SHARD_ROW_ID_BITS
- Concept
- Examples

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-clustered 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

For details on the usage, see the Troubleshoot Hotspot Issues guide.

Examples

CREATE TABLE t (
    id INT PRIMARY KEY NONCLUSTERED
) SHARD_ROW_ID_BITS = 4;

ALTER TABLE t SHARD_ROW_ID_BITS = 4;