Constant UPSERT_CHECKPOINT_WRITES_SQL 

pub const UPSERT_CHECKPOINT_WRITES_SQL: &str = r#"
INSERT INTO checkpoint_writes (thread_id, checkpoint_ns, checkpoint_id, task_id, task_path, idx, channel, type, blob)
VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9)
ON CONFLICT (thread_id, checkpoint_ns, checkpoint_id, task_id, idx) DO UPDATE SET
    channel = excluded.channel,
    type = excluded.type,
    blob = excluded.blob
"#;

Upsert checkpoint writes (overwrite on conflict). Used for special channels like __error__ whose value may legitimately change.