Minor Description
The Http2SolrClient loses MDC context information when running an async request in Solr 9.x.
The issue is the 'Request#send' [0] call is actually async itself and by the time the response listener kicks in to push the response processing to the executor the MDC context is already lost, so the executor will no longer have access to the original MDC in order to push it forward onto the thread that will process the response.
This is very difficult to capture on a running system, there are no logs during this window. I only saw it because I was specifically looking at thread names for a different reason.
This is how it is reflected in the thread names:
- how it should be (Solr 8 style. containing all MDC data):
httpShardExecutor-5-thread-19-processing-gettingstarted_shard2_replica_n2 core_node5 localhost:8983_solr gettingstarted shard2 localhost-4
- how it is in Solr 9 (due to no MDC context)
httpShardExecutor-5-thread-10
I can't tell if there is anything breaking due to this.
