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Lightweight transaction (LWT) query

A lightweight transaction query can be expressed just like any other query, via Session, with the notable difference of having an additional consistency level parameter - the serial_consistency_level.

Format of the query

A lightweight transaction query is not a separate type - it can be expressed just like any other queries: via SimpleQuery, PreparedStatement, batches, and so on. The difference lays in the query string itself - when it contains a condition (e.g. IF NOT EXISTS), it becomes a lightweight transaction. It’s important to remember that CQL specification requires a separate, additional consistency level to be defined for LWT queries - serial_consistency_level. The serial consistency level can only be set to two values: SerialConsistency::Serial or SerialConsistency::LocalSerial. The “local” variant makes the transaction consistent only within the same datacenter. For convenience, Scylla Rust Driver sets the default consistency level to LocalSerial, as it’s more commonly used. For cross-datacenter consistency, please remember to always override the default with SerialConsistency::Serial.


use scylla::query::Query;
use scylla::statement::{Consistency, SerialConsistency};

// Create a Query manually to change the Consistency to ONE
let mut my_query: Query = Query::new("INSERT INTO ks.tab (a) VALUES(?) IF NOT EXISTS".to_string());
my_query.set_consistency(Consistency::One);
// Use cross-datacenter serial consistency
my_query.set_serial_consistency(Some(SerialConsistency::Serial));

// Insert a value into the table
let to_insert: i32 = 12345;
session.query(my_query, (to_insert,)).await?;

The rest of the API remains identical for LWT and non-LWT queries.

See Query API documentation for more options