IBM 000-8697 Benutzerhandbuch
2-58
IBM Informix OnLine Database Server Administrator’s Guide
LRU Queues and Buffer Pool Management
LRU Queues and Buffer Pool Management
Before processing begins, all page buffers are empty. Every page buffer is
associated with a buffer header in the buffer table. Every buffer header is
represented by an entry in one of the
associated with a buffer header in the buffer table. Every buffer header is
represented by an entry in one of the
FLRU
queues. The buffer headers are
evenly distributed among the
FLRU
queues. (Refer to
for more
information about the
FLRU
and
MLRU
queues.)
When a user process needs to acquire a buffer, OnLine randomly selects one
of the
of the
FLRU
queues and uses the “oldest” or “least-recently used” entry in the
list. If the least-recently used page can be latched, that page is removed from
the queue.
the queue.
If the
FLRU
queue is locked and the end page cannot be latched, OnLine
randomly selects another
FLRU
queue.
If a user process is searching for a specific page currently stored in shared
memory, it obtains the
memory, it obtains the
page’s LRU
queue location from the control infor-
mation stored in the buffer table.
After an executing process finishes its work, it releases the buffer. If the page
has been modified, the buffer is placed at the “most-recently used” end of an
has been modified, the buffer is placed at the “most-recently used” end of an
MLRU
queue. If the page was read but not modified, the buffer is returned to
the
FLRU
queue at its “most-recently used” end.
You can monitor
LRU
status by executing the command tbstat -R.