Deferring restart processing

When a specific object is causing problems, you can defer its restart processing by starting Db2 and preventing the problem object from going through restart processing.

About this task

When you defer restart of an object, Db2 puts pages that are necessary for restart of the object in the logical page list (LPL). Only those pages are inaccessible; the rest of the object can still be accessed after restart.

Restrictions apply to Db2 activation of restart processing for available objects. When DEFER ALL is specified at a site that has RECOVERYSITE for the SITETYP subsystem parameter value, all pages for an object that is deferred are placed in the LPL (as a page range, not as a large list of individual pages). The following conditions apply:

  • If Db2 cannot open and read the DBD01 table space it does not put Db2 into ACCESS(MAINT), and DSNX204I is not issued. Instead either DSNT500I or DSNT501I 'resource unavailable' is issued.
  • For a deferred restart scenario that needs to recover all Db2 objects after Db2 is up, the recommendation is to set the DEFER and ALL subsystem parameters on panel DSNTIPS and start Db2 with the ACCESS(MAINT) option.
  • If DEFER ALL is specified, DSNX204I is not issued.
  • With DEFER ALL, Db2 will not open any data sets, including SYSLGRNX and DSNRTSTS, during any phase of restart, and will not attempt to apply any log records.

Procedure

To defer restart processing, use one of the following approaches:

  • To vary the device (or volume) on which the objects reside offline:

    If the data sets that contain an object are not available, and the object requires recovery during restart, Db2 flags it as stopped and requiring deferred restart. Db2 then restarts without it.

  • To delay the backout of a long-running UR, specify the following subsystem parameters:
    • LBACKOUT defined as YES, AUTO, LIGHT, or LIGHTAUTO indicates that some backout processing is to postponed when restarting Db2. Issue the RECOVER POSTPONED command to complete the backout processing when the YES option is selected. Db2 does the backout work automatically after Db2 is running and receiving new work when the AUTO option is selected. For more information, see LIMIT BACKOUT field (LBACKOUT subsystem parameter).
    • BACKODUR indicates the number of log records, specified as a multiplier, that are to be read during the backward log scan phase of restart. For more information see BACKOUT DURATION field (BACKODUR subsystem parameter).

    The amount of backout processing that is to be postponed is determined by:

    • The frequency of checkpoints
    • The BACKODUR subsystem parameter
    • The characteristics of the inflight and in-abort activity when Db2 stopped

    Selecting a limited backout affects log processing during restart. The backward processing of the log proceeds until the oldest inflight or in-abort UR with activity against the catalog or directory is backed out, and until the requested number of log records have been processed.

  • To name the object with DEFER when installing Db2:
    On installation panel DSNTIPS, you can use the following options:
    • DEFER ALL defers restart log apply processing for all objects, including Db2 catalog and directory objects.
    • DEFER list_of_objects defers restart processing only for objects in the list.

    Alternatively, you can specify RESTART list_of_objects, which limits restart processing to the list of objects in the list.

    DEFER does not affect processing of the log during restart. Therefore, even if you specify DEFER ALL, Db2 still processes the full range of the log for both the forward and backward log recovery phases of restart. However, logged operations are not applied to the data set. For more information, see DSNTIPS: Databases and spaces to start automatically panel.