it static.
> Remove lock contention generated by getCapacity function in SSTableReader
> -------------------------------------------------------------------------
>
> Key: CASSANDRA-19429
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19429
> Project: Cassandra
> Issue Type: Bug
> Components: Local/SSTable
> Reporter: Dipietro Salvatore
> Assignee: Dipietro Salvatore
> Priority: Normal
> Fix For: 4.0.x, 4.1.x
>
> Attachments: Screenshot 2024-02-26 at 10.27.10.png, Screenshot
> 2024-02-27 at 11.29.41.png, Screenshot 2024-03-19 at 15.22.50.png,
> asprof_cass4.1.3__lock_20240216052912lock.html,
> image-2024-03-08-15-51-30-439.png, image-2024-03-08-15-52-07-902.png
>
> Time Spent: 2h 50m
> Remaining Estimate: 0h
>
> Profiling Cassandra 4.1.3 on large AWS instances, a high number of lock
> acquires is measured in the `getCapacity` function from
> `org/apache/cassandra/cache/InstrumentingCache` (1.9M lock acquires per 60
> seconds). Based on our tests on r8g.24xlarge instances (using Ubuntu 22.04),
> this limits the CPU utilization of the system to under 50% when testing at
> full load and therefore limits the achieved throughput.
> Removing the lock contention from the SSTableReader.java file by replacing
> the call to `getCapacity` with `size` achieves up to 2.95x increase in
> throughput on r8g.24xlarge and 2x on r7i.24xlarge:
> |Instance type|Cass 4.1.3|Cass 4.1.3 patched|
> |r8g.24xlarge|168k ops|496k ops (2.95x)|
> |r7i.24xlarge|153k ops|304k ops (1.98x)|
>
> Instructions to reproduce:
> {code:java}
> ## Requirements for Ubuntu 22.04
> sudo apt install -y ant git openjdk-11-jdk
> ## Build and run
> CASSANDRA_USE_JDK11=true ant realclean && CASSANDRA_USE_JDK11=true ant jar &&
> CASSANDRA_USE_JDK11=true ant stress-build && rm -rf data && bin/cassandra -f
> -R
> # Run
> bin/cqlsh -e 'drop table if exists keyspace1.standard1;' && \
> bin/cqlsh -e 'drop keyspace if exists keyspace1;' && \
> bin/nodetool clearsnapshot --all && tools/bin/cassandra-stress write
> n=10000000 cl=ONE -rate threads=384 -node 127.0.0.1 -log file=cload.log
> -graph file=cload.html && \
> bin/nodetool compact keyspace1 && sleep 30s && \
> tools/bin/cassandra-stress mixed ratio\(write=10,read=90\) duration=10m
> cl=ONE -rate threads=406 -node localhost -log file=result.log -graph
> file=graph.html
> {code}
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