Lesson 5	Starting Oracle Shared Server
Objective	Start and verify Shared Server correctly, then connect.

Start Oracle Shared Server (the correct way)

What Shared Server is: an Oracle database architecture in which many client sessions share a smaller pool of server processes. It helps when you have thousands of concurrent, mostly idle or short-lived connections (e.g., many web users).

When to use it: prefer mid-tier connection pooling (UCP/ODP.NET/OCI) for app servers. Consider Shared Server when you cannot reduce session counts (many ad-hoc or tool sessions), or for specific legacy deployments. It is optional and fully supported in modern releases.

Prerequisites

A running database instance you can administer as SYSDBA.
Listener running and registering services (lsnrctl status should show your service).
Know your service name (CDB/PDB as appropriate).

Enable Shared Server

You can enable it dynamically or persistently. In CDBs, run in the correct container.

Option A - Dynamically (no restart)


-- As SYSDBA
-- Minimum pool
ALTER SYSTEM SET SHARED_SERVERS = 2 SCOPE=BOTH;

\-- Create TCP dispatchers (adjust protocol/attributes for your network)
ALTER SYSTEM SET DISPATCHERS = '(PROTOCOL=TCP)(DISPATCHERS=2)' SCOPE=BOTH;

\-- Optional: request multiple shared servers during peak periods
ALTER SYSTEM SET MAX\_SHARED\_SERVERS = 50 SCOPE=BOTH;

Option B - Persistent (init parameters)


-- In SPFILE (persists across restarts)
ALTER SYSTEM SET SHARED_SERVERS      = 2 SCOPE=SPFILE;
ALTER SYSTEM SET DISPATCHERS         = '(PROTOCOL=TCP)(DISPATCHERS=2)' SCOPE=SPFILE;
ALTER SYSTEM SET MAX_SHARED_SERVERS  = 50 SCOPE=SPFILE;

\-- Then restart the instance

Verify configuration


-- Check parameters
SHOW PARAMETER shared_servers
SHOW PARAMETER dispatchers
SHOW PARAMETER max_shared_servers

\-- Sessions and queues (simple sanity checks)
SELECT NAME, VALUE FROM V\$PARAMETER
WHERE NAME IN ('shared\_servers','dispatchers','max\_shared\_servers');

SELECT \* FROM V\$SHARED\_SERVER WHERE STATUS = 'BUSY' OR STATUS = 'FREE';
SELECT \* FROM V\$DISPATCHER;

\-- Listener view (if available)
\-- lsnrctl status  (run at OS prompt)

Connect from SQL*Plus

There is no special client syntax required. Use standard Easy Connect or a TNS alias.


-- OS authentication (local)
sqlplus / AS SYSDBA

\-- Or service-based (password file / remote)
sqlplus sys@//dbhost:1521/ORCLPDB1 AS SYSDBA

Sizing guidelines (quick start)

SHARED_SERVERS: start small (1–4). Increase if request queues form or response time degrades under load.
DISPATCHERS: begin with 1–2 per protocol (e.g., TCP). Scale from metrics in V$DISPATCHER.
MAX_SHARED_SERVERS: a ceiling to prevent runaway growth; set comfortably above expected peak.

Troubleshooting


-- Are dispatchers up?
SELECT NAME, STATUS, MESSAGES FROM V$DISPATCHER;

\-- Are shared servers spawning?
SELECT SERVER\_ID, STATUS, REQUESTS FROM V\$SHARED\_SERVER;

\-- Are requests queuing?
SELECT \* FROM V\$QUEUE WHERE TYPE IN ('COMMON','DISPATCHER');

\-- Is the listener seeing the service?
\-- lsnrctl status  (look for your service and handler(s))

Common mistakes to avoid

Starting a “shared server executable”: There isn’t one. Shared Server is an instance configuration, not a separate binary.
Confusing with DRCP: Database Resident Connection Pooling is different. Don’t mix concepts when sizing.
Legacy logins: CONNECT INTERNAL is desupported. Use SYSDBA connections.

Modern administration note

For monitoring, automation, and fleet operations, use Enterprise Manager Cloud Control. For connectivity modernization from legacy SQL*Net/Net8 content, prefer Easy Connect Plus with service names and wallets where appropriate.

Historical corner (condensed)

Server Manager (svrmgrl) was Oracle’s pre-9i DBA tool (CLI/GUI). It was retired and functionality moved into SQL*Plus. Any references to svrmgr, svrmgr30, or CONNECT INTERNAL are strictly historical; follow the modern equivalents above.

Quick reference


-- Minimal enablement
ALTER SYSTEM SET SHARED_SERVERS = 2 SCOPE=BOTH;
ALTER SYSTEM SET DISPATCHERS = '(PROTOCOL=TCP)(DISPATCHERS=2)' SCOPE=BOTH;

\-- Verify
SHOW PARAMETER shared\_servers
SHOW PARAMETER dispatchers
SELECT \* FROM V\$DISPATCHER;
SELECT \* FROM V\$SHARED\_SERVER;

\-- Connect (examples)
sqlplus / AS SYSDBA
sqlplus sys@//dbhost:1521/ORCLPDB1 AS SYSDBA