Help Center/ Distributed Database Middleware/ User Guide (ME-Abu Dhabi Region)/ SQL Syntax/ DDL/ Sharding Algorithms/ RIGHT_SHIFT
Updated on 2022-02-22 GMT+08:00
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RIGHT_SHIFT

Application Scenarios

This algorithm applies if a large difference appears in high-digit part but a small difference in low-digit part of sharding key values. Using this algorithm ensures uniform distribution of remainders calculated from sharding key values. Therefore, data is evenly routed to different shards.

Instructions

The sharding key must be the numeric data type (INT, INTEGER, BIGINT, MEDIUMINT, SMALLINT, TINYINT, DECIMAL, or NUMERIC).

Data Routing

The data route depends on the remainder of the changed sharding key value divided by the number of shards or sharded tables. To change the sharding key value, you need to convert the value into a binary number and right shift its bits to gain a new binary number. The number of moved bits is specified in DDL statements. Then, convert the new binary number into a decimal number. This decimal number is the changed sharding key value.

Calculation Method

Table 1 Required calculation methods

Condition

Calculation Method

Example

Database sharding key ≠ Table sharding key

Database routing result = Database sharding key value % Database shards

Table routing result = Table sharding key value % Table shards

Database shard: (123456 >> 4)% 8 = 4

Table shard: (123456 >> 4) % 3 = 0

Database sharding key = Table sharding key

Database routing result = Sharding key value % Database shards

Table routing result = (Sharding key value % Database shards) x Table shards + (Sharding key value / Database shards) % Table shards

Database shard: (123456 >> 4)% 8 = 4

Table table: ((123456 >> 4) % 8) *3 + ((123456 >> 4)/8)%3= 13

Syntax for Creating Tables

create table RIGHT_SHIFT (    
    id int, 
    name varchar(30) DEFAULT NULL,  
    create_time datetime DEFAULT NULL,
    primary key(id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 
dbpartition by RIGHT_SHIFT(id, 4) 
tbpartition by RIGHT_SHIFT(id, 4) tbpartitions 2;

Precautions

  • The sharding key and its value cannot be modified.
  • The number of shifts cannot exceed the number of bits occupied by the integer type. If it exceeds, data will be routed to shard 0.
Parent topic: Sharding Algorithms