Fix pg_log_backend_memory_contexts() 's delay

[bt21tanigaway]

Hi,

Log output takes time between several seconds to a few tens when using 
‘SELECT pg_log_backend_memory_contexts(1234)’ with PID of ‘autovacuum 
launcher’.
I made a patch for this problem.
regards,
Koyu Tanigawa
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 3b3df8fa8c..7ebe5ae8dc 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -836,6 +836,9 @@ HandleAutoVacLauncherInterrupts(void)
 	if (ProcSignalBarrierPending)
 		ProcessProcSignalBarrier();
 
+	if (LogMemoryContextPending)
+	  ProcessLogMemoryContextInterrupt();
+
 	/* Process sinval catchup interrupts that happened while sleeping */
 	ProcessCatchupInterrupt();
 }