In SearchStax, a 504 Gateway Timeout Error simply means that Solr did not respond to the Load Balancer within a reasonable time, usually about two minutes.
This usually means that Solr has become overloaded with update requests, and is fully occupied rebuilding replicas. It may need to be restarted to clear the backlog and allow the replicas to recover.
Common Causes of 504 Errors
- Expensive updates: New users sometimes overload Solr indexing by demanding a commit after every add (commit=true) or within a second of every add (commitWithin=1000). Frequent commits are expensive and can overload the system to the point of putting replicas into recovery mode. See Timeouts during ingestion: Too many commits!
- Expensive queries: Another way to cause a gateway timeout is to send Solr a stream of expensive queries. New users often request a million response-items (rows=1000000) when ten would do. Queries using “deep pagination” can take a long time to complete. Logically complex queries (with many AND/OR clauses) can also be very slow. See Solr Out of Memory (OOM): Causes and Solutions.
Do not hesitate to contact the SearchStax Support Desk.