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https://issues.apache.org/jira/browse/CASSANDRA-20250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17925359#comment-17925359
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Dmitry Konstantinov edited comment on CASSANDRA-20250 at 2/9/25 11:29 AM:
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{quote}It would be possible to simulate this in a JMH benchmark, but probably
not well. Just something to note in any analysis.
{quote}
This is very similar to what I am trying to play a bit with now :) I am trying
to emulate a surrounded activity which pollutes cpu caches to evict metrics
from it, like:
{code:java}
private final long[] anotherMemory = new long[128 * 1024];
@Setup(Level.Invocation)
public void polluteCpuCaches() {
for (int i = 0; i < anotherMemory.length; i++)
anotherMemory[i]++;
}
{code}
In parallel I am re-executing the e2e test which I mentioned in the ticket
description in 2 variations:
* the current trunk state as is (the original test was done for 5.0.x branch
with my changes from CASSANDRA-20165)
* vs a version when all metrics are disabled in write path
to double check that there is no too much skid in async profiler output.
was (Author: dnk):
{quote}
It would be possible to simulate this in a JMH benchmark, but probably not
well. Just something to note in any analysis.
{quote}
This is very similar to what I am trying to play a bit with now :-) I am trying
to emulate a surrounded activity which pollute cpu caches to evict metrics from
it, like:
{code}
private final long[] anotherMemory = new long[128 * 1024];
@Setup(Level.Invocation)
public void polluteCpuCaches() {
for (int i = 0; i < anotherMemory.length; i++)
anotherMemory[i]++;
}
{code}
In parallel I am re-executing the e2e test which I mentioned in the ticket
description in 2 variations:
* the current trunk state as is (the original test was done for 5.0.x branch
with my changes from CASSANDRA-20165)
* vs a version when all metrics are disabled in write path, to double check
that there is no too much skid in async profiler output
> Provide the ability to disable specific metrics collection
> ----------------------------------------------------------
>
> Key: CASSANDRA-20250
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20250
> Project: Apache Cassandra
> Issue Type: New Feature
> Components: Observability/Metrics
> Reporter: Dmitry Konstantinov
> Assignee: Dmitry Konstantinov
> Priority: Normal
> Attachments: async_profiler_cpu_profiles.zip,
> cpu_profile_insert.html, jmh-result.json
>
>
> Cassandra has a lot of metrics collected, many of them are collected per
> table, so their instance number is multiplied by number of tables. From one
> side it gives a better observability, from another side metrics are not for
> free, there is an overhead associated with them:
> 1) CPU overhead: in case of simple CPU bound load: I already see like 5.5% of
> total CPU spent for metrics in cpu framegraphs for read load and 11% for
> write load.
> Example: [^cpu_profile_insert.html] (search by "codahale" pattern). The
> framegraph is captured using Async profiler build:
> async-profiler-3.0-29ee888-linux-x64
> 2) memory overhead: we spend memory for entities used to aggregate metrics
> such as LongAdders and reservoirs + for MBeans (String concatenation within
> object names is a major cause of it, for each table+metric name combination a
> new String is created)
>
> The idea of this ticket is to allow an operator to configure a list of
> disabled metrics in cassandra.yaml, like:
> {code:java}
> disabled_metrics:
> - metric_a
> - metric_b
> {code}
> From implementation point of view I see two possible approaches (which can be
> combined):
> # Generic: when a metric is registering if it is listed in disabled_metrics
> we do not publish it via JMX and provide a noop implementation of metric
> object (such as histogram) for it.
> Logging analogy: log level check within log method
> # Specialized: for some metrics the process of value calculation is not for
> free and introduces an overhead as well, in such cases it would be useful to
> check within specific logic using an API (like: isMetricEnabled) do we need
> to do it. Example of such metric:
> ClientRequestSizeMetrics.recordRowAndColumnCountMetrics
> Logging analogy: an explicit 'if (isDebugEnabled())' condition used when a
> message parameter is expensive.
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