From 33b86adb3fb0b63f6142d04c19ad4b2217ca8c6f Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
Date: Thu, 13 Oct 2022 16:06:24 -0700
Subject: [PATCH 1/2] BUG: pickling subset of Arrow-backed data would serialize
 the entire data

---
 doc/source/whatsnew/v2.0.0.rst                 |  2 +-
 pandas/core/arrays/arrow/array.py              | 11 +++++++++++
 .../tests/arrays/string_/test_string_arrow.py  | 18 ++++++++++++++++++
 pandas/tests/extension/test_arrow.py           | 17 +++++++++++++++++
 4 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.0.0.rst b/doc/source/whatsnew/v2.0.0.rst
index 9d1e0c7485092..7d93ce3a58c1b 100644
--- a/doc/source/whatsnew/v2.0.0.rst
+++ b/doc/source/whatsnew/v2.0.0.rst
@@ -240,7 +240,7 @@ MultiIndex
 I/O
 ^^^
 - Bug in :func:`read_sas` caused fragmentation of :class:`DataFrame` and raised :class:`.errors.PerformanceWarning` (:issue:`48595`)
--
+- Bug when a pickling a subset PyArrow-backed data that would serialize the entire data instead of the subset (:issue:`42600`)
 
 Period
 ^^^^^^
diff --git a/pandas/core/arrays/arrow/array.py b/pandas/core/arrays/arrow/array.py
index f6f933b1b9917..da7b90935beb2 100644
--- a/pandas/core/arrays/arrow/array.py
+++ b/pandas/core/arrays/arrow/array.py
@@ -373,6 +373,17 @@ def __pos__(self: ArrowExtensionArrayT) -> ArrowExtensionArrayT:
     def __abs__(self: ArrowExtensionArrayT) -> ArrowExtensionArrayT:
         return type(self)(pc.abs_checked(self._data))
 
+    # GH 42600: __getstate__/__setstate__ not necessary once
+    # https://issues.apache.org/jira/browse/ARROW-10739 is addressed
+    def __getstate__(self):
+        state = self.__dict__.copy()
+        state["_data"] = self._data.combine_chunks()
+        return state
+
+    def __setstate__(self, state) -> None:
+        state["_data"] = pa.chunked_array(state["_data"])
+        self.__dict__.update(state)
+
     def _cmp_method(self, other, op):
         from pandas.arrays import BooleanArray
 
diff --git a/pandas/tests/arrays/string_/test_string_arrow.py b/pandas/tests/arrays/string_/test_string_arrow.py
index f43cf298857a0..ce11892394d20 100644
--- a/pandas/tests/arrays/string_/test_string_arrow.py
+++ b/pandas/tests/arrays/string_/test_string_arrow.py
@@ -1,3 +1,4 @@
+import pickle
 import re
 
 import numpy as np
@@ -197,3 +198,20 @@ def test_setitem_invalid_indexer_raises():
 
     with pytest.raises(ValueError, match=None):
         arr[[0, 1]] = ["foo", "bar", "baz"]
+
+
+@skip_if_no_pyarrow
+def test_pickle_roundtrip():
+    # GH 42600
+    expected = pd.Series(range(10), dtype="string[pyarrow]")
+    expected_sliced = expected.head(2)
+    full_pickled = pickle.dumps(expected)
+    sliced_pickled = pickle.dumps(expected_sliced)
+
+    assert len(full_pickled) > len(sliced_pickled)
+
+    result = pickle.loads(full_pickled)
+    tm.assert_series_equal(result, expected)
+
+    result_sliced = pickle.loads(sliced_pickled)
+    tm.assert_series_equal(result_sliced, expected_sliced)
diff --git a/pandas/tests/extension/test_arrow.py b/pandas/tests/extension/test_arrow.py
index 92e4dbaea4eea..0136e0ff0da5e 100644
--- a/pandas/tests/extension/test_arrow.py
+++ b/pandas/tests/extension/test_arrow.py
@@ -16,6 +16,7 @@
     time,
     timedelta,
 )
+import pickle
 
 import numpy as np
 import pytest
@@ -1765,3 +1766,19 @@ def test_is_bool_dtype():
     result = s[data]
     expected = s[np.asarray(data)]
     tm.assert_series_equal(result, expected)
+
+
+def test_pickle_roundtrip(data_missing):
+    # GH 42600
+    expected = pd.Series(data_missing)
+    expected_sliced = expected.head(2)
+    full_pickled = pickle.dumps(expected)
+    sliced_pickled = pickle.dumps(expected_sliced)
+
+    assert len(full_pickled) > len(sliced_pickled)
+
+    result = pickle.loads(full_pickled)
+    tm.assert_series_equal(result, expected)
+
+    result_sliced = pickle.loads(sliced_pickled)
+    tm.assert_series_equal(result_sliced, expected_sliced)

From 34bac1e8c7d890e4163e7c11c9a91f75e8f5c27a Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
Date: Thu, 13 Oct 2022 16:08:32 -0700
Subject: [PATCH 2/2] Use data

---
 pandas/tests/extension/test_arrow.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/extension/test_arrow.py b/pandas/tests/extension/test_arrow.py
index 0136e0ff0da5e..57c97889cef64 100644
--- a/pandas/tests/extension/test_arrow.py
+++ b/pandas/tests/extension/test_arrow.py
@@ -1768,9 +1768,9 @@ def test_is_bool_dtype():
     tm.assert_series_equal(result, expected)
 
 
-def test_pickle_roundtrip(data_missing):
+def test_pickle_roundtrip(data):
     # GH 42600
-    expected = pd.Series(data_missing)
+    expected = pd.Series(data)
     expected_sliced = expected.head(2)
     full_pickled = pickle.dumps(expected)
     sliced_pickled = pickle.dumps(expected_sliced)