Infrastructure at your Service

Franck Pachot

Active Data Guard services in Multitenant

By September 16, 2017 Oracle No Comments

A database (or the CDB in multitenant) registers its name as the default service. When a standby database is on the same server, or same cluster, you have no problem because this database name is the db_unique_name which is different between the primary and the standby(s).

In multitenant, in addition to that, each PDB registers its name as a service. But the PDB name is the same in the primary and the standby database. This means that we have the same service name registered for the PDB in primary and standby:

Service "pdb1" has 2 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Instance "CDB2B", status READY, has 1 handler(s) for this service...

We cannot change that, and then it is strongly recommended to create different services for the PDB in primary and standby.

The PDB default service name

Here is what we want to avoid.
I’ve a container database (db_name=CDB2) with its primary (db_unique_name=CDB2A) and standby (db_unique_name=CDB2B) on the same server, registered to the same listener:

Service "59408d6bed2c1c8ee0536a4ea8c0cfa9" has 2 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "CDB2A" has 1 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Service "CDB2AXDB" has 1 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Service "CDB2A_DGB" has 1 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Service "CDB2A_DGMGRL" has 1 instance(s).
Instance "CDB2A", status UNKNOWN, has 1 handler(s) for this service...
Service "CDB2B" has 1 instance(s).
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "CDB2BXDB" has 1 instance(s).
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "CDB2B_DGB" has 1 instance(s).
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "CDB2B_DGMGRL" has 1 instance(s).
Instance "CDB2B", status UNKNOWN, has 1 handler(s) for this service...
Service "CDB2_CFG" has 2 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "pdb1" has 2 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Instance "CDB2B", status READY, has 1 handler(s) for this service...

The PDB1 service is registered from both instances, and then when I use it in my connection string I’m connected at random to the primary or the standby:

22:27:46 SQL> connect sys/oracle@//localhost:1522/pdb1 as sysdba
Connected.
22:27:51 SQL> select * from v$instance;
 
INSTANCE_NUMBER INSTANCE_NAME HOST_NAME VERSION STARTUP_TIME STATUS PARALLEL THREAD# ARCHIVER LOG_SWITCH_WAIT LOGINS SHUTDOWN_PENDING DATABASE_STATUS INSTANCE_ROLE ACTIVE_STATE BLOCKED CON_ID INSTANCE_MODE EDITION FAMILY DATABASE_TYPE
--------------- ------------- --------- ------- ------------ ------ -------- ------- -------- --------------- ------ ---------------- --------------- ------------- ------------ ------- ------ ------------- ------- ------ -------------
1 CDB2B VM106 12.2.0.1.0 15-SEP-17 OPEN NO 1 STARTED ALLOWED NO ACTIVE PRIMARY_INSTANCE NORMAL NO 0 REGULAR EE SINGLE
 
22:28:00 SQL> connect sys/oracle@//localhost:1522/pdb1 as sysdba
Connected.
22:28:06 SQL> /
 
INSTANCE_NUMBER INSTANCE_NAME HOST_NAME VERSION STARTUP_TIME STATUS PARALLEL THREAD# ARCHIVER LOG_SWITCH_WAIT LOGINS SHUTDOWN_PENDING DATABASE_STATUS INSTANCE_ROLE ACTIVE_STATE BLOCKED CON_ID INSTANCE_MODE EDITION FAMILY DATABASE_TYPE
--------------- ------------- --------- ------- ------------ ------ -------- ------- -------- --------------- ------ ---------------- --------------- ------------- ------------ ------- ------ ------------- ------- ------ -------------
1 CDB2A VM106 12.2.0.1.0 15-SEP-17 OPEN NO 1 STARTED ALLOWED NO ACTIVE PRIMARY_INSTANCE NORMAL NO 0 REGULAR EE SINGLE
 
22:28:07 SQL> connect sys/oracle@//localhost:1522/pdb1 as sysdba
Connected.
22:28:10 SQL> /
 
INSTANCE_NUMBER INSTANCE_NAME HOST_NAME VERSION STARTUP_TIME STATUS PARALLEL THREAD# ARCHIVER LOG_SWITCH_WAIT LOGINS SHUTDOWN_PENDING DATABASE_STATUS INSTANCE_ROLE ACTIVE_STATE BLOCKED CON_ID INSTANCE_MODE EDITION FAMILY DATABASE_TYPE
--------------- ------------- --------- ------- ------------ ------ -------- ------- -------- --------------- ------ ---------------- --------------- ------------- ------------ ------- ------ ------------- ------- ------ -------------
1 CDB2B VM106 12.2.0.1.0 15-SEP-17 OPEN NO 1 STARTED ALLOWED NO ACTIVE PRIMARY_INSTANCE NORMAL NO 0 REGULAR EE SINGLE
 
22:28:11 SQL> connect sys/oracle@//localhost:1522/pdb1 as sysdba
Connected.
22:28:13 SQL> /
 
INSTANCE_NUMBER INSTANCE_NAME HOST_NAME VERSION STARTUP_TIME STATUS PARALLEL THREAD# ARCHIVER LOG_SWITCH_WAIT LOGINS SHUTDOWN_PENDING DATABASE_STATUS INSTANCE_ROLE ACTIVE_STATE BLOCKED CON_ID INSTANCE_MODE EDITION FAMILY DATABASE_TYPE
--------------- ------------- --------- ------- ------------ ------ -------- ------- -------- --------------- ------ ---------------- --------------- ------------- ------------ ------- ------ ------------- ------- ------ -------------
1 CDB2A VM106 12.2.0.1.0 15-SEP-17 OPEN NO 1 STARTED ALLOWED NO ACTIVE PRIMARY_INSTANCE NORMAL NO 0 REGULAR EE SINGLE

I don’t want to use a service that connects at random and then I need to create different services.

Read-Only service for the Active Data Guard standby

I’m in Oracle Restart and I create the service with srvctl (but you can also create it with dbms_service when not running with Grid Infrastructure):


srvctl add service -db cdb2b -service pdb1_ro -pdb pdb1 -role physical_standby

This creates the service for the standby database (CDB2B) to be started when in physical standby role, and the service connects to the pluggable database PDB1.
But I cannot start it:

srvctl start service -db cdb2b -service pdb1_ro -pdb pdb1
 
 
PRCD-1084 : Failed to start service pdb1_ro
PRCR-1079 : Failed to start resource ora.cdb2b.pdb1_ro.svc
CRS-5017: The resource action "ora.cdb2b.pdb1_ro.svc start" encountered the following error:
ORA-16000: database or pluggable database open for read-only access
ORA-06512: at "SYS.DBMS_SERVICE", line 5
ORA-06512: at "SYS.DBMS_SERVICE", line 288
ORA-06512: at line 1
. For details refer to "(:CLSN00107:)" in "/u01/app/12.2/diag/crs/vm106/crs/trace/ohasd_oraagent_oracle.trc".
 
CRS-2674: Start of 'ora.cdb2b.pdb1_ro.svc' on 'vm106' failed

The reason is that the service information must be stored in the dictionary, SYS.SERVICE$ table, and you cannot do that on a read-only database.

This has been explained a long time ago by Ivica Arsov on his blog: https://iarsov.com/oracle/data-guard/active-services-on-physical-standby-database/ and nothing has changed. You need to create the service on the primary so that the update of SYS.SERVICE$ is propagated to the standby database through log shipping:


srvctl add service -db cdb2a -service pdb1_ro -pdb pdb1 -role physical_standby

This is not sufficient because the insert in SYS.SERVICE$ does not occur yet:

SQL> alter session set container=PDB1;
 
Session altered.
 
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
------ -------- --------- ----------
3 PDB1 READ WRITE NO
 
SQL> select * from service$;
 
SERVICE_ID NAME NAME_HASH NETWORK_NAME CREATION_DATE CREATION_DATE_HASH DELETION_DATE FAILOVER_METHOD FAILOVER_TYPE FAILOVER_RETRIES FAILOVER_DELAY MIN_CARDINALITY MAX_CARDINALITY GOAL FLAGS EDITION PDB RETENTION_TIMEOUT REPLAY_INITIATION_TIMEOUT SESSION_STATE_CONSISTENCY SQL_TRANSLATION_PROFILE MAX_LAG_TIME GSM_FLAGS PQ_SVC STOP_OPTION FAILOVER_RESTORE DRAIN_TIMEOUT
---------- ---- --------- ------------ ------------- ------------------ ------------- --------------- ------------- ---------------- -------------- --------------- --------------- ---- ----- ------- --- ----------------- ------------------------- ------------------------- ----------------------- ------------ --------- ------ ----------- ---------------- -------------
14 pdb1 1888881990 pdb1 15-SEP-17 1332716667 136 PDB1

As explained by Ivica in his blog post, we need to start the service once to have the row inserted in SERVICE$:

srvctl start service -db cdb2a -service pdb1_ro -pdb pdb1
srvctl stop service -db cdb2a -service pdb1_ro

Now the service information is persistent in the dictionary:

SQL> alter session set container=PDB1;
Session altered.
 
SQL> show pdbs
 
CON_ID CON_NAME OPEN MODE RESTRICTED
------ -------- ---- ---- ----------
3 PDB1 READ WRITE NO
 
SQL> select * from service$;
 
SERVICE_ID NAME NAME_HASH NETWORK_NAME CREATION_DATE CREATION_DATE_HASH DELETION_DATE FAILOVER_METHOD FAILOVER_TYPE FAILOVER_RETRIES FAILOVER_DELAY MIN_CARDINALITY MAX_CARDINALITY GOAL FLAGS EDITION PDB RETENTION_TIMEOUT REPLAY_INITIATION_TIMEOUT SESSION_STATE_CONSISTENCY SQL_TRANSLATION_PROFILE MAX_LAG_TIME GSM_FLAGS PQ_SVC STOP_OPTION FAILOVER_RESTORE DRAIN_TIMEOUT
---------- ---- --------- ------------ ------------- ------------------ ------------- --------------- ------------- ---------------- -------------- --------------- --------------- ---- ----- ------- --- ----------------- ------------------------- ------------------------- ----------------------- ------------ --------- ------ ----------- ---------------- -------------
14 pdb1 1888881990 pdb1 15-SEP-17 1332716667 136 PDB1
1 pdb1_ro 1562179816 pdb1_ro 15-SEP-17 1301388390 0 0 0 8 PDB1 86400 300 DYNAMIC ANY 0 0 0 0

This is from the primary, but after the redo has been transported and applied, I have the same on the standby. Now I can start the service I’ve created for the standby:

srvctl start service -db cdb2b -service pdb1_ro -pdb pdb1

Here is the new service registered on the listener, which I can use to connect to the read-only PDB1 on the Active Data Guard standby:

Service "pdb1" has 2 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "pdb1_ro" has 1 instance(s).
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "pdb1_rw" has 1 instance(s).

Read-Write service for the primary

You can see above that in order to select from SERVICE$ I connected to CDB$ROOT and switched to PDB1 with ‘set container’. There’s no other choice because using the service name directs me at random to any instance. Then, I need a service to connect to the primary only, and I’ll call it PDB1_RW as it is opened in Read Write there.

srvctl add service -db cdb2a -service pdb1_rw -pdb pdb1 -role primary
srvctl start service -db cdb2a -service pdb1_rw

Finally, here are the services registered from the listener:

Service "pdb1" has 2 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "pdb1_ro" has 1 instance(s).
Instance "CDB2B", status READY, has 1 handler(s) for this service...
Service "pdb1_rw" has 1 instance(s).
Instance "CDB2A", status READY, has 1 handler(s) for this service...

I’ll probably never use the ‘PDB1′ service because I want to know where I connect to.

In case of switchover, I also create the Read Write service in for the standby:

srvctl add service -db cdb2b -service pdb1_rw -pdb pdb1 -role primary

Here are the resources when CDB2A is the primary:

$ crsctl stat resource -t -w "TYPE = ora.service.type"
--------------------------------------------------------------------------------
Name Target State Server State details
--------------------------------------------------------------------------------
Cluster Resources
--------------------------------------------------------------------------------
ora.cdb2a.pdb1_ro.svc
1 OFFLINE OFFLINE STABLE
ora.cdb2a.pdb1_rw.svc
1 ONLINE ONLINE vm106 STABLE
ora.cdb2b.pdb1_ro.svc
1 ONLINE ONLINE vm106 STABLE
ora.cdb2b.pdb1_rw.svc
1 OFFLINE OFFLINE STABLE
--------------------------------------------------------------------------------

I test as switchover to CDB2B:

$ dgmgrl sys/oracle
DGMGRL for Linux: Release 12.2.0.1.0 - Production on Fri Sep 15 23:41:26 2017
 
Copyright (c) 1982, 2017, Oracle and/or its affiliates. All rights reserved.
 
Welcome to DGMGRL, type "help" for information.
Connected to "CDB2B"
Connected as SYSDG.
DGMGRL> switchover to cdb2b;
Performing switchover NOW, please wait...
New primary database "cdb2b" is opening...
Oracle Clusterware is restarting database "cdb2a" ...
Switchover succeeded, new primary is "cdb2b"

Here are the services:

[oracle@VM106 blogs]$ crsctl stat resource -t -w "TYPE = ora.service.type"
--------------------------------------------------------------------------------
Name Target State Server State details
--------------------------------------------------------------------------------
Cluster Resources
--------------------------------------------------------------------------------
ora.cdb2a.pdb1_ro.svc
1 ONLINE ONLINE vm106 STABLE
ora.cdb2a.pdb1_rw.svc
1 OFFLINE OFFLINE STABLE
ora.cdb2b.pdb1_ro.svc
1 OFFLINE OFFLINE STABLE
ora.cdb2b.pdb1_rw.svc
1 ONLINE ONLINE vm106 STABLE
--------------------------------------------------------------------------------

So what?

The recommendations are not new here:

  • Always do the same on the primary and the standby. Create services on both sites, then have started them depending on the role
  • Always use one or several application services rather than the default one, in order to have better control and flexibility on where you connect

In multitenant, because services are mandatory to connect to a container with a local user, all the recommendations about services are even more important than before. If you follow them, you will see that multitenant is not difficult at all.

This case may seem improbable, because you probably don’t put the standby on the same server or cluster as the primary. But you may have several standby databases on the same server. About the service registered from the PDB name, just don’t use it. I’m more concerned by the GUID service name (here 59408d6bed2c1c8ee0536a4ea8c0cfa9) which is also declared by both databases. If you plan to use online PDB relocate in a Data Guard configuration then be careful with that. I’ve not tested it, but it is probably better to keep the standby PDB closed, or at least do not register it on the same listener.

 

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Franck Pachot
Franck Pachot

Technology Leader