The database server creates portions in shared memory to
handle different processes.
The database server creates the following portions of shared memory:
The resident portion
The buffer
pool portion
The virtual portion
The IPC communications or message portion
If the sqlhosts file
specifies shared-memory communications, the database server allocates
memory for the communications portion.
The virtual-extension portion
The database server adds operating-system segments, as required,
to the virtual and virtual-extension portions of shared memory.
For more information about shared-memory settings for your platform,
see the machine notes. The following figure shows the contents of
each portion of shared memory.
All database server virtual processors have access to the same
shared-memory segments. Each virtual processor manages its work by
maintaining its own set of pointers to shared-memory resources such
as buffers, locks, and latches. Virtual processors attach to shared
memory when you take the database server from offline mode to quiescent,
administration, or online. The database server uses locks and latches
to manage concurrent access to shared-memory resources by multiple
threads.Figure 1: Contents of
database server shared memory