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From dyozie <...@git.apache.org>
Subject [GitHub] incubator-hawq-docs pull request #46: HAWQ-1119 - create doc content for PXF...
Date Mon, 31 Oct 2016 22:25:51 GMT
Github user dyozie commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq-docs/pull/46#discussion_r85812589
  
    --- Diff: pxf/HDFSWritablePXF.html.md.erb ---
    @@ -0,0 +1,410 @@
    +---
    +title: Writing Data to HDFS
    +---
    +
    +The PXF HDFS plug-in supports writable external tables using the `HdfsTextSimple` and
`SequenceWritable` profiles.  You might create a writable table to export data from a HAWQ
internal table to HDFS.
    +
    +This section describes how to use these PXF profiles to create writable external tables.
    +
    +**Note**: You cannot directly query data in a HAWQ writable table.  After creating the
external writable table, you must create a HAWQ readable external table accessing the HDFS
file, then query that table. ??You can also create a Hive table to access the HDFS file.??
    +
    +## <a id="pxfwrite_prereq"></a>Prerequisites
    +
    +Before working with HDFS file data using HAWQ and PXF, ensure that:
    +
    +-   The HDFS plug-in is installed on all cluster nodes. See [Installing PXF Plug-ins](InstallPXFPlugins.html)
for PXF plug-in installation information.
    +-   All HDFS users have read permissions to HDFS services and that write permissions
have been restricted to specific users.
    +
    +## <a id="hdfsplugin_writeextdata"></a>Writing to PXF External Tables
    +The PXF HDFS plug-in supports writable two profiles: `HdfsTextSimple` and `SequenceWritable`.
    +
    +Use the following syntax to create a HAWQ external writable table representing HDFS data: 
    +
    +``` sql
    +CREATE EXTERNAL WRITABLE TABLE <table_name> 
    +    ( <column_name> <data_type> [, ...] | LIKE <other_table> )
    +LOCATION ('pxf://<host>[:<port>]/<path-to-hdfs-file>
    +    ?PROFILE=HdfsTextSimple|SequenceWritable[&<custom-option>=<value>[...]]')
    +FORMAT '[TEXT|CSV|CUSTOM]' (<formatting-properties>);
    +```
    +
    +HDFS-plug-in-specific keywords and values used in the [CREATE EXTERNAL TABLE](../reference/sql/CREATE-EXTERNAL-TABLE.html)
call are described in the table below.
    +
    +| Keyword  | Value |
    +|-------|-------------------------------------|
    +| \<host\>[:\<port\>]    | The HDFS NameNode and port. |
    +| \<path-to-hdfs-file\>    | The path to the file in the HDFS data store. |
    +| PROFILE    | The `PROFILE` keyword must specify one of the values `HdfsTextSimple`
or `SequenceWritable`. |
    +| \<custom-option\>  | \<custom-option\> is profile-specific. These options
are discussed in the next topic.|
    +| FORMAT 'TEXT' | Use '`TEXT`' `FORMAT` with the `HdfsTextSimple` profile when \<path-to-hdfs-file\>
will reference a plain text delimited file. The `HdfsTextSimple` '`TEXT`' `FORMAT` supports
only the built-in `(delimiter=<delim>)` \<formatting-property\>. |
    +| FORMAT 'CSV' | Use '`CSV`' `FORMAT` with `HdfsTextSimple` when \<path-to-hdfs-file\>
will reference a comma-separated value file.  |
    +| FORMAT 'CUSTOM' | Use the `'CUSTOM'` `FORMAT` with the `SequenceWritable` profile.
The `SequenceWritable` '`CUSTOM`' `FORMAT` supports only the built-in `(formatter='pxfwritable_export)`
(write) and `(formatter='pxfwritable_import)` (read) \<formatting-properties\>.
    +
    +**Note**: When creating PXF external tables, you cannot use the `HEADER` option in your
`FORMAT` specification.
    +
    +## <a id="profile_hdfstextsimple"></a>Custom Options
    +
    +The `HdfsTextSimple` and `SequenceWritable` profiles support the following \<custom-options\>:
    +
    +| Keyword  | Value Description |
    +|-------|-------------------------------------|
    +| COMPRESSION_CODEC    | The compression codec Java class name. If this option is not
provided, no data compression is performed. Supported compression codecs include: `org.apache.hadoop.io.compress.DefaultCodec`,
`org.apache.hadoop.io.compress.BZip2Codec`, and `org.apache.hadoop.io.compress.GzipCodec`
(`HdfsTextSimple` profile only) |
    +| COMPRESSION_TYPE    | The compression type to employ; supported values are `RECORD`
(the default) or `BLOCK`. |
    +| DATA-SCHEMA    | (`SequenceWritable` profile only) The name of the writer serialization/deserialization
class. The jar file in which this class resides must be in the PXF class path. This option
has no default value. |
    +| THREAD-SAFE | Boolean value determining if a table query can run in multi-thread mode.
Default value is `TRUE`, requests run in multi-threaded mode. When set to `FALSE`, requests
will be handled in a single thread.  `THREAD-SAFE` should be set appropriately when operations
that are not thread-safe are performed (i.e. compression). |
    --- End diff --
    
    multi-thread -> multi-threaded.  Also, the rest  some edits:
    
    The default value is true. Set this option to `FALSE` to handle all requests in a single
thread for operations that are not thread-safe (for example, compression).


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