SET TRANSACTION() SQL Commands SET TRANSACTION()NAME
SET TRANSACTION - Set the characteristics of the current SQL-transac‐
tion
SYNOPSIS
SET TRANSACTION ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE }
SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE }
DESCRIPTION
This command sets the transaction isolation level. The SET TRANSACTION
command sets the characteristics for the current SQL-transaction. It
has no effect on any subsequent transactions. This command cannot be
used after the first DML statement (SELECT, INSERT, DELETE, UPDATE,
FETCH, COPY) of a transaction has been executed. SET SESSION CHARACTER‐
ISTICS sets the default transaction isolation level for each transac‐
tion for a session. SET TRANSACTION can override it for an individual
transaction.
The isolation level of a transaction determines what data the transac‐
tion can see when other transactions are running concurrently.
READ COMMITTED
A statement can only see rows committed before it began. This is
the default.
SERIALIZABLE
The current transaction can only see rows committed before first
DML statement was executed in this transaction.
Tip: Intuitively, serializable means that two concurrent trans‐
actions will leave the database in the same state as if the two
has been executed strictly after one another in either order.
COMPATIBILITY
SQL92, SQL99
SERIALIZABLE is the default level in SQL. Postgres does not provide
the isolation levels READ UNCOMMITTED and REPEATABLE READ. Because of
multi-version concurrency control, the serializable level is not truly
serializable. See the User's Guide for details.
In SQL there are two other transaction characteristics that can be set
with these commands: whether the transaction is read-only and the size
of the diagnostics area. Neither of these concepts are supported in
Postgres.
SQL - Language Statements 2000-11-24 SET TRANSACTION()
