Tom Lane wrote:
Are we keeping use of SIGUSR2 in this scheme?
What for? Just protect the write pointer with a lwlock and have
listeners check whether somebody has written something.
You do want something comparable to SIGUSR2 to prod active backends to
consume messages, in case they are busy doing a query and hence not
checking the ring. I'm envisioning something like having the SIGUSR2
signal handler set a flag that's checked by CHECK_FOR_INTERRUPTS(),
and if set then ProcessInterrupts will go off and absorb messages.
Onlookers can tell who's falling behind by noting where their read
pointers are, and can issue SIGUSR2 to the laggards --- in particular,
any backend that finds itself unable to insert a NOTIFY into the ring
for lack of space can SIGUSR2 the laggards and then sleep a little.
I just wondered idly if we could piggyback on the existing
WAKEN_CHILDREN/SIGUSR1 mechanism? It might mean we signal more children
than necessary, but most won't have much to do anyway.
cheers
andrew
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