close;"
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Can the gateway connections be controlled with Net services parameters such as
expire_time etc?
No. Gateway connections cannot be controlled by any of the
Net services parameters
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Is it possible to have the connection between the Oracle Server and the
gateway closed but the connection between the gateway and the non-Oracle system
be open? Is there any workaround for this problem?
No. It is not possible to
have a open connection between the gateway and the non-Oracle system when the
connection between Oracle Server and the gateway is closed. For some strange
reason, if a customer sees this behavior, the workaround is to manually teminate
the gateway process at the non-Oracle system platform.
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How does the Transparent Gateway support non-Oracle
datatypes?
The Transparent Gateway maps the non-Oracle datatypes to
the most appropriate Oracle datatypes. This is done transparently to the user.
These mappings are listed in the appropriate manuals. For unsupported datatypes,
an error is reported to the application user.
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How does an Transparent Gateway handle non-Oracle capabilities?
Oracle
SQL Functions and Oracle capabilities that are not supported by the non-Oracle
system can be still used in SELECT statements but not in DML statements. When
these unsupported functions are used in SELECT statements, Oracle (HS) strips
this function from teh SELECT statement and sends the SELECT statement to the
gateway without the function reference. In the following example, assume SUBSTR
funtion is not supported by the non-Oracle system that is being accessed via
dblink, GTWLINK:
Original Query: SELECT SUBSTR(ENAME,1,5) FROM EMP@GTWLINK;
Statement sent to the gateway by Oracle: SELECT ENAME FROM EMP;
If SUBSTR function is used with any DML statements, Oracle will raise an
error.
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Are there general guidelines one can use to improve the gateway
performance?
The Gateways are not tunable. To troubleshoot gateway
performance issues, turn on gateway tracing (HS_FDS_TRACE_LEVEL= debug). Observe the trace file for things
like:
the entire SQL statement in question is being sent across to the non-Oracle
system or the entire table is being fetched
Application users can then re-write their SQL such that most of the
processing is done at non-Oracle systems and only the relevant data is fetched
across the network. Post processing at Oracle is probably the most common cause
of performance degradation.
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Can Transparent Gateways be used for Heterogeneous Replication?
All of
our Transparent Gateway products from v8.1.6 onwards support read-only complete
refresh materialized views (snapshots).
You can create the Oracle snapshot by issuing the standard replication SQL:
CREATE MATERIALIZED VIEW mv_name REFRESH COMPLETE AS query;
where query represents the data you want to retrieve from the non-Oracle
system. Multiple MVs are grouped together in a refresh group by the following
statement: execute dbms_refresh.make('groupname', 'list_of_MVs', NULL, NULL);
and can be refreshed by: execute dbms_refresh.refresh('groupname');
If you want the refresh to be done at regular intervals you can setup a
database job for this. Please refer to the replication manual for more details
on the replication SQL syntax and related procedures.
Another way to replicate data is by setting trigger(s) on the Oracle tables
which you want to replicate to the non-Oracle system. When a change occurs in
the Oracle table the trigger fire thus 'replicating' the change to the
non-Oracle system.
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What's the difference between the Messaging Gateway and the Procedural
Gateway for MQ Series?
Oracle Messaging Gateway and the Procedural Gateway
for MQ can both propagate messages between Oracle9i and MQ Series. However, the
Messaging Gateway works with Advanced Queuing to propagate AQ messages to and
from MQ Series. The procedural gateway allows customers executing PL/SQL
applications to put or get messages to or from MQ Series--AQ is not required.
The Messaging Gateway is designed to allow customers who have MQ Series to
easily add AQ-based solutions into their environment. AQ and the Message Gateway
are included free of charge with the database, and offer significant advantages
over MQ Series for message queuing applications. Customers who have to build new
message queuing functionality should consider building their solution using AQ
and then integrating with MQ via the message gateway, rather than simply
connecting their application to MQ via the procedural gateway.
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