![]() Oracle Database converts a service name into an ORACLE_HOME and ORACLE_SID.Ī traditional read-write Oracle home contains instance-specific files. When connecting to a database instance, clients can specify the SID in an Oracle Net connection or use a net service name. On most platforms, the ORACLE_SID environment variable sets the SID, and the ORACLE_HOME variable sets the Oracle home. Also, Oracle Database uses the SID by default to locate the initialization parameter file, which locates relevant files such as the database control files. On UNIX and Linux, Oracle Database uses the SID and Oracle home values to create a key to shared memory. The system identifier (SID) is a unique name for an Oracle database instance on a specific host. In the following example, the first path is a read-only Oracle home, and the second path is the Oracle base home for this Oracle home: /u01/app/oracle/product/18.0.0/ro_dbhome_1 The Oracle base configuration directory ( ORACLE_BASE_CONFIG), which is shared by all Oracle homes in an Oracle base, stores instance-specific dynamic files. ![]() The Oracle base home ( ORACLE_BASE_HOME) directory, which is located in ORACLE_BASE/homes/ home_name, stores dynamic files specific to an Oracle home. The read-only Oracle home stores static files such as binaries. Starting in Oracle Database 18c, you can create a read-only Oracle home as a software image. The /u01/app/oracle/product/12.1.0/ directory contains two separate Oracle homes: dbhome_1 and dbhome_2. ![]() The part of the path name after the Oracle base ( /u01/app/oracle/) includes the product release number (for example, 12.1.0) and Oracle home relative directory (for example, dbhome_1). The following example shows the full path names of three different Oracle homes, all within the same Oracle base directory of /u01/app/oracle/: Multiple databases, of different versions and owned by different user accounts, can coexist concurrently. You can install this release, or earlier releases of the database software, more than once on the same host, in different Oracle home directories within a single Oracle base. By default, the Oracle home directory is a descendent within the Oracle base ( ORACLE_BASE) directory tree. You must specify a new Oracle home directory for each new installation of Oracle Database software. ![]() The Oracle home is the software location for an Oracle database. The different start time shows that this instance is different from the one that shut down the database. This query shows the time that the current instance was started. TO_CHAR(STARTUP_TIME, 'MON-DD-RR HH24:MI:SS') The STARTUP command creates a new instance and mounts and open the database. The instance closes the database and shuts down, ending the life of this instance. TO_CHAR(STARTUP_TIME,'MON-DD-RR HH24:MI:SS') The STARTUP command creates an instance, which mounts and opens the database. Table 13-1 Duration of an Instance Statement The default value of the parameter is READ_WRITE. To designate an instance as read-only, set the INSTANCE_MODE initialization parameter to READ_ONLY. Unlike read/write instances, read-only instances have the following characteristics:Ĭan only open a database that has already been opened by a read/write instanceĭisable many background processes, including the checkpoint and archiver processes, which are not necessaryĬan mount a disabled redo thread or a thread without any online redo log This configuration is useful for parallel SQL statements that both query and modify data, because both read/write and read-only instances can query, while the read/write instances modify. Starting in Oracle Database 12c Release 2 (12.2), read-only and read/write instances can coexist within a single database. In previous releases, all database instances-unless they accessed a standby database-were read/write. Check Startup, uptime and creation time of PDB database
0 Comments
Leave a Reply. |