HBASE-25588 Excessive logging of "hbase.zookeeper.useMulti is deprecated. Default to true always." (#3640)

Signed-off-by: Viraj Jasani <vjasani@apache.org>
Reviewed-by: Duo Zhang <zhangduo@apache.org>

Author: apurtell

hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java

@@ -1760,6 +1760,12 @@ private static Op toZooKeeperOp(ZKWatcher zkw, ZKUtilOp op) throws UnsupportedOp
     }
   }
 
+  // Static boolean for warning about useMulti because ideally there will be one warning per
+  // process instance. It is fine if two threads end up racing on this for a bit. We do not
+  // need to use an atomic type for this, that is overkill. The goal of reducing the number of
+  // warnings from many to one or a few at startup is still achieved.
+  private static boolean useMultiWarn = true;
+
   /**
    * Use ZooKeeper's multi-update functionality.
    *
@@ -1780,14 +1786,16 @@ private static Op toZooKeeperOp(ZKWatcher zkw, ZKUtilOp op) throws UnsupportedOp
    * @throws KeeperException if a ZooKeeper operation fails
    */
   public static void multiOrSequential(ZKWatcher zkw, List<ZKUtilOp> ops,
-                                       boolean runSequentialOnMultiFailure) throws KeeperException {
-    if (zkw.getConfiguration().get("hbase.zookeeper.useMulti") != null) {
-      LOG.warn("hbase.zookeeper.useMulti is deprecated. Default to true always.");
-    }
+      boolean runSequentialOnMultiFailure) throws KeeperException {
     if (ops == null) {
       return;
     }
-
+    if (useMultiWarn) { // Only check and warn at first use
+      if (zkw.getConfiguration().get("hbase.zookeeper.useMulti") != null) {
+        LOG.warn("hbase.zookeeper.useMulti is deprecated. Default to true always.");
+      }
+      useMultiWarn = false;
+    }
     List<Op> zkOps = new LinkedList<>();
     for (ZKUtilOp op : ops) {
       zkOps.add(toZooKeeperOp(zkw, op));