Speed up StringDtype arrow implementation

Author: phofl

pandas/core/reshape/merge.py

@@ -76,6 +76,7 @@
     na_value_for_dtype,
 )
 
+import pandas as pd
 from pandas import (
     ArrowDtype,
     Categorical,
@@ -2407,13 +2408,20 @@ def _factorize_keys(
                 or is_string_dtype(lk.dtype)
                 and not sort
             )
+            or is_string_dtype(lk.dtype)
+            and lk.dtype.storage == "pyarrow"
         ):
             lk, _ = lk._values_for_factorize()
 
             # error: Item "ndarray" of "Union[Any, ndarray]" has no attribute
             # "_values_for_factorize"
             rk, _ = rk._values_for_factorize()  # type: ignore[union-attr]
-        elif isinstance(lk.dtype, ArrowDtype) and is_string_dtype(lk.dtype):
+        elif (
+            isinstance(lk.dtype, ArrowDtype)
+            and is_string_dtype(lk.dtype)
+            or isinstance(lk.dtype, pd.StringDtype)
+            and lk.dtype.storage == "pyarrow"
+        ):
             import pyarrow as pa
             import pyarrow.compute as pc