Structure Rebuild Processing

There are two types of structure rebuild processing. Rebuild involves the construction of a new instance of a structure. Duplexing rebuild involves the construction of a secondary instance of a structure and the subsequent maintenance of both instances of the structure in a synchronized manner.

There are two methods by which rebuild can be accomplished: user-managed and system-managed. The primary difference between the two methods is in the amount of direct participation by the connectors.

The user-managed method requires that connectors to the coupling facility containing the structure develop protocols to coordinate the rebuilding or duplexing of the structure and the propagation of data within the structure. User-managed rebuild processing requires that there be at least one active connector to the coupling facility containing the structure.
The system-managed method requires that connectors recognize that the structure will become temporarily unavailable for requests but does not require them to develop protocols to coordinate rebuild processing. The system provides the support necessary for rebuild or duplexing rebuild and therefore does not require that there be any active connectors to the coupling facility structure being rebuilt.

The following table outlines the basic differences between user-managed rebuild and system-managed rebuild.

Table 1. User-Managed vs. System-Managed Rebuild Processing
Feature	User-Managed Rebuild	User-Managed Duplexing Rebuild	System-Managed Rebuild	System-Managed Duplexing Rebuild
Purpose	Planned reconfiguration and recovery.	Improved availability and usability for cache structures.	Primarily planned reconfiguration. Cannot recover for loss of structure connectivity, structure failure, or coupling facility failure.	Robust failover capability.
Minimum CFLEVEL	None.	None.	CFLEVEL=8.	CFLEVEL=11.
Minimum release	MVS™ SP5.1.0.	OS/390® V2 R6	OS/390 V2 R8	z/OS® V1 R2
Active CFRM couple data set requirements	Any.	Any.	Formatted to support system-managed rebuild.	Formatted to support system-managed duplexing rebuild.
Connector requirements	At least one active connector required.	At least one active connector required.	No active connector requirements.	No active connector requirements.
Treatment of failed-persistent connectors	Not preserved across the rebuild.		Preserved across the rebuild.	Preserved across the rebuild.
Connector support	Controlled by connector specification of IXLCONN ALLOWREBLD keyword.	Controlled by connector specification of IXLCONN ALLOWDUPREBLD and ALLOWREBLD keywords.	Controlled by connector specification of IXLCONN ALLOWAUTO keyword.	Controlled by connector specification of IXLCONN ALLOWAUTO keyword.
Initiation	SETXCF START,REBUILD command or IXLREBLD macro	SETXCF START,REBUILD, DUPLEX command or IXLREBLD macro, or internally by the system.	SETXCF START,REBUILD command or IXLREBLD macro	SETXCF START,REBUILD, DUPLEX command, IXLREBLD macro, or internally by the system.
Quiescing access to the structure	Responsibility of the connected users.	Responsibility of the connected users.	Responsibility of the system on behalf of the users. Events are presented that allow the connectors to optionally do some quiescing of requests at the connection level.	Responsibility of the system on behalf of the users. Events are presented that allow the connectors to optionally do some quiescing of requests at the connection level.
Events received by active connection(s)	May include: Rebuild Quiesce Rebuild Connect Rebuild Connects Complete Rebuild New Connection Rebuild Existing Connection Rebuild Connect Failure Rebuild Cleanup Rebuild Complete Rebuild Stop Rebuild Stop Complete	May include, in addition to the events listed for user-managed rebuld: Rebuild Duplex Established Rebuild Switch	May include: Structure Temporarily Unavailable Structure State Change Structure Available Alter Begin Alter End Alter events are presented only if the connector supports alter processing.	May include: Structure Temporarily Unavailable Structure State Change Structure Available
Creation of new structure	Allocated by first connector to perform rebuild connect.	Allocated by first connector to perform rebuild connect.	Allocated by the system without connector participation.	Allocated by the system without connector participation.
CONTOKEN use	Two CONTOKENs for the user to manage, both of which the system might invalidate during the user-managed rebuild process.	Two CONTOKENS.	One CONTOKEN that is neither changed nor invalidated.	One CONTOKEN.
Structure attribute changes	Changes can be requested at rebuild connect.	Changes can be requested at rebuild connect.	Original structure attributes are preserved. The structure size might differ from the old structure, and if the connectors allow alter, the structure object counts might differ as well. The user-id limit for list and lock structures can change if all the connectors support user-id limit changes by specifying MAXCONN on the IXLCONN request.	Original structure attributes are preserved. The user-id limit for list and lock structures can change if all the connectors support user-id limit changes by specifying MAXCONN on the IXLCONN request.
Connection to new structure	All connectors must reconnect via IXLCONN REBUILD.	All connectors must reconnect.	Reconnected by the system without connector participation.	Reconnected by the system without connector participation.
Population of new structure	Connectors coordinate to populate new structure with all pertinent data.	Connectors coordinate to populate new (secondary) structure with all pertinent data.	The system copies data from old structure to new without connector participation.	The system copies data from primary structure to secondary without connector participation.
New connections during rebuild processing	Permitted only during the Rebuild Quiesce phase.	Permitted only during the Rebuild Quiesce, Rebuild Connect, and Duplex Established phases.	Not permitted.	Permitted only during the Duplex Established phase.