Handle is common term for a memory address pointer, and this is the case with the library cache. There is a one-to-one relationship between a handle and a library cache memory object. So referring to a handle is synonymous as referring to its associated object. When mutexes are used instead of library cache latches, each individual handle has an associated mutex. Each library cache object refers to an object of a specific type, sometimes called a namespace, such as a cursor, a child cursor, a table, or a programmatic construct.

Figure 7-3 abstracts the library cache implementing mutexes and highlighting the various architectural components, yet without specific object names. Library cache objects are searched using a hashing structure, so you would expect to see buckets, such as bucket BKT 200. When mutexes are implemented, there is a mutex associated with each handle, so each memory chunk shown in Figure 7-3 has an associated mutex. Each hash chain can contain zero or more handles, which relates to zero or more library cache objects, such as cursor CSR 500 and table TBL 400. Each parent cursor will have at least one child cursor. As described earlier, a parent cursor, such as CSR 500 in Figure 7-3, can be associated multiple child cursors, such as CCSR 600 and CCSR 610.

Figure 7-3. A simple conceptual model of an Oracle library cache. The model shows hash buckets (BKT), cursors (CSR), child cursors (CCSR), and table references (TBL).