[ https://issues.apache.org/jira/browse/CASSANDRA-15834?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Jaroslaw Grabowski reassigned CASSANDRA-15834: ---------------------------------------------- Assignee: Jaroslaw Grabowski > Bloom filter false positive rate calculation does not take into account true > negatives > -------------------------------------------------------------------------------------- > > Key: CASSANDRA-15834 > URL: https://issues.apache.org/jira/browse/CASSANDRA-15834 > Project: Cassandra > Issue Type: Bug > Reporter: Jaroslaw Grabowski > Assignee: Jaroslaw Grabowski > Priority: Normal > > The bloom filter false positive ratio is [currently > computed|https://github.com/apache/cassandra/blob/ded62076e7fdfd1cfdcf96447489ea607ca796a0/src/java/org/apache/cassandra/metrics/TableMetrics.java#L738] > as: > {{bf_fp_ratio = false_positive_count / (false_positive_count + > true_positive_count)}} > However, this calculation doesn't take into account true negatives (false > negatives never happen on bloom filters). > In a situation where there are 1000 reads for non existing rows, and there > are 10 false positives, the bloom filter false positive ratio will be wrongly > calculated as 10/10 = 1.0, while it should be 10/1000 = 0.01. > We should update the calculation to: > {{bf_fp_ratio = false_positive_count / #bf_queries}} > Original jira by [~pauloricardomg] -- This message was sent by Atlassian Jira (v8.3.4#803005) --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org