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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. 
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 for detailed information on commit strategies, requirements, and best practices.