Oracle 23ai — Control PDB Open Order

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 Question: If a CDB contains multiple PDBs, how can we control the order in which these PDBs open?

Answer:
Before Oracle 23ai, there was no direct solution for managing the order of PDB openings. Executing the startup command provided no guarantee about the opening sequence of the PDBs, as they typically opened based on their container numbers. However, Oracle 23ai introduced a new feature allowing users to assign a PRIORITY to each PDB, which determines the order of operations such as opening, upgrading, or restoring PDBs.

The general syntax for the command is as follows:

ALTER PLUGGABLE DATABASE <PDB name> PRIORITY <value>
  • PDB name is mandatory.
  • PRIORITY can take a value between 1 and 4096. A lower number indicates a higher priority. For example, a PDB with priority 1 will open before one with priority 2.

Example: Assigning Priorities

SQL> show pdbs
    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ ONLY  NO
         3 RANPDB                      READ WRITE NO
         4 BABOLPDB                       READ WRITE NO
         5 VARAMINPDB                     READ WRITE NO
         6 ABADANPDB                      READ WRITE NO
SQL> ALTER PLUGGABLE DATABASE babolpdb PRIORITY 1;
Pluggable database altered.
SQL> ALTER PLUGGABLE DATABASE ABADANPDB PRIORITY 2;
Pluggable database altered.
SQL> ALTER PLUGGABLE DATABASE VARAMINPDB PRIORITY 3;
Pluggable database altered.
SQL> ALTER PLUGGABLE DATABASE RANPDB PRIORITY 4;
Pluggable database altered.

Result After Restart

Upon restarting the database, PDBs open in the specified order:

SQL> startup force;
SQL> select OPEN_TIME, NAME, PRIORITY from v$pdbs order by 1;
OPEN_TIME                                NAME         PRIORITY
---------------------------------------- ---------- ----------
10-MAY-23 05.52.43.190 PM +04:30         PDB$SEED            1
10-MAY-23 05.52.43.812 PM +04:30         BABOLPDB            1
10-MAY-23 05.52.44.889 PM +04:30         ABADANPDB           2
10-MAY-23 05.52.45.929 PM +04:30         VARAMINPDB          3
10-MAY-23 05.52.47.102 PM +04:30         RANPDB              4

Result After Restart

The opening sequence is also recorded in the Alert Log:

PDB$SEED(2):Opening pdb with Resource Manager plan: DEFAULT_PLAN
BABOLPDB(4):SUPLOG: Initialize PDB SUPLOG SGA, old value 0x0, new value 0x18
2023-05-10T17:52:44.739491+04:30
ABADANPDB(6):SUPLOG: Initialize PDB SUPLOG SGA, old value 0x0, new value 0x18
2023-05-10T17:52:45.784421+04:30
VARAMINPDB(5):SUPLOG: Initialize PDB SUPLOG SGA, old value 0x0, new value 0x18
2023-05-10T17:52:46.828984+04:30
RANPDB(3):SUPLOG: Initialize PDB SUPLOG SGA, old value 0x0, new value 0x18

PDB Upgrade Priority (12cR2 and Later)

Starting with Oracle 12cR2, upgrade priorities for PDBs can also be set using a similar command:

SQL*Plus: Release 12.0.0.0.0 - Production on Wed May 10 16:56:59 2023
SQL> ALTER PLUGGABLE DATABASE babolpdb UPGRADE PRIORITY 5;
Pluggable database altered.

This ensures precise control over PDB behavior during upgrades.

Telegram channel :https://t.me/oracledb

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