Limitations|V3.2.4|OceanBase Database| docs|Distributed Database

Limitations

Last Updated：2023-10-24 09:23:03 Updated

Identifier length limits

MySQL mode

Item	Maximum length
Cluster name	128 bytes
Tenant name	63 bytes
Username	64 bytes
Database name	128 bytes
Table name	64 bytes
Column name	128 bytes
Index name	64 bytes
View name	64 bytes
Alias	255 bytes
Table group name	127 bytes

Oracle mode

Item	Maximum length
Cluster name	128 bytes
Tenant name	63 bytes
Username	64 bytes
Table name	128 bytes
Column name	128 bytes
Index name	128 bytes
View name	128 bytes
Alias	255 bytes
Object name	128 bytes
Table group name	127 bytes

Maximum number of ODP connections

Item	Upper limit
Number of connections per OceanBase Database Proxy (ODP)	You can specify the `client_max_connections` parameter of an ODP to specify the maximum number of connections of the ODP. The default value is 8192. Note You can increase the number of ODP nodes or the value of the `client_max_connections` parameter to increase the maximum number of connections for a cluster.

Maximum number of partition replicas

Item	Upper limit
Number of partition replicas per OBServer node	500,000 Note The number of partition replicas on each OBServer node depends on server configurations. If the server configuration is moderate, we recommend that you set the number of partition replicas to 30,000 for each OBServer node.

Single-table limits

Item	Upper limit
Row length	1.5 MB
Number of rows	Unlimited
Number of columns	4,096
Number of indexes	128
Total number of index columns	512
Index length	16 KB
Total number of primary key columns	64
Primary key length	16 KB
Number of partitions	Oracle mode: 65,536 MySQL mode: 8,192

Single-column limits

Item	Upper limit
Length of an index column	16 KB

String type limits

MySQL mode

Item	Maximum length
`CHAR`	256 bytes
`VARCHAR`	262144 bytes
`BINARY`	256 bytes
`VARBINARY`	1048576 bytes
`TINYBLOB`	256 bytes
`BLOB`	65536 bytes
`MEDIUMBLOB`	16777216 bytes
`LONGBLOB`	50331648 bytes
`TINYTEXT`	256 bytes
`TEXT`	65536 bytes
`MEDIUMTEXT`	16777216 bytes
`LONGTEXT`	50331648 bytes

Oracle mode

Item	Maximum length
`CHAR`	2000 bytes
`VARCHAR`	32767 bytes
`VARCHAR2`	32767 bytes
`NCHAR`	2000 bytes
`NVARCHAR2`	32767 bytes
`BLOB`	67108864 bytes
`CLOB`	67108864 bytes

Feature limitations

Backup and restore limitations

When you perform a secondary backup, ensure that at least one valid backup copy exists in the source backup location.

Primary/standby cluster limitations

Item	Description
Cluster-level synchronization	Data is synchronized from the primary cluster to standby clusters by cluster.
Tenant-level synchronization	Data cannot be synchronized from the primary cluster to standby clusters by tenant.
Maximum number of standby clusters	31
Maximum number of DDL statements for the `sys` tenant of a standby cluster	Less than 500 per second
Synchronization of parameters	Modifications to parameters in the primary cluster are not synchronized to standby clusters.
Synchronization of system variables of user tenants	Modifications to regular system variables in the primary cluster are synchronized to standby clusters.
Table- or database-level locality and primary zone settings in the primary cluster	Not supported
Tenant-level locality and primary zone settings in the primary cluster	Supported
Replica types	Full-featured, log-only, read-only, and encrypted voting replicas are supported. Hybrid deployment of replicas cannot be configured in Locality.
Upgrade mode	Rolling upgrades are supported starting from OceanBase Database V2.2.60.
GTS	GTS must be enabled for all user tenants.
One-phase commits of distributed transactions	`enable_one_phase_commit` must be set to False for the primary and standby clusters.
Schema objects	Tables can be copied, but locality cannot be set for tables.
Adding a standby cluster	After an upgrade, a standby cluster can be added only after a major compaction is performed. The standby cluster must be empty. The primary cluster must not contain tables that are being split. The primary cluster can contain only locality and primary zone configurations of tenants. The primary cluster must not be upgrading. The OceanBase Database version of the standby cluster must be consistent with that of the primary cluster. The replicas deleted from the schema must all be garbage collected. GTS must be enabled for all user tenants. `enable_one_phase_commit` must be set to False for the primary cluster.
Standby cluster operations	DML operations, explicit transaction enabling, `SELECT FOR UPDATE`, and DDL operations cannot be performed on a standby cluster.
Switchover	All servers of the primary and standby clusters must be online. No major compaction error is allowed. If write is stopped during a switchover, the original primary cluster returns a `4688` error or a timeout error. If the switchover duration exceeds the value of `max_stale_time_for_weak_consistency`, which is 5s by default, the standby cluster stops the weak-consistency read service. `enable_rereplication` must be set to True for the standby cluster. Otherwise, the switchover cannot be performed. When one primary cluster and multiple standby clusters are configured, all standby clusters, except those in `DISABLED` state, must be active. The primary and standby clusters must be of the same version. The primary cluster must not be undergoing a physical backup operation. No replica in the Restore state is allowed. In maximum protection mode, the log transfer mode of the primary cluster must be `SYNC`. The primary cluster must not be upgrading.
Failover	Failovers are supported in maximum performance mode. Failovers are supported in maximum protection mode. Failovers are supported in maximum availability mode. A lossy failover requires that all servers be active. After a failover, a standby cluster can be added only after a major compaction is performed.
Protection mode	The maximum performance, maximum protection, and maximum availability modes are supported. The configurations of standby clusters in maximum protection or maximum availability mode are subject to the following limits: You have one standby cluster in `SYNC` mode. The standby cluster in `SYNC` mode cannot be modified, deleted, or disabled. The log transfer mode of the standby cluster in `SYNC` mode must not be changed to `ASYNC`. Switchovers in maximum protection or maximum availability mode are subject to the following limits: Only the standby cluster in `SYNC` mode can be switched to the primary role. The log transfer mode of the primary cluster must be set to `SYNC` to ensure that it is in maximum protection mode after a primary/standby switchover.
Physical backup and restore	When standby clusters exist, the primary cluster cannot be restored. Standby clusters do not support backup and log archiving. Standby clusters cannot be physically restored. After a tenant is physically restored in the primary cluster, a standby cluster can be added only after a major compaction is performed.
Disconnecting a standby cluster	The role of the standby cluster is `PHYSICAL STANDBY`. All servers in the standby cluster are active. The primary cluster must not be upgrading. You can run the disconnecting command for the following switchover states: `NOT ALLOWED`, `TO PRIMARY`, and `DISCONNECT`.