perf(rename): avoid unnecessary rewrites and dereferencing in rename (

#9641)

ibis/expr/types/relations.py

@@ -2359,22 +2359,13 @@ def rename(
         # A mapping from old_name -> renamed expr
         renamed = {}
 
-        if substitutions:
-            for new_name, old_name in substitutions.items():
-                col = self[old_name]
-                if old_name not in renamed:
-                    renamed[old_name] = col.name(new_name)
-                else:
-                    raise ValueError(
-                        "duplicate new names passed for renaming {old_name!r}"
-                    )
-
-        if method is None:
-
-            def rename(c):
-                return None
+        for new_name, old_name in substitutions.items():
+            if old_name not in renamed:
+                renamed[old_name] = (new_name, self[old_name].op())
+            else:
+                raise ValueError("duplicate new names passed for renaming {old_name!r}")
 
-        elif isinstance(method, str) and method in {"snake_case", "ALL_CAPS"}:
+        if isinstance(method, str) and method in {"snake_case", "ALL_CAPS"}:
 
             def rename(c):
                 c = c.strip()
@@ -2412,17 +2403,19 @@ def rename(name):
         else:
             rename = method
 
-        exprs = []
+        exprs = {}
+        fields = self.op().fields
         for c in self.columns:
-            if c in renamed:
-                expr = renamed[c]
+            if (new_name_op := renamed.get(c)) is not None:
+                new_name, op = new_name_op
             else:
-                expr = self[c]
-                if (name := rename(c)) is not None:
-                    expr = expr.name(name)
-            exprs.append(expr)
+                op = fields[c]
+                if rename is None or (new_name := rename(c)) is None:
+                    new_name = c
+
+            exprs[new_name] = op
 
-        return self.select(exprs)
+        return ops.Project(self, exprs).to_expr()
 
     def drop(self, *fields: str | Selector) -> Table:
         """Remove fields from a table.

ibis/tests/benchmarks/test_benchmarks.py

@@ -918,6 +918,33 @@ def test_wide_drop_compile(benchmark, wide_table, cols_to_drop):
     )
 
 
+@pytest.mark.parametrize(
+    "method",
+    [
+        "snake_case",
+        "ALL_CAPS",
+        lambda x: f"t_{x}",
+        "t_{name}",
+        lambda x: x,
+        "{name}",
+        {"b0": "a0"},
+    ],
+    ids=[
+        "snake_case",
+        "ALL_CAPS",
+        "function",
+        "format_string",
+        "no_op_function",
+        "no_op_string",
+        "mapping",
+    ],
+)
+@pytest.mark.parametrize("cols", [1_000, 10_000])
+def test_wide_rename(benchmark, method, cols):
+    t = ibis.table(name="t", schema={f"a{i}": "int" for i in range(cols)})
+    benchmark(t.rename, method)
+
+
 def test_duckdb_timestamp_conversion(benchmark):
     pytest.importorskip("duckdb")