align: Avoid reindexing when join="exact" (#7736)

dcherian · web-flow · commit 67ff171367ad · 2023-04-12T08:41:50.000-06:00
* align: Avoid reindexing when join="exact" xref #7730 * Aligner.copy always copies ecen with join="exact" * Move logic to Aligner.align * Add whats-new
diff --git a/doc/whats-new.rst b/doc/whats-new.rst
@@ -41,6 +41,12 @@ Breaking changes
 Deprecations
 ~~~~~~~~~~~~
 
+Performance
+~~~~~~~~~~~
+- Optimize alignment with ``join="exact", copy=False`` by avoiding copies. (:pull:`7736`)
+  By `Deepak Cherian <https://github.com/dcherian>`_.
+- Avoid unnecessary copies of ``CFTimeIndex``. (:pull:`7735`)
+  By `Deepak Cherian <https://github.com/dcherian>`_.
 
 Bug fixes
 ~~~~~~~~~
diff --git a/xarray/core/alignment.py b/xarray/core/alignment.py
@@ -574,6 +574,8 @@ def align(self) -> None:
 
         if self.join == "override":
             self.override_indexes()
+        elif self.join == "exact" and not self.copy:
+            self.results = self.objects
         else:
             self.reindex_all()
 
