Github user amberarrow commented on a diff in the pull request:
https://github.com/apache/apex-malhar/pull/368#discussion_r74611442
--- Diff: docs/operators/fsInputOperator.md ---
@@ -0,0 +1,101 @@
+File Input Operator
+=============
+
+## Operator Objective
+This operator scans a directory for files. Files are then read and split
into tuples, which are emitted. The default implementation scans a single
directory. The operator is fault tolerant. It tracks previously read files and
current offset as part of checkpoint state. In case of failure the operator
will skip files that were already processed and fast forward to the offset of
the current file. Supports partitioning and changes to number of partitions.
The directory scanner is responsible to only accept the files that belong to a
partition.
+
+File Input Operator is **idempotent**, **fault-tolerant** and
**partitionable**.
+
+## Operator Usecase
+1. Read all files of a directory and then keep scanning it for newly added
files.
+
+## Operator Information
+1. Operator location: ***malhar-library***
+2. Available since: ***1.0.2***
+3. Operator state: ***Stable***
+3. Java Packages:
+ * Operator:
***[com.datatorrent.lib.io.fs.AbstractFileInputOperator](https://www.datatorrent.com/docs/apidocs/com/datatorrent/lib/io/fs/AbstractFileInputOperator.html)***
+
+### AbstractFileInputOperator
+This is the abstract implementation that serves as base class for scanning
a directory for files and read the files one by one. This class doesnât have
any ports.
--- End diff --
Add an overview here of what the operator does here, what parts need to be
implemented by concrete subclasses and show code fragments for example from the
LineByLine operator. Describe what the DirectoryScanner does. Some obvious
questions that will come up in the reader's mind should be answered, for
example:
1. What happens if a file that has already been processed has new data
appended to it ?
2. What happens if a processed file is deleted ?
3. What happens if a separate actor is in the process of writing a new file
in the monitored directory ? How will this operator know when the file is ready
to be read ?
4. What if the number of files in the scanned directory grows over time to
be very large -- what impact, if any, does it have on this operator ?
5. Can this operator be used to monitor multiple directories ? (Point
people to the fileIO-multidir example)
6. This class already implements the Partitioner interface; can a custom
partitioner be set on this operator ? More generally, since we are saying this
operator supports dynamic partitioning, it is useful to describe (with a code
fragment if possible) how to trigger it.
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
