Introduction to Oracle processes for Linux systems

There are two types of processes associated with running an Oracle database: Oracle listener and database instance. Both types must be running on the system when running Teamcenter. Process Description Oracle listener The Oracle listener (tnslsnr) process monitors database connections from remote clients. This is a SQLNet V2/Net process and is required for Teamcenter to connect. Under SQLNet V2/Net, several listeners may run on the same system, each listening for connect requests to particular databases. Even if Teamcenter is run on the Oracle server, it is necessary to start this process because all Teamcenter database requests use the remote connect mechanism. Database instance Database processes are associated with a particular Oracle database instance. There are six processes associated with each database instance when it is first started. The processes are: ora_pmon_SID Process monitor; performs Oracle process recovery when a user process fails. ora_dbw0_SID Database writer process; writes dirty Oracle buffers to disk. ora_ckpt_SID Checkpoint process; updates the headers of all Oracle data files to record the details of the checkpoint. ora_smon_SID System monitor process; performs Oracle instance recovery at instance startup. ora_reco_SID Oracle recovery process; process used with distributed database configuration that automatically resolves failures involving distributed transactions. ora_lgwr_SID Log writer process; writes the Oracle redo log buffer to a redo log file on disk. SID represents the database instance system identifier. Starting these processes on an Oracle database server is referred to as initializing a database instance. Use one of the following methods to initialize a database instance: To start all database instances flagged in the oratab file, use the Oracle dbstart utility. Only those instances marked with a Y flag are started. To start a single database instance defined by the ORACLE_SID environment variable, use the Oracle SQLPlus utility. All databases instances present on the system should be listed in the oratab configuration file. This file is located in the /var/opt/oracle directory on Solaris systems and in the /etc directory on all other platforms. Each instance should be listed on a separate line and conform to the following format: ORACLE_SID:ORACLE_HOME:FLAG ORACLE_SID is the system identifier of the instance (for example tc), ORACLE_HOME is the Oracle home directory associated with that instance (for example, /u01/app/oracle/product/oracle-version), and FLAG is Y or N. These flags are used by the Oracle dbstart and dbshut utilities to determine which instances to start or stop. Caution Never shut down a database instance by killing database processes or by restarting the system. Oracle databases require orderly shutdowns to ensure that all necessary database transactions are completed. Failure to observe this may result in the corruption of the database. Manual termination of processes also prevents the Oracle Relational Database Management System (RDBMS) from releasing memory that is no longer needed, and could require additional database recovery procedures at the next database startup. There are two methods for shutting down a database instance: Use the Oracle dbshut utility to shut down all database instances flagged in the oratab file. Only those instances marked with a Y flag are stopped. Use the Oracle SQLPlus utility to stop a single database instance defined by the ORACLE_SID environment variable.