workaround for issue #46

- in Windows prior to 8 and Server 2012 there is no GetSystemTimePreciseAsFileTime(), so in case of
  very fast forking - we take 100ms for calculation of "stat_fork_rate"
- fixes #46

src/aof.c

@@ -1489,7 +1489,14 @@ int rewriteAppendOnlyFileBackground(void) {
 #endif
         /* Parent */
         server.stat_fork_time = ustime()-start;
-        server.stat_fork_rate = (double) (zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024*1024*1024)); /* GB per second. */  WIN_PORT_FIX
+//[tporadowski/redis] issue #46: ustime() -> gettimeofday_highres() uses GetSystemTimePreciseAsFileTime when available (Windows 8, Windows Server 2012) or
+//                    falls back to GetSystemTimeAsFileTime which does not have such high resolution, so "stat_fork_time" may be 0 here
+#ifdef _WIN32
+        if (server.stat_fork_time == 0) {
+            server.stat_fork_time = 100000; //let's pretend it took 100ms (100000 microseconds)
+        }
+#endif
+        server.stat_fork_rate = (double)(zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024 * 1024 * 1024)); /* GB per second. */  WIN_PORT_FIX
         latencyAddSampleIfNeeded("fork",server.stat_fork_time/1000);
         if (childpid == -1) {
             closeChildInfoPipe();

src/rdb.c

@@ -1127,7 +1127,14 @@ int rdbSaveBackground(char *filename, rdbSaveInfo *rsi) {
 #endif
         /* Parent */
         server.stat_fork_time = ustime()-start;
-        server.stat_fork_rate = (double) (zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024*1024*1024)); /* GB per second. */
+//[tporadowski/redis] issue #46: ustime() -> gettimeofday_highres() uses GetSystemTimePreciseAsFileTime when available (Windows 8, Windows Server 2012) or
+//                    falls back to GetSystemTimeAsFileTime which does not have such high resolution, so "stat_fork_time" may be 0 here
+#ifdef _WIN32
+        if (server.stat_fork_time == 0) {
+            server.stat_fork_time = 100000; //let's pretend it took 100ms (100000 microseconds)
+        }
+#endif
+        server.stat_fork_rate = (double)(zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024 * 1024 * 1024)); /* GB per second. */  WIN_PORT_FIX
         latencyAddSampleIfNeeded("fork",server.stat_fork_time/1000);
         if (childpid == -1) {
             closeChildInfoPipe();
@@ -2019,7 +2026,14 @@ int rdbSaveToSlavesSockets(rdbSaveInfo *rsi) {
             closeChildInfoPipe();
         } else {
             server.stat_fork_time = ustime()-start;
-            server.stat_fork_rate = (double) (zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024*1024*1024)); /* GB per second. */
+//[tporadowski/redis] issue #46: ustime() -> gettimeofday_highres() uses GetSystemTimePreciseAsFileTime when available (Windows 8, Windows Server 2012) or
+//                    falls back to GetSystemTimeAsFileTime which does not have such high resolution, so "stat_fork_time" may be 0 here
+#ifdef _WIN32
+            if (server.stat_fork_time == 0) {
+                server.stat_fork_time = 100000; //let's pretend it took 100ms (100000 microseconds)
+            }
+#endif
+            server.stat_fork_rate = (double)(zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024 * 1024 * 1024)); /* GB per second. */  WIN_PORT_FIX
             latencyAddSampleIfNeeded("fork",server.stat_fork_time/1000);
 
             serverLog(LL_NOTICE,"Background RDB transfer started by pid %d",