If the number of Paxos replicas of a log stream is different from that of full-featured replicas specified in the locality of the tenant due to exceptions, you can execute the ALTER SYSTEM MODIFY statement to specify the paxos_replica_num parameter to modify the number of Paxos replicas.
Limitations
You can modify the number of Paxos replicas of log streams of all tenants in the
systenant but modify only the number of Paxos replicas of log streams of the current tenant in a user tenant.For the same log stream in a tenant, multiple replica migration tasks can be performed in parallel, but other disaster recovery tasks (such as adding replicas, deleting replicas, converting replica types, and modifying the quorum size of the log stream) can be performed only one at a time.
You can query ongoing replica tasks from the
CDB_OB_LS_REPLICA_TASKSview in thesystenant or from theDBA_OB_LS_REPLICA_TASKSview in a user tenant.You can only decrease the value of the
paxos_replica_numparameter.
Prerequisites
You have the
ALTER SYSTEMprivilege.You have the
SELECTprivilege on the following views:DBA_OB_TENANTSDBA_OB_LS/CDB_OB_LSDBA_OB_LS_LOCATIONS/CDB_OB_LS_LOCATIONS
Procedure
Assume that log stream 1002 of a tenant named tenant1 has four full-featured replicas but the value of the paxos_replica_num parameter is 5. In this case, you can change the value of the paxos_replica_num parameter to 4 to make it consistent with the number of full-featured replicas specified in the locality of the tenant.
Log in to the target tenant.
Here is an example:
obclient -h172.30.xxx.xxx -P2883 -uroot@tenant1#obdemo -pxxxx -AFor more information about how to connect to a database, see Overview (MySQL mode) or Overview (Oracle mode).
Query the tenant ID of the target tenant.
systenantobclient(root@sys)[oceanbase]> SELECT TENANT_NAME,TENANT_ID FROM oceanbase.DBA_OB_TENANTS WHERE TENANT_NAME='tenant1';User tenant
MySQL modeOracle modeExecute the following statement in MySQL mode:
obclient(root@tenant1)[oceanbase]> SELECT TENANT_NAME, TENANT_ID FROM oceanbase.DBA_OB_TENANTS;Execute the following statement in Oracle mode:
obclient(SYS@tenant1)[SYS]> SELECT TENANT_NAME, TENANT_ID FROM SYS.DBA_OB_TENANTS;A sample query result is as follows:
+-------------+-----------+ | TENANT_NAME | TENANT_ID | +-------------+-----------+ | tenant1 | 1002 | +-------------+-----------+ 1 row in setThe query result shows that the tenant ID is
1002.For more information about the fields in the
DBA_OB_TENANTSview, see DBA_OB_TENANTS.
Query all log streams of the target tenant.
systenantobclient(root@sys)[oceanbase]> SELECT * FROM oceanbase.CDB_OB_LS WHERE TENANT_ID=1002;For more information about the fields in the
CDB_OB_LSview, see CDB_OB_LS.User tenant
MySQL modeOracle modeExecute the following statement in MySQL mode:
obclient(root@tenant1)[oceanbase]> SELECT * FROM oceanbase.DBA_OB_LS;Execute the following statement in Oracle mode:
obclient(SYS@tenant1)[SYS]> SELECT * FROM SYS.DBA_OB_LS;A sample query result is as follows:
+-------+--------+--------------+---------------+-------------+---------------------+----------+---------------------+---------------------+-----------+----------------+ | LS_ID | STATUS | PRIMARY_ZONE | UNIT_GROUP_ID | LS_GROUP_ID | CREATE_SCN | DROP_SCN | SYNC_SCN | READABLE_SCN | FLAG | UNIT_LIST | +-------+--------+--------------+---------------+-------------+---------------------+----------+---------------------+---------------------+-----------+----------------+ | 1 | NORMAL | z1;z2 | 0 | 0 | NULL | NULL | 1712455113896017202 | 1712455113896017202 | | | | 1001 | NORMAL | z1;z2 | 0 | 1001 | 1712125812893680165 | NULL | 1712455113896017202 | 1712455113896017202 | | 1002,1004,1006 | | 1002 | NORMAL | z1;z2 | 0 | 1002 | 1712125812908098857 | NULL | 1712455114041323052 | 1712455113540551113 | | 1001,1003,1005 | | 1003 | NORMAL | z1;z2 | 0 | 0 | 1712125828880850585 | NULL | 1712455113896017202 | 1712455113896017202 | DUPLICATE | | +-------+--------+--------------+---------------+-------------+---------------------+----------+---------------------+---------------------+-----------+----------------+ 4 rows in setThe query result shows that the
tenant1tenant has log streams1,1001, and1002, as well as broadcast log stream1003.For more information about the fields in the
DBA_OB_LSview, see DBA_OB_LS.
Query the replica distribution of each log stream.
The following example queries the replica distribution and the
paxos_replica_numvalue of log stream1002.systenantobclient(root@sys)[oceanbase]> SELECT * FROM oceanbase.CDB_OB_LS_LOCATIONS WHERE LS_ID=1002 AND TENANT_ID=1002;For more information about the fields in the
CDB_OB_LS_LOCATIONSview, see CDB_OB_LS_LOCATIONS.User tenant
MySQL modeOracle modeExecute the following statement in MySQL mode:
obclient(root@tenant1)[oceanbase]> SELECT * FROM oceanbase.DBA_OB_LS_LOCATIONS WHERE LS_ID=1002;Execute the following statement in Oracle mode:
obclient(SYS@tenant1)[SYS]> SELECT * FROM SYS.DBA_OB_LS_LOCATIONS WHERE LS_ID=1002;A sample query result is as follows:
+----------------------------+----------------------------+-------+----------------+----------+----------+------+----------+--------------------------------------------------------------------------------------------------------------------------------------+----------------------+--------------+--------------+---------+ | CREATE_TIME | MODIFY_TIME | LS_ID | SVR_IP | SVR_PORT | SQL_PORT | ZONE | ROLE | MEMBER_LIST | PAXOS_REPLICA_NUMBER | REPLICA_TYPE | LEARNER_LIST | REBUILD | +----------------------------+----------------------------+-------+----------------+----------+----------+------+----------+--------------------------------------------------------------------------------------------------------------------------------------+----------------------+--------------+--------------+---------+ | 2024-01-31 16:50:06.856652 | 2024-01-31 16:52:54.618093 | 1002 | 100.xx.xxx.012 | 5070 | 5105 | z1 | LEADER | 100.xx.xxx.012:5070:1,100.xx.xxx.001:5071:1706691024376341,100.xx.xxx.003:5073:1706691171162545,100.xx.xxx.004:5074:1706691096303187 | 5 | FULL | | FALSE | | 2024-01-31 16:50:24.450775 | 2024-01-31 16:52:54.760939 | 1002 | 100.xx.xxx.001 | 5071 | 5106 | z1 | FOLLOWER | NULL | NULL | FULL | | FALSE | | 2024-01-31 16:52:51.216095 | 2024-01-31 16:52:57.135393 | 1002 | 100.xx.xxx.003 | 5073 | 5108 | z2 | FOLLOWER | NULL | NULL | FULL | | FALSE | | 2024-01-31 16:51:36.356401 | 2024-01-31 16:52:54.686229 | 1002 | 100.xx.xxx.004 | 5074 | 5109 | z3 | FOLLOWER | NULL | NULL | FULL | | FALSE | +----------------------------+----------------------------+-------+----------------+----------+----------+------+----------+--------------------------------------------------------------------------------------------------------------------------------------+----------------------+--------------+--------------+---------+ 4 rows in setThe query result shows that log stream
1002has four full-featured replicas but itsPAXOS_REPLICA_NUMBERvalue is5. You must change thePAXOS_REPLICA_NUMBERvalue to4.
Execute the
ALTER SYSTEM MODIFYstatement to modify thepaxos_replica_numparameter.The syntax is as follows:
ALTER SYSTEM MODIFY LS [=] ls_id PAXOS_REPLICA_NUM [=] paxos_replica_num [TENANT [=] 'tenant_name'];The parameters in the syntax are described as follows:
ls_id: the ID of the target log stream.paxos_replica_num: the modified number of Paxos replicas of the log stream, which is the number of full-featured replicas specified in the locality of the tenant.When you specify the
paxos_replica_numparameter, take note of the following considerations:After you modify the value of the
paxos_replica_numparameter, both the Paxos replicas and the members in theMEMBER_LISTof the leader meet the majority principle.The value of the
paxos_replica_numparameter must be greater than or equal to the number of members in theMEMBER_LISTof the leader. You can query theMEMBER_LISTfrom theCDB_OB_LS_LOCATIONSview in thesystenant or from theDBA_OB_LS_LOCATIONSview in a user tenant.You can only decrease the value of the
paxos_replica_numparameter, and the decrease cannot exceed 1. In this example, you can only change the value to4.
If any one of the preceding conditions is not met, the system will return an error.
tenant_name: the name of the target tenant. You can specify another tenant in thesystenant and specify only the current tenant in a user tenant. If this parameter is not explicitly specified, the name of the current tenant is used. You cannot use theall,all_user, orall_metaoption in this statement to specify all tenants, all user tenants, or all meta tenants.
Here is an example:
obclient> ALTER SYSTEM MODIFY LS = 1002 paxos_replica_num = 4;Query the replica distribution of the log stream again.
systenantobclient(root@sys)[oceanbase]> SELECT * FROM oceanbase.CDB_OB_LS_LOCATIONS WHERE LS_ID=1002 AND TENANT_ID=1002;User tenant
MySQL modeOracle modeExecute the following statement in MySQL mode:
obclient(root@tenant1)[oceanbase]> SELECT * FROM oceanbase.DBA_OB_LS_LOCATIONS WHERE LS_ID=1002;Execute the following statement in Oracle mode:
obclient(SYS@tenant1)[SYS]> SELECT * FROM SYS.DBA_OB_LS_LOCATIONS WHERE LS_ID=1002;A sample query result is as follows:
+----------------------------+----------------------------+-------+----------------+----------+----------+------+----------+--------------------------------------------------------------------------------------------------------------------------------------+----------------------+--------------+--------------+---------+ | CREATE_TIME | MODIFY_TIME | LS_ID | SVR_IP | SVR_PORT | SQL_PORT | ZONE | ROLE | MEMBER_LIST | PAXOS_REPLICA_NUMBER | REPLICA_TYPE | LEARNER_LIST | REBUILD | +----------------------------+----------------------------+-------+----------------+----------+----------+------+----------+--------------------------------------------------------------------------------------------------------------------------------------+----------------------+--------------+--------------+---------+ | 2024-01-31 16:50:06.856652 | 2024-01-31 17:17:23.032797 | 1002 | 100.xx.xxx.012 | 5070 | 5105 | z1 | LEADER | 100.xx.xxx.012:5070:1,100.xx.xxx.001:5071:1706691024376341,100.xx.xxx.003:5073:1706691171162545,100.xx.xxx.004:5074:1706691096303187 | 4 | FULL | | FALSE | | 2024-01-31 16:50:24.450775 | 2024-01-31 17:17:22.976381 | 1002 | 100.xx.xxx.001 | 5071 | 5106 | z1 | FOLLOWER | NULL | NULL | FULL | | FALSE | | 2024-01-31 16:52:51.216095 | 2024-01-31 17:17:23.113112 | 1002 | 100.xx.xxx.003 | 5073 | 5108 | z2 | FOLLOWER | NULL | NULL | FULL | | FALSE | | 2024-01-31 16:51:36.356401 | 2024-01-31 17:17:23.715470 | 1002 | 100.xx.xxx.004 | 5074 | 5109 | z3 | FOLLOWER | NULL | NULL | FULL | | FALSE | +----------------------------+----------------------------+-------+----------------+----------+----------+------+----------+--------------------------------------------------------------------------------------------------------------------------------------+----------------------+--------------+--------------+---------+ 4 rows in setThe query result shows that the
PAXOS_REPLICA_NUMBERvalue of log stream1002is changed to4.