General Guidelines

Database Features

**Table 1** Recommended Database Features
Category	Feature	Description
Table type	Hash distributed table	It supports automatic sharding, suitable for tables with a large amount of data (for example, transaction records).
Table type	REPLICATE distributed table	It is a common table without sharding, suitable for tables with a small amount of data (for example, the country name table).
Transaction	Distributed transaction (weak consistency)	In GTM free mode, strong consistency is ensured in sharding scenarios, but cross-DN shard read consistency is not ensured. It is recommended that the perfect sharding services be used.
Transaction	Distributed transaction (strong consistency)	The GTM lite mode ensures cross-DN read and write consistency. It is recommended that non-perfect sharding services be used.
Capacity expansion	On-line smooth expansion	Online services are interrupted for less than 5s. To synchronize logs written during the switchover/failover, the capacity can be scaled up to 100 GB per hour.
Deployment	3 AZs and 3 replicas	You are advised to use the 3-AZ 3-replica deployment by default.
Data type	Integer	TINYINT, SMALLINT, INTEGER, BIGINT
	Any precision	NUMERIC/DECIMAL
	Floating point	REAL/FLOAT4,DOUBLE PRECISION/FLOAT8,FLOAT
	Boolean	BOOLEAN
	Fixed-length character	CHAR(n)
	Variable-length character	VARCHAR(n),NVARCHAR2(n), TEXT
	Time	DATE, TIME, TIMETZ, TIMESTAMP, TIMESTAMPTZ, SMALLDATETIME, INTERVAL, REALTIME
	Binary	BYTEA (variable-length binary)
	Bit string	BIT(n), VARBIT(n)
Function	Character processing function	String data type processing function
	Binary string function	Binary string type processing function
	Numeric operation function	Numeric type processing function
	Time and date processing function	Time and date type processing function
Index	Primary key or unique index	Single-column or multi-column primary key or unique index
Index	B-tree index	Index type

Features that are not listed include but are not limited to user-defined and UUID data types, and trigger features. If you want to use them, contact GaussDB database technical personnel for evaluation.

Database Indicators

**Table 2** Database indicators
Indicator	Recommended Value
Optimal number of shards in a DB instance (number of primary DNs)	< 256
Optimal number of long connections in a DB instance	< 100,000
Maximum data volume on a single DN	2 TB
Optimal number of fields in a single table	< 50
Optimal number of indexes in a table	< 5
Optimal number of composite indexes in a table	< 3
Optimal number of columns in a single composite index	< 5
Optimal width of a single line	< 2,000
Recommended maximum value of a single field	10 MB
Optimal SQL statement length	< 5,000
Information indicating insufficient disk capacity (considering capacity expansion)	45%
Alarm indicating insufficient disk capacity (considering capacity expansion)	55%