Resource locking considerations with block-level data sharing

Resource locking can occur either locally in a non-sysplex environment or globally in a sysplex environment.

In a non-sysplex environment, local locks can be granted in one of three ways:

• Immediately because of either of the following reasons:
  • IMS was able to get the required IRLM latches, and there is no other interest on this resource.
  • The request is compatible with other holders or waiters.
• Asynchronously because the request could not get the required IRLM latches and was suspended. (This can also occur in a sysplex environment.) The lock is granted when latches become available and one of two conditions exist:
  • No other holders exist.
  • The request is compatible with other holders or waiters.
• Asynchronously because the request is not compatible with the holders or waiters and was granted after their interest was released. (This could also occur in a sysplex environment.)

In a sysplex environment, global locks can be granted in one of three ways:

• Locally by the IRLM because either of the following two reasons:
  • There is no other interest for this resource.
  • This IRLM has the only interest, this request is compatible with the holders or waiters on this system, and XES already knows about the resource.
• Synchronously on the XES CALL because:
  • Either XES shows no other interest for this resource.
  • Or XES shows only SHARE interest for the hash class.
• Asynchronously on the XES CALL because of one of two conditions:
  • Either XES shows EXCLUSIVE interest on the hash class by an IRLM, but the resource names do not match (FALSE CONTENTION by RMF).
  • Or the request is incompatible with the other HOLDERs and is granted by the CONTENTION Exit after their interest is released (IRLM REAL CONTENTION).