Using Oracle External Tables To Access Oracle NoSQL Database Data

This guide walks you through the usage of Oracle External Tables to read data from an Oracle NoSQL Database into an Oracle Database. The end result is that you can query (read) the NoSQL Database data while accessing the Oracle Database.

This document only provides an example walk-through of this feature. For a more complete description of using External Tables to read an Oracle NoSQL Database, see the Package oracle.kv.exttab Description.

Assumptions

This guide assumes:

You have an Oracle Database instance running and accessible.
You have sysdba privileges on that instance.
You are familiar with Oracle Database External Table concepts.
You are able to compile and execute a Java program.
You have an Oracle NoSQL Database running (either the single-process "lite" version or a multi-node cluster).
You are familiar with the NoSQL Database Java API.

Introduction

The Oracle Database External Table feature allows a user to create a table that reads data from one or more sources which are external to the Oracle Database. These external sources are usually one or more flat text files, but in this case you will be using an Oracle NoSQL Database as the external data source. The NoSQL database is read with the aid of a preprocessor utility.

To use this feature, you define an External Table with one or more Location Files and the nosql_stream utility specified as the External Table PREPROCESSOR. After the External Table is declared to Oracle, but prior to invoking a SELECT command, the user runs a NoSQL Database "publish" utility, passing it several parameters:

Connection information for both the Oracle Database and Oracle NoSQL Database instances.
The name of the Oracle Database External Table.
Selection information about which records in the ONDB to process.
(optionally) The name of a Formatter class to be used for converting the K/V pairs from the NoSQL record format to the External Table format.

The publish utility then writes this information into the External Table Location File(s). Note that you only have to run the publish utility once. After that, you only need to run the publish utility again if you want to change the way the NoSQL Database is accessed (for example, using a different key prefix, or if you change the port or the rep nodes where you access the database).

Once the publish utility has been run, you can query the External Table in the same way as you would query any other Oracle database table.

Define An External Table

Perform the following steps to create an External Table:

Create directory objects in Oracle where the External Table location files will reside and the NoSQL Database exttab/bin directory where the nosql_stream script can be found.
NOTE: Consult with your Oracle DBA regarding the appropriate locations and permissions for these directories. It may be desireable from a security point of view to copy the nosql_stream script from the <KVHOME>/exttab/bin/ directory to some other location.
```
sqlplus / as sysdba
SQL> CREATE DIRECTORY ext_tab AS '<exttab_pathname>';
SQL> CREATE DIRECTORY nosql_bin_dir AS '<bin_pathname>';
```
exttab_pathname is the directory containing the Location File(s) for the External Table. This directory does not require a large amount of storage as the Location Files will only ever hold a small amount of configuration data. bin_pathname refers to the exttab/bin/ directory of the NoSQL Database installation.

Grant appropriate permissions to Oracle users needing access to the External Table. In this example, the user accessing the NoSQL Database data with an External Table is nosqluser.

sqlplus / as sysdba
SQL> CREATE USER nosqluser IDENTIFIED BY password;
SQL> GRANT CREATE SESSION TO nosqluser;
SQL> GRANT EXECUTE ON SYS.UTL_FILE TO nosqluser;
SQL> GRANT READ, WRITE ON DIRECTORY ext_tab TO nosqluser;
SQL> GRANT READ, EXECUTE ON DIRECTORY nosql_bin_dir TO nosqluser;
SQL> GRANT CREATE TABLE TO nosqluser;

Define the External Table.

You should do this as the user who will be accessing the External Table, not as sysdba. In this example, create the table as nosqluser.


SQL> CONNECT nosqluser/password
SQL> CREATE TABLE nosql_data (email VARCHAR2(30),
  2                           gender CHAR(1),
  3                           address VARCHAR2(40),
  4                           phone VARCHAR2(20))
  5      ORGANIZATION EXTERNAL
  6          (type oracle_loader
  7           default directory ext_tab
  8           access parameters (records delimited by newline
  9           preprocessor nosql_bin_dir:'nosql_stream'
 10           fields terminated by '|')
 11      LOCATION ('nosql.dat'))
 12      PARALLEL;

Table created.

SQL>

For more information on External Tables and the parameters, see External Tables Access Parameters.

Create Some Sample Data In NoSQL Database

Compile the LoadCookbookData program in the <KVHOME>/examples/externaltables directory:

cd <KVHOME>
javac -classpath lib/kvstore-ee.jar:examples examples/externaltables/*.java

Run the LoadCookbookData program to load some data into the KV Store:
```
java -classpath lib/kvclient.jar:examples externaltables.LoadCookbookData \
     -store <storename> -host <hostname> -port <port> -nops 10
```
-nops specifies the number of records to create. A small number is all that is necessary in order to demonstrate access from External Tables. Optionally, you can pass -delete if you want to delete all previously created data in your KV Store.

Edit The Configuration File

Make a copy of the configuration file in <KVHOME>/examples/externaltables/config.xml and edit your site-specific values for the oracle.kv.exttab.connection.url, oracle.kv.exttab.connection.user, oracle.kv.exttab.connection.wallet_location (optional), oracle.kv.kvstore, and oracle.kv.hosts properties based on your Oracle Database and Oracle NoSQL Database installations.

Publish The Configuration

Run the oracle.kv.exttab.Publish utility to publish the configuration to the External Table Location files.

cd <KVHOME>
java -classpath lib/kvstore.jar:$ORACLE_HOME/jdbc/lib/ojdbc6.jar \
     oracle.kv.exttab.Publish \
     -config <pathname-to-edited-copy-of-config.xml> -publish

If you are using the Oracle wallet as an external password store, then you should also include $ORACLE_HOME/jlib/oraclepki.jar in your classpath. If the process executes successfully, there will be no output. If you have read access to the Location file(s), you can verify the Publish operation by looking inside one to see if the configuration XML is written there. You will see that two additional properties have been added to the XML: oracle.kv.exttab.totalExternalTableFiles and oracle.kv.exttab.externalTableFileNumber. Optionally, you can specify the -verbose argument to the Publish utility to see more verbose (i.e. debugging) output.

Test The `nosql_stream` Script

Edit the <KVHOME>/exttab/bin/nosql_stream script to have the correct values for PATH, KVHOME, and CLASSPATH when the script is run in the execution environment of the Oracle Database server. For this example, CLASSPATH should include the KVHOME/examples directory (in addition to the kvstore.jar).

Test the nosql_stream script by running it in a shell:

$ <KVHOME>/exttab/bin/nosql_stream <exttab_pathname>/nosql.dat

where <exttab_pathname> is the path of the LOCATION files specified earlier in the CREATE DIRECTORY command. You should see output similar to the following:

user6@example.com|F|#6 Example St, Example Town, AZ|666.666.6666
user1@example.com|M|#1 Example St, Example Town, AZ|111.111.1111
user9@example.com|M|#9 Example St, Example Town, AZ|999.999.9999
user0@example.com|F|#0 Example St, Example Town, AZ|000.000.0000
user7@example.com|M|#7 Example St, Example Town, AZ|777.777.7777
user8@example.com|F|#8 Example St, Example Town, AZ|888.888.8888
user5@example.com|M|#5 Example St, Example Town, AZ|555.555.5555
user2@example.com|F|#2 Example St, Example Town, AZ|222.222.2222
user4@example.com|F|#4 Example St, Example Town, AZ|444.444.4444
user3@example.com|M|#3 Example St, Example Town, AZ|333.333.3333

Use The External Table To Read Data From NoSQL Database

Using sqlplus (as nosqluser or whatever user you created the external table with), perform a SELECT on the nosql_data External Table.

SQL> select * from nosql_data;

EMAIL                          G ADDRESS
------------------------------ - ----------------------------------------
PHONE
--------------------
user6@example.com              F #6 Example St, Example Town, AZ
666.666.6666

user1@example.com              M #1 Example St, Example Town, AZ
111.111.1111

user9@example.com              M #9 Example St, Example Town, AZ
999.999.9999
...
SQL>