Index for Section TRANSACTION

Alphabetical listing for S

Bottom of page

SET
NAME
  SET TRANSACTION - set the characteristics of the current transaction

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 query or data-modification statement (SELECT, INSERT, DELETE,
  UPDATE, FETCH, COPY) of a transaction has been executed. SET SESSION
  CHARACTERISTICS sets the default transaction isolation level for each
  transaction for a session. SET TRANSACTION can override it for an
  individual transaction.

  The isolation level of a transaction determines what data the transaction
  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 query
       or data-modification statement was executed in this transaction.

       Tip: Intuitively, serializable means that two concurrent transactions
       will leave the database in the same state as if the two has been
       executed strictly after one another in either order.

NOTES
  The session default transaction isolation level can also be set with the
  command

  SET default_transaction_isolation = 'value'

  and in the configuration file. Consult the Administrator's Guide for more
  information.

COMPATIBILITY
  SQL92, SQL99

  SERIALIZABLE is the default level in SQL. PostgreSQL does not provide the
  isolation levels READ UNCOMMITTED and REPEATABLE READ. Because of
  multiversion 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 PostgreSQL.

Index for Section TRANSACTION

Alphabetical listing for S

Top of page