SET  TRANSACTION  - Set the characteristics of the current
       SQL-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 cur­
       rent 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
       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 run­
       ning 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 con­
              current transactions 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 con­
       trol,  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 transac­
       tion is read-only and the size of  the  diagnostics  area.
       Neither of these concepts are supported in Postgres.


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