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Oracle Job Scheduling

Chapter 3 - Time-Based Job Scheduling

Calendar Syntax in Oracle10g
  • When there are not enough clauses to determine the precise run date, the missing clauses are derived from the start_date.  For example, if there is no bysecond clause in the calendar string, the value of seconds from the start_date is used to create one.
     

  • When a number range is not fixed, the last value of the range can be determined using a negative integer as a count-back.  As such bymonthday=-1 equates to the last day of the month. The documentation states that count-backs are not supported for fixed number ranges such as those used by the bymonth, byhour, byminute and bysecond clauses, but they do appear to work consistently.
     

  • The first day of the week is Monday.
     

  • A calendar string cannot specify time zones.  Instead the time zone is derived from one of the following places in this order: the start_date, the current session’s time zone, the DEFAULT_TIMEZONE scheduler attribute, or time zone returned by the systimestamp function.

Now that calendar syntax has been introduced in detail, the following section will compare the use of PL/SQL expressions and the use of calendar syntax for scheduling jobs.

Complex Date Rules for Job Execution

Prior to Oracle10g, the only way to define a jobs repeat interval was to use a PL/SQL expression that evaluated to a date.  In Oracle10g, the calendar syntax is the preferred way to define a jobs repeat interval, although PL/SQL expression can still be used if they evaluate to a timestamp.  In this section we will compare how each method works.


The above text is an excerpt from:


Oracle Job Scheduling
Creating Robust Task Management with dbms_job and Oracle10g dbms_scheduler

ISBN 0-9744486-6-4

by Dr. Timothy S. Hall
 

http://www.rampant-books.com/book_2005_1_scheduling.htm


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