warning cross-shard-tx

Транзакция с разными ключами шардирования или cross_shard: true.

What it means#

In the built-in store a transaction MUST touch one shard key (§11.2). atomic(db, cross_shard: true) asks for a two-phase commit, which this implementation does not provide (determined by the implementation, D-7790): the flag is accepted with this warning and the transaction runs as an ordinary single-shard one; at run time it fails with CrossShardTx when its rows live on different shards. The analyzer also reports a body whose Db.find / Db.deleteById of a sharded table use different literal keys.

Example#

use std.orm { Db }

@table("accounts")
data Account {
  @pk id: i64
  balance: i64
}

fn transfer(db: Db, a: Account, b: Account) db {
  atomic(db, cross_shard: true) {      // <- cross-shard-tx
    db.update(a)
    db.update(b)
  }
}

cross-shard-tx

How to fix#

Keep one shard key per transaction: route the work to the shard of the key, or use a saga for several shards.

use std.orm { Db }

@table("accounts")
data Account {
  @pk id: i64
  balance: i64
}

fn debit(db: Db, a: Account) db {
  atomic(db) {
    db.update(a)
  }
}

See also#

• atomic-db-effects