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file. The original code probed the PGPROC array separately for each PID, which was not good for large numbers of backends: not only is the runtime O(N^2) but most of it is spent holding ProcArrayLock. Instead, take the lock just once and copy the active PIDs into an array, then use qsort and bsearch so that the lookup time is more like O(N log N).
$PostgreSQL: pgsql/src/backend/storage/ipc/README,v 1.4 2003/11/29 19:51:56 pgsql 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 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.