Difference between revisions of "BEGIN TRANSACTION"

Latest revision as of 14:36, 10 November 2009

Purpose

Begin transaction Before Image Journaling

Syntax

BEGIN TRANSACTION [<path name>]

<commands>

END TRANSACTION

See Also

COMPLETED(), END TRANSACTION, ISMARKED(), RESET IN, ROLLBACK, ROLLBACK(), SET ROLLBACK

Description

The BEGIN TRANSACTION command is used to flag the beginning of a transaction for Before Image Journaling (BIJ). A 'transaction' consists of all file modifications that occur within the commands BEGIN TRANSACTION and END TRANSACTION.

When BEGIN TRANSACTION is issued all currently open files and all files opened between BEGIN and END TRANSACTION will have BIJ invoked automatically. If BIJ is not required on a particular table then the RESET IN command should be issued for the relevant workarea so that journaling will no longer occur in that workarea. The journals are stored in a log file (with a file extension of '.log') which the Recital/4GL generates automatically. You can optionally specify the disk and directory <path name> where the log file will be stored when the BEGIN TRANSACTION command is issued.

A "rollback" causes record contents to be restored to their value before modification (i.e. at the time BEGIN TRANSACTION was issued). This is particularly useful if an error occurs during a program that modifies files.

If SET ROLLBACK is ON, the Recital/4GL will automatically execute the ROLLBACK command if an error occurs during the transaction process. Otherwise, error trapping should be handled manually using the ON ERROR command.

The COMPLETED() function can be used after the END TRANSACTION command to determine if any errors occurred during processing of the commands between BEGIN and END TRANSACTION.

Please note that the following commands are not allowed during a transaction:

• CLEAR ALL
• CLOSE ALL
• CLOSE DATABASES
• CLOSE INDEX
• MODIFY STRUCTURE
• PACK
• ZAP

Example

procedure recovery
 
rollback
if rollback()
    dialog box "Rollback was ok."
else
    dialog box "Rollback not completed."
endif
 
return
 
use accounts
on error do recovery
begin transaction
    delete first 15
    insert
    replace all t1 with (t2*t3)/100
    list
end transaction
if completed()
    dialog box "Transaction completed"
else
    dialog box "Errors occurred during transaction"
endif

Products

Recital Server, Recital