The following usages of std::rand have been recently introduced on the query analyzer code path:

• https://github.com/mongodb/mongo/blob/c47affa6b78dbf1da11a648f22ce7c196ff4bddf/src/mongo/s/query_analysis_sampler_util.cpp#L70
• https://github.com/mongodb/mongo/blob/c47affa6b78dbf1da11a648f22ce7c196ff4bddf/src/mongo/s/query_analysis_sampler_util.cpp#L75
• https://github.com/mongodb/mongo/blob/c47affa6b78dbf1da11a648f22ce7c196ff4bddf/src/mongo/s/commands/cluster_analyze_shard_key_cmd.cpp#L92

And in some related unit tests.

The use of std::rand is discouraged in production for the reasons pointed out in SERVER-72373 and does not provide real randomization in unit tests because of SERVER-72366.