David Manning created HBASE-27159:
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Summary: Emit source metrics for BlockCacheExpressHitPercent,
getHitCachingRatio, getHitCachingCount, getMissCachingCount
Key: HBASE-27159
URL: https://issues.apache.org/jira/browse/HBASE-27159
Project: HBase
Issue Type: Improvement
Components: BlockCache, metrics
Affects Versions: 2.0.0, 3.0.0-alpha-1
Reporter: David Manning
[https://github.com/apache/hbase/blob/d447fa01ba36a11d57927b78cce1bbca361b1d52/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/CacheStats.java#L346-L400]
{code:java}
public double getHitCachingRatio() {
double requestCachingCount = getRequestCachingCount();
if (requestCachingCount == 0) {
return 0;
}
return getHitCachingCount() / requestCachingCount;
} {code}
This code is responsible for the metric {{{}BlockCacheExpressHitPercent{}}}.
The metric represents the percentage of requests which were cacheable, but not
found in the cache. Unfortunately, since the counters are process-level
counters, the ratio is for the lifetime of the process. This makes it less
useful for looking at cache behavior during a smaller time period.
The underlying counters are {{hitCachingCount}} and {{{}missCachingCount{}}}.
Having access to the underlying counters allows for offline computation of the
same metric for any given time period. But these counters are not emitted today
from {{{}MetricsRegionServerWrapperImpl.java{}}}.
Compare this to {{hitCount}} and {{missCount}} which are emitted as metrics
{{blockCacheHitCount}} and {{{}blockCacheMissCount{}}}. But these are raw
counts for the cache, which include requests that are not cacheable. The
cacheable metrics are more interesting, since it can be common to miss on a
request which is not cacheable.
We should emit blockCache{{{}HitCachingCount{}}} and
{{blockCacheMissCachingCount}} along with the current metrics.
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