There is a feature called "Partition Pruning" ( entry point:
prune_partitions()) where the optimizer figures out the set of
partitions it will need to read for a given table when running the
query.

One can see its result in "partitions" column in EXPLAIN PARTITIONS or
in EXPLAIN FORMAT=JSON.

Nothing is printed in the optimizer trace about this.

EXPLAIN FORMAT=JSON
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "t10",
          "access_type": "range",


EXPLAIN PARTITIONS
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t10	NULL	range	a	a	5	NULL	2	Using index condition; Using where



trace
{
  "steps": [
    {
      "join_preparation": {
        "select_id": 1,
        "steps": [
          {
            "expanded_query": "select t10.a AS a,t10.b AS b,t10.c AS c from t10 where t10.a < 3 and t10.b <> 5 and t10.c < 10"
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select_id": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "t10.a < 3 and t10.b <> 5 and t10.c < 10",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "t10.a < 3 and t10.b <> 5 and t10.c < 10"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "t10.a < 3 and t10.b <> 5 and t10.c < 10"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "t10.a < 3 and t10.b <> 5 and t10.c < 10"
                }
              ]
            }
          },
          {
            "table_dependencies": [
              {
                "table": "t10",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": []
              }
            ]
          },
          {
            "ref_optimizer_key_uses": []
          },
          {
            "rows_estimation": [
              {
                "table": "t10",
                "range_analysis": {
                  "table_scan": {
                    "rows": 10266,
                    "cost": 2082.2
                  },
                  "potential_range_indexes": [
                    {
                      "index": "a",
                      "usable": true,
                      "key_parts": ["a", "b"]
                    }
                  ],
                  "setup_range_conditions": [],
                  "analyzing_range_alternatives": {
                    "range_scan_alternatives": [
                      {
                        "index": "a",
                        "ranges": ["(NULL) < (a) < (3)"],
                        "rowid_ordered": false,
                        "using_mrr": false,
                        "index_only": false,
                        "rows": 2,
                        "cost": 2.545390601,
                        "chosen": true
                      }
                    ],
                    "analyzing_roworder_intersect": {
                      "cause": "too few roworder scans"
                    },
                    "analyzing_index_merge_union": []
                  },
                  "group_index_range": {
                    "chosen": false,
                    "cause": "no group by or distinct"
                  },
                  "chosen_range_access_summary": {
                    "range_access_plan": {
                      "type": "range_scan",
                      "index": "a",
                      "rows": 2,
                      "ranges": ["(NULL) < (a) < (3)"]
                    },
                    "rows_for_plan": 2,
                    "cost_for_plan": 2.545390601,
                    "chosen": true
                  }
                }
              },
              {
                "table": "t10",
                "rowid_filters": [
                  {
                    "key": "a",
                    "build_cost": 0.149253545,
                    "rows": 2
                  }
                ]
              },
              {
                "selectivity_for_indexes": [
                  {
                    "index_name": "a",
                    "selectivity_from_index": 1.948178e-4
                  }
                ],
                "selectivity_for_columns": [],
                "cond_selectivity": 1.948178e-4
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [],
                "get_costs_for_tables": [
                  {
                    "best_access_path": {
                      "table": "t10",
                      "considered_access_paths": [
                        {
                          "access_type": "range",
                          "resulting_rows": 2,
                          "cost": 2.545390601,
                          "chosen": true
                        }
                      ],
                      "chosen_access_method": {
                        "type": "range",
                        "records": 2,
                        "cost": 2.545390601,
                        "uses_join_buffering": false
                      }
                    }
                  }
                ]
              },
              {
                "plan_prefix": [],
                "table": "t10",
                "rows_for_plan": 2,
                "cost_for_plan": 2.945390601
              }
            ]
          },
          {
            "best_join_order": ["t10"]
          },
          {
            "substitute_best_equal": {
              "condition": "WHERE",
              "resulting_condition": "t10.a < 3 and t10.b <> 5 and t10.c < 10"
            }
          },
          {
            "attaching_conditions_to_tables": {
              "attached_conditions_computation": [],
              "attached_conditions_summary": [
                {
                  "table": "t10",
                  "attached": "t10.c < 10",
                  "index": "t10.a < 3 and t10.b <> 5"
                }
              ]
            }
          }
        ]
      }
    },
    {
      "join_execution": {
        "select_id": 1,
        "steps": []
      }
    }
  ]
}