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    Command:

    set_transaction

    
    
    
    

    SYNOPSIS

           SET TRANSACTION transaction_mode [, ...]
           SET SESSION CHARACTERISTICS AS TRANSACTION transaction_mode [, ...]
    
           where transaction_mode is one of:
    
               ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
               READ WRITE | READ ONLY
    
    
    

    DESCRIPTION

           The  SET  TRANSACTION  command  sets the characteristics of the current
           transaction. It has no effect on any subsequent transactions. SET  SES-
           SION  CHARACTERISTICS  sets the default transaction characteristics for
           subsequent transactions of a session. These defaults can be  overridden
           by SET TRANSACTION 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  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
                  All statements of the current transaction can only see rows com-
                  mitted before the first query or data-modification statement was
                  executed in this transaction.
    
           The SQL standard defines two additional levels,  READ  UNCOMMITTED  and
           REPEATABLE  READ.   In  PostgreSQL  READ UNCOMMITTED is treated as READ
           COMMITTED, while REPEATABLE READ is treated as SERIALIZABLE.
    
           The transaction isolation level cannot be changed after the first query
           or  data-modification statement (SELECT, INSERT, DELETE, UPDATE, FETCH,
           or COPY) of a transaction has been executed. See in  the  documentation
           for  more  information about transaction isolation and concurrency con-
           trol.
    
           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 FROM 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 all writes to disk.
    
    
    
    

    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 men-
           tioned above. Because of lack of predicate  locking,  the  SERIALIZABLE
           level  is not truly serializable. See 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 specific to embedded SQL, and therefore is  not  implemented
           in the PostgreSQL server.
    
           The  SQL standard requires commas between successive transaction_modes,
           but for historical reasons PostgreSQL allows the commas to be  omitted.
    
    
    

    SQL - Language Statements 2014-02-17 SET TRANSACTION(7)

    
    
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