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

SYNOPSIS
  SET TRANSACTION
      [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
  SET SESSION CHARACTERISTICS AS TRANSACTION
      [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]

DESCRIPTION
  The SET TRANSACTION command sets the transaction characteristics of the
  current transaction. It has no effect on any subsequent transactions. SET
  SESSION CHARACTERISTICS sets the default transaction characteristics for
  each transaction of a session. SET TRANSACTION can override it for an
  individual transaction.

  The available transaction characteristics are the transaction isolation
  level and the transaction access mode (read/write or read-only).

  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.

  The transaction isolation level cannot be set after the first query or
  data-modification statement (SELECT, INSERT, DELETE, UPDATE, FETCH, COPY)
  of a transaction has been executed. See the chapter called ``Concurrency
  Control'' in the documentation for more information about transaction
  isolation and concurrency control.

  The transaction access mode determines whether the transaction is
  read/write or read-only. Read/write is the default. When a transaction is
  read-only, the following SQL commands are disallowed: INSERT, UPDATE,
  DELETE, and COPY TO if the table they would write to is not a temporary
  table; all CREATE, ALTER, and DROP commands; COMMENT, GRANT, REVOKE,
  TRUNCATE; and EXPLAIN ANALYZE and EXECUTE if the command they would execute
  is among those listed. This is a high-level notion of read-only that does
  not prevent writes to disk.

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 section called ``Run-time
  Configuration'' in the documentation for more information.

COMPATIBILITY
  Both commands are defined in the SQL standard.  SERIALIZABLE is the default
  transaction isolation level in the standard; in PostgreSQL the default is
  ordinarily READ COMMITTED, but you can change it as described above.
  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 chapter called
  ``Concurrency Control'' in the documentation for details.

  In the SQL standard, there is one other transaction characteristic that can
  be set with these commands: the size of the diagnostics area. This concept
  is only for use in embedded SQL.

Index for Section TRANSACTION

Alphabetical listing for S

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