$PostgreSQL: pgsql/src/backend/storage/ipc/README,v 1.5 2008/03/20 17:55:15 momjian Exp $

Cache Invalidation Synchronization Routines
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Mon Jul 18 11:09:22 PDT 1988  W.KLAS

The cache synchronization is done using a message queue. Every
backend can register a message which then has to be read by
all backends. A message read by all backends is removed from the 
queue automatically. If a message has been lost because the buffer
was full, all backends that haven't read this message will be
told that they have to reset their cache state. This is done
at the time when they try to read the message queue.

The message queue is implemented as a shared buffer segment. Actually,
the queue is a circle to allow fast inserting, reading (invalidate data) and
maintaining the buffer.
