[GitHub] [arrow] wjones127 commented on a change in pull request #12112: ARROW-15183: [Python][Docs] Add Missing Dataset Write Options

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wjones127 commented on a change in pull request #12112:
URL: https://github.com/apache/arrow/pull/12112#discussion_r827096582



##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,72 @@ guidelines apply. Row groups can provide parallelism when reading and allow data
 based on statistics, but very small groups can cause metadata to be a significant portion
 of file size. Arrow's file writer provides sensible defaults for group sizing in most cases.
 
+Configuring files open during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When writing data to the disk, there are a few parameters that can be 
+important to optimize the writes, i.e number of rows per file and
+number of files open during write. 

Review comment:
       ```suggestion
   important to optimize the writes, such as the number of rows per file and
   the number of files open during write. 
   ```

##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,60 @@ guidelines apply. Row groups can provide parallelism when reading and allow data
 based on statistics, but very small groups can cause metadata to be a significant portion
 of file size. Arrow's file writer provides sensible defaults for group sizing in most cases.
 
+Configuring files open during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When writing data to the disk, there are a few parameters that can be 
+important to optimize the writes, i.e number of rows per file and
+number of files open during write. 
+
+Set the maximum number of files opened with the ``max_open_files`` parameter of
+:meth:`write_dataset`.
+
+If  ``max_open_files`` is set greater than 0 then this will limit the maximum 
+number of files that can be left open. If an attempt is made to open too many 
+files then the least recently used file will be closed.  If this setting is set 
+too low you may end up fragmenting your data into many small files.
+
+The default value is 900 which also allows some number of files to be open 
+by the scannerbefore hitting the default Linux limit of 1024. Modify this value 
+depending on the nature of write operations associated with the usage. 
+
+Another important configuration used in `write_dataset` is ``max_rows_per_file``. 
+
+Set the maximum number of files opened with the ``max_rows_per_files`` parameter of
+:meth:`write_dataset`.
+
+If ``max_rows_per_file`` is set greater than 0 then this will limit how many 
+rows are placed in any single file. Otherwise there will be no limit and one 
+file will be created in each output directory unless files need to be closed to respect 
+``max_open_files``. 
+
+Configuring rows per group during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When writing data to disk, depending on the volume of data obtained, 
+(in a mini-batch setting where, records are obtained in batch by batch)
+the volume of data written to disk per each group can be configured. 
+This can be configured using a minimum and maximum parameter. 
+

Review comment:
       Those are good examples.
   
   Could you add a paragraph discussing how `row_groups` affect later reads for Parquet and Feather/IPC, but not CSV or JSON? 

##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,72 @@ guidelines apply. Row groups can provide parallelism when reading and allow data
 based on statistics, but very small groups can cause metadata to be a significant portion
 of file size. Arrow's file writer provides sensible defaults for group sizing in most cases.
 
+Configuring files open during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When writing data to the disk, there are a few parameters that can be 
+important to optimize the writes, i.e number of rows per file and
+number of files open during write. 
+
+Set the maximum number of files opened with the ``max_open_files`` parameter of
+:meth:`write_dataset`.
+
+If  ``max_open_files`` is set greater than 0 then this will limit the maximum 
+number of files that can be left open. This only applies to writing partitioned
+datasets, where rows are dispatched to the appropriate file depending on their
+partition values. If an attempt is made to open too many  files then the least
+recently used file will be closed.  If this setting is set too low you may end
+up fragmenting your data into many small files.
+
+If your process is concurrently using other file handlers, either with a 
+dataset scanner or otherwise, you may hit a system file handler limit. For 
+example, if you are scanning a dataset with 300 files and writing out to
+900 files, the total of 1200 files may be over a system limit. (On Linux,
+this might be a "Too Many Open Files" error.) You can either reduce this
+``max_open_files`` setting or increasing your file handler limit on your
+system. The default value is 900 which also allows some number of files
+to be open by the scanner before hitting the default Linux limit of 1024. 
+
+Another important configuration used in :meth:`write_dataset` is ``max_rows_per_file``. 
+
+Set the maximum number of rows written in each file with the ``max_rows_per_files``
+parameter of :meth:`write_dataset`.
+
+If ``max_rows_per_file`` is set greater than 0 then this will limit how many 
+rows are placed in any single file. Otherwise there will be no limit and one 
+file will be created in each output directory unless files need to be closed to respect 
+``max_open_files``. This setting is the primary way to control file size. 
+For workloads writing a lot of data files can get very large without a 

Review comment:
       ```suggestion
   For workloads writing a lot of data, files can get very large without a
   ```




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