SOLR-17160: Time based tracking of core admin requests

[psalagnac]

https://issues.apache.org/jira/browse/SOLR-17160

Description

Core admin completed/failed requests are tracked in-memory, but we only track a maximum of 100 requests by dropping the oldest ones. If for any reason we drop a request before the client (an other Solr node) fetched the status, we will get unexpected errors at the top level command.

Solution

Instead of the hard limit of 100 tracked requests, we track all requests with a expiration timeout. This is a trade-off to not keep memory forever and to be sure we won't lose status in the case of many incoming requests.

The change adds two different timeouts:

• an hour for every requests (overridable with property "solr.admin.requests.running.timeout.minutes")
• 5 minutes for completed/failed requests once the status is already retrieved by client (overridable with property "solr.admin.requests.completed.timeout.minutes")

Tests

Added a unit test in CoreAdminHandlerTest to check expired requests are not tracked in-memory anymore.

Also checks we don't have any issue for collection backup with very high numbers of shards.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[dsmiley]

Instead of the manual cache management, can't we use CaffeineCache as is used elsewhere in Solr? CC @bruno-roustant

[psalagnac]

Instead of the manual cache management, can't we use CaffeineCache as is used elsewhere in Solr? CC @bruno-roustant

Thanks for the suggestion. I filled #2304 that achieves the same, with a Caffeine cache.