Github user hornn commented on a diff in the pull request:
https://github.com/apache/incubator-hawq/pull/1344#discussion_r171073052
--- Diff: pxf/pxf-ignite/README.md ---
@@ -0,0 +1,67 @@
+# Accessing Ignite database using PXF
+
+The PXF Ignite plug-in enables to access the [Ignite
database](https://ignite.apache.org/) (both read and write operations are
supported) via REST API.
+
+
+# Prerequisites
+
+Check the following before using the plug-in:
+
+* The Ignite plug-in is installed on all PXF nodes;
+
+* The Ignite client is installed and running at the `IGNITE_HOST`
(`localhost` by default; see below), and it accepts http queries from the PXF
(note that *enabling Ignite REST API does not require changes in Ignite
configuration*; see the instruction on how to do that at
https://apacheignite.readme.io/docs/rest-api#section-getting-started).
+
+
+# Syntax
+
+```
+CREATE [READABLE] EXTERNAL TABLE <table_name> (
+ <column_name> <data_type>[, <column_name> <data_type>, ...] | LIKE
<other_table>
+)
+LOCATION
('pxf://<ignite_table_name>?PROFILE=Ignite[&<extra-parameter>&<extra-parameter>&...]')
+FORMAT 'CUSTOM' (formatter='pxfwritable_import');
+```
+where each `<extra-parameter>` is one of the following:
+* `IGNITE_HOST=<ignite_host_address_with_port>`. The location of Ignite
client node. If not given, `127.0.0.1:8080` is used by default;
+* `IGNITE_CACHE=<ignite_cache_name>`. The name of Ignite cache to use. If
not given, this parameter is not included in queries from PXF to Ignite, thus
Ignite default values will be used (at the moment, this is `Default` cache).
This option is **case-sensitive**;
+* `BUFFER_SIZE=<unsigned_int>`. The number of tuples send to (from) Ignite
per a response. The same number of tuples is stored in in-plug-in cache. The
values `0` and `1` are equal (cache is not used, each tuple is passed in it's
own query to Ignite). If not given, `128` is used by default;
+* `PARTITION_BY=<column>:<column_type>`. See below;
+* `RANGE=<start_value>:<end_value>`. See below;
+* `INTERVAL=<value>[:<unit>]`. See below.
+
+
+# Partitioning
+## Introduction
+
+PXF Ignite plugin supports simultaneous access to Ignite database from
multiple PXF segments. *Partitioning* should be used in order to perform such
operation.
+
+If the partitioning is not used, all the data will be retrieved by a
single PXF segment.
+
+Partitioning in PXF Ignite plug-in works just like in PXF JDBC plug-in.
+
+This feature is optional. However, a bug in the `pxf-service` which makes
partitioning necessary for any query was fixed only on 17th Jan 2018 in [this
commit](https://github.com/apache/incubator-hawq/commit/0d620e431026834dd70c9e0d63edf8bb28b38227),
so the older versions of PXF may return an exception if a query does not
contain a meaningful `PARTITION_BY` parameter.
+
+
+## Syntax
+
+To use partitions, add a set of `<ignite-parameter>`s:
+```
+&PARTITION_BY=<column>:<column_type>&RANGE=<start_value>:<end_value>[&INTERVAL=<value>[:<unit>]]
+```
+
+* The `PARTITION_BY` parameter indicates which column to use as the
partition column. Only one column can be used as a partition column.
+ * The `<column>` is the name of a partition column;
+ * The `<column_type>` is the datatype of a partition column. At the
moment, the **supported types** are `INT`, `DATE` and `ENUM`. The `DATE` format
is `yyyy-MM-dd`.
+
+* The `RANGE` parameter indicates the range of data to be queried. It is
left-closed, thus it produces ranges like:
+ * `[ <start_value> ; <end_value> )`,
+ * `... >= start_value AND ... < end_value`;
+
+* The `INTERVAL` parameter is **required** for `INT` and `DATE`
partitions. This parameter is ignored if `<column_type>` is `ENUM`.
+ * The `<value>` is the size of each fragment (the last one may be
smaller). Note that by default PXF does not support more than 100 fragments;
+ * The `<unit>` **must** be provided if `<column_type>` is `DATE`. At
the moment, only `year`, `month` and `day` are supported. This parameter is
ignored in case of any other `<column_type>`.
+
+Example partitions:
+* `&PARTITION_BY=id:int&RANGE=42:142&INTERVAL=1`
+*
`&PARTITION_BY=createdate:date&RANGE=2008-01-01:2010-01-01&INTERVAL=1:month`
+* `&PARTITION_BY=grade:enum&RANGE=excellent:good:general:bad`
--- End diff --
looks like for `ENUM` type, the `RANGE` is a list of the supported values.
Could you please update the documentation for `RANGE` with that syntax?
---
