Limitations

Note:

At present, OceanBase Advanced Tutorial for DBAs applies only to MySQL tenants of OceanBase Database Community Edition. Features of Oracle tenants of OceanBase Database Enterprise Edition are not described in this topic. For more information about the differences between the two editions, see Differences between Enterprise Edition and Community Edition.

Cluster Name Length

Item	Maximum length
Cluster name	128 bytes

Identifier Length

Item	Maximum length
Username	64 bytes
Tenant name	63 bytes
Database name	128 bytes
Table name	64 characters
Column name	128 bytes
Index name	64 bytes
View name	64 bytes
Alias	255 bytes
Table group name	127 bytes
User-defined variable	64 characters

ODP Connections

Connections to databases

When you connect to OceanBase Database V4.x by using OceanBase Database Proxy (ODP), free routing between primary and standby databases is not supported.

Maximum number of connections

Item	Upper limit
Number of connections per ODP	It is specified by the client_max_connections parameter of 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.

Number of Partition Replicas

Item	Upper limit
Number of partition replicas per OBServer node	Unlimited. You can estimate the number of partition replicas of each OBServer node based on the memory size of the tenant. 1 GB of memory supports about 20,000 tablets.

Single Table

Item	Upper limit
Row length	1.5 MB
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	8,192 to 65,536. The maximum number of partitions in a single table in MySQL mode is specified by the tenant-level parameter max_partition_num. The default value is 8192.

Single Column

Item	Upper limit
Length of an index column	16 KB

String Type

Item	Maximum length
CHAR	256 characters
VARCHAR	262,144 characters
BINARY	256 bytes
VARBINARY	1,048,576 bytes
TINYBLOB	255 bytes
BLOB	65,535 bytes
MEDIUMBLOB	16,777,215 bytes
LONGBLOB	536,870,910 bytes
TINYTEXT	255 bytes
TEXT	65,535 bytes
MEDIUMTEXT	16,777,215 bytes
LONGTEXT	536,870,910 bytes

Feature Usage

The following table describes the limitations for using the Physical Standby Database feature.

Item	Description
Maximum number of standby tenants supported by one primary tenant	Unlimited.
Whether homogeneous resources are required for the primary and standby tenants	Resources of the primary and standby tenants do not need to be homogeneous. We recommend that you use the same resource specifications for the primary and standby tenants.
Parameters	The parameters of the primary tenant are independent of those of a standby tenant, and parameter modifications are not physically synchronized. After you modify a parameter of the primary tenant, you must assess whether to modify the corresponding parameter of the standby tenants.
System variables	System variables of the primary and standby tenants are physically synchronized. If you modify a system variable of the primary tenant, the system synchronously modifies the corresponding system variable of the standby tenants.
Users and passwords	You can create users and change user passwords only in the primary tenant. The updated information is synchronized to the standby tenants.
Read/write operations	A standby tenant supports only read operations.
Minor and major compactions	Minor compactions in the primary tenant are independent of those in the standby tenants. Major compactions are not performed in a standby tenant. Instead, the major compaction information is synchronized from the primary tenant to the standby tenants.
Switchover	All replicas of log streams of the standby tenants must be online.
Failover	All replicas of log streams of the standby tenants must be online.