Oracle Interview Preparation Notes Part 14

2-Tier (Client / Server)	N-Tier
Not scalable - 100 or less simultaneous users	Scalable – handles more than 100 users
Client connects directly to server	Uses a middle tier (application server).
Single protocol (client and server must be same)	Translation between network protocols.
Difficult to administer (all clients must be updated)	Easy maintenance – only middle tier gets updated.
More network traffic.	Less network traffic (data stored on middle tier)

Tools Overview:

· Net8 Assistant: GUI tool to configure network services files.

· Net8 Trace Assistant: Used in conjunction with trace files for diagnostics and identifying bottlenecks.

· Oracle Names Server: (ONS) - Central store for all addresses for all databases (distributed name server, centrally administered) – can have multiple ONS servers for failover and load balancing.

· Connection Manager: (n-tier): Stored on middle tier, uses multiplexing to handle connection requests. Establishes 1 connection that is used by subsequent requests. Handles multiple protocols transparent to the user.

· Advanced Networking Option (ANO): provides security with data encryption and checksumming. ANO must be installed on both client and server to use encryption. DCE – Distrib. Computing Environ. – uses RPC (Remote Procedure Calls) – single sign-on in a multivendor environment.

· Oracle Security Server: Uses X.509 certificate standard - provides authentication of users by validating identities, allowing a single sign-on to be used for multiple databases. Uses security server to validate users, Web servers, and other servers.

· Oracle Open Gateway: allows access of non-Oracle data – transparent and procedural.

Basic Architecture

Establishing a connection:

1. Listener process on server is configured and active.

2. Client application provides username, password, and service name.

3. Service name is resolved into connect descriptor using host naming, local naming (tnsnames) or ONS.

4. Connection information is passed from the client to the server listener process.

5. Listener process on server determines where the request is directed.

6. Listener creates a new server process or redirects to an existing connection.

7. The process address information is passed back to the client.

8. The client process communicates directly with the server process.

3 Files involved: Listener.ora (server), tnsnames.ora (client), sqlnet.ora (client and server),

Dead Connection Detection: periodically sends packet to check that the client connection is still valid. If dead connection is discovered, uncommitted transactions are rolled back and all locks are released.

(PMON may recognize a terminated session and return ORA-3113 “end of file on communication channel)

Client Protocol Stack

Application	Front end application presented to the user.
Oracle Call Interface (OCI) or User Program Intrfc (UPI)	Info necessary to perform an action at the database server. SQL command parsing, cursors, bind variables, execution, fetch data.
Two Task Common	Performs datatype and character conversions between client & server.
Transparent Network Substrate (TNS)	Handles send and receive functions – the heart of Oracle networking. Passes information to the Oracle protocol adapter. Has 5 layers.
Oracle Protocol Adapter (OPA)	Maps the Oracle functions to the network-specific protocols. The Network Transport (NT) layer.
Network Protocol	Network specified protocol (ie. TCP). Handles actual machine level connection process, passes data in packets between client and server.

Server Protocol Stack

Server	Receives and executes SQL commands and returns results to OPI.
Oracle Program Inter. (OPI)	Counterpart to OCI. Processes SQL code and returns data.
Two Task Common	Performs datatype and character conversions between client & server.
Transparent Network Substrate (TNS)	Handles send and receive functions as well as interrupts.
Oracle Protocol Adapter (OPA)	Maps the Oracle functions to the network-specific protocols. The Network Transport (NT) layer.
Network Protocol	Network specified protocol (ie. TCP). Handles actual machine level connection process, passes data in packets between client and server.

Transparent Network Substrate (TNS) Layers

TNS Layer	Short Name	Purpose
Network Interface	NI	Interface to Net8, handles breaks and reset requests.
Network Naming	NN	Converts alias address to destination.
Network Routing	NR	Handles routing issues between client and server.
Network Authentication	NA	Handles authentication between client and server.
Network Session	NS	Establish handshake, manage buffers, multiplexin, pooling.
Network Transport	NT	Main, secondary, and operating system layers

Name Resolution Methods:

Method	File Required	Process used for name resolution
Host Naming	Sqlnet.ora	Port 1521, global names -requires TCP/IP & external naming(DNS)
Local Naming	Tnsnames.ora	File on the client
Oracle Names	Sqlnet.ora	Oracle Names Server
External Naming	Sqlnet.ora	Oracle Native Naming Adapters (3^rd party software).

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