Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Understanding The SQL*Net Listener

Copyright (a) Oracle Corporation 1993. All rights reserved.

Connecting to (ADDRESS=(PROTOCOL=TCP)(HOST=seagull)(PORT=1521))
Services Summary...
tdb000 has 4 service handlers
DISPATCHER established:1 refused:0 current:2 max:55 state:ready
D001 (machine: seagull, pid: 4146)
(ADDRESS=(PROTOCOL=tcp)(DEV=5)(HOST=141.123.224.38)(PORT=1323))
DISPATCHER established:1 refused:0 current:2 max:55 state:ready
D000 (machine: seagull, pid: 4145)
(ADDRESS=(PROTOCOL=tcp)(DEV=5)(HOST=141.123.224.38)(PORT=1321))
DISPATCHER established:0 refused:0 current:1 max:55 state:ready
D002 (machine: seagull, pid: 4147)
(ADDRESS=(PROTOCOL=tcp)(DEV=5)(HOST=141.123.224.38)(PORT=1325))
DEDICATED SERVER established:0 refused:0
The command completed successfully

As a service request is intercepted by an Oracle server, the listener may direct the request via a dedicated server, an MTS, or an existing process (pre-spawned shadow). The key is whether the connection contacts the listener via a service name or bypasses the listener with the TWO_TASK connect string. If the listener is contacted as part of the connection and the MTS parms are defined to init.ora, the client will use the MTS.

There are five basic listener commands: RELOAD, START, STOP, STATUS, and SERVICES. Based on the request, the listener decides whether to dispatch a connection to a dedicated-server process (which it spawns) or use the MTS. The programmer has several options when deciding how Oracle will manage the process. Dedicated requests can be specified by a version 1.0 connect string or by using a service name that specifies server=dedicated in the tnsnames.ora file.

Note: Local connections will use the listener if multithreaded servers are defined. Even internal invocations to Oracle (for example, sqlplus/) will add a connection to an MTS.

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