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bf70bf4c71
There was a timing window between when oldestActiveXid was derived and when it should have been derived that only shows itself under heavy load. Move code around to ensure correct timing of derivation. No change to StartupSUBTRANS() code, which is where this failed. Bug report by Chris Redekop
src/backend/storage/ipc/README Cache Invalidation Synchronization Routines =========================================== 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.