readme updates

Author: bbakerman

README.md

@@ -269,6 +269,38 @@ In some circumstances you may wish to clear the cache for these individual probl
         });
 ```
 
+
+## Statistics on what is happening
+
+`DataLoader` keeps statistics on what is happening.  It can tell you the number of objects asked for, the cache hit number, the number of objects
+asked for via batching and so on.
+
+Knowing what the behaviour of your data is important for you to understand how efficient you are in serving the data via this pattern.
+
+
+```java
+        Statistics statistics = userDataLoader.getStatistics();
+        
+        System.out.println(format("load : %d", statistics.getLoadCount()));
+        System.out.println(format("batch load: %d", statistics.getBatchLoadCount()));
+        System.out.println(format("cache hit: %d", statistics.getCacheHitCount()));
+        System.out.println(format("cache hit ratio: %d", statistics.getCacheHitRatio()));
+
+```
+
+`DataLoaderRegistry` can also roll up the statistics for all data loaders inside it.
+
+You can configure the statistics collector used when you build the data loader
+
+```java
+        DataLoaderOptions options = DataLoaderOptions.newOptions().setStatisticsCollector(() -> new ThreadLocalStatisticsCollector());
+        DataLoader<String,User> userDataLoader = DataLoader.newDataLoader(userBatchLoader,options);
+
+```
+
+Which collector you use is up to you.  It ships with the following: `SimpleStatisticsCollector`, `ThreadLocalStatisticsCollector`, `DelegatingStatisticsCollector` 
+and `NoOpStatisticsCollector`.
+
 ## The scope of a data loader is important
 
 If you are serving web requests then the data can be specific to the user requesting it.  If you have user specific data

src/test/java/ReadmeExamples.java

@@ -5,13 +5,17 @@
 import org.dataloader.Try;
 import org.dataloader.fixtures.User;
 import org.dataloader.fixtures.UserManager;
+import org.dataloader.stats.Statistics;
+import org.dataloader.stats.ThreadLocalStatisticsCollector;
 
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
 import java.util.stream.Collectors;
 
+import static java.lang.String.format;
+
 @SuppressWarnings("ALL")
 public class ReadmeExamples {
 
@@ -75,7 +79,6 @@ public CompletionStage<List<User>> load(List<Long> userIds) {
     }
 
 
-
     private void tryExample() {
         Try<String> tryS = Try.tryCall(() -> {
             if (rollDice()) {
@@ -185,4 +188,19 @@ private boolean rollDice() {
     }
 
 
+    private void statsExample() {
+        Statistics statistics = userDataLoader.getStatistics();
+
+        System.out.println(format("load : %d", statistics.getLoadCount()));
+        System.out.println(format("batch load: %d", statistics.getBatchLoadCount()));
+        System.out.println(format("cache hit: %d", statistics.getCacheHitCount()));
+        System.out.println(format("cache hit ratio: %d", statistics.getCacheHitRatio()));
+    }
+
+    private void statsConfigExample() {
+
+        DataLoaderOptions options = DataLoaderOptions.newOptions().setStatisticsCollector(() -> new ThreadLocalStatisticsCollector());
+        DataLoader<String,User> userDataLoader = DataLoader.newDataLoader(userBatchLoader,options);
+    }
+
 }