Dynamic DMCL Management

Impact of Changes

When a DMCL is being varied, certain changes cause:

Change	Quiesce area?	Reallocate file?
Segment changes
Dropping and recreating the segment	Yes	Yes
Page group	Yes	Yes
Maximum number of records per page	Yes	Yes
Segment's schema	No	No
Area changes
Adding an area		Allocate
Dropping an area	Yes	Deallocate
Primary page range	Yes	Yes
Extending page range	Yes	Yes
Page size	Yes	Yes
Original page size	Yes	Yes
Symbolic parameters	Yes	Yes
Area-to-file mapping	Yes	Yes
Page reserve	No	No
Maximum space	No	No
Area's timestamp	No	No
File changes
Dataset name	Yes	Yes
z/VM user id/virtual address	Yes	Yes
Access method	Yes	Yes
Disposition	No	Yes
External name (DDNAME)	No	Yes
DMCL changes
Adding a segment		Allocate
Dropping a segment	Yes	Deallocate
Buffer associated with a file	No 1	No
Shared cache usage for a file	No	No
File's external name (DDNAME)	No	Yes
File's disposition	No	Yes
Area status	No	Yes
Shared cache for a file	No	Yes
Disk Journal changes
Adding a disk journal		Allocate
Dropping a disk journal	Yes (2)	Deallocate
Number of pages in file	Yes (2)	No
Dataset name	Yes (2)	Yes
File's external name (DDNAME)	No	Yes

1 If a file is associated with a new buffer, the area's pages are first purged from the buffer pool.

2 Use of the disk journal file is quiesced.

Considerations

Changing the page size of a buffer causes the buffer to be closed and re-opened with the new size. All other buffer changes (such as the number of pages) are ignored. To change these parameters while the system is active, issue a DCMT VARY BUFFER command.
Changes to a journal buffer, tape, or archive journal file have no impact on the runtime system.
In a data sharing environment, if an area is shared, most changes to the area and its associated files will not take effect until the area is varied offline in all group members in which it is shared.