go - In CockroachDB, how do batches and transactions interact? -

when should use batches , when should use transactions? can embed transaction in batch? batch in transaction?

a batch collection of operations sent server single unit efficiency. equivalent sending same operations individual requests different threads. requests in batch may executed out of order, , it's possible operations in batch succeed while others fail.

in go, batches created batcher object db.b, , must passed db.run(). example:

err := db.run(db.b.put("a", "1").put("b", "2")) 

is equivalent to:

_, err1 := db.put("a", "1") _, err2 := db.put("b", "2") 

a transaction defines consistent , atomic sequence of operations. transactions guarantee consistency respect other operations in system: results of transaction cannot seen unless , until transaction committed. since transactions may need retried, transactions defined function objects (typically closures) may called multiple times.

in go, transactions created db.tx method. *client.tx parameter closure implements similar interface db; inside transaction must perform operations on object instead of original db. if function returns error, transaction aborted; otherwise commit. here transactional version of previous example (but see below more efficient version):

err := db.tx(func(tx *client.tx) error {     err := tx.put("a", "1")     if err != nil {         return err     }     return tx.put("b", "2") }) 

the previous example waits "a" write complete before starting "b" write, , waits "b" write complete before committing transaction. possible make more efficient using batches inside transaction. tx.b batcher object, db.b. in transaction, can run batches either tx.run or tx.commit. tx.commit commit transaction if , if other operations in batch succeed, , more efficient letting transaction commit automatically when closure returns. practice make last operation in transaction batch executed tx.commit:

err := db.tx(func(tx *client.tx) error {     return tx.commit(tx.b.put("a", "1").put("b", "2")) })