Hi, On Fri, Sep 12, 2008 at 12:41 AM, Tom Lane <[EMAIL PROTECTED]> wrote: > Markus Wanner <[EMAIL PROTECTED]> writes: >> Tom Lane wrote: >>> Sooner or later we shall have to bite the bullet and set up a >>> multiplexing system to transmit multiple event types to backends with >>> just one signal. We already did it for signals to the postmaster. > >> Agreed. However, it's non-trivial if you want reliable queues (i.e. no >> message skipped, as with signals) for varying message sizes. > > No, that's not what I had in mind at all, just the ability to deliver > one of a specified set of event notifications --- ie, get around the > fact that Unix only gives us two user-definable signal types. > > For signals sent from other backends, it'd be sufficient to put a > bitmask field into PGPROC entries, which the sender could OR bits into > before sending the one "real" signal event (either SIGUSR1 or SIGUSR2). > > I'm not sure what to do if we need signals sent from processes that > aren't connected to shared memory; but maybe we need not cross that > bridge here. > > (Also, I gather that the Windows implementation could already support > a bunch more signal types without much trouble.)
There was discussion of event notification to backends from other process in the thread, "Synchronous Log Shipping Replication" (http://archives.postgresql.org/pgsql-hackers/2008-09/msg00802.php). The problem is that it's difficult to define new event notification using signal to backends since they already use SIGUSR1 and SIGUSR2. Attached is a WIP patch for the mechanism to transmit multiple event notifications with one signal. This mechanism would be useful for various uses, at least I would use this for implementing synchronous replication. In this patch, * I put a bitmask field into PGPROC for the communication of event type as advised by Tom in the above thread. * I replaced CatchupInterruptHandler() by new signal handler for SIGUSR1, adjusted the codes around "catchup interrupt" to this mechanism. * remaining work is adjusting the comments around "catchup interrupt". Comments welcome. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
multiplexer_v1.patch
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