Mark Kirkwood <markir_at_paradise.net.nz> writes: > 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. Correct. The behavior Kris describes is surely bad, but it's not relevant to Postgres' usage of SysV semaphores. regards, tom laneReceived on Tue Apr 10 2007 - 12:39:18 UTC
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