improve per comments

ratis-common/src/main/java/org/apache/ratis/conf/ConfUtils.java

@@ -68,7 +68,7 @@ static BiConsumer<String, Integer> requireMax(int max) {
     };
   }
 
-  static BiConsumer<String, Float> requireMax(float max) {
+  static BiConsumer<String, Double> requireMax(double max) {
     return (key, value) -> {
       if (value > max) {
         throw new IllegalArgumentException(
@@ -159,10 +159,10 @@ static long getLong(
   }
 
   @SafeVarargs
-  static float getFloat(
-      BiFunction<String, Float, Float> floatGetter,
-      String key, float defaultValue, Consumer<String> logger, BiConsumer<String, Float>... assertions) {
-    return get(floatGetter, key, defaultValue, logger, assertions);
+  static double getDouble(
+      BiFunction<String, Double, Double> doubleGetter,
+      String key, double defaultValue, Consumer<String> logger, BiConsumer<String, Double>... assertions) {
+    return get(doubleGetter, key, defaultValue, logger, assertions);
   }
 
   @SafeVarargs
@@ -235,10 +235,10 @@ static void setLong(
   }
 
   @SafeVarargs
-  static void setFloat(
-      BiConsumer<String, Float> floatSetter, String key, float value,
-      BiConsumer<String, Float>... assertions) {
-    set(floatSetter, key, value, assertions);
+  static void setDouble(
+      BiConsumer<String, Double> doubleSetter, String key, double value,
+      BiConsumer<String, Double>... assertions) {
+    set(doubleSetter, key, value, assertions);
   }
 
   @SafeVarargs

ratis-server-api/src/main/java/org/apache/ratis/server/RaftServerConfigKeys.java

@@ -120,15 +120,17 @@ static void setByteLimit(RaftProperties properties, SizeInBytes byteLimit) {
       setSizeInBytes(properties::set, BYTE_LIMIT_KEY, byteLimit, requireMin(1L));
     }
 
-    String FOLLOWER_MAX_GAP_RATIO_KEY = PREFIX + ".follower-max-gap-ratio";
-    float FOLLOWER_MAX_GAP_RATIO_DEFAULT = 1;
+    String FOLLOWER_GAP_RATIO_MAX_KEY = PREFIX + ".follower.gap.ratio.max";
+    // The valid range is [1, 0) and -1, -1 means disable this feature
+    double FOLLOWER_GAP_RATIO_MAX_KEY_DEFAULT = -1d;
+    double FOLLOWER_GAP_RATIO_MAX_DISABLED = -1d;
 
-    static float followerMaxGapRatio(RaftProperties properties) {
-      return getFloat(properties::getFloat, FOLLOWER_MAX_GAP_RATIO_KEY,
-          FOLLOWER_MAX_GAP_RATIO_DEFAULT, getDefaultLog(), requireMax(1f));
+    static double followerGapRatioMax(RaftProperties properties) {
+      return getDouble(properties::getDouble, FOLLOWER_GAP_RATIO_MAX_KEY,
+          FOLLOWER_GAP_RATIO_MAX_DISABLED, getDefaultLog(), requireMax(1d));
     }
-    static void setFollowerMaxGapRatio(RaftProperties properties, float ratio) {
-      setFloat(properties::setFloat, FOLLOWER_MAX_GAP_RATIO_KEY, ratio, requireMax(1f));
+    static void setFollowerGapRatioMax(RaftProperties properties, float ratio) {
+      setDouble(properties::setDouble, FOLLOWER_GAP_RATIO_MAX_KEY, ratio, requireMax(1d));
     }
   }
 

ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderStateImpl.java

@@ -79,7 +79,8 @@
 import java.util.stream.Stream;
 
 import static org.apache.ratis.server.RaftServer.Division.LOG;
-import static org.apache.ratis.server.RaftServerConfigKeys.Write.FOLLOWER_MAX_GAP_RATIO_KEY;
+import static org.apache.ratis.server.RaftServerConfigKeys.Write.FOLLOWER_GAP_RATIO_MAX_KEY;
+import static org.apache.ratis.server.RaftServerConfigKeys.Write.FOLLOWER_GAP_RATIO_MAX_DISABLED;
 
 /**
  * States for leader only. It contains three different types of processors:
@@ -251,7 +252,6 @@ boolean removeAll(Collection<LogAppender> c) {
   private final long placeHolderIndex;
   private final RaftServerMetricsImpl raftServerMetrics;
   private final LogAppenderMetrics logAppenderMetrics;
-  private final long maxPendingRequests;
   private final long followerMaxGapThreshold;
 
   LeaderStateImpl(RaftServerImpl server) {
@@ -272,13 +272,17 @@ boolean removeAll(Collection<LogAppender> c) {
     this.pendingRequests = new PendingRequests(server.getMemberId(), properties, raftServerMetrics);
     this.watchRequests = new WatchRequests(server.getMemberId(), properties);
     this.messageStreamRequests = new MessageStreamRequests(server.getMemberId());
-    this.maxPendingRequests = RaftServerConfigKeys.Write.elementLimit(properties);
-    float followerMaxGapRatio = RaftServerConfigKeys.Write.followerMaxGapRatio(properties);
-
-    if (followerMaxGapRatio > 1f || followerMaxGapRatio <= 0f) {
-      throw new IllegalArgumentException(FOLLOWER_MAX_GAP_RATIO_KEY + "s value must between [1, 0)");
+    long maxPendingRequests = RaftServerConfigKeys.Write.elementLimit(properties);
+    double followerMaxGapRatio = RaftServerConfigKeys.Write.followerGapRatioMax(properties);
+
+    if (followerMaxGapRatio == FOLLOWER_GAP_RATIO_MAX_DISABLED) {
+      this.followerMaxGapThreshold = -1;
+    } else if (followerMaxGapRatio > 1f || followerMaxGapRatio <= 0f) {
+      throw new IllegalArgumentException(FOLLOWER_GAP_RATIO_MAX_KEY +
+          "s value must between [1, 0) to enable the feature");
+    } else {
+      this.followerMaxGapThreshold = (long) (followerMaxGapRatio * maxPendingRequests);
     }
-    this.followerMaxGapThreshold = (long)(followerMaxGapRatio * maxPendingRequests);
 
     final RaftConfigurationImpl conf = state.getRaftConf();
     Collection<RaftPeer> others = conf.getOtherPeers(server.getId());
@@ -713,7 +717,7 @@ static MinMajorityMax valueOf(long[] sorted) {
     static MinMajorityMax valueOf(long[] sorted, long gapThreshold) {
       long majority = getMajority(sorted);
       long min = sorted[0];
-      if ((majority - min) > gapThreshold) {
+      if (gapThreshold != -1 && (majority - min) > gapThreshold) {
         // The the gap between majority and min(the slow follower) is greater than gapThreshold,
         // set the majority to min, which will skip one round of lastCommittedIndex update in updateCommit().
         majority = min;