[SOLR-17190] Replace org.apache.solr.util.LongSet with hppc LongHashSet

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: main (10.0), 9.5.0
• Fix Version/s: 9.6
• Assignee: Michael Gibney
• Reporter: Michael Gibney
• Created: 01/Mar/24 16:25
• Updated: 28/Apr/24 19:22
• Resolved: 05/Mar/24 21:32

Description

The functionality provided by org.apache.solr.util.LongSet is redundant to that provided by com.carrotsearch.hppc.LongHashSet. Since hppc is already a dependency of solr-core, we should replace usages of org.apache.solr.util.LongSet and remove/deprecate it.

The motivation for this is practical as well: the hash function used by org.apache.solr.util.LongSet is quite suboptimal for certain common usage patterns (specifically, if the values stored vary by powers of two (the larger the worse), values end up disproportionately hashing to the same bucket and you basically have an array scan for get and put).

This issue proposes to replace usages on main and branch_9x, remove org.apache.solr.util.LongSet on main, and either remove it or deprecate it on branch_9x.

Issue Links

• links to: GitHub Pull Request #2328