A page lock is a lock that is used within a data sharing group to protect database pages while they reside in a member's local buffer pool. Page locks are only placed on pages of areas that are designated for data sharing and only if there is inter-CV interest in the area.
Managing Page Locks
The coupling facility lock structure associated with the data sharing group is used to record and manage global page locks, just as is done for global transaction locks. And just as a proxy represents all of the records on the page, it also represents the page itself. Therefore, proxy locks reduce the need to acquire and release global page locks each time a page is moved into and out of the buffer pool.
Page Lock Protection
Before a database page is read into the buffer pool, an exclusive or shared lock is placed on that page, depending on whether the active transaction intends to update the page. Once the lock is acquired, no other group member may place a conflicting lock on the page until the first member relinquishes its lock. This means that no other sharing member may read the page contents while another member has it locked exclusively. Page locks are held until another group member wants access to the page in a conflicting mode. Before an exclusive page lock can be released on an updated page, the page is written to the disk and to the shared cache.
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