IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

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

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

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.

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

 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

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.