westonpace commented on a change in pull request #12112:
URL: https://github.com/apache/arrow/pull/12112#discussion_r836838039
##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,76 @@ 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, such as the number of rows per file and
+the maximum number of open files allowed during the 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 increase the file handler limit on your
+system. The default value is 900 which 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
+row count cap, leading to out-of-memory errors in downstream readers. The
+relationship between row count and file size depends on the dataset schema
+and how well compressed (if at all) the data is. For most applications,
+it's best to keep file sizes below 1GB.
+
+Configuring rows per group during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The volume of data written to the disk per each group can be configured.
+This configuration includes a lower and an upper bound.
+Set the minimum number of rows required to form a row group.
+Defined with the ``min_rows_per_group`` parameter of :meth:`write_dataset`.
+
+Note: if ``min_rows_per_group`` is set greater than 0 then this will cause the
+dataset writer to batch incoming data and only write the row groups to the
+disk when sufficient rows have accumulated. The final row group size may be
+less than this value if other options such as ``max_open_files`` or
+``max_rows_per_file`` force smaller row group sizes.
+
+Set the maximum number of rows allowed per group. Defined as
``max_rows_per_group`` parameter of
+:meth:`write_dataset`.
Review comment:
```suggestion
The maximum number of rows allowed per group is defined with the
``max_rows_per_group`` parameter of :meth:`write_dataset`.
```
##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,76 @@ 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, such as the number of rows per file and
+the maximum number of open files allowed during the 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 increase the file handler limit on your
+system. The default value is 900 which 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
+row count cap, leading to out-of-memory errors in downstream readers. The
+relationship between row count and file size depends on the dataset schema
+and how well compressed (if at all) the data is. For most applications,
+it's best to keep file sizes below 1GB.
+
+Configuring rows per group during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The volume of data written to the disk per each group can be configured.
+This configuration includes a lower and an upper bound.
+Set the minimum number of rows required to form a row group.
+Defined with the ``min_rows_per_group`` parameter of :meth:`write_dataset`.
+
+Note: if ``min_rows_per_group`` is set greater than 0 then this will cause the
+dataset writer to batch incoming data and only write the row groups to the
+disk when sufficient rows have accumulated. The final row group size may be
+less than this value if other options such as ``max_open_files`` or
+``max_rows_per_file`` force smaller row group sizes.
+
+Set the maximum number of rows allowed per group. Defined as
``max_rows_per_group`` parameter of
+:meth:`write_dataset`.
+
+Note: if ``max_rows_per_group`` is set greater than 0 then the dataset writer
may split
Review comment:
There are
"[notes](https://sublime-and-sphinx-guide.readthedocs.io/en/latest/notes_warnings.html)"
in RST format:
```
.. note:
This is the note content
Resume regular content
```
Perhaps we should use that instead of a regular paragraph here?
##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,76 @@ 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, such as the number of rows per file and
+the maximum number of open files allowed during the 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 increase the file handler limit on your
+system. The default value is 900 which 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
+row count cap, leading to out-of-memory errors in downstream readers. The
+relationship between row count and file size depends on the dataset schema
+and how well compressed (if at all) the data is. For most applications,
+it's best to keep file sizes below 1GB.
+
+Configuring rows per group during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The volume of data written to the disk per each group can be configured.
+This configuration includes a lower and an upper bound.
+Set the minimum number of rows required to form a row group.
+Defined with the ``min_rows_per_group`` parameter of :meth:`write_dataset`.
Review comment:
```suggestion
This configuration includes a lower and an upper bound.
The minimum number of rows required to form a row group is
defined with the ``min_rows_per_group`` parameter of :meth:`write_dataset`.
```
##########
File path: docs/source/python/dataset.rst
##########
@@ -613,6 +613,76 @@ 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, such as the number of rows per file and
+the maximum number of open files allowed during the 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 increase the file handler limit on your
+system. The default value is 900 which 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
+row count cap, leading to out-of-memory errors in downstream readers. The
+relationship between row count and file size depends on the dataset schema
+and how well compressed (if at all) the data is. For most applications,
+it's best to keep file sizes below 1GB.
+
+Configuring rows per group during a write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The volume of data written to the disk per each group can be configured.
+This configuration includes a lower and an upper bound.
+Set the minimum number of rows required to form a row group.
+Defined with the ``min_rows_per_group`` parameter of :meth:`write_dataset`.
+
+Note: if ``min_rows_per_group`` is set greater than 0 then this will cause the
+dataset writer to batch incoming data and only write the row groups to the
+disk when sufficient rows have accumulated. The final row group size may be
+less than this value if other options such as ``max_open_files`` or
+``max_rows_per_file`` force smaller row group sizes.
+
+Set the maximum number of rows allowed per group. Defined as
``max_rows_per_group`` parameter of
+:meth:`write_dataset`.
+
+Note: if ``max_rows_per_group`` is set greater than 0 then the dataset writer
may split
+up large incoming batches into multiple row groups. If this value is set then
+``min_rows_per_group`` should also be set or else you may end up with very
small
+row groups (e.g. if the incoming row group size is just barely larger than
this value).
+Row groups are built into the Parquet and IPC/Feather formats but don't affect
JSON or CSV.
Review comment:
```suggestion
row groups (e.g. if the incoming row group size is just barely larger than
this value).
Row groups are built into the Parquet and IPC/Feather formats but don't
affect JSON or CSV.
```
I think there is a "note" saying "make sure to set both properties" and then
a paragraph talking about how row groups affect downstream readers. We should,
at a minimum, make them two different paragraphs (though we might also make the
note a proper "note").
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