How do you troubleshoot slow Solr queries?

Diagnosing slow queries in Solr is mostly a process of isolating which stage of the request is expensive.

1. Add debugQuery=true and inspect the timing block in the response - it breaks down time spent per component (query, facet, highlight).
2. Check the admin UI's Query tab and cache statistics - a low hit ratio on the filter or query result cache means repeated work that could be reduced with better fq reuse or larger cache sizes.
3. Review the field types involved - sorting or faceting on a field without docValues forces an expensive uninverted field cache to build on first use.
4. Look at wildcard and leading-wildcard queries (e.g. *term) - these can't use the index efficiently and often scan far more terms than expected.
5. Check deep pagination - a high start value forces Solr to compute and discard many results before returning the requested page.

Most real-world slowness traces back to one of these five causes rather than needing more hardware, so profiling before scaling out saves both time and infrastructure cost.