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https://issues.apache.org/jira/browse/CASSANDRA-20250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17927110#comment-17927110
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Dmitry Konstantinov edited comment on CASSANDRA-20250 at 2/14/25 12:11 PM:
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> We can probably improve our reservoir performance if we want to, perhaps in a
> follow-up patch?
Yes, think so, even for the current design I see few possible places which can
be tuned:
* bucket id can be calculated once (currently we do it 2 times for decaying
and current buckets), like:
{code:java}
int stripe = (int) (Thread.currentThread().getId() & (nStripes - 1));
int bucket = stripedIndex(index, stripe);
rescaledDecayingBuckets.update(bucket, now);
updateBucket(buckets, bucket, 1); {code}
* for histograms on highly loaded paths we can use another number of stripes
(by default it is 2, we can set for example 4 for them)
* I noticed some variation in performance for a micro-benchmark (existing one:
DecayingEstimatedHistogramBench) depending on what exact value for
distributionPrime is used (but I need to double check it)
* forwardDecayWeight function depends on SampledClock value, so we can try to
recalculate the weight only when time is changed
was (Author: dnk):
> We can probably improve our reservoir performance if we want to, perhaps in a
> follow-up patch?
Yes, think so, even for the current design I see few possible places which can
be tuned:
* bucket id can be calculated once (currently we do it 2 times for decaying
and current buckets), like:
{code:java}
int stripe = (int) (Thread.currentThread().getId() & (nStripes - 1));
int bucket = stripedIndex(index, stripe);
rescaledDecayingBuckets.update(bucket, now);
updateBucket(buckets, bucket, 1); {code}
* for histograms on highly loaded paths we can use another number of stripes
(by default it is 2, we can set for example 4 for them)
* I noticed some variation in performance for a micro-benchmark (existing one:
DecayingEstimatedHistogramBench) depending on what exact value for
distributionPrime is used (but I need to double check it)
*
forwardDecayWeight function depends on SampledClock value, so we can try to
recalculate the weight only when time is changed
> 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: 5.1_profile_cpu.html,
> 5.1_profile_cpu_without_metrics.html, 5.1_tl4_profile_cpu.html,
> Histogram_AtomicLong.png, async_profiler_cpu_profiles.zip,
> cpu_profile_insert.html, jmh-result.json, vmstat.log,
> vmstat_without_metrics.log
>
>
> 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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