Revert "tmp fix dns cache problem"

This reverts commit e5d83d8.

Author: Hastyshell

fe/fe-core/src/main/java/org/apache/doris/common/DNSCache.java

@@ -68,27 +68,10 @@ public String get(String hostname) {
      * @return The IP address for the given hostname, or an empty string if the hostname cannot be resolved.
      */
     private String resolveHostname(String hostname) {
-        String cachedIp = cache.get(hostname);
         try {
-            String ip = NetUtils.getIpByHost(hostname, 0);
-            if (ip == null || ip.isEmpty()) {
-                if (cachedIp != null && !cachedIp.isEmpty()) {
-                    LOG.warn("Failed to resolve hostname {}, use cached ip: {}", hostname, cachedIp);
-                    return cachedIp;
-                } else {
-                    LOG.warn("Failed to resolve hostname {}, no cached ip available", hostname);
-                    return "";
-                }
-            }
-            return ip;
+            return NetUtils.getIpByHost(hostname, 0);
         } catch (UnknownHostException e) {
-            if (cachedIp != null && !cachedIp.isEmpty()) {
-                LOG.warn("Failed to resolve hostname {}, use cached ip: {}", hostname, cachedIp);
-                return cachedIp;
-            } else {
-                LOG.warn("Failed to resolve hostname {}, no cached ip available", hostname);
-                return "";
-            }
+            return "";
         }
     }
 
@@ -100,12 +83,15 @@ private String resolveHostname(String hostname) {
      */
     private void refresh() {
         for (String hostname : cache.keySet()) {
-            String resolvedHostname = resolveHostname(hostname);
-            String currentHostname = cache.get(hostname);
-            if (!resolvedHostname.equals(currentHostname)) {
-                cache.put(hostname, resolvedHostname);
-                LOG.info("IP for hostname {} has changed from {} to {}", hostname, currentHostname,
-                        resolvedHostname);
+            String resolvedIp = resolveHostname(hostname);
+            String currentIp = cache.get(hostname);
+            if (resolvedIp.isEmpty()) {
+                LOG.warn("Failed to resolve hostname {}, using cached IP: {}", hostname, currentIp);
+                continue;
+            }
+            if (!resolvedIp.equals(currentIp)) {
+                cache.put(hostname, resolvedIp);
+                LOG.info("IP for hostname {} has changed from {} to {}", hostname, currentIp, resolvedIp);
             }
         }
     }