Manually control a major compaction

After you use the MAJOR FREEZE statement to initiate a major compaction, the system automatically schedules the major compaction task. Starting from OceanBase Database V4.0.x, a unified major compaction strategy is used to implement the major compaction process. In other words, a major compaction is performed for all zones of the tenant at the same time. When the major compaction is completed for all zones, the major compaction is considered completed for the tenant.

During the major compaction, you do not need to manually control the compaction sequence of the zones and rotating compaction is not involved. If an error occurs during the major compaction, you can manually control the major compaction. For example, if a checksum verification error occurs, the current major compaction for the tenant cannot end. In this case, you can suspend the current major compaction. After the checksum resumes normal as a result of manual intervention, you can clear the checksum error tag and resume the major compaction.

Prerequisites

A major compaction has been initiated by using the MAJOR FREEZE statement. For more information about how to manually initiate a major compaction, see Manually initiate a major compaction.

Considerations

When the major compaction task is suspended, you can initiate a tenant-level major compaction, but not a partition-level major compaction. However, the system does not immediately execute the tenant-level major compaction task, but waits until the major compaction task is resumed.

Manually control a major compaction from the sys tenant

After a major compaction begins, you can control the major compaction for all tenants or specified tenants from the sys tenant. You can control tenant-level and partition-level major compactions.

To do so, perform the following steps:

1. Log on to the sys tenant of the cluster as the root user.

2. Perform the following steps to control the major compaction based on the actual situation.

   • Suspend the major compaction for all user tenants, all meta tenants, or specified tenants

     You can execute the following statements to suspend the major compaction for all user tenants, all meta tenants, or specified tenants.

     • Suspend the major compaction for all user tenants

       ALTER SYSTEM SUSPEND MERGE TENANT = all_user;
       

       or

       ALTER SYSTEM SUSPEND MERGE TENANT = all;
       

       Note

       In OceanBase Database V4.2.1 and later, TENANT = all_user and TENANT = all express the same semantics. If you want an operation to take effect on all user tenants, we recommend that you use TENANT = all_user. TENANT = all will be deprecated.

     • Suspend the major compaction for all meta tenants

       ALTER SYSTEM SUSPEND MERGE TENANT = all_meta;
       

     • Suspend the major compaction for specified tenants

       ALTER SYSTEM SUSPEND MERGE TENANT = tenant1,tenant2;
       

     Note that the equal sign (=) is optional, and you must replace tenant1 and tenant2 with the actual tenant names.

   • Resume a major compaction

     You can resume a major compaction by execute the following statements:

     • Resume the major compaction for all user tenants

       ALTER SYSTEM RESUME MERGE TENANT = all_user;
       

       or

       ALTER SYSTEM RESUME MERGE TENANT = all;
       

       Note

       In OceanBase Database V4.2.1 and later, TENANT = all_user and TENANT = all express the same semantics. If you want an operation to take effect on all user tenants, we recommend that you use TENANT = all_user. TENANT = all will be deprecated.

     • Resume the major compaction for all meta tenants

       ALTER SYSTEM RESUME MERGE TENANT = all_meta;
       

     • Resume the major compaction for specified tenants

       ALTER SYSTEM RESUME MERGE TENANT = tenant1,tenant2;
       

     Note that the equal sign (=) is optional, and you must replace tenant1 and tenant2 with the actual tenant names.

   • Clear the checksum error tag

     If a checksum verification error occurs during a major compaction and is resolved after manual intervention, you can clear this checksum error tag to resume the major compaction by executing the following statements:

     • Clear the checksum error tags for all user tenants

       ALTER SYSTEM CLEAR MERGE ERROR TENANT = all_user;
       

       or

       ALTER SYSTEM CLEAR MERGE ERROR TENANT = all;
       

       Note

       In OceanBase Database V4.2.1 and later, TENANT = all_user and TENANT = all express the same semantics. If you want an operation to take effect on all user tenants, we recommend that you use TENANT = all_user. TENANT = all will be deprecated.

     • Clear the checksum error tags for all meta tenants

       ALTER SYSTEM CLEAR MERGE ERROR TENANT = all_meta;
       

     • Clear the checksum error tags for specified tenants

       ALTER SYSTEM CLEAR MERGE ERROR TENANT = tenant1,tenant2;
       

     Note that the equal sign (=) is optional, and you must replace tenant1 and tenant2 with the actual tenant names.

Manually control a major compaction from a user tenant

In a user tenant, you can control the major compaction of only the current tenant. You can control tenant-level and partition-level major compactions.

1. Log on to the database as an administrator of a user tenant.

2. Perform the following steps to control the major compaction based on the actual situation.

   • Suspend the major compaction for the current tenant

     To suspend the major compaction for the current tenant, execute the following statement:

     obclient> ALTER SYSTEM SUSPEND MERGE;
     

   • Resume a major compaction

     After a major compaction is suspended, you can resume it.

     The statement is as follows:

     obclient> ALTER SYSTEM RESUME MERGE;
     

   • Clear the checksum error tag

     If a checksum verification error occurs during a major compaction and is resolved after manual intervention, you can clear this checksum error tag and resume the major compaction.

     The statement is as follows:

     obclient> ALTER SYSTEM CLEAR MERGE ERROR;
     

References

• Automatically trigger a major compaction

• Configure scheduled major compactions

• Manually initiate a major compaction

• View the major compaction process