mirror of
https://github.com/postgres/postgres.git
synced 2025-11-12 05:01:15 +03:00
626eca697c
connections by the superuser only. This patch replaces the last patch I sent a couple of days ago. It closes a connection that has not been authorised by a superuser if it would leave less than the GUC variable ReservedBackends (superuser_reserved_connections in postgres.conf) backend process slots free in the SISeg. This differs to the first patch which only reserved the last ReservedBackends slots in the procState array. This has made the free slot test more expensive due to the use of a lock. After thinking about a comment on the first patch I've also made it a fatal error if the number of reserved slots is not less than the maximum number of connections. Nigel J. Andrews
$Header: /cvsroot/pgsql/src/backend/storage/ipc/README,v 1.1.1.1 1996/07/09 06:21:54 scrappy Exp $ Mon Jul 18 11:09:22 PDT 1988 W.KLAS Cache invalidation synchronization routines: =========================================== 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 noticed 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. Access to this shared message buffer is synchronized by the lock manager. The lock manager treats the buffer as a regular relation and sets relation level locks (with mode = LockWait) to block backends while another backend is writing or reading the buffer. The identifiers used for this special 'relation' are database id = 0 and relation id = 0. The current implementation prints regular (e)log information when a message has been removed from the buffer because the buffer is full, and a backend has to reset its cache state. The elog level is NOTICE. This can be used to improve teh behavior of backends when invalidating or reseting their cache state.