Oracle® Database Heterogeneous Connectivity Administrator's Guide 10g Release 2 (10.2) Part Number B14232-01 |
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This chapter explains how to use Heterogeneous Services (HS) agents. It contains the following sections:
Copying Data from the Oracle Database Server to the Non-Oracle Database System
Copying Data from the Non-Oracle Database System to the Oracle Database Server
This section explains the generic steps to configure access to a non-Oracle system.
Note:
The instructions for configuring your agent may differ slightly from the following instructions. Please see the installation and user's guide for your specific agent for more complete installation information.The steps for setting up access to a non-Oracle system are:
Step 1: Configure Oracle Net Services to Access Heterogeneous Services Agents
Step 2: Create the Database Link to the Non-Oracle System
To initiate a connection to the non-Oracle system, the Oracle server starts an agent process through the Oracle Net listener. For the Oracle server to be able to connect to the agent, you must perform the following tasks:
Set up an Oracle Net service name for the agent that can be used by the Oracle server. The Oracle Net service name descriptor includes protocol-specific information needed to access the Oracle Net listener. The service name descriptor must include the (HS=OK)
clause to ensure that the connection uses Oracle Heterogeneous Services. The description of this service name is defined in tnsnames.ora
, the Oracle Names server, or in third-party name servers using the Oracle naming adapter.
The following is a sample entry for a service name in the tnsnames.ora
file:
Sybase_sales= (DESCRIPTION= (ADDRESS=(PROTOCOL=tcp) (HOST=sales) (PORT=1521) ) (CONNECT_DATA = (SERVICE_NAME=SalesDB) ) (HS = OK) )
Set up the listener on the gateway to listen for incoming requests from the Oracle server and spawn Heterogeneous Services agents. Then, start the listener on the gateway system.
The following is a sample entry for the listener in listener.ora
:
LISTENER =
(ADDRESS_LIST =
(ADDRESS= (PROTOCOL=tcp)
(HOST = sales)
(PORT = 1521)
)
)
...
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC = (SID_NAME=SalesDB)
(ORACLE_HOME=/home/oracle/megabase/9.0.1)
(PROGRAM=tg4mb80)
(ENVS=LD_LIBRARY_PATH=non_oracle_system_lib_directory)
)
)
The value associated with the PROGRAM
keyword defines the name of the agent executable. The full path of the directory which contains the DLLs that are loaded by the Heterogeneous Services agent is specified by LD_LIBRARY_PATH
. You must use the same SID_NAME
as used in the name of the initialization parameter file for the agent.
See Also:
Oracle Database Net Services Administrator's Guide for more information about configuring the Oracle Net listener and a net service name for heterogeneous connectivity
Section 4.2.1 about the initialization parameter file
Section 5.3 for information about starting multithreaded agents
To create a database link to the non-Oracle system, use the CREATE DATABASE LINK
statement. The service name that is used in the USING
clause of the CREATE DATABASE LINK
statement is the Oracle Net service name.
Use quotes with the username and password to avoid differences in case-sensitive behavior between Oracle and non-Oracle databases. For example:
CREATE DATABASE LINK sales CONNECT TO "sales1" IDENTIFIED BY "Sales1" USING 'Sybase_sales';
To test the connection to the non-Oracle system, use the database link in a SQL or PL/SQL statement. If the non-Oracle system is a SQL-based database, you can execute a SELECT
statement from an existing table or view using the database link. For example:
SELECT * FROM product@sales WHERE product_name like '%pencil%';
When you try to access the non-Oracle system for the first time, the Heterogeneous Services agent uploads information into the Heterogeneous Services data dictionary. The uploaded information includes:
Type of Data | Explanation |
---|---|
Capabilities of the non-Oracle system | The agent specifies whether it can perform a join or a GROUP BY . |
SQL translation information | The agent specifies how to translate Oracle functions and operators into functions and operators of the non-Oracle system. |
Data dictionary translations | To make the data dictionary information of the non-Oracle system available just as if it were an Oracle data dictionary, the agent specifies how to translate Oracle data dictionary tables into tables and views of the non-Oracle system. |
Note:
Most agents upload information into the Oracle data dictionary automatically the first time they are accessed. Some agent vendors may provide scripts, however, that you must run on the Oracle server.Configure the gateway using initialization parameters. This is done by creating an initialization file and setting the desired parameters in this file. See Section 2.5 for configuration information.
Heterogeneous Services initialization parameters are distinct from Oracle database server initialization parameters. Heterogeneous Services initialization parameters are set in the Heterogeneous Services initialization file and not in the Oracle database initialization parameter file (init.ora
file). There is a Heterogeneous Services initialization file for each gateway instance.
The name of the file is init
sid
.ora
, where sid
is the Oracle system identifier used for the gateway.
In the case of Generic Connectivity, the Heterogeneous Services initialization file is located in the directory $ORACLE_HOME/hs/admin
. In the case of Transparent Gateways, it is located in the directory $ORACLE_HOME/
product_name
/admin
where product_name
reflects the name of the product. For example, the Sybase gateway initialization file is located in the directory $ORACLE_HOME/tg4sybs/admin
.
The initialization file contains a list of initialization parameter settings each of which should be on a separate line. The syntax to set an initialization parameter is as follows:
[SET] [PRIVATE] parameter = parameter_value
The SET
and PRIVATE
keywords are optional. If the SET
keyword is present, the variable is also set in the environment. If the PRIVATE
keyword is present, the parameter is not uploaded to the server. Oracle recommends that you do not use the PRIVATE
keyword unless the initialization parameter value contains sensitive information (like a password) that should not be sent over the network from the gateway to the Oracle server.
In the initialization parameter syntax, all keywords (SET
, PRIVATE
, and IFILE
) are case-insensitive. Initialization parameter names and values are case-sensitive. Most initialization parameter names are uppercase. String values for Heterogeneous Services parameters must be lowercase. Exceptions to this rule are explicitly noted.
Another initialization file can be included in an Heterogeneous Services initialization file by using the IFILE
directive. The syntax for this is as follows:
IFILE = path_name
Initialization parameters may contain sensitive information, such as user IDs or passwords. Initialization parameters are stored in plain text files and are insecure. An encryption feature has been added to Heterogeneous Services making it possible to encrypt parameter values. This is done through the tg4pwd
utility. To use this feature requires setting the value of a parameter in the initialization file to an unquoted asterisk (*). For example:
HD_FDS_CONNECT_INFO = *
With the value set to this security marker, all Heterogeneous Services agents know that the real value will be stored in a related, encrypted password file. The name of this file will be init
sid
.pwd
, where sid
is the Oracle system identifier used for the gateway. This file is created by the tg4pwd
utility in the current directory containing the initialization file. Running the utility prompts for the real value of the parameter, which the utility will encrypt and store in the password file. It should be noted that encrypted initialization parameters are implicitly treated as PRIVATE
parameters and are not uploaded to the server.
The tg4pwd
utility is used to encrypt initialization parameters that would normally be stored in the initialization parameter file in plain text. The utility works by reading the initialization parameter file in the current directory and looking for parameters having a security marker for the value. The security marker is an unquoted asterisk (*). This designates that the value of this parameter is to be stored in an encrypted form in a password file. The following is an example of an initialization parameter set to this value:
HS_FDS_CONNECT_INFO = *
The initialization parameter file in the current directory is first edited to set the value of the parameter to this security marker. Then the utility is run, specifying the gateway SID on the command line, with an optional user ID to designate a different owner of the encrypted information. The utility reads the initialization parameter file and prompts you to enter the real values that are to be encrypted. The syntax of the command is:
tg4pwd [sid] {userid}
Where [
sid
]
is the SID of the gateway and {
userid
}
is an optional user ID used to encrypt the contents. If no user ID is specified, then the current user's ID is used. Values are encrypted using this ID. In order to decrypt the values, the agent must be run as that user. The following example assumes a gateway SID of SYBASE:
tg4pwd SYBASE ORACLE Gateway Password Utility Constructing password file for Gateway SID SYBASE Enter the value for HS_FDS_CONNECT_INFO sybasew
In the previous example, the initialization parameter file, initSYBASE.ora
, is read. The parameter, HS_FDS_CONNECT_INFO
, is identified as requiring encryption. Enter the value (for example, sybasew
) and presses enter. If more parameters require encryption, they are prompted for in turn. The encrypted data is stored in the same directory as the initialization file.Any initialization parameters needing encryption should be encrypted before using the Gateway or Generic Connectivity.
Gateway initialization parameters can be divided into two groups. One is a set of generic initialization parameters that are common to all gateways and the other is a set of initialization parameters that are specific to individual gateways. The following generic initialization parameters are the only initialization parameters discussed in this document:
HS_CALL_NAME
HS_COMMIT_POINT_STRENGTH
HS_DB_DOMAIN
HS_DB_INTERNAL_NAME
HS_DB_NAME
HS_DESCRIBE_CACHE_HWM
HS_FDS_CONNECT_INFO
HS_FDS_DEFAULT_SCHEMA_NAME
HS_FDS_SHAREABLE_NAME
HS_FDS_TRACE_LEVEL
HS_LANGUAGE
HS_LONG_PIECE_TRANSFER_SIZE
HS_NLS_DATE_FORMAT
HS_NLS_DATE_LANGUAGE
HS_NLS_NCHAR
HS_NLS_NUMERIC_CHARACTERS
HS_NLS_TIMESTAMP_FORMAT
HS_NLS_TIMESTAMP_TZ_FORMAT
HS_OPEN_CURSORS
HS_ROWID_CACHE_SIZE
HS_RPC_FETCH_REBLOCKING
HS_RPC_FETCH_SIZE
HS_TIME_ZONE
Do not use the PRIVATE
keyword when setting any of these parameters. Using the PRIVATE
keyword prevents the parameter from being uploaded to the server and can cause errors in SQL processing. None of these parameters needs to be set in the environment, so you do not need to use the SET
keyword.
See Also:
Appendix A, "Heterogeneous Services Initialization Parameters" for descriptions of the generic Heterogeneous Services initialization parameters
Individual gateway documentation for the list of initialization parameters specific to a gateway
When an application fetches data from a non-Oracle system using Heterogeneous Services, data is transferred:
From the non-Oracle system to the agent process.
From the agent process to the Oracle database server.
From the Oracle database server to the application.
Oracle optimizes all three data transfers, as illustrated in Figure 4-1.
This section contains the following topics:
Using OCI, an Oracle Precompiler, or Another Tool for Array Fetches
Controlling the Array Fetch Between the Oracle Database Server and the Agent
Controlling the Array Fetch Between Agent and Non-Oracle Server
You can optimize data transfers between your application and the Oracle server by using array fetches. See your application development tool documentation for information about array fetching and how to specify the amount of data to be sent and each network round-trip.
When Oracle retrieves data from a non-Oracle system, the Heterogeneous Services initialization parameter, HS_RPC_FETCH_SIZE
, defines the number of bytes sent for each fetch between the agent and the Oracle server. The agent fetches data from the non-Oracle system until one of the following occurs:
It has accumulated the specified number of bytes to send back to the Oracle database server.
The last row of the result set is fetched from the non-Oracle system.
The initialization parameter, HS_FDS_FETCH_ROWS
, determines the number of rows to be retrieved from a non-Oracle system. Note that the array fetch must be supported by the agent. See your agent-specific documentation to ensure that your agent supports array fetching.
By default, an agent fetches data from the non-Oracle system until it has enough data retrieved to send back to the server. It continues until the number of bytes fetched from the non-Oracle system is equal to or higher than the value of HS_RPC_FETCH_SIZE
initialization parameter. In other words, the agent reblocks the data between the agent and the Oracle database server in sizes defined by the value of the HS_RPC_FETCH_SIZE
initialization parameter.
When the non-Oracle system supports array fetches, you can immediately send the data fetched from the non-Oracle system by the array fetch to the Oracle database server without waiting until the exact value of the HS_RPC_FETCH_SIZE
initialization parameter is reached. That is, you can stream the data from the non-Oracle system to the Oracle database server and disable reblocking by setting the value of the HS_RPC_FETCH_REBLOCKING
initialization parameter to OFF
.
For example, assume that you set HS_RPC_FETCH_SIZE
to 64 kilobytes (KB) and HS_FDS_FETCH_ROWS
to 100 rows. Also assume that each row is approximately 600 bytes in size, so that the 100 rows are approximately 60 KB. When the HS_RPC_FETCH_REBLOCKING
initialization parameter is set to ON
, the agent starts fetching 100 rows from the non-Oracle system.
Because there is only 60 KB of data in the agent, the agent does not send the data back to the Oracle database server. Instead, the agent fetches the next 100 rows from the non-Oracle system. Because there is now 120 KB of data in the agent, the first 64 KB can be sent back to the Oracle database server.
Now there is 56 KB of data left in the agent. The agent fetches another 100 rows from the non-Oracle system before sending the next 64 KB of data to the Oracle database server. By setting the HS_RPC_FETCH_REBLOCKING
initialization parameter to OFF
, the first 100 rows are immediately sent back to the Oracle database server.
Registration is an operation through which Oracle stores information about an agent in the data dictionary. Agents do not have to be registered. If an agent is not registered, Oracle stores information about the agent in memory instead of in the data dictionary. When a session involving an agent terminates, this information ceases to be available.
Self-registration is an operation in which a database administrator sets an initialization parameter that lets the agent automatically upload information into the data dictionary. Self-registration occurs when the HS_AUTOREGISTER
initialization parameter is set to TRUE
(default).
Note:
HS_AUTOREGISTER
is an Oracle initialization parameter that you set in the init.ora
file; it is not a Heterogeneous Services initialization parameter that is set in the gateway initialization file.This section contains the following topics:
To ensure correct operation over heterogeneous database links, agent self-registration automates updates to Heterogeneous Services configuration data that describe agents on remote hosts. Agent self-registration is the default behavior. If you do not want to use the agent self-registration feature, set the HS_AUTOREGISTER
initialization parameter to FALSE
.
Both the server and the agent rely on three types of information to configure and control operation of the Heterogeneous Services connection. These three sets of information are collectively called HS configuration data:
Heterogeneous Services Configuration Data | Description |
---|---|
Heterogeneous Services initialization parameters | Provide control over various connection-specific details of operation. |
Capability definitions | Identify details like SQL language features supported by the non-Oracle data source. |
Data dictionary translations | Map references to Oracle data dictionary tables and views into equivalents specific to the non-Oracle data source. |
HS configuration data is stored in the data dictionary of the Oracle database server. Because the agent may be remote and may therefore be administered separately, several circumstances can lead to configuration mismatches between servers and agents. For example:
An agent can be newly installed on a separate machine so that the server has no Heterogeneous Services data dictionary content to represent the agent's Heterogeneous Services configuration data.
A server can be newly installed and lack the necessary Heterogeneous Services configuration data for existing agents and non-Oracle data stores.
A non-Oracle instance can be upgraded from an older version to a newer version, requiring modification of the Heterogeneous Services configuration data.
A Heterogeneous Services agent at a remote site can be upgraded to a new version or patched, requiring modification of the Heterogeneous Services configuration data.
A database administrator (DBA) at the non-Oracle site can change the agent setup, possibly for tuning or testing purposes, in a manner which affects Heterogeneous Services configuration data.
Agent self-registration permits successful operation of Heterogeneous Services in all these scenarios. Specifically, agent self-registration enhances interoperability between any Oracle database server and any Heterogeneous Services agent (if each is Version 8.0.3 or higher). The basic mechanism for this functionality is the ability to upload Heterogeneous Services configuration data from agents to servers.
Self-registration provides automatic updating of Heterogeneous Services configuration data residing in the Oracle database server data dictionary. This update ensures that the agent self-registration uploads need to be done only once, on the initial use of a previously unregistered agent. Instance information is uploaded on each connection, not stored in the server data dictionary.
The Heterogeneous Services agent self-registration feature can perform the following tasks:
Identify the agent and the non-Oracle data store to the Oracle database server
Permit agents to define Heterogeneous Services initialization parameters for use both by the agent and connected Oracle servers
Upload capability definitions and data dictionary translations, if available, from a Heterogeneous Services agent during connection initialization
Note:
The upload of class information occurs only when the class is undefined in the server data dictionary. Similarly, instance information is uploaded only if the instance is undefined in the server data dictionary.The information required for agent self-registration is accessed in the server data dictionary by using these agent-supplied names:
FDS_CLASS
FDS_CLASS_VERSION
See Also:
Section 4.10, "Using Heterogeneous Services Data Dictionary Views" to learn how to use the Heterogeneous Services data dictionary viewsFDS_CLASS
and FDS_CLASS_VERSION
are defined by Oracle or by third-party vendors for each individual Heterogeneous Services agent and version. Oracle Heterogeneous Services concatenates these names to form FDS_CLASS_NAME
, which is used as a primary key to access class information in the server data dictionary.
FDS_CLASS
should specify the type of non-Oracle data store to be accessed and FDS_CLASS_VERSION
should specify a version number for both the non-Oracle data store and the agent that connects to it. Note that when any component of an agent changes, FDS_CLASS_VERSION
must also change to uniquely identify the new release.
Note:
This information is uploaded when you initialize each connection.Instance-Specific Information can be stored in the server data dictionary. The instance name, FDS_INST_NAME
, is configured by the database administrator (DBA) who administers the agent. How the DBA performs this configuration depends on the specific agent in use.
The Oracle database server uses FDS_INST_NAME
to look up instance-specific configuration information in its data dictionary. Oracle uses the value as a primary key for columns of the same name in these views:
FDS_INST_INIT
FDS_INST_CAPS
FDS_INST_DD
Server data dictionary accesses that use FDS_INST_NAME
also use FDS_CLASS_NAME
to uniquely identify configuration information rows. For example, if you port a database from class Sybase816 to class Sybase817, both databases can simultaneously operate with instance name SCOTT
and use separate sets of configuration information.
Unlike class information, instance information is not automatically self-registered in the server data dictionary:
If available, instance information is always uploaded by the agent. However, it is never stored in the server data dictionary. Instead, the information is kept in memory and it is only valid for that connection.
If the server data dictionary contains instance information, it represents the DBA's defined setup details which correspond to the instance configuration. Data dictionary defined instance information takes precedence over class information. However, uploaded instance information takes precedence over data dictionary defined instance information.
The HS_AUTOREGISTER
Oracle database server initialization parameter enables or disables automatic self-registration of Heterogeneous Services agents. Note that this parameter is specified in the Oracle initialization parameter file, not the agent initialization file. For example, you can set the parameter as follows:
HS_AUTOREGISTER = TRUE
When set to TRUE
, the agent uploads information describing a previously unknown agent class or a new agent version into the server's data dictionary.
Oracle recommends that you use the default value for this parameter (TRUE
), which ensures that the server's data dictionary content always correctly represents definitions of class capabilities and data dictionary translations as used in Heterogeneous Services connections.
See Also:
Oracle Database Reference for a description of this parameterTo disable agent self-registration, set the HS_AUTOREGISTER
initialization parameter as follows:
HS_AUTOREGISTER = FALSE
Disabling agent self-registration means that agent information is not stored in the data dictionary. Consequently, the Heterogeneous Services data dictionary views are not useful sources of information. Nevertheless, the Oracle server still requires information about the class and instance of each agent. If agent self-registration is disabled, the server stores this information in local memory.
Heterogeneous Services and the gateway rewrite SQL statements when the statements need to be translated or postprocessed.
For the following examples, assume the INITCAP
function is not supported in the non-Oracle database. Consider a program that requests the following from the non-Oracle database. For example:
SELECT "COLUMN_A" FROM "test"@remote_db WHERE "COLUMN_A" = INITCAP("COLUMN_B");
The non-Oracle database does not recognize the INITCAP
function, so the Oracle database server fetches the data from the table test
in the remote database and filters the results locally. The gateway rewrites the SELECT
statement as follows:
SELECT "COLUMN_A", "COLUMN_B" FROM "test"@remote_db;
The results of the query are sent from the gateway to Oracle and are filtered by the Oracle database server.
If a string literal or bind variable is supplied in place of "COLUMN_B"
as shown in the previous example, the Heterogeneous Services component of the Oracle server would apply the INITCAP
function before sending the SQL command to the gateway. For example, if the following SQL command is issued:
SELECT "COLUMN_A" FROM "test"@remote_db WHERE "COLUMN_A" = INITCAP('jones');
The following SQL command would be sent to the gateway:
SELECT "COLUMN_A" FROM "test"@remote_db WHERE "COLUMN_A" = 'Jones';
Consider the following UPDATE
request:
UPDATE "test"@remote_db SET "COLUMN_A" = 'new_value' WHERE "COLUMN_A" = INITCAP("COLUMN_B");
In this case, the Oracle database server and the gateway cannot compensate for the lack of support at the non-Oracle side, so an error is issued.
If a string literal or bind variable is supplied in place of "COLUMN_B"
as shown in the preceding example, the Heterogeneous Services component of the Oracle server would apply the INITCAP
function before sending the SQL command to the gateway. For example, if the following SQL command is issued:
UPDATE "test"@remote_db SET "COLUMN_A" = 'new_value' WHERE "COLUMN_A" = INITCAP('jones');
The following SQL command would be sent to the gateway:
UPDATE "test"@remote_db SET "COLUMN_A" = 'new_value' WHERE "COLUMN_A" = 'Jones';
In previous releases, the preceding UPDATE
statement would have raised an error due to the lack of INITCAP
function support in the non-Oracle database.
The Oracle database has always performed data type checking and data type coercion in a homogeneous environment. For example, SELECT * FROM EMP WHERE EMPNO='7934'
would return the same result as SELECT * FROM EMPNO WHERE EMPNO=7934
. There is also full data type checking support for remote-mapped statements in a heterogeneous environment. In general, the operands in SQL statements whether its a column, literal, or bind variable would be processed internally for data type checking. Consider the following examples:
SELECT * FROM EMP@LINK WHERE NUMBER_COLUMN='123' SELECT * FROM EMP@LINK WHERE NUMBER_COLUMN=CHAR_COLUMN; SELECT * FROM EMP@LINK WHERE NUMBER_COLUMN=CHAR_BIND_VARIABLE;
Most non-Oracle databases do not support data type coercion, and the previous statements fail if they are sent to a non-Oracle database as is. The Heterogeneous Services component for the Oracle database performs data type checking and the necessary data type coercion before sending an acceptable statement to a non-Oracle database.
Data type checking provides consistent behavior on post-processed or remote-mapped statements. Consider the following two statements:
SELECT * FROM EMP@LINK WHERE TO_CHAR(EMPNO)='7933' + '1';
And:
SELECT * FROM EMP@LINK WHERE EMPNO='7933' + '1';
Both of the previous statements provide the same result and coercion regardless if the TO_CHAR
function is supported in the non-Oracle database or not. Now, consider the following statement:
SELECT * FROM EMP@LINK WHERE EMPNO='123abc' + '1';
As data type checking is enforced, the coercion attempt within Oracle generates an error and returns it without sending any statements to a non-Oracle database.
In summary, there is consistent data type checking and coercion behavior regardless of post-processed or remote-mapped statements.
You can execute user-defined functions in a remote non-Oracle database. For example:
SELECT getdeptforemp@Remote_DB(7782) FROM dual;
In this example, a SELECT
statement was issued that executes a user-defined function in the remote database that returns department information for employee 7782.
When the remote function resides in an Oracle database, the Oracle database automatically ensures that the remote function does not update any database state (such as updating rows in a database or updating the PL/SQL package state). The gateway cannot verify this when the remote function resides in a non-Oracle database. Therefore, you are responsible for ensuring that the user-defined functions do not update the state in any database. Ensuring no updates to the database is required to guarantee read consistency.
As a security measure, you must specify the functions that you want to execute remotely and their owners in the HS_CALL_NAME
parameter in the gateway-specific initialization parameter file. For example:
HS_CALL_NAME = "owner1.A1, owner2.A2 "
owner1
and owner2
are the remote function owner names. A1
and A2
are the remote function names. You do not need to specify the remote function owner in the SQL statement. By default, the remote function needs to reside in the schema that the Transparent Gateway connects to. If this is not the case, then you must specify the owner of the remote function in the SQL statement.
Some other examples of executing user-defined remote functions are as follows:
A remote function in a subquery
The function uses the employee_id
column data to retrieve the department_id
from the EMPLOYEES
table in the remote database. The outer query then determines all department numbers in the remote database that match the returned list.
SELECT * FROM departments@remotedb WHERE department_id IN (SELECT getdeptforemp@remotedb (employee_id) FROM employees@remotedb);
Applying a local function to the result of a user-defined remote function
This query returns the maximum salary of all employees on the remote database.
SELECT max (getsalforemp@remotedb (employee_id)) FROM employees@remotedb;
A DML statement
The statement uses the output from a user-defined query in the remote database to update the salary column with new salary information.
UPDDATE employee_history SET salary = emp_changed_salary@remote_db;
In these examples, the Oracle database passes the function name and owner to the Transparent Gateway. The user-defined function is executed on the remote database.
See Also:
Section A.1, "HS_CALL_NAME"You can provide complete data location transparency and network transparency by using the synonym feature of the Oracle database server. When a synonym is defined, you do not have to know the underlying table or network protocol. A synonym can be public, which means that all Oracle users can refer to the synonym. A synonym can also be defined as private, which means every Oracle user must have a synonym defined to access the non-Oracle table.
The following statement creates a system-wide synonym for the emp
table in the schema of user ORACLE
in the Sybase database:
CREATE PUBLIC SYNONYM emp FOR "ORACLE"."EMP"@SYBS;
See Also:
Oracle Database Administrator's Guide for information about synonymsNote:
Modify these examples for your environment. Do not try to execute them as they are written.The following statement joins data between the Oracle database server, an IBM DB2 database, and a Sybase database:
SELECT O.CUSTNAME, P.PROJNO, E.ENAME, SUM(E.RATE*P."HOURS") FROM ORDERS@DB2 O, EMP@ORACLE9 E, "PROJECTS"@SYBS P WHERE O.PROJNO = P."PROJNO" AND P."EMPNO" = E.EMPNO GROUP BY O.CUSTNAME, P."PROJNO", E.ENAME;
Through a combination of views and synonyms, using the following SQL statements, the process of distributed queries is transparent:
CREATE SYNONYM ORDERS FOR ORDERS@DB2; CREATE SYNONYM PROJECTS FOR "PROJECTS"@SYBS; CREATE VIEW DETAILS (CUSTNAME,PROJNO,ENAME,SPEND) AS SELECT O.CUSTNAME, P."PROJNO", E.ENAME, SUM(E.RATE*P."HOURS") SPEND FROM ORDERS O, EMP E, PROJECTS P WHERE O.PROJNO = P."PROJNO" AND P."EMPNO" = E.EMPNO GROUP BY O.CUSTNAME, P."PROJNO", E.ENAME;
Use the following SQL statement to retrieve information from the data stores in one statement:
SELECT * FROM DETAILS;
The statement retrieves the following table:
CUSTNAME PROJNO ENAME SPEND -------- ------ ----- ----- ABC Co. 1 Jones 400 ABC Co. 1 Smith 180 XYZ Inc. 2 Jones 400 XYZ Inc. 2 Smith 180
Heterogeneous Services supports callback links. This enables SQL statements like the following to be executed:
INSERT INTO table_name@dblink SELECT column_list FROM table_name;
Even though Heterogeneous Services supports the callback functionality, not all gateways have implemented it. If the gateway that you are using has not implemented this functionality, the preceding INSERT
statement returns the following error message:
ORA-02025: All tables in the SQL statement must be at the remote database
See Also:
Your gateway documentation for information about support for callback linksFor gateways that do not support callback links, you can use the SQL*Plus COPY
command. The syntax is as follows:
COPY FROM username/password@db_name - INSERT destination_table - USING query;
The following example selects all rows from the local Oracle emp
table, inserts them into the emp
table on the non-Oracle database, and commits the transaction:
COPY FROM SCOTT/TIGER@inst1 - INSERT EMP@remote_db - USING SELECT * FROM EMP; The COPY command supports the APPEND, CREATE, INSERT, and REPLACE options. However, INSERT is the only option supported when copying to non-Oracle databases. The SQL*Plus COPY command does not support copying to tables with lowercase table names. Use the following PL/SQL syntax with lowercase table names:
DECLARE v1 oracle_table.column1%TYPE; v2 oracle_table.column2%TYPE; v3 oracle_table.column3%TYPE; . . . CURSOR cursor_name IS SELECT * FROM oracle_table; BEGIN OPEN cursor_name; LOOP FETCH cursor_name INTO v1, v2, v3, ... ; EXIT WHEN cursor_name%NOTFOUND; INSERT INTO destination_table VALUES (v1, v2, v3, ...); END LOOP; CLOSE cursor_name; END;
The CREATE TABLE
statement lets you copy data from a non-Oracle database to the Oracle database. To create a table on the local database and insert rows from the non-Oracle table, use the following syntax:
CREATE TABLE table_name AS query;
The following example creates the table emp
in the local Oracle database and inserts the rows from the EMP
table of the non-Oracle database:
CREATE TABLE table1 AS SELECT * FROM "EMP"@remote_db; Alternatively, you can use the SQL*Plus COPY command to copy data from the non-Oracle database to the Oracle database server.
You can use the Heterogeneous Services data dictionary views to access information about Heterogeneous Services. This section addresses the following topics:
The Heterogeneous Services data dictionary views, whose names all begin with the HS_
prefix, can be divided into the following categories:
Most of the data dictionary views are defined for both classes and instances. For most types of data there is a *_CLASS
view and a *_INST
view. See Table 4-1 for additional details.
Table 4-1 Data Dictionary Views for Heterogeneous Services
Like all Oracle data dictionary tables, these views are read-only. Do not change the content of any of the underlying tables.
The values used for data dictionary content in any particular connection on a Heterogeneous Services database link can come from any of the following sources, in order of precedence:
Instance information uploaded by the connected Heterogeneous Services agent at the start of the session. This information overrides corresponding content in the Oracle data dictionary, but is never stored into the Oracle data dictionary.
Instance information stored in the Oracle data dictionary. This data overrides any corresponding content for the connected class.
Class information stored in the Oracle data dictionary.
If the Oracle database server runs with the HS_AUTOREGISTER
server initialization parameter set to FALSE
, then information is not stored automatically in the Oracle data dictionary. The equivalent data is uploaded by the Heterogeneous Services agent on a connection-specific basis each time a connection is made, with any instance-specific information taking precedence over class information.
Note:
It is not possible to determine positively what capabilities and what data dictionary translations are in use for a given session due to the possibility that an agent can upload instance information.You can determine the values of Heterogeneous Services initialization parameters by querying the VALUE
column of the V$HS_PARAMETER
view. Note that the VALUE
column of V$HS_PARAMETER
truncates the actual initialization parameter value from a maximum of 255 characters to a maximum of 64 characters. It truncates the parameter name from a maximum of 64 characters to a maximum of 30 characters.
The views that are common for all services are as follows:
View | Contains |
---|---|
HS_FDS_CLASS |
Names of the classes that are uploaded into the Oracle data dictionary |
HS_FDS_INST |
Names of the instances that are uploaded into the Oracle data dictionary |
HS_CLASS_INIT |
Information about the Heterogeneous Services initialization parameters |
For example, you can access multiple Sybase gateways from an Oracle database server. After accessing the gateways for the first time, the information uploaded into the Oracle database server could appear as follows:
SQL> SELECT * FROM HS_FDS_CLASS; FDS_CLASS_NAME FDS_CLASS_COMMENTS FDS_CLASS_ID --------------------- ------------------------------ ------------ Sybase816 Uses Sybase driver, R1.1 1 Sybase817 Uses Sybase driver, R1.2 21 Two classes are uploaded: a class that accesses Sybase816 and a class that accesses Sybase817. The data dictionary in the Oracle database server now contains capability information, SQL translations, and data dictionary translations for both Sybase816 and Sybase817. The Oracle database server data dictionary also contains instance information in the HS_FDS_INST view for each non-Oracle system instance that is accessed.
When a non-Oracle system is involved in a distributed transaction, the transaction capabilities of the non-Oracle system and the agent control whether it can participate in distributed transactions. Transaction capabilities are stored in the HS_CLASS_CAPS
tables.
The ability of the non-Oracle system and agent to support two-phase commit protocols is specified by the 2PC type capability, which can specify one of the types shown in the following table.
Type | Capability |
---|---|
Read-Only (RO) | The non-Oracle system can be queried only with SQL SELECT statements. Procedure calls are not allowed because procedure calls are assumed to write data. |
Single-Site (SS) | The non-Oracle system can handle remote transactions but not distributed transactions. That is, it cannot participate in the two-phase commit protocol. |
Commit Confirm (CC) | The non-Oracle system can participate in distributed transactions. It can participate in the server's two-phase commit protocol but only as the commit point site. That is, it cannot prepare data, but it can remember the outcome of a particular transaction if asked by the global coordinator. |
Two-Phase Commit (2PC) | The non-Oracle system can participate in distributed transactions. It can participate in the server's two-phase commit protocol, as a regular two-phase commit node, but not as a commit point site. That is, it can prepare data, but it cannot remember the outcome of a particular transaction if asked to by the global coordinator. |
Two-Phase Commit Confirm (2PCC) | The non-Oracle system can participate in distributed transactions. It can participate in the server's two-phase commit protocol as a regular two-phase commit node or as the commit point site. That is, it can prepare data and it can remember the outcome of a particular transaction if asked by the global coordinator. |
The transaction model supported by the driver and non-Oracle system can be queried from the HS_CLASS_CAPS
Heterogeneous Services data dictionary view.
The following example shows one of the capabilities is of the 2PC type:
SELECT cap_description, translation FROM hs_class_caps WHERE cap_description LIKE '2PC%' AND fds_class_name LIKE 'SYBASE%'; CAP_DESCRIPTION TRANSLATION ---------------------------------------- ----------- 2PC type (RO-SS-CC-PREP/2P-2PCC) CC When the non-Oracle system and agent support distributed transactions, the non-Oracle system is treated like any other Oracle server. When a failure occurs during the two-phase commit protocol, the transaction is recovered automatically. If the failure persists, the in-doubt transaction may need to be manually overridden by the database administrator.
Data dictionary views that are specific for the SQL service contain information about:
SQL capabilities and SQL translations of the non-Oracle data source
Data dictionary translations to map Oracle data dictionary views to the data dictionary of the non-Oracle system
Note:
This section describes only a portion of the SQL Service-related capabilities. Because you should never need to alter these settings for administrative purposes, these capabilities are not discussed here.The HS_*_CAPS
data dictionary tables contain information about the SQL capabilities of the non-Oracle data source and required SQL translations. These views specify whether the non-Oracle data store or the Oracle database server implements certain SQL language features. If a capability is turned off, then Oracle does not send any SQL statements to the non-Oracle data source that require this particular capability, but it still performs postprocessing.
In order to make the non-Oracle system appear similar to an Oracle database server, Heterogeneous Services connections map a limited set of Oracle data dictionary views onto the non-Oracle system's data dictionary. This mapping permits applications to issue queries as if these views belonged to an Oracle data dictionary. Data dictionary translations make this access possible. These translations are stored in Heterogeneous Services views whose names have the _DD
suffix.
For example, the following SELECT
statement transforms into a Sybase query that retrieves information about emp
tables from the Sybase data dictionary table:
Data dictionary tables can be mimicked instead of translated. If a data dictionary translation is not possible because the non-Oracle data source does not have the required information in its data dictionary, then Heterogeneous Services causes it to appear as if the data dictionary table is available, but the table contains no information.
To retrieve information about which Oracle data dictionary views or tables are translated or mimicked for the non-Oracle system, connect as user SYS
and issue the following query on the HS_CLASS_DD
view:
SELECT DD_TABLE_NAME, TRANSLATION_TYPE FROM HS_CLASS_DD WHERE FDS_CLASS_NAME LIKE 'SYBASE%'; DD_TABLE_NAME T ----------------------------- - ALL_ARGUMENTS M ALL_CATALOG T ALL_CLUSTERS T ALL_CLUSTER_HASH_EXPRESSIONS M ALL_COLL_TYPES M ALL_COL_COMMENTS T ALL_COL_PRIVS M ALL_COL_PRIVS_MADE M ALL_COL_PRIVS_RECD M ...
The T
translation type specifies that a translation exists. When the translation type is M
, the data dictionary table is mimicked.
See Also:
Appendix C, "Data Dictionary Translation Support" for a list of data dictionary views that are supported through Heterogeneous Services mappingThe Oracle database server stores information about agents, sessions, and parameters. You can use the dynamic performance views to access this information. This section contains the following topics:
Determining Which Agents Are Running on a Host: V$HS_AGENT View
Determining the Open Heterogeneous Services Sessions: V$HS_SESSION View
Determining the Heterogeneous Services Parameters: V$HS_PARAMETER View
The V$HS_AGENT
view identifies the set of Heterogeneous Services agents currently operating on a specified host. Table 4-2 shows the most relevant columns. For a description of all the columns in the view, see Oracle Database Reference.
Table 4-2 Important Columns in the V$HS_AGENT View
Column | Description |
---|---|
AGENT_ID |
Oracle Net session identifier used for connections to agent (listener.ora SID ) |
MACHINE |
Operating system machine name |
PROGRAM |
Program name of agent |
AGENT_TYPE |
Type of agent |
FDS_CLASS_ID |
The ID of the foreign data store class |
FDS_INST_ID |
The instance name of the foreign data store |
The V$HS_SESSION
view shows the sessions for each agent and specifies the database link that is used. Table 4-3 shows the most relevant columns. For a description of all the columns in the view, see Oracle Database Reference.
Table 4-3 Important Columns in the V$HS_SESSION View
Column | Description |
---|---|
HS_SESSION_ID |
Unique Heterogeneous Services session identifier |
AGENT_ID |
Oracle Net session identifier used for connections to agent (listener.ora SID ) |
DB_LINK |
Server database link name used to access the agent NULL means that no database link is used (for example, when using external procedures) |
DB_LINK_OWNER |
Owner of the database link in DB_LINK |
The V$HS_PARAMETER
view lists the Heterogeneous Services parameters and their values that are registered in the Oracle database server. Table 4-4 shows the most relevant columns. For a description of all the columns in the view, see Oracle Database Reference.
Table 4-4 Important Columns in the V$HS_SESSION View
Column | Description |
---|---|
HS_SESSION_ID |
Unique Heterogeneous Services session identifier |
PARAMETER |
The name of the Heterogeneous Services parameter |
VALUE |
The value of the Heterogeneous Services parameter |
Information about the database link that was used for establishing the distributed connection, the startup time, and the set of initialization parameters used for the session is also available. All of the runtime information is derived from dynamically updated tables.