{
  "$schema": "https://myflames.dev/schemas/sidecar-v1.json",
  "schema_version": "1.3",
  "generated_at": "2026-04-25T12:51:27Z",
  "myflames_version": "1.5.0",
  "source": {
    "type": "file",
    "engine": "mysql",
    "fixture_path": "/Users/viniciusgrippa/Downloads/git/myflames/test/mysql-explain-hash-join-probe.json"
  },
  "plan_summary": {
    "total_time_ms": 1.944,
    "rows_sent": 0,
    "rows_examined_estimate": 7000,
    "operator_count": 3,
    "max_depth": 2
  },
  "optimizer_switches": [
    {
      "name": "hash_join",
      "value": "on",
      "explanation": "Builds an in-memory hash table on the smaller (build) input and probes it from the other side. Uses join_buffer_size; spills to a tmp file (and tmpdir) if the build side does not fit.",
      "node_labels": [
        "Inner hash join (t1.d = concat('r',t2.y))"
      ]
    }
  ],
  "warnings": [
    {
      "severity": "error",
      "category": "nonsargable_join",
      "text": "Non-sargable join predicate: CONCAT(...) in Inner hash join (t1.d = concat('r',t2.y)) — a function wrapped around the join column prevents index use.",
      "source": "plan",
      "node_labels": [
        "Inner hash join (t1.d = concat('r',t2.y))"
      ]
    },
    {
      "severity": "warn",
      "category": "full_scan",
      "text": "Full table scan: t1 (5000 rows), t2 (2000 rows)",
      "source": "plan",
      "node_labels": [
        "Table scan [t1]",
        "Table scan [t2]"
      ]
    },
    {
      "severity": "warn",
      "category": "hash_join",
      "text": "1 hash join(s) — uses join_buffer_size",
      "source": "plan",
      "node_labels": [
        "Inner hash join (t1.d = concat('r',t2.y))"
      ]
    }
  ],
  "suggestions": [
    {
      "severity": "high",
      "category": "rewrite",
      "action": "Rewrite the join condition to compare the bare column on both sides (e.g. 'a.id = b.other_id' instead of 'CONCAT(a.id)=CONCAT(b.other_id)').",
      "source": "plan",
      "why": "wrapping a column in a function means the optimizer cannot use any index on that column — every row-pair is evaluated in the server layer, making the cost O(outer × inner). Dropping the function lets MySQL/MariaDB pick an index lookup or hash join with real selectivity, typically 100–1000× faster on mid-sized tables."
    },
    {
      "severity": "high",
      "category": "index",
      "action": "Add indexes on filter/join columns to avoid full table scans",
      "source": "plan"
    },
    {
      "severity": "medium",
      "category": "tuning_variable",
      "action": "Increase join_buffer_size if hash joins are slow or spill to disk",
      "source": "plan",
      "target_variable": "join_buffer_size"
    }
  ],
  "executive_summary": "Query scans 2 tables and hash-joins 1 pair; examines ~7,000 rows to return 0 in 1.9 ms. Main finding: join predicate wraps the column in CONCAT() — no index can be used.",
  "plan_tree": {
    "node_id": "n:a528a4ef61ee",
    "short_label": "Inner hash join (t1.d = concat('r',t2.y))",
    "folded_label": "Inner hash join (t1.d = concat('r',t2.y)) starts=1 rows=0",
    "children": [
      {
        "node_id": "n:0aa992c09c72",
        "short_label": "Table scan [t1]",
        "folded_label": "TABLE SCAN [t1] starts=1 rows=5000",
        "children": []
      },
      {
        "node_id": "n:4d0b633addc1",
        "short_label": "Table scan [t2]",
        "folded_label": "TABLE SCAN [t2] starts=1 rows=2000",
        "children": []
      }
    ]
  },
  "query": {
    "raw": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d`,`testdb`.`t2`.`id` AS `id`,`testdb`.`t2`.`x` AS `x`,`testdb`.`t2`.`y` AS `y` from `testdb`.`t1` join `testdb`.`t2` where (`testdb`.`t1`.`d` = concat('r',`testdb`.`t2`.`y`))",
    "beautified": "select testdb.t1.id AS id,testdb.t1.a AS a,testdb.t1.b AS b,testdb.t1.c AS c,testdb.t1.d AS d,testdb.t2.id AS id,testdb.t2.x AS x,testdb.t2.y AS y\nfrom testdb.t1\n  join testdb.t2\nwhere (testdb.t1.d = concat('r',testdb.t2.y))"
  },
  "primary_action": {
    "ref": "suggestions[0]"
  },
  "teach_hooks": [
    {
      "lesson": "hash",
      "match": {
        "folded_label": "Inner hash join (t1.d = concat('r',t2.y)) starts=1 rows=0",
        "short_label": "Inner hash join (t1.d = concat('r',t2.y))"
      },
      "controls": {
        "build_rows": 2000,
        "probe_rows": 5000,
        "row_size": 200
      },
      "note": "Inner hash join (t1.d = concat('r',t2.y))",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d`,`testdb`.`t2`.`id` AS `id`,`testdb`.`t2`.`x` AS `x`,`testdb`.`t2`.`y` AS `y` from `testdb`.`t1` join `testdb`.`t2` where (`testdb`.`t1`.`d` = concat('r',`testdb`.`t2`.`y`))"
    },
    {
      "lesson": "full_scan",
      "match": {
        "folded_label": "TABLE SCAN [t1] starts=1 rows=5000",
        "short_label": "Table scan [t1]"
      },
      "controls": {
        "rows": 5000,
        "row_size": 200,
        "selectivity": 100.0
      },
      "note": "Table scan on t1 (t1)",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d`,`testdb`.`t2`.`id` AS `id`,`testdb`.`t2`.`x` AS `x`,`testdb`.`t2`.`y` AS `y` from `testdb`.`t1` join `testdb`.`t2` where (`testdb`.`t1`.`d` = concat('r',`testdb`.`t2`.`y`))"
    },
    {
      "lesson": "full_scan",
      "match": {
        "folded_label": "TABLE SCAN [t2] starts=1 rows=2000",
        "short_label": "Table scan [t2]"
      },
      "controls": {
        "rows": 2000,
        "row_size": 200,
        "selectivity": 100.0
      },
      "note": "Table scan on t2 (t2)",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d`,`testdb`.`t2`.`id` AS `id`,`testdb`.`t2`.`x` AS `x`,`testdb`.`t2`.`y` AS `y` from `testdb`.`t1` join `testdb`.`t2` where (`testdb`.`t1`.`d` = concat('r',`testdb`.`t2`.`y`))"
    }
  ],
  "operator_complexities": [
    {
      "node_id": "n:a528a4ef61ee",
      "folded_label": "Inner hash join (t1.d = concat('r',t2.y)) starts=1 rows=0",
      "short_label": "Inner hash join (t1.d = concat('r',t2.y))",
      "complexity": {
        "big_o": "O(n + m)",
        "short": "n + m",
        "severity": "good",
        "rationale": "Hash join: builds a hash on one side (O(m)), streams the other past it (O(n)). Disk-spill does NOT change the asymptotic class — only the constants.",
        "confidence": "exact",
        "learn_more": "hash_join"
      }
    },
    {
      "node_id": "n:0aa992c09c72",
      "folded_label": "TABLE SCAN [t1] starts=1 rows=5000",
      "short_label": "Table scan [t1]",
      "complexity": {
        "big_o": "O(n)",
        "short": "n",
        "severity": "medium",
        "rationale": "Full table scan: the storage engine returns every row; cost scales with the table size.",
        "confidence": "exact",
        "learn_more": "full_table_scan"
      }
    },
    {
      "node_id": "n:4d0b633addc1",
      "folded_label": "TABLE SCAN [t2] starts=1 rows=2000",
      "short_label": "Table scan [t2]",
      "complexity": {
        "big_o": "O(n)",
        "short": "n",
        "severity": "medium",
        "rationale": "Full table scan: the storage engine returns every row; cost scales with the table size.",
        "confidence": "exact",
        "learn_more": "full_table_scan"
      }
    }
  ]
}