SHARD_ROW_ID_BITS

This document introduces the SHARD_ROW_ID_BITS table attribute, which is used to set the number of bits of the shards after the implicit _tidb_rowid is sharded.

Concept

For the tables with a non-integer primary key or no primary key, TiDB uses an implicit auto-increment row ID. When a large number of INSERT operations are performed, the data is written into a single Region, causing a write hot spot.

To mitigate the hot spot issue, you can configure SHARD_ROW_ID_BITS. The row IDs are scattered and the data are written into multiple different Regions.

• SHARD_ROW_ID_BITS = 4 indicates 16 shards
• SHARD_ROW_ID_BITS = 6 indicates 64 shards
• SHARD_ROW_ID_BITS = 0 indicates the default 1 shard

Examples

• CREATE TABLE: CREATE TABLE t (c int) SHARD_ROW_ID_BITS = 4;
• ALTER TABLE: ALTER TABLE t SHARD_ROW_ID_BITS = 4;