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ASF GitHub Bot commented on HAWQ-1119: -------------------------------------- Github user dyozie commented on a diff in the pull request: https://github.com/apache/incubator-hawq-docs/pull/46#discussion_r86049842 --- Diff: pxf/HDFSWritablePXF.html.md.erb --- @@ -0,0 +1,416 @@ +--- +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 binary or text HDFS files. + +Use the `HdfsTextSimple` profile when writing text data. Use the `SequenceWritable` profile when dealing with binary data. + +This section describes how to use these PXF profiles to create writable external tables. + +**Note**: Tables that you create with writable profiles can only be used for INSERT operations. If you want to query inserted data, you must define a separate external readable table that references the new HDFS file using the equivalent readable profile. ??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. +- HDFS write permissions are provided to a restricted set of users. + +## <a id="hdfsplugin_writeextdata"></a>Writing to PXF External Tables +The PXF HDFS plug-in supports two writable profiles: `HdfsTextSimple` and `SequenceWritable`. + +Use the following syntax to create a HAWQ external writable table representing HDFS data: + +``` sql +CREATE WRITABLE EXTERNAL 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 to create a plain-text-delimited file at the location specified by \<path-to-hdfs-file\>. The `HdfsTextSimple` '`TEXT`' `FORMAT` supports only the built-in `(delimiter=<delim>)` \<formatting-property\>. | +| FORMAT 'CSV' | Use '`CSV`' `FORMAT` with the `HdfsTextSimple` profile to create a comma-separated-value file at the location specified by \<path-to-hdfs-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: + +| Option | Value Description | Profile | +|-------|-------------------------------------|--------| +| 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` and `org.apache.hadoop.io.compress.BZip2Codec` | HdfsTextSimple, SequenceWritable | +| | `org.apache.hadoop.io.compress.GzipCodec` | HdfsTextSimple | +| COMPRESSION_TYPE | The compression type to employ; supported values are `RECORD` (the default) or `BLOCK`. | HdfsTextSimple, SequenceWritable | +| DATA-SCHEMA | 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 is required for the `SequenceWritable` profile and has no default value. | SequenceWritable| +| THREAD-SAFE | Boolean value determining if a table query can run in multi-threaded mode. 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). | HdfsTextSimple, SequenceWritable| + +## <a id="profile_hdfstextsimple"></a>HdfsTextSimple Profile + +Use the `HdfsTextSimple` profile when writing delimited data to a plain text file where each row is a single record. + +Writable tables created using the `HdfsTextSimple` profile can optionally use record or block compression. The following compression codecs are supported: + +- org.apache.hadoop.io.compress.DefaultCodec +- org.apache.hadoop.io.compress.GzipCodec +- org.apache.hadoop.io.compress.BZip2Codec + +The `HdfsTextSimple` profile supports the following \<formatting-properties\>: + +| Keyword | Value | +|-------|-------------------------------------| +| delimiter | The delimiter character to use when writing the file. Default value is a comma `,`.| + + +### <a id="profile_hdfstextsimple_writing"></a>Example: Writing Data Using the HdfsTextSimple Profile + +This example uses the data schema introduced in [Example: Using the HdfsTextSimple Profile] (HDFSFileDataPXF.html#profile_hdfstextsimple_query): + + +| Field Name | Data Type | +|-------|-------------------------------------| +| location | text | +| month | text | +| number\_of\_orders | int | +| total\_sales | float8 | + +The example also uses the HAWQ table `pxf_hdfs_textsimple` created in that exercise and expects it to exist. + + +Perform the following operations to use the PXF `HdfsTextSimple` profile to create a HAWQ writable external table with the same data schema as defined above. You will also create a separate external readable table to read the associated HDFS file. + +1. Create a writable HAWQ external table with the data schema described above. Write to the HDFS file `/data/pxf_examples/pxfwritable_hdfs_textsimple1`. Create the table specifying a comma `,` as the delimiter: + + ``` sql + gpadmin=# CREATE WRITABLE EXTERNAL TABLE pxf_hdfs_writabletbl_1(location text, month text, num_orders int, total_sales float8) + LOCATION ('pxf://namenode:51200/data/pxf_examples/pxfwritable_hdfs_textsimple1?PROFILE=HdfsTextSimple') + FORMAT 'TEXT' (delimiter=E','); + ``` + + The `FORMAT` subclause `delimiter` value is specified as the single ascii comma character `,`. `E` escapes the character. + +2. Write a few records to the `pxfwritable_hdfs_textsimple1` HDFS file by invoking the SQL `INSERT` command on `pxf_hdfs_writabletbl_1`: + + ``` sql + gpadmin=# INSERT INTO pxf_hdfs_writabletbl_1 VALUES ( 'Frankfurt', 'Mar', 777, 3956.98 ); + gpadmin=# INSERT INTO pxf_hdfs_writabletbl_1 VALUES ( 'Cleveland', 'Oct', 3812, 96645.37 ); + ``` + +3. Insert the contents of the `pxf_hdfs_textsimple` table created in [Example: Using the HdfsTextSimple Profile] (HDFSFileDataPXF.html#profile_hdfstextsimple_query) into `pxf_hdfs_writabletbl_1`: + + ``` sql + gpadmin=# INSERT INTO pxf_hdfs_writabletbl_1 SELECT * FROM pxf_hdfs_textsimple; + ``` + +4. View the file contents in HDFS: + + ``` shell + $ hdfs dfs -cat /data/pxf_examples/pxfwritable_hdfs_textsimple1/* + Frankfurt,Mar,777,3956.98 + Cleveland,Oct,3812,96645.37 + Prague,Jan,101,4875.33 + Rome,Mar,87,1557.39 + Bangalore,May,317,8936.99 + Beijing,Jul,411,11600.67 + ``` + + Because you specified comma `,` as the delimiter, this character is the field separator used in each record of the HDFS file. + +5. Querying an external writable table is not supported in HAWQ. To query data from the newly-created HDFS file, create a readable external HAWQ table referencing the HDFS file: + + ``` sql + gpadmin=# CREATE EXTERNAL TABLE pxf_hdfs_textsimple_r1(location text, month text, num_orders int, total_sales float8) + LOCATION ('pxf://namenode:51200/data/pxf_examples/pxfwritable_hdfs_textsimple1?PROFILE=HdfsTextSimple') + FORMAT 'CSV'; + ``` + + The table is created with the `'CSV'` `FORMAT` because the delimiter character used when creating the writable table was a comma `,`. + +6. Query the readable external table `pxf_hdfs_textsimple_r1`: + + ``` sql + gpadmin=# SELECT * FROM pxf_hdfs_textsimple_r1; + ``` + + ``` pre + location | month | num_orders | total_sales + -----------+-------+------------+------------- + Frankfurt | Mar | 777 | 3956.98 + Cleveland | Oct | 3812 | 96645.37 + Prague | Jan | 101 | 4875.33 + Rome | Mar | 87 | 1557.39 + Bangalore | May | 317 | 8936.99 + Beijing | Jul | 411 | 11600.67 + (6 rows) + ``` + + The table includes the records you individually inserted, as well as the full contents of the `pxf_hdfs_textsimple` table. + +7. Create a second HAWQ external writable table, this time using Gzip compression and employing a colon `:` as the delimiter: + + ``` sql + gpadmin=# CREATE WRITABLE EXTERNAL TABLE pxf_hdfs_writabletbl_2 (location text, month text, num_orders int, total_sales float8) + LOCATION ('pxf://namenode:51200/data/pxf_examples/pxfwritable_hdfs_textsimple2?PROFILE=HdfsTextSimple&COMPRESSION_CODEC=org.apache.hadoop.io.compress.GzipCodec') + FORMAT 'TEXT' (delimiter=E':'); + ``` + +8. Write a few records to the `pxfwritable_hdfs_textsimple2` HDFS file by inserting into the `pxf_hdfs_writabletbl_2` table: + + ``` sql + gpadmin=# INSERT INTO pxf_hdfs_writabletbl_2 VALUES ( 'Frankfurt', 'Mar', 777, 3956.98 ); + gpadmin=# INSERT INTO pxf_hdfs_writabletbl_2 VALUES ( 'Cleveland', 'Oct', 3812, 96645.37 ); + ``` + +9. View the file contents in HDFS; use the `-text` option to `hdfs dfs` to view the compressed data as text: + + ``` shell + $ hdfs dfs -text /data/pxf_examples/pxfwritable_hdfs_textsimple2/* + Frankfurt:Mar:777:3956.98 + Cleveland:Oct:3812:96645.3 + ``` + + Notice that the colon `:` is the field separator in the HDFS file. + + As described in Step 5 above, to query data from the newly-created HDFS file named `pxfwritable_hdfs_textsimple2`, you can create a readable external HAWQ table referencing this HDFS file. + + +## <a id="profile_hdfsseqwritable_using"></a>SequenceWritable Profile + +Use the HDFS plug-in `SequenceWritable` profile when writing SequenceFile format files. Files of this type consist of binary key/value pairs. Sequence files are a common data transfer format between MapReduce jobs. + +SequenceFile format files can optionally use record or block compression. The following compression codecs are supported: + +- org.apache.hadoop.io.compress.DefaultCodec +- org.apache.hadoop.io.compress.BZip2Codec + +When using the `SequenceWritable` profile to write a SequenceFile format file, you must provide the name of the Java class used to serialize/deserialize the data. This class will provide custom read and write methods for the fields in the schema associated with the data you will be writing. + +### <a id="profile_hdfsseqwritable_writing"></a>Example: Writing Using the SequenceWritable Profile + +Before creating a writable external table with the `SequenceWritable` profile, you will first create a Java class named `PxfExample_CustomWritable` that will serialize/deserialize the fields in the sample schema used in previous examples. --- End diff -- Edit: In this example you will create a Java class named PxfExample_CustomWritable that will serialize/deserialize the fields in the sample schema used in previous examples. You will then use this class to access a writable external table that uses the SequenceWritable profile, > create new documentation topic for PXF writable profiles > -------------------------------------------------------- > > Key: HAWQ-1119 > URL: https://issues.apache.org/jira/browse/HAWQ-1119 > Project: Apache HAWQ > Issue Type: Improvement > Components: Documentation > Reporter: Lisa Owen > Assignee: David Yozie > Fix For: 2.0.1.0-incubating > > > certain profiles supported by the existing PXF plug-ins support writable > tables. create some documentation content for these profiles. -- This message was sent by Atlassian JIRA (v6.3.4#6332)