[CASSANDRA-15259] Selecting Index by Lowest Mean Column Count Selects Random Index

• Type: Bug
• Status: Resolved
• Priority: Urgent
• Resolution: Fixed
• Fix Version/s: 3.0.19, 3.11.7, 4.0-alpha1, 4.0
• Component/s: Feature/2i Index
• Bug Category: Degradation - Performance Bug/Regression
• Severity: Critical
• Complexity: Normal
• Discovered By: User Report
• Platform: All
• Since Version: 3.0.0

Source Control Link

https://github.com/apache/cassandra/commit/da8d41f497efedf57e335ec2664680da583a3aba

Test and Documentation Plan

Regression test added as part of patch

• Assignee: Jordan West
• Reporter: Jordan West

Authors

Jordan West

Reviewers

Blake Eggleston

• Created: 05/Aug/19 16:39
• Updated: 01/Aug/21 11:17
• Resolved: 06/Aug/19 17:27

Description

CassandraIndex uses ColumnFamilyStore#getMeanColumns, average columns per partition, which always returns the same answer for index CFs because they contain no regular columns and clustering columns aren't included in the count in Cassandra 3.0+.