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https://issues.apache.org/jira/browse/CASSANDRA-19429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17820442#comment-17820442
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Stefan Miklosovic edited comment on CASSANDRA-19429 at 2/25/24 8:43 AM:
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I think it is <= 0 when key_cache_size: 0MiB in cassandra.yaml (so you
effectively turn the key cache off)
Just set a breakpoint in CacheService constructor and follow the execution in
its constructor where keyCache = initKeyCache(); is called.
If we do not want to check "if (maybeKeyCache.getCapacity() > 0)" I think the
same effect would be to check "if (DatabaseDescriptor.getKeyCacheSizeInMiB() >
0)" and it would be same (but WAY more performant)
I am not sure you can check size instead of capacity like that.
"capacity" is the maximum number of entries you can put into that cache.
"size" is the current number of entries in that cache.
So that "if (maybeKeyCache.getCapacity > 0)" basically checks if keyCache is
enabled or not. I think that checking it via "maybeKeyCache.size() > 0" is a
little bit misleading. I think that checking it via DatabaseDescriptor's
property is better.
You can have a cache with positive capacity but that cache might hold 0 entries
so in that case you would evaluate that "hey, we dont have cache" which is not
technically true.
was (Author: smiklosovic):
I think it is <= 0 when key_cache_size: 0MiB in cassandra.yaml (so you
effectively turn the key cache off)
Just set a breakpoint in CacheService constructor and follow the execution in
its constructor where keyCache = initKeyCache(); is called.
If we do not want to check "if (maybeKeyCache.getCapacity() > 0)" I think the
same effect would be to check "if (DatabaseDescriptor.getKeyCacheSizeInMiB() >
0)" and it would be same (but WAY more performant)
I am not sure you can check size instead of capacity like that.
"capacity" is the maximum number of entries you can put into that cache.
"size" is the current number of entries in that cache.
I think that it always holds size <= capacity. So that "if
(maybeKeyCache.getCapacity > 0)" basically checks if keyCache is enabled or
not. I think that checking it via "maybeKeyCache.size() > 0" is a little bit
misleading. I think that checking it via DatabaseDescriptor's property is
better.
You can have a cache with positive capacity but that cache might hold 0 entries
so in that case you would evaluate that "hey, we dont have cache" which is not
technically true.
> 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: asprof_cass4.1.3__lock_20240216052912lock.html
>
>
> 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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