Transactions and Sessions¶

GQL provides transaction control and session configuration commands.

Transaction Control¶

Starting Transactions¶

-- Start a read-write transaction (default)
START TRANSACTION

-- Explicit read-write
START TRANSACTION READ WRITE

-- Read-only transaction (mutations will be rejected)
START TRANSACTION READ ONLY

Isolation Levels¶

Specify the isolation level when starting a transaction:

-- Read committed (default)
START TRANSACTION ISOLATION LEVEL READ COMMITTED

-- Snapshot isolation (repeatable reads)
START TRANSACTION ISOLATION LEVEL SNAPSHOT ISOLATION

-- Serializable (strongest isolation)
START TRANSACTION ISOLATION LEVEL SERIALIZABLE

-- Combine with access mode
START TRANSACTION READ ONLY ISOLATION LEVEL SERIALIZABLE

Committing and Rolling Back¶

-- Commit the current transaction
COMMIT

-- Roll back the current transaction
ROLLBACK

Savepoints¶

Create named savepoints within a transaction for partial rollback:

-- Create a savepoint
SAVEPOINT sp1

-- Roll back to savepoint (undo changes made after it)
ROLLBACK TO SAVEPOINT sp1

-- Release a savepoint (discard it, keep changes)
RELEASE SAVEPOINT sp1

Example: Savepoint Workflow¶

START TRANSACTION READ WRITE

-- First update
MATCH (a:Account {id: 'A001'})
SET a.balance = a.balance + 500

SAVEPOINT before_bonus

-- Tentative bonus
MATCH (a:Account {id: 'A001'})
SET a.bonus = 100

-- Changed our mind, undo the bonus
ROLLBACK TO SAVEPOINT before_bonus

-- The +500 balance change is preserved
COMMIT

Nested Transactions¶

Starting a transaction inside an existing transaction creates an implicit savepoint:

START TRANSACTION READ WRITE
MATCH (n:Counter) SET n.value = 1

-- Creates implicit savepoint (inner transaction)
START TRANSACTION
MATCH (n:Counter) SET n.value = 99
ROLLBACK  -- Rolls back to the implicit savepoint

-- n.value is still 1
COMMIT

Example: Transaction Workflow¶

-- Transfer between accounts
START TRANSACTION READ WRITE

MATCH (src:Account {id: 'A001'})
SET src.balance = src.balance - 100

MATCH (dst:Account {id: 'A002'})
SET dst.balance = dst.balance + 100

COMMIT

-- Read-only reporting query
START TRANSACTION READ ONLY

MATCH (p:Person)-[:WORKS_AT]->(c:Company)
RETURN c.name, count(p) AS employees
ORDER BY employees DESC

COMMIT

Session Commands¶

Switching Graphs¶

-- Set the active graph for the session
USE GRAPH my_graph

-- SESSION SET equivalent
SESSION SET GRAPH my_graph

Time Zone¶

-- Set session time zone
SESSION SET TIME ZONE 'UTC'
SESSION SET TIME ZONE 'America/New_York'

Schema¶

-- Set the default schema for the session
SESSION SET SCHEMA analytics

Session Parameters¶

Set named parameters that persist for the session:

-- Set a session parameter
SESSION SET PARAMETER $threshold = 0.5

-- Use it in subsequent queries
MATCH (p:Person)
WHERE p.score > $threshold
RETURN p.name

Reset and Close¶

-- Reset all session settings to defaults
SESSION RESET

-- Reset all settings
SESSION RESET ALL

-- Close the session
SESSION CLOSE

Programmatic API¶

For transaction control from host languages (Python, Node.js, Rust), see Transactions.