> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pg-sharding.tech/llms.txt
> Use this file to discover all available pages before exploring further.

# Distributed Transactions

SPQR supports distributed transactions across multiple shards with different commit strategies.

The `__spqr__commit_strategy` parameter controls how transactions are committed:

* `best-effort` or `1pc` - One-phase commit with no coordination between shards
* `2pc` - Two-phase commit with atomicity guarantees across shards

For atomic cross-shard transactions, use two-phase commit (2PC). Set `__spqr__commit_strategy` to `2pc` and ensure `max_prepared_transactions` > 0 on all shards.

```sql theme={null}
SET __spqr__commit_strategy TO '2pc';

BEGIN;
INSERT INTO shard1_table (id, data) VALUES (1, 'data1');
INSERT INTO shard2_table (id, data) VALUES (2, 'data2');
COMMIT; -- Atomically commits across shards
```

See [Distributed Transactions](/sharding/distributed_transactions) for detailed information on commit strategies, requirements, and best practices.