[PostgreSQL-Hackers] Re: [BUGS] BUG #4961: pg_standby.exe crashes with no args

Magnus Hagander writes:
If I just move those two lines into the #ifndef WIN32 block just
around it, it compiles and doesn't crash on running-with-no-arguments.
I haven't tried to actually use it though - can someone confirm if
this will actually make pg_standby not work properly?

On Mon, Aug 10, 2009 at 20:44, Tom Lanewrote:
Magnus Hagander <magnus@hagander.net> writes:
It would mean there's no way to trigger failover via signal.

I think what we need is for pg_ctl to be able to send these signals...

On Mon, Aug 10, 2009 at 20:44, Tom Lanewrote:
Those signals don't *exist* on Windows. The whole idea of
cross-process signals don't *exist* on Windows.

We emulate it in the main backend, by creating a background thread
that sets a global variable. That is then polled in the
CHECK_FOR_INTERRUPTS macro. pg_ctl is perfectly capable of sending
these signals, but pg_standby can't receive them.

We could implement the same type of check in pg_standby, but it
requires something like CHECK_FOR_INTERRUPTS. And these interrupts
won't, by default, cause any kind of interruption of the process. In
the backend, we interrupt socket calls because we have the socket
wrapper layer, and nothing else. I don't know how doable this would be
in pg_standby - does it always block on a single thing where we could
stick some win32 synchronization code? If it's a single, or limited,
places we could implement something similar to the backend. But if we
need to interrupt at arbitrary locations, that's just not possible.

I can't compile nor read source, but can tell you that
pg_standby.exe in 8.3.7 works fine.

Magnus Hagander wrote:

On Wed, Aug 12, 2009 at 19:08, Fujii Masaowrote:
Hi,

On Tue, Aug 11, 2009 at 3:10 AM, Magnus Haganderwrote:
SIGINT has been used in pg_standby for a while (e.g., v8.3.7). I wonder
why this problem arises only in v8.4.0.

On Wed, Aug 19, 2009 at 08:38, Fujii Masaowrote:
On Thu, Aug 13, 2009 at 2:24 AM, Magnus Haganderwrote:
I think that CHECK_FOR_INTERRUPTS should be placed just before
checking the flag 'signaled' which may be enabled by the signal handler.
Here is the pseudo-code.

--------------------
{
/* Check for trigger file or signal first */
CheckForExternalTrigger();
+ #ifdef WIN32
+               CHECK_FOR_INTERRUPTS();
+ #endif /* WIN32 */
if (signaled)
{
Failover = FastFailover;
--------------------

Magnus Hagander wrote:
This would amount to fairly major surgery for pg_standby on Win32. Is
that something we'd want to backpatch, or do we want to backpatch just
the removal of the signal() calls which would amount to not supporting
signals in pg_standby on win32?

On Wed, Aug 19, 2009 at 11:45, Heikki Linnakangaswrote:
Magnus Hagander wrote:
I think we should just remove the signals support for win32. The trigger
file method still works, and the signal method has always been a bit
iffy (it doesn't work when pg_standby isn't running, for example, which
happens between processing of each WAL file, because there's no process
to signal).