Suggested patch edits the polar_drop_log_page_cache function.

In particular:

- an early return is added when open() fails to avoid calling
fadvise()/close() on an invalid fd.

- platform specific posix_fadvise() call was replaced with
appropriate polar_posix_fadvise() call. The invocation is
guarded with directives USE_POSIX_FADVISE and POSIX_FADV_DONTNEED.
Falls back to no-op when the call is unavailable. This aligns
the function's behavior with existing PolarDB practice in fd.c,
xlog.c, etc.

- the polar_fd.h header file was included to make the
polar_posix_fadvise() function available.

Author: Giperboloid

src/backend/postmaster/syslogger.c

@@ -56,6 +56,7 @@
 
 /* POLAR */
 #include "storage/fd.h"
+#include "storage/polar_fd.h"
 #include "utils/builtins.h"
 
 /*
@@ -2092,9 +2093,20 @@ polar_drop_log_page_cache(const char *filename)
 	{
 		ereport(LOG,
 				(errmsg("the old log file doesn't exist")));
+
+		/* no need to go further */
+		return;
 	}
-	ret = posix_fadvise(last_log_fd, 0, 0, POSIX_FADV_DONTNEED);
-	/* return zero means success */
+	/*
+	 * on platforms that support posix_fadvise, advise the kernel to drop
+	 * cached pages for the old log file. Otherwise, skip silently.
+	 */
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+	ret = polar_posix_fadvise(last_log_fd, 0, 0, POSIX_FADV_DONTNEED);
+#else
+	ret = 0;
+#endif
+
 	if (ret != 0)
 	{
 		ereport(LOG,