Kris Kennaway wrote:
If so, then your task is the following:

Make SYSV semaphores less dumb about process wakeups.  Currently
whenever the semaphore state changes, all processes sleeping on the
semaphore are woken, even if we only have released enough resources
for one waiting process to claim.  i.e. there is a thundering herd
wakeup situation which destroys performance at high loads.  Fixing
this will involve replacing the wakeup() calls with appropriate
amounts of wakeup_one().

I'm forwarding this to the pgsql-hackers list so that folks more qualified than I can comment, but as I understand the way postgres implements locking each process has it *own* semaphore it waits on - and who is waiting for what is controlled by an in (shared) memory hash of lock structs (access to these is controlled via platform Dependant spinlock code). So a given semaphore state change should only involve one process wakeup.

Cheers

Mark

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