Improve map_blocks docs (#5076)

* improve map_blocks docs

* clarify load

Author: malmans2

doc/user-guide/dask.rst

@@ -511,6 +511,13 @@ Notice that the 0-shaped sizes were not printed to screen. Since ``template`` ha
     mapped.identical(expected)
 
 
+.. tip::
+
+   As :py:func:`map_blocks` loads each block into memory, reduce as much as possible objects consumed by user functions.
+   For example, drop useless variables before calling ``func`` with :py:func:`map_blocks`.
+
+
+
 Chunking and performance
 ------------------------
 

xarray/core/dataarray.py

@@ -3666,8 +3666,8 @@ def map_blocks(
         Notes
         -----
         This function is designed for when ``func`` needs to manipulate a whole xarray object
-        subset to each block. In the more common case where ``func`` can work on numpy arrays, it is
-        recommended to use ``apply_ufunc``.
+        subset to each block. Each block is loaded into memory. In the more common case where
+        ``func`` can work on numpy arrays, it is recommended to use ``apply_ufunc``.
 
         If none of the variables in this object is backed by dask arrays, calling this function is
         equivalent to calling ``func(obj, *args, **kwargs)``.

xarray/core/dataset.py

@@ -6274,8 +6274,8 @@ def map_blocks(
         Notes
         -----
         This function is designed for when ``func`` needs to manipulate a whole xarray object
-        subset to each block. In the more common case where ``func`` can work on numpy arrays, it is
-        recommended to use ``apply_ufunc``.
+        subset to each block. Each block is loaded into memory. In the more common case where
+        ``func`` can work on numpy arrays, it is recommended to use ``apply_ufunc``.
 
         If none of the variables in this object is backed by dask arrays, calling this function is
         equivalent to calling ``func(obj, *args, **kwargs)``.

xarray/core/parallel.py

@@ -208,8 +208,8 @@ def map_blocks(
     Notes
     -----
     This function is designed for when ``func`` needs to manipulate a whole xarray object
-    subset to each block. In the more common case where ``func`` can work on numpy arrays, it is
-    recommended to use ``apply_ufunc``.
+    subset to each block. Each block is loaded into memory. In the more common case where
+    ``func`` can work on numpy arrays, it is recommended to use ``apply_ufunc``.
 
     If none of the variables in ``obj`` is backed by dask arrays, calling this function is
     equivalent to calling ``func(obj, *args, **kwargs)``.