On Sun, 2009-01-11 at 15:11 +0900, Fujii Masao wrote: > Yes, using semaphores for the communication is also my first approach. > The problem of this approach is that walsender cannot wait for both > signal from backends and the response from walreceiver concurrently, > because > wait-for-semaphore is blocking at least. So, I use signal for the > communication.
IIUC: In sync mode backend sends signal to walsender, then adds itself to wait queue on semaphore. walsender responds to signal, sends more WAL then waits for response. When response comes it then wakes backends on the semaphore. In async mode, no signal is sent and we do not wait, we just allow the walsender to wake up periodically and send. Does it release waiters as soon as possible, or does it always respond to new requests for sending? i.e. which has priority - responding to waiters who need to be woken or responding to new requests to send? -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
