Core: DistributorDirectory shouldn't search for directory when readin…

…g existing file

This was causing too much work e.g. when pulling node stats or when
opening a new reader, because the least_used distributor would
unnecessarily check free disk space on all path.data entires every
time we try to open a file for reading or check its length.

Closes #7306

Closes #7323

src/main/java/org/elasticsearch/index/store/DistributorDirectory.java

@@ -159,11 +159,14 @@ private Directory getDirectory(String name, boolean failIfNotAssociated, boolean
         if (usePrimary(name)) {
             return distributor.primary();
         }
-        if (!nameDirMapping.containsKey(name)) {
-            if (iterate) { // in order to get stuff like "write.lock" that might not be written though this directory
+        Directory directory = nameDirMapping.get(name);
+        if (directory == null) {
+            // name is not yet bound to a directory:
+
+            if (iterate) { // in order to get stuff like "write.lock" that might not be written through this directory
                 for (Directory dir : distributor.all()) {
                     if (dir.fileExists(name)) {
-                        final Directory directory = nameDirMapping.putIfAbsent(name, dir);
+                        directory = nameDirMapping.putIfAbsent(name, dir);
                         return directory == null ? dir : directory;
                     }
                 }
@@ -172,10 +175,17 @@ private Directory getDirectory(String name, boolean failIfNotAssociated, boolean
             if (failIfNotAssociated) {
                 throw new FileNotFoundException("No such file [" + name + "]");
             }
+
+            // Pick a directory and associate this new file with it:
+            final Directory dir = distributor.any();
+            directory = nameDirMapping.putIfAbsent(name, dir);
+            if (directory == null) {
+                // putIfAbsent did in fact put dir:
+                directory = dir;
+            }
         }
-        final Directory dir = distributor.any();
-        final Directory directory = nameDirMapping.putIfAbsent(name, dir);
-        return directory == null ? dir : directory;
+
+        return directory;
     }
 
     @Override

src/test/java/org/elasticsearch/index/store/DistributorDirectoryTest.java

@@ -18,19 +18,21 @@
  */
 package org.elasticsearch.index.store;
 
-import com.carrotsearch.randomizedtesting.annotations.Listeners;
-import com.carrotsearch.randomizedtesting.annotations.ThreadLeakFilters;
-import com.carrotsearch.randomizedtesting.annotations.ThreadLeakScope;
-import com.carrotsearch.randomizedtesting.annotations.TimeoutSuite;
+import java.io.File;
+import java.io.IOException;
+
 import org.apache.lucene.store.BaseDirectoryTestCase;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TimeUnits;
+import org.elasticsearch.index.store.distributor.Distributor;
 import org.elasticsearch.test.ElasticsearchThreadFilter;
 import org.elasticsearch.test.junit.listeners.LoggingListener;
-
-import java.io.File;
-import java.io.IOException;
+import com.carrotsearch.randomizedtesting.annotations.Listeners;
+import com.carrotsearch.randomizedtesting.annotations.ThreadLeakFilters;
+import com.carrotsearch.randomizedtesting.annotations.ThreadLeakScope;
+import com.carrotsearch.randomizedtesting.annotations.TimeoutSuite;
 
 @ThreadLeakFilters(defaultFilters = true, filters = {ElasticsearchThreadFilter.class})
 @ThreadLeakScope(ThreadLeakScope.Scope.NONE)
@@ -48,4 +50,40 @@ protected Directory getDirectory(File path) throws IOException {
         return new DistributorDirectory(directories);
     }
 
+    // #7306: don't invoke the distributor when we are opening an already existing file
+    public void testDoNotCallDistributorOnRead() throws Exception {      
+        Directory dir = newDirectory();
+        dir.createOutput("one.txt", IOContext.DEFAULT).close();
+
+        final Directory[] dirs = new Directory[] {dir};
+
+        Distributor distrib = new Distributor() {
+
+            @Override
+            public Directory primary() {
+                return dirs[0];
+            }
+
+            @Override
+            public Directory[] all() {
+                return dirs;
+            }
+
+            @Override
+            public synchronized Directory any() {
+                throw new IllegalStateException("any should not be called");
+            }
+            };
+
+        Directory dd = new DistributorDirectory(distrib);
+        assertEquals(0, dd.fileLength("one.txt"));
+        dd.openInput("one.txt", IOContext.DEFAULT).close();
+        try {
+            dd.createOutput("three.txt", IOContext.DEFAULT).close();
+            fail("didn't hit expected exception");
+        } catch (IllegalStateException ise) {
+            // expected
+        }
+        dd.close();
+    }
 }