diff --git a/src/port/pqsignal.c b/src/port/pqsignal.c
index 83d876db6c..4ea2dea77e 100644
--- a/src/port/pqsignal.c
+++ b/src/port/pqsignal.c
@@ -11,16 +11,34 @@
  * IDENTIFICATION
  *	  src/port/pqsignal.c
  *
- *	We now assume that all Unix-oid systems have POSIX sigaction(2)
- *	with support for restartable signals (SA_RESTART).  We used to also
- *	support BSD-style signal(2), but there really shouldn't be anything
- *	out there anymore that doesn't have the POSIX API.
+ *	This is the signal() implementation from "Advanced Programming in the UNIX
+ *	Environment", with minor changes.  It was originally a replacement needed
+ *	for old SVR4 systems whose signal() behaved as if sa_flags = SA_RESETHAND |
+ *	SA_NODEFER, also known as "unreliable" signals due to races when the
+ *	handler was reset.
+ *
+ *	By now, all known modern Unix systems have a "reliable" signal() call.
+ *	We still don't want to use it though, because it remains
+ *	implementation-defined by both C99 and POSIX whether the handler is reset
+ *	or signals are blocked when the handler runs, and default restart behavior
+ *	is also unspecified.  Therefore we take POSIX's advice and call sigaction()
+ *	so we can provide explicit sa_flags, but wrap it in this more convenient
+ *	traditional interface style.  It also provides a place to set any extra
+ *	flags we want everywhere, such as SA_NOCLDSTOP.
  *
  *	Windows, of course, is resolutely in a class by itself.  In the backend,
- *	we don't use this file at all; src/backend/port/win32/signal.c provides
- *	pqsignal() for the backend environment.  Frontend programs can use
- *	this version of pqsignal() if they wish, but beware that this does
- *	not provide restartable signals on Windows.
+ *	this relies on pqsigaction() in src/backend/port/win32/signal.c, which
+ *	provides limited emulation of reliable signals.
+ *
+ * 	Frontend programs can use this version of pqsignal() to forward to the
+ * 	native Windows signal() call if they wish, but beware that Windows signals
+ * 	behave quite differently.  Only the 6 signals required by C are supported.
+ * 	SIGINT handlers run in another thread instead of interrupting an existing
+ * 	thread, and the others don't interrupt system calls either, so SA_RESTART
+ * 	is moot.  All except SIGFPE have SA_RESETHAND semantics, meaning the
+ * 	handler is reset to SIG_DFL each time it runs.  The set of things you are
+ * 	allowed to do in a handler is also much more restricted than on Unix,
+ * 	according to the documentation.
  *
  * ------------------------------------------------------------------------
  */