Accessing Hive Data

Apache Hive is a distributed data warehousing infrastructure. Hive facilitates managing large data sets supporting multiple data formats, including comma-separated value (.csv), RC, ORC, and parquet. The PXF Hive plug-in reads data stored in Hive, as well as HDFS or HBase.

This section describes how to use PXF to access Hive data. Options for querying data stored in Hive include:

  • Querying Hive tables via PXF’s integration with HCatalog
  • Creating an external table in PXF and querying that table

Prerequisites

Before accessing Hive data with HAWQ and PXF, ensure that:

  • The PXF HDFS plug-in is installed on all HAWQ and HDFS cluster nodes (master, segment, NameNode, DataNode). See Installing PXF Plug-ins for PXF plug-in installation information.
  • The PXF Hive plug-in is installed on all HAWQ and HDFS cluster nodes.
  • If you configured Hadoop with high availability, PXF must also be installed on all HDFS nodes running NameNode services.
  • The Hive client is installed on all PXF nodes.
  • The Hive JAR files and conf directory are installed on all cluster nodes.
  • You have tested PXF on HDFS.
  • You are running the Hive Metastore service on a machine in your cluster. 
  • You have set the hive.metastore.uris property in the hive-site.xml on the NameNode.

Hive File Formats

The PXF Hive plug-in supports several file formats and profiles for accessing these formats:

File Format Description Profile
TextFile Flat file with data in comma-, tab-, or space-separated value format or JSON notation. Hive, HiveText
SequenceFile Flat file consisting of binary key/value pairs. Hive
RCFile Record columnar data consisting of binary key/value pairs; high row compression rate. Hive, HiveRC
ORCFile Optimized row columnar data with stripe, footer, and postscript sections; reduces data size. Hive
Parquet Compressed columnar data representation. Hive
Avro JSON-defined, schema-based data serialization format. Hive

Refer to File Formats for detailed information about the file formats supported by Hive.

Data Type Mapping

Primitive Data Types

To represent Hive data in HAWQ, map data values that use a primitive data type to HAWQ columns of the same type.

The following table summarizes external mapping rules for Hive primitive types.

Hive Data Type Hawq Data Type
boolean bool
int int4
smallint int2
tinyint int2
bigint int8
float float4
double float8
string text
binary bytea
timestamp timestamp

Complex Data Types

Hive supports complex data types including array, struct, map, and union. PXF maps each of these complex types to text. While HAWQ does not natively support these types, you can create HAWQ functions or application code to extract subcomponents of these complex data types.

An example using complex data types with the Hive profile is provided later in this topic.

Sample Data Set

Examples used in this topic will operate on a common data set. This simple data set models a retail sales operation and includes fields with the following names and data types:

Field Name Data Type
location text
month text
number_of_orders integer
total_sales double

Prepare the sample data set for use:

  1. First, create a text file:

    $ vi /tmp/pxf_hive_datafile.txt
    
  2. Add the following data to pxf_hive_datafile.txt; notice the use of the comma , to separate the four field values:

    Prague,Jan,101,4875.33
    Rome,Mar,87,1557.39
    Bangalore,May,317,8936.99
    Beijing,Jul,411,11600.67
    San Francisco,Sept,156,6846.34
    Paris,Nov,159,7134.56
    San Francisco,Jan,113,5397.89
    Prague,Dec,333,9894.77
    Bangalore,Jul,271,8320.55
    Beijing,Dec,100,4248.41
    

Make note of the path to pxf_hive_datafile.txt; you will use it in later exercises.

Hive Command Line

The Hive command line is a subsystem similar to that of psql. To start the Hive command line:

$ HADOOP_USER_NAME=hdfs hive

The default Hive database is named default.

Example: Create a Hive Database

Create a Hive table to expose our sample data set.

  1. Create a Hive table named sales_info in the default database:

    hive> CREATE TABLE sales_info (location string, month string,
            number_of_orders int, total_sales double)
            ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
            STORED AS textfile;
    

    Notice that:

    • The STORED AS textfile subclause instructs Hive to create the table in Textfile (the default) format. Hive Textfile format supports comma-, tab-, and space-separated values, as well as data specified in JSON notation.
    • The DELIMITED FIELDS TERMINATED BY subclause identifies the field delimiter within a data record (line). The sales_info table field delimiter is a comma (,).
  2. Load the pxf_hive_datafile.txt sample data file into the sales_info table you just created:

    hive> LOAD DATA LOCAL INPATH '/tmp/pxf_hive_datafile.txt'
            INTO TABLE sales_info;
    

    In examples later in this section, you will access the sales_info Hive table directly via PXF. You will also insert sales_info data into tables of other Hive file format types, and use PXF to access those directly as well.

  3. Perform a query on sales_info to verify that the data was loaded successfully:

    hive> SELECT * FROM sales_info;
    

Determine the HDFS location of a Hive Table

Should you need to identify the HDFS file location of a Hive managed table, reference it using its HDFS file path. You can determine a Hive table’s location in HDFS using the DESCRIBE command, for example:

hive> DESCRIBE EXTENDED sales_info;
Detailed Table Information
...
location:hdfs://<namenode>:<port>/apps/hive/warehouse/sales_info
...

The location value identifies the HDFS file path of the table.

Using PXF and HCatalog to Query Hive

You can query Hive tables directly through HCatalog integration with HAWQ and PXF, regardless of the underlying file storage format. This integration allows HAWQ to directly use table metadata stored in HCatalog.

HCatalog is built on top of the Hive metastore and incorporates Hive’s DDL. This provides several advantages:

  • You do not need to know the table schema of your Hive tables
  • You do not need to manually enter information about Hive table location or format
  • If Hive table metadata changes, HCatalog provides updated metadata. This is in contrast to the use of static external PXF tables to define Hive table metadata for HAWQ.

The following diagram depicts how HAWQ integrates with HCatalog to query Hive tables:

  1. HAWQ retrieves table metadata from HCatalog using PXF.
  2. HAWQ creates in-memory catalog tables from the retrieved metadata. If a table is referenced multiple times in a transaction, HAWQ uses its in-memory metadata to reduce external calls to HCatalog.
  3. PXF queries Hive using table metadata that is stored in the HAWQ in-memory catalog tables. Table metadata is dropped at the end of the transaction.

Enabling HCatalog Integration

To enable HCatalog query integration in HAWQ, perform the following steps:

  1. Make sure your deployment meets the requirements listed in Prerequisites.
  2. If necessary, set the pxf_service_address global configuration property to the hostname or IP address and port where you have installed the PXF Hive plug-in. By default, the value is set to localhost:51200.

    postgres=# SET pxf_service_address TO <hivenode>:51200
    
  3. HCatalog internally uses the pxf protocol to query. Grant this protocol privilege to all roles requiring access:

    postgres=# GRANT ALL ON PROTOCOL pxf TO <role>;
    
  4. It is not recommended to create a HAWQ table using the WITH (OIDS) clause. If any user tables were created using the WITH (OIDS) clause, additional operations are required to enable HCatalog integration. To access a Hive table via HCatalog when user tables were created using WITH (OIDS), HAWQ users must have SELECT permission to query every user table within the same schema that was created using the WITH (OIDS) clause.

    1. Determine which user tables were created using the WITH (OIDS) clause:

      postgres=# SELECT oid, relname FROM pg_class
                   WHERE relhasoids = true
                     AND relnamespace <> (SELECT oid FROM pg_namespace WHERE nspname = 'pg_catalog');
      
    2. Grant SELECT privilege on all returned tables to all roles to which you chose to provide HCatalog query access. For example:

      postgres=# GRANT SELECT ON <table-created-WITH-OIDS> TO <role>
      

Usage

To query a Hive table with HCatalog integration, query HCatalog directly from HAWQ. The query syntax is:

postgres=# SELECT * FROM hcatalog.hive-db-name.hive-table-name;

For example:

postgres=# SELECT * FROM hcatalog.default.sales_info;

To obtain a description of a Hive table with HCatalog integration, you can use the psql client interface.

  • Within HAWQ, use either the \d hcatalog.hive-db-name.hive-table-name or \d+ hcatalog.hive-db-name.hive-table-name commands to describe a single table. \d displays only HAWQ’s interpretation of the underlying source (Hive in this case) data type, while \d+ displays both the HAWQ interpreted and Hive source data types. For example, from the psql client interface:

    $ psql -d postgres
    
    postgres=# \d+ hcatalog.default.sales_info;
    
       PXF Hive Table "default.sales_info"
          Column      |  Type  | Source type 
    ------------------+--------+-------------
     location         | text   | string
     month            | text   | string
     number_of_orders | int4   | int
     total_sales      | float8 | double
    
  • Use \d hcatalog.hive-db-name.* to describe the whole database schema, i.e. all tables in hive-db-name.

  • Use \d hcatalog.*.* to describe the whole schema, i.e. all databases and tables.

When using \d or \d+ commands in the psql HAWQ client, hcatalog will not be listed as a database. If you use other psql compatible clients, hcatalog will be listed as a database with a size value of -1 since hcatalog is not a real database in HAWQ.

Alternatively, you can use the pxf_get_item_fields user-defined function (UDF) to obtain Hive table descriptions from other client interfaces or third-party applications. The UDF takes a PXF profile and a table pattern string as its input parameters. Note: The only supported input profile at this time is 'Hive'.

  • The following statement returns a description of a specific table. The description includes path, itemname (table), fieldname, fieldtype (HAWQ type), and sourcefieldtype (Hive type).

    postgres=# SELECT * FROM pxf_get_item_fields('Hive','default.sales_info');
    
      path   |  itemname  |    fieldname     | fieldtype | sourcefieldtype 
    ---------+------------+------------------+-----------+-----------------
     default | sales_info | location         | text      | string
     default | sales_info | month            | text      | string
     default | sales_info | number_of_orders | int4      | int
     default | sales_info | total_sales      | float8    | double
    
  • The following statement returns table descriptions from the default database.

    postgres=# SELECT * FROM pxf_get_item_fields('Hive','default.*');
    
  • The following statement returns a description of the entire schema.

    postgres=# SELECT * FROM pxf_get_item_fields('Hive', '*.*');
    

Limitations

HCatalog integration has the following limitations:

  • HCatalog queries on Hive tables with complex type fields return those fields serialized as text.
  • Even for primitive types, HCatalog metadata descriptions produced by \d are HAWQ’s interpretation of the underlying Hive data types. For example, the Hive type tinyint is converted to HAWQ type int2. (See Data Type Mapping.)
  • HAWQ reserves the database name hcatalog for system use. You cannot connect to or alter the system hcatalog database.

Querying External Hive Data

In the previous section, you used HCatalog integration to query a Hive table. You can also create a PXF/HAWQ external table to access Hive table data. This Hive table access mechanism requires that you identify an appropriate Hive profile.

The PXF Hive plug-in supports several Hive-related profiles. These include Hive, HiveText, and HiveRC. The HiveText and HiveRC profiles are specifically optimized for text and RC file formats, respectively. The Hive profile is optimized for all file storage types; use the Hive profile when the underlying Hive table is composed of multiple partitions with differing file formats.

Use the following syntax to create a HAWQ external table representing Hive data:

CREATE EXTERNAL TABLE <table_name>
    ( <column_name> <data_type> [, ...] | LIKE <other_table> )
LOCATION ('pxf://<host>[:<port>]/<hive-db-name>.<hive-table-name>
    ?PROFILE=Hive|HiveText|HiveRC[&DELIMITER=<delim>'])
FORMAT 'CUSTOM|TEXT' (formatter='pxfwritable_import' | delimiter='<delim>')

Hive-plug-in-specific keywords and values used in the CREATE EXTERNAL TABLE call are described below.

Keyword Value
<host> The PXF host. While <host> may identify any PXF agent node, use the HDFS NameNode as it is guaranteed to be available in a running HDFS cluster. If HDFS High Availability is enabled, <host> must identify the HDFS NameService.
<port> The PXF port. If <port> is omitted, PXF assumes <host> identifies a High Availability HDFS Nameservice and connects to the port number designated by the pxf_service_port server configuration parameter value. Default is 51200.
<hive-db-name> The name of the Hive database. If omitted, defaults to the Hive database named default.
<hive-table-name> The name of the Hive table.
PROFILE The PROFILE keyword must specify one of the values Hive, HiveText, or HiveRC.
DELIMITER The DELIMITER clause is required for both the HiveText and HiveRC profiles and identifies the field delimiter used in the Hive data set. <delim> must be a single ascii character or specified in hexadecimal representation.
FORMAT (Hive profile) The FORMAT clause must specify CUSTOM. The CUSTOM format supports only the built-in pxfwritable_import formatter.
FORMAT (HiveText and HiveRC profiles) The FORMAT clause must specify TEXT. The delimiter must be specified a second time in ’<delim>’.

Hive Profile

Use the Hive profile with any Hive file storage format. With the Hive profile, you can also access heterogenous format data in a single table where each partition may be stored in a different file format. In both cases, the Hive profile will use the optimal Hive* profile for the underlying file storage type. Refer to the Partition Filtering discussion later in this topic for additional information on partitioning and the Hive profile.

Example: Using the Hive Profile

Use the Hive profile to create a queryable HAWQ external table from the Hive sales_info textfile format table created earlier.

  1. Create a queryable HAWQ external table from the Hive sales_info textfile format table created earlier:

    postgres=# CREATE EXTERNAL TABLE salesinfo_hiveprofile(location text, month text, num_orders int, total_sales float8)
                LOCATION ('pxf://namenode:51200/default.sales_info?PROFILE=Hive')
              FORMAT 'custom' (formatter='pxfwritable_import');
    
  2. Query the table:

    postgres=# SELECT * FROM salesinfo_hiveprofile;
    
       location    | month | num_orders | total_sales
    ---------------+-------+------------+-------------
     Prague        | Jan   |        101 |     4875.33
     Rome          | Mar   |         87 |     1557.39
     Bangalore     | May   |        317 |     8936.99
     ...
    
    

HiveText Profile

Use the HiveText profile to query text format files.

Note: When using the HiveText profile, you must specify a delimiter option in both the LOCATION and FORMAT clauses.

Example: Using the HiveText Profile

Use the PXF HiveText profile to create a queryable HAWQ external table from the Hive sales_info textfile format table created earlier.

  1. Create the external table:

    postgres=# CREATE EXTERNAL TABLE salesinfo_hivetextprofile(location text, month text, num_orders int, total_sales float8)
                 LOCATION ('pxf://namenode:51200/default.sales_info?PROFILE=HiveText&DELIMITER=\x2c')
               FORMAT 'TEXT' (delimiter=E',');
    

    (You can safely ignore the “nonstandard use of escape in a string literal” warning and related messages.)

    Notice that:

    • The LOCATION subclause DELIMITER value is specified in hexadecimal format. \x is a prefix that instructs PXF to interpret the following characters as hexadecimal. 2c is the hex value for the comma character.
    • The FORMAT subclause delimiter value is specified as the single ascii comma character ','. E escapes the character.
  2. Query the external table:

    postgres=# SELECT * FROM salesinfo_hivetextprofile WHERE location="Beijing";
    
     location | month | num_orders | total_sales
    ----------+-------+------------+-------------
     Beijing  | Jul   |        411 |    11600.67
     Beijing  | Dec   |        100 |     4248.41
    (2 rows)
    

HiveRC Profile

The RCFile Hive format is used for row columnar formatted data. The HiveRC profile provides access to RCFile data.

Note: When using the HiveRC profile, you must specify a delimiter option in both the LOCATION and FORMAT clauses.

Example: Using the HiveRC Profile

Use the HiveRC profile to query RCFile-formatted data in Hive tables.

  1. Create a Hive table with RCFile format:

    $ HADOOP_USER_NAME=hdfs hive
    
    hive> CREATE TABLE sales_info_rcfile (location string, month string,
            number_of_orders int, total_sales double)
          ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
          STORED AS rcfile;
    
  2. Insert the data from the sales_info table into sales_info_rcfile:

    hive> INSERT INTO TABLE sales_info_rcfile SELECT * FROM sales_info;
    

    A copy of the sample data set is now stored in RCFile format in sales_info_rcfile.

  3. Perform a Hive query on sales_info_rcfile to verify that the data was loaded successfully:

    hive> SELECT * FROM sales_info_rcfile;
    
  4. Use the PXF HiveRC profile to create a queryable HAWQ external table from the Hive sales_info_rcfile table created in the previous step. You must specify a delimiter option in both the LOCATION and FORMAT clauses.:

    postgres=# CREATE EXTERNAL TABLE salesinfo_hivercprofile(location text, month text, num_orders int, total_sales float8)
                 LOCATION ('pxf://namenode:51200/default.sales_info_rcfile?PROFILE=HiveRC&DELIMITER=\x2c')
               FORMAT 'TEXT' (delimiter=E',');
    

    (Again, you can safely ignore the “nonstandard use of escape in a string literal” warning and related messages.)

  5. Query the external table:

    postgres=# SELECT location, total_sales FROM salesinfo_hivercprofile;
    
       location    | total_sales
    ---------------+-------------
     Prague        |     4875.33
     Rome          |     1557.39
     Bangalore     |     8936.99
     Beijing       |    11600.67
     ...
    

Accessing Parquet-Format Hive Tables

The PXF Hive profile supports both non-partitioned and partitioned Hive tables that use the Parquet storage format in HDFS. Simply map the table columns using equivalent HAWQ data types. For example, if a Hive table is created using:

hive> CREATE TABLE hive_parquet_table (fname string, lname string, custid int, acctbalance double)
        STORED AS parquet;

Define the HAWQ external table using:

postgres=# CREATE EXTERNAL TABLE pxf_parquet_table (fname text, lname text, custid int, acctbalance double precision)
    LOCATION ('pxf://namenode:51200/hive-db-name.hive_parquet_table?profile=Hive')
    FORMAT 'CUSTOM' (formatter='pxfwritable_import');

And query the HAWQ external table using:

postgres=# SELECT fname,lname FROM pxf_parquet_table;

Hive Profile Complex Data Type Example

This example employs the Hive profile and the array and map complex types, specifically an array of integers and a string key/value pair map.

The data schema for this example includes fields with the following names and data types:

Field Name Data Type
index int
name string
intarray array of integers
propmap map of string key and value pairs

When specifying an array field in a Hive table, you must identify the terminator for each item in the collection. Similarly, the map key termination character must also be specified.

  1. Create a text file from which you will load the data set:

    $ vi /tmp/pxf_hive_complex.txt
    
  2. Add the following data to pxf_hive_complex.txt. The data uses a comma , to separate field values, the percent symbol % to separate collection items, and a : to terminate map key values:

    3,Prague,1%2%3,zone:euro%status:up
    89,Rome,4%5%6,zone:euro
    400,Bangalore,7%8%9,zone:apac%status:pending
    183,Beijing,0%1%2,zone:apac
    94,Sacramento,3%4%5,zone:noam%status:down
    101,Paris,6%7%8,zone:euro%status:up
    56,Frankfurt,9%0%1,zone:euro
    202,Jakarta,2%3%4,zone:apac%status:up
    313,Sydney,5%6%7,zone:apac%status:pending
    76,Atlanta,8%9%0,zone:noam%status:down
    
  3. Create a Hive table to represent this data:

    $ HADOOP_USER_NAME=hdfs hive
    
    hive> CREATE TABLE table_complextypes( index int, name string, intarray ARRAY<int>, propmap MAP<string, string>)
             ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
             COLLECTION ITEMS TERMINATED BY '%'
             MAP KEYS TERMINATED BY ':'
             STORED AS TEXTFILE;
    

    Notice that:

    • FIELDS TERMINATED BY identifies a comma as the field terminator.
    • The COLLECTION ITEMS TERMINATED BY subclause specifies the percent sign as the collection items (array item, map key/value pair) terminator.
    • MAP KEYS TERMINATED BY identifies a colon as the terminator for map keys.
  4. Load the pxf_hive_complex.txt sample data file into the table_complextypes table you just created:

    hive> LOAD DATA LOCAL INPATH '/tmp/pxf_hive_complex.txt' INTO TABLE table_complextypes;
    
  5. Perform a query on Hive table table_complextypes to verify that the data was loaded successfully:

    hive> SELECT * FROM table_complextypes;
    
    3   Prague  [1,2,3] {"zone":"euro","status":"up"}
    89  Rome    [4,5,6] {"zone":"euro"}
    400 Bangalore   [7,8,9] {"zone":"apac","status":"pending"}
    ...
    
  6. Use the PXF Hive profile to create a queryable HAWQ external table representing the Hive table_complextypes:

    postgres=# CREATE EXTERNAL TABLE complextypes_hiveprofile(index int, name text, intarray text, propmap text)
                 LOCATION ('pxf://namenode:51200/table_complextypes?PROFILE=Hive')
               FORMAT 'CUSTOM' (formatter='pxfwritable_import');
    

    Notice that the integer array and map complex types are mapped to type text.

  7. Query the external table:

    postgres=# SELECT * FROM complextypes_hiveprofile;
    
     index |    name    | intarray |              propmap
    -------+------------+----------+------------------------------------
         3 | Prague     | [1,2,3]  | {"zone":"euro","status":"up"}
        89 | Rome       | [4,5,6]  | {"zone":"euro"}
       400 | Bangalore  | [7,8,9]  | {"zone":"apac","status":"pending"}
       183 | Beijing    | [0,1,2]  | {"zone":"apac"}
        94 | Sacramento | [3,4,5]  | {"zone":"noam","status":"down"}
       101 | Paris      | [6,7,8]  | {"zone":"euro","status":"up"}
        56 | Frankfurt  | [9,0,1]  | {"zone":"euro"}
       202 | Jakarta    | [2,3,4]  | {"zone":"apac","status":"up"}
       313 | Sydney     | [5,6,7]  | {"zone":"apac","status":"pending"}
        76 | Atlanta    | [8,9,0]  | {"zone":"noam","status":"down"}
    (10 rows)
    

    intarray and propmap are each serialized as text strings.

Partition Filtering

The PXF Hive plug-in supports the Hive partitioning feature and directory structure. This enables partition exclusion on selected HDFS files comprising the Hive table. To use the partition filtering feature to reduce network traffic and I/O, run a PXF query using a WHERE clause that refers to a specific partition in the partitioned Hive table.

To take advantage of PXF partition filtering push-down, the Hive and PXF partition field names should be the same. Otherwise, PXF ignores partition filtering and the filtering is performed on the HAWQ side, impacting performance.

Note: The Hive plug-in filters only on partition columns, not on other table attributes.

Configure Partition Filtering Push-Down

PXF partition filtering push-down is enabled by default. To disable PXF partition filtering push-down, set the pxf_enable_filter_pushdown HAWQ server configuration parameter to off:

postgres=# SHOW pxf_enable_filter_pushdown;
 pxf_enable_filter_pushdown
-----------------------------
 on
(1 row)
postgres=# SET pxf_enable_filter_pushdown=off;

Example: Using the Hive Profile to Access Partitioned Homogenous Data

In this example, you will use the Hive profile to query a Hive table named sales_part you partition on delivery_state and delivery_city fields. You will then create a HAWQ external table to query sales_part, including specific examples illustrating filter pushdown.

  1. Create a Hive table named sales_part with two partition columns, delivery_state and delivery_city:

    hive> CREATE TABLE sales_part (name string, type string, supplier_key int, price double)
            PARTITIONED BY (delivery_state string, delivery_city string)
            ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';
    
  2. Load data into this Hive table and add some partitions:

    hive> INSERT INTO TABLE sales_part 
            PARTITION(delivery_state = 'CALIFORNIA', delivery_city = 'Fresno') 
            VALUES ('block', 'widget', 33, 15.17);
    hive> INSERT INTO TABLE sales_part 
            PARTITION(delivery_state = 'CALIFORNIA', delivery_city = 'Sacramento') 
            VALUES ('cube', 'widget', 11, 1.17);
    hive> INSERT INTO TABLE sales_part 
            PARTITION(delivery_state = 'NEVADA', delivery_city = 'Reno') 
            VALUES ('dowel', 'widget', 51, 31.82);
    hive> INSERT INTO TABLE sales_part 
            PARTITION(delivery_state = 'NEVADA', delivery_city = 'Las Vegas') 
            VALUES ('px49', 'pipe', 52, 99.82);
    
  3. Query the sales_part table:

    hive> SELECT * FROM sales_part;
    

    SELECT * statement on a Hive partitioned table shows the partition fields at the end of the record.

  4. Examine the Hive/HDFS directory structure for the sales_part table:

    $ sudo -u hdfs hdfs dfs -ls -R /apps/hive/warehouse/sales_part
    /apps/hive/warehouse/sales_part/delivery_state=CALIFORNIA/delivery_city=Fresno/
    /apps/hive/warehouse/sales_part/delivery_state=CALIFORNIA/delivery_city=Sacramento/
    /apps/hive/warehouse/sales_part/delivery_state=NEVADA/delivery_city=Reno/
    /apps/hive/warehouse/sales_part/delivery_state=NEVADA/delivery_city=Las Vegas/
    
  5. Create a PXF external table to read the partitioned sales_part Hive table. To take advantage of partition filter push-down, define fields corresponding to the Hive partition fields at the end of the CREATE EXTERNAL TABLE attribute list.

    $ psql -d postgres
    
    postgres=# CREATE EXTERNAL TABLE pxf_sales_part(
                 item_name TEXT, item_type TEXT, 
                 supplier_key INTEGER, item_price DOUBLE PRECISION, 
                 delivery_state TEXT, delivery_city TEXT)
               LOCATION ('pxf://namenode:51200/sales_part?Profile=Hive')
               FORMAT 'CUSTOM' (FORMATTER='pxfwritable_import');
    
  6. Query the table:

    postgres=# SELECT * FROM pxf_sales_part;
    
  7. Perform another query (no pushdown) on pxf_sales_part to return records where the delivery_city is Sacramento and  item_name is cube

    postgres=# SELECT * FROM pxf_sales_part WHERE delivery_city = 'Sacramento' AND item_name = 'cube';
    

    The query filters the delivery_city partition Sacramento. The filter on  item_name is not pushed down, since it is not a partition column. It is performed on the HAWQ side after all the data in the Sacramento partition is transferred for processing.

  8. Query (with pushdown) for all records where delivery_state is CALIFORNIA:

    postgres=# SET pxf_enable_filter_pushdown=on;
    postgres=# SELECT * FROM pxf_sales_part WHERE delivery_state = 'CALIFORNIA';
    

    This query reads all of the data in the CALIFORNIA delivery_state partition, regardless of the city.

Example: Using the Hive Profile to Access Partitioned Heterogenous Data

The Hive profile supports multiple data format types. This support enables you to query a partitioned Hive table that may be composed of data of different formats.

In this example, you will use the Hive profile both directly and indirectly via PXF HCatalog integration to query a partitioned Hive external table. The table is composed of the HDFS data files associated with the sales_info (text format) and sales_info_rcfile (RC format) Hive tables you created in previous exercises. You will partition the data by year, assigning the data from sales_info to the year 2013, and the data from sales_info_rcfile to the year 2016. (Ignore at the moment the fact that the tables contain the same data.)

  1. Create a Hive external table named hive_multiformpart that is partitioned by a string field named year:

    $ HADOOP_USER_NAME=hdfs hive
    
    hive> CREATE EXTERNAL TABLE hive_multiformpart( location string, month string, number_of_orders int, total_sales double)
            PARTITIONED BY( year string )
            ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';
    
  2. Describe the sales_info and sales_info_rcfile tables, making note of the HDFS file locations:

    hive> DESCRIBE EXTENDED sales_info;
    hive> DESCRIBE EXTENDED sales_info_rcfile;
    
  3. Create partitions in the hive_multiformpart table for the HDFS locations associated with each of the sales_info and sales_info_rcfile tables:

    hive> ALTER TABLE hive_multiformpart ADD PARTITION (year = '2013') LOCATION 'hdfs://namenode:8020/apps/hive/warehouse/sales_info';
    hive> ALTER TABLE hive_multiformpart ADD PARTITION (year = '2016') LOCATION 'hdfs://namenode:8020/apps/hive/warehouse/sales_info_rcfile';
    
  4. Explicitly identify the file format of the partition associated with the sales_info_rcfile table:

    hive> ALTER TABLE hive_multiformpart PARTITION (year='2016') SET FILEFORMAT RCFILE;
    

    You need not specify the file format of the partition associated with the sales_info table, as TEXTFILE format is the default.

  5. Query the hive_multiformpart table:

    hive> SELECT * from hive_multiformpart;
    ...
    Bangalore   Jul 271 8320.55 2016
    Beijing Dec 100 4248.41 2016
    Prague  Jan 101 4875.33 2013
    Rome    Mar 87  1557.39 2013
    ...
    hive> SELECT * from hive_multiformpart WHERE year='2013';
    hive> SELECT * from hive_multiformpart WHERE year='2016';
    
  6. Show the partitions defined for the hive_multiformpart table and exit hive:

    hive> SHOW PARTITIONS hive_multiformpart;
    year=2013
    year=2016
    hive> quit;
    
  7. Start the psql subsystem:

    $ psql -d postgres
    
  8. Use PXF HCatalog integration to query the Hive hive_multiformpart external table you created in the previous steps:

    postgres=# SELECT * FROM hcatalog.default.hive_multiformpart;
    
       location    | month | number_of_orders | total_sales | year 
    ---------------+-------+------------------+-------------+------
     ...
     Prague        | Dec   |              333 |     9894.77 | 2013
     Bangalore     | Jul   |              271 |     8320.55 | 2013
     Beijing       | Dec   |              100 |     4248.41 | 2013
     Prague        | Jan   |              101 |     4875.33 | 2016
     Rome          | Mar   |               87 |     1557.39 | 2016
     Bangalore     | May   |              317 |     8936.99 | 2016
     ...
    
  9. Use the PXF Hive profile to create a readable HAWQ external table derived from the Hive hive_multiformpart external table you created in the previous steps:

    postgres=# CREATE EXTERNAL TABLE pxf_multiformpart(location text, month text, num_orders int, total_sales float8, year text)
                 LOCATION ('pxf://namenode:51200/default.hive_multiformpart?PROFILE=Hive')
               FORMAT 'CUSTOM' (formatter='pxfwritable_import');
    
  10. Query the PXF external table:

    postgres=# SELECT * FROM pxf_multiformpart;
    
       location    | month | num_orders | total_sales | year 
    ---------------+-------+------------+-------------+--------
     ....
     Prague        | Dec   |        333 |     9894.77 | 2013
     Bangalore     | Jul   |        271 |     8320.55 | 2013
     Beijing       | Dec   |        100 |     4248.41 | 2013
     Prague        | Jan   |        101 |     4875.33 | 2016
     Rome          | Mar   |         87 |     1557.39 | 2016
     Bangalore     | May   |        317 |     8936.99 | 2016
     ....
    
  11. Perform a second query to calculate the total number of orders for the year 2013:

    postgres=# SELECT sum(num_orders) FROM pxf_multiformpart WHERE month='Dec' AND year='2013';
     sum 
    -----
     433
    

Using PXF with Hive Default Partitions

This topic describes a difference in query results between Hive and PXF queries when Hive tables use a default partition. When dynamic partitioning is enabled in Hive, a partitioned table may store data in a default partition. Hive creates a default partition when the value of a partitioning column does not match the defined type of the column (for example, when a NULL value is used for any partitioning column). In Hive, any query that includes a filter on a partition column excludes any data that is stored in the table’s default partition.

Similar to Hive, PXF represents a table’s partitioning columns as columns that are appended to the end of the table. However, PXF translates any column value in a default partition to a NULL value. This means that a HAWQ query that includes an IS NULL filter on a partitioning column can return different results than the same Hive query.

Consider a Hive partitioned table that is created with the statement:

hive> CREATE TABLE sales (order_id bigint, order_amount float) PARTITIONED BY (xdate date);

The table is loaded with five rows that contain the following data:

1.0    1900-01-01
2.2    1994-04-14
3.3    2011-03-31
4.5    NULL
5.0    2013-12-06

The insertion of row 4 creates a Hive default partition, because the partition column xdate contains a null value.

In Hive, any query that filters on the partition column omits data in the default partition. For example, the following query returns no rows:

hive> SELECT * FROM sales WHERE xdate IS null;

However, if you map this table as a PXF external table in HAWQ, all default partition values are translated into actual NULL values. In HAWQ, executing the same query against the PXF table returns row 4 as the result, because the filter matches the NULL value.

Keep this behavior in mind when executing IS NULL queries on Hive partitioned tables.