[SOLR-9524] SolrIndexSearcher.getIndexFingerprint uses dubious sunchronization

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 6.3
• Fix Version/s: 6.3, 7.0
• Assignee: Noble Paul
• Reporter: Mike Drob
• Created: 16/Sep/16 16:03
• Updated: 08/Jun/19 15:31
• Resolved: 21/Sep/16 06:05

Description

In SOLR-9310 we added more code that does some fingerprint caching in SolrIndexSearcher. However, the synchronization looks like it could be made more efficient and may have issues with correctness.

https://github.com/apache/lucene-solr/blob/branch_6x/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java#L2371-L2385

Some of the issues:

• Double checked locking needs use of volatile variables to ensure proper memory semantics.
• sync on a ConcurrentHashMap is usually a code smell

Issue Links

• relates to: SOLR-9310 PeerSync fails on a node restart due to IndexFingerPrint mismatch