Wednesday, September 25, 2024

How to plug and unplug a PDB in a multitenant configuration

What exactly does it mean to unlug and plug a database, in a multitenant architecture?

  • To unplug means to close the PDB and then generate its manifest file.
  • To plug means using the manifest file to create a new pluggable database.

    In the examples below, I am unplugging the databases pdb1 and pdb2 into two different manifest files:
    sqlplus / as sysdba
    alter pluggable database pdb1 close immediate;
    alter pluggable database pdb1 unplug into '/u01/app/oracle/oradata/pdb1.xml';
    
    alter pluggable database pdb2 close immediate;
    alter pluggable database pdb2 unplug into '/u01/app/oracle/oradata/pdb2.xml';
    
    The XML file created in the unplug operation contains information about the names and the full paths of the tablespaces, as well as data files of the unplugged PDB.

    This information will then be used by a subsequent plugg-in operation.

    After having unplugged a pdb you can drop the pluggable database but physically keep the datafiles belonging to it, like this:
    drop pluggable database pdb1 keep datafiles;
    
    If you wish to plug the database into a different CDB, it is a good idea to check the compatability of the database with the CDB first. This is particulary true if the new CDB is created with newer binaries than the original CDB, or if it is on a different host.In the new CDB, execute the following pl/sql code:
    set serveroutput on
    
    DECLARE
       compatible BOOLEAN := FALSE;
    BEGIN  
       compatible := DBMS_PDB.CHECK_PLUG_COMPATIBILITY(
            pdb_descr_file => '/u01/app/oracle/oradata/pdb1.xml');
       if compatible then
          DBMS_OUTPUT.PUT_LINE('Is pluggable PDB1 compatible? YES');
       else DBMS_OUTPUT.PUT_LINE('Is pluggable PDB1 compatible? NO');
       end if;
    END;
    /
    
    If the output shows that the database is compatible with the new CDB, proceed to plugin the database.

    Plug operations can be done using two different methods: NOCOPY and COPY.

    Using the NOCOPY method will use the data files of the unplugged PDB to plug the PDB into another (or the same) CDB without any physical file copy:
    create pluggable database pdb_plug_nocopy using '/u01/app/oracle/oradata/pdb1.xml'
    NOCOPY
    TEMPFILE REUSE;
    
    When using the NOCOPY option, the plugin operation lasts a few seconds. The original data files of the unplugged PDB now belong to the new plugged-in PDB in the new (or the same) CDB. A file with the same name as the temp file specified in the XML file exists in the target location. Therefore, the TEMPFILE_REUSE clause is required.

    Using the COPY method, will physically move datafiles from the original destination to a new destination:
    mkdir -p /u01/app/oracle/oradata/cdb2/pdb_plug_copy
    
    create pluggable database pdb_plug_copy using '/u01/app/oracle/oradata/pdb2.xml'
    COPY
    FILE_NAME_CONVERT=('/u01/app/oracle/oradata/cdb1/pdb2','/u01/app/oracle/oradata/cdb2/pdb_plug_copy');
    
    Verify the status, open mode and the file location of the plugged-in PDB (In the example below, I am showing the output for the pdb created using the COPY method, but it should always be done regardless of the method used):
    select pdb_name, status from cdb_pdbs where pdb_name='PDB_PLUG_COPY'; --> should return PDB_PLUG_COPY and NEW
    select open_mode from v$pdbs where name='PDB_PLUG_COPY'; --> should return MOUNTED
    
    select name from v$datafile where con_id=(select con_id from v$pdbs where name='PDB_PLUG_COPY';) --> should return the full path and name of the datafiles belonging to the system and sysaux tablespaces.
    
    Whether or not you are using the NOCOPY or COPY method, you will now have to open the newly plugged in database in the new CDB:

    alter pluggable database pdb_plug_nocopy open;
    
    alter pluggable database pdb_plug_copy open;
    
    show con_name
    show pdbs
    
    Source: Oracle 12cR1 tutorial
  • Monday, September 23, 2024

    How prevent dbca to create folders in capital letters during database creation

    This post is derived from my previous post, but I have come to realize that I have needed to look up this particular detail at at least a couple of occasions, so it deserves a post of their own.

    To keep dbca to create folders with capital letters during database cration, you need to alter the directions
    datafileDestination=/disk1/oradata/{DB_UNIQUE_NAME}/
    recoveryAreaDestination=/disk2/flash_recovery_area/{DB_UNIQUE_NAME}
    
    to
    datafileDestination=/disk1/oradata/mydb
    recoveryAreaDestination=/disk2/flash_recovery_area/mydb
    
    in your response file.

    The response file would then look something like:
    #-------------------------------------------------------------------------------
    # Do not change the following system generated value.
    #-------------------------------------------------------------------------------
    responseFileVersion=/oracle/assistants/rspfmt_dbca_response_schema_v19.0.0
    gdbName=mydb.oric.no
    sid=mydb
    databaseConfigType=SI
    createAsContainerDatabase=false
    templateName=/u01/oracle/product/19c/assistants/dbca/templates/General_Purpose.dbc
    sysPassword=manager1
    systemPassword=manager1
    datafileDestination=/disk1/oradata/mydb
    recoveryAreaDestination=/disk2/flash_recovery_area/mydb
    storageType=FS
    characterSet=al32utf8
    variables=
    initParams=db_recovery_file_dest_size=50G
    memoryPercentage=75
    databaseType=MULTIPURPOSE
    enableArchive=true
    redoLogFileSize=2048
    

    Thursday, September 19, 2024

    What is the $ORACLE_HOME/dbs/hc_$ORACLE_SID.dat file?

    In every $ORACLE_HOME/dbs folder you will find a file named hc_$ORACLE_SID.dat.

    What is it, and is it essential for your instance?

    Oracle Support states:

    The $ORACLE_HOME/dbs/hc_.dat is created for the instance health check monitoring. It contains information used to monitor the instance health and to determine why it went down if the instance isn't up.

    The file can be deleted while the instance is up, it won't cause any harm to your instance.

    In earlier versions of the Oracle database software a bug existed that would trigger an ORA-7445 if the file was deleted while the database was up, but this was fixed as early as in version 11.2.

    The file is created at every instance startup.

    Source: What Is The $ORACLE_HOME/dbs/hc_.dat File? (Doc ID 390474.1) from Oracle Support

    Tuesday, September 17, 2024

    Where does an Oracle EBS 12.2 appserver save logs from the concurrent worker processes?

    Look in the directory $ADOP_LOG_HOME

    In here, every session will create its own subfolder. In my case
    10  11  2  3  4  5  6  7  8  9
    
    In my case, I had to enter the folder named after session 11.

    In here you will find folders named according to exection time, for example

    20240916_135516

    Inside this folder, you will find folders named according to action, for example "prepare", "cutover", or "apply".

    In my case, step inside the "apply" directory and you will find a folder named after your appserver.

    Finally, you will find a folder named according to the patch number, for example
    36876222_N
    
    with a log directory underneath it.

    So the path $ADOP_LOG_HOME/11/20240916_135516/apply/oric-ebsapp01/36876222_N/log is the complete path to your my log directory for the session I am looking for.

    Thursday, September 5, 2024

    How do I store multiple connections to the same database in my wallet?

    If you have a wallet which already contains an alias for a database, you cannot add another one pointing to the same alias. If you do, mkstore will give you the following error:
    Secret Store error occurred: oracle.security.pki.OracleSecretStoreException: Credential already exists
    
    This is actually documented:

    Each user account must have its own unique connection string; you cannot create one connection string for multiple users.

    So what to do, then, if you find yourself in a situation where you need two different users to access the database in a passwordless manner using a wallet?

    Workaround:

    Use multiple aliases in tnsnames.ora pointing to the same database service.

    List the current contents of the wallet:
    mkstore -wrl $TNS_ADMIN/wallet -listCredential
    Oracle Secret Store Tool Release 19.0.0.0.0 - Production
    Version 19.4.0.0.0
    Copyright (c) 2004, 2024, Oracle and/or its affiliates. All rights reserved.
    
    Enter wallet password:
    List credential (index: connect_string username)
    1: mydb1_scott scott
    
    So user scott can log into the database passwordless using his own password which is securly stored in the wallet.

    The tnsnames.ora knows which service to connect to whenever "mydb01" is called:
    mydb1_scott =
      (DESCRIPTION =
        (ADDRESS = (PROTOCOL = TCP)(HOST = server1.oric.no)(PORT = 1521))
        (CONNECT_DATA =
          (SERVER = DEDICATED)
          (SERVICE_NAME = mydb1.oric.no)
          (INSTANCE_NAME = cdb)
        )
      )
    
    Let's add another connect_identifier in the tnsnames.ora file:
    mydb1_jim =
      (DESCRIPTION =
        (ADDRESS = (PROTOCOL = TCP)(HOST = server1.oric.no)(PORT = 1521))
        (CONNECT_DATA =
          (SERVER = DEDICATED)
          (SERVICE_NAME = mydb1.skead.no)
          (INSTANCE_NAME = cdb)
        )
      )
    
    Let's test it, using a random user, for example, system:
    sqlplus system@mydb1_jim
    Enter password:
    SQL>show user
    USER is "SYSTEM"
    
    So the connect identifier is working, it points towards a valid service being serviced by the listener on the server.

    Let's add another entry to the wallet for user jim, so that he can connect without supplying his password:
    mkstore -wrl $TNS_ADMIN/wallet -createCredential mydb1_jim jim
    Oracle Secret Store Tool Release 19.0.0.0.0 - Production
    Version 19.4.0.0.0
    Copyright (c) 2004, 2024, Oracle and/or its affiliates. All rights reserved.
    
    Your secret/Password is missing in the command line
    Enter your secret/Password: <-- password for user jim
    Re-enter your secret/Password: <-- reenter password for user jim
    Enter wallet password: <-- wallet password
    
    Jim can now login using his own password stored in the wallet:
    sqlplus /@mydb1_jim
    SQL>show user
    USER is "JIM"
    
    The contents of the wallet is now:
    mkstore -wrl $TNS_ADMIN/wallet -listCredential
    Oracle Secret Store Tool Release 19.0.0.0.0 - Production
    Version 19.4.0.0.0
    Copyright (c) 2004, 2024, Oracle and/or its affiliates. All rights reserved.
    
    Enter wallet password:
    List credential (index: connect_string username)
    2: mydb1_jim jim
    1: mydb1_scott scott