added new option no-appendfsync-on-rewrite to avoid blocking on fsync() in the...

added new option no-appendfsync-on-rewrite to avoid blocking on fsync() in the main thread while a background process is doing big I/O

redis.c

@@ -369,6 +369,7 @@ struct redisServer {
     int daemonize;
     int appendonly;
     int appendfsync;
+    int no_appendfsync_on_rewrite;
     int shutdown_asap;
     time_t lastfsync;
     int appendfd;
@@ -1685,6 +1686,7 @@ static void initServerConfig() {
     server.daemonize = 0;
     server.appendonly = 0;
     server.appendfsync = APPENDFSYNC_EVERYSEC;
+    server.no_appendfsync_on_rewrite = 0;
     server.lastfsync = time(NULL);
     server.appendfd = -1;
     server.appendseldb = -1; /* Make sure the first time will not match */
@@ -1941,6 +1943,11 @@ static void loadServerConfig(char *filename) {
         } else if (!strcasecmp(argv[0],"appendfilename") && argc == 2) {
             zfree(server.appendfilename);
             server.appendfilename = zstrdup(argv[1]);
+        } else if (!strcasecmp(argv[0],"no-appendfsync-on-rewrite")
+                   && argc == 2) {
+            if ((server.no_appendfsync_on_rewrite= yesnotoi(argv[1])) == -1) {
+                err = "argument must be 'yes' or 'no'"; goto loaderr;
+            }
         } else if (!strcasecmp(argv[0],"appendfsync") && argc == 2) {
             if (!strcasecmp(argv[1],"no")) {
                 server.appendfsync = APPENDFSYNC_NO;
@@ -8236,6 +8243,11 @@ static void flushAppendOnlyFile(void) {
     sdsfree(server.aofbuf);
     server.aofbuf = sdsempty();
 
+    /* Don't Fsync if no-appendfsync-on-rewrite is set to yes and we have
+     * childs performing heavy I/O on disk. */
+    if (server.no_appendfsync_on_rewrite &&
+        (server.bgrewritechildpid != -1 || server.bgsavechildpid != -1))
+            return;
     /* Fsync if needed */
     now = time(NULL);
     if (server.appendfsync == APPENDFSYNC_ALWAYS ||
@@ -9960,6 +9972,11 @@ static void configSetCommand(redisClient *c) {
         } else {
             goto badfmt;
         }
+    } else if (!strcasecmp(c->argv[2]->ptr,"no-appendfsync-on-rewrite")) {
+        int yn = yesnotoi(o->ptr);
+
+        if (yn == -1) goto badfmt;
+        server.no_appendfsync_on_rewrite = yn;
     } else if (!strcasecmp(c->argv[2]->ptr,"appendonly")) {
         int old = server.appendonly;
         int new = yesnotoi(o->ptr);
@@ -10075,6 +10092,11 @@ static void configGetCommand(redisClient *c) {
         addReplyBulkCString(c,server.appendonly ? "yes" : "no");
         matches++;
     }
+    if (stringmatch(pattern,"no-appendfsync-on-rewrite",0)) {
+        addReplyBulkCString(c,"no-appendfsync-on-rewrite");
+        addReplyBulkCString(c,server.no_appendfsync_on_rewrite ? "yes" : "no");
+        matches++;
+    }
     if (stringmatch(pattern,"appendfsync",0)) {
         char *policy;