add tunable for repository invalidation concurrency level

Also, do not rebuild repository tags in the web app.

fixes #3157

Author: Vladimir Kotal

opengrok-indexer/src/main/java/org/opengrok/indexer/configuration/Configuration.java

@@ -179,6 +179,7 @@ public final class Configuration {
     private boolean compressXref;
     private boolean indexVersionedFilesOnly;
     private int indexingParallelism;
+    private int repositoryInvalidationParallelism;
     private int historyParallelism;
     private int historyFileParallelism;
     private boolean tagsEnabled;
@@ -1149,6 +1150,14 @@ public void setIndexingParallelism(int value) {
         this.indexingParallelism = Math.max(value, 0);
     }
 
+    public int getRepositoryInvalidationParallelism() {
+        return repositoryInvalidationParallelism;
+    }
+
+    public void setRepositoryInvalidationParallelism(int value) {
+        this.repositoryInvalidationParallelism = Math.max(value, 0);
+    }
+
     public int getHistoryParallelism() {
         return historyParallelism;
     }

opengrok-indexer/src/main/java/org/opengrok/indexer/configuration/RuntimeEnvironment.java

@@ -1114,6 +1114,16 @@ public int getIndexingParallelism() {
                 parallelism;
     }
 
+    /**
+     * Gets the value of {@link Configuration#getRepositoryInvalidationParallelism()} -- or
+     * if zero, then as a default gets the number of available processors halved.
+     * @return a natural number >= 1
+     */
+    public int getRepositoryInvalidationParallelism() {
+        int parallelism = syncReadConfiguration(Configuration::getRepositoryInvalidationParallelism);
+        return parallelism < 1 ? (Runtime.getRuntime().availableProcessors() / 2) : parallelism;
+    }
+
     /**
      * Gets the value of {@link Configuration#getHistoryParallelism()} -- or
      * if zero, then as a default gets the number of available processors.

opengrok-indexer/src/main/java/org/opengrok/indexer/history/HistoryGuru.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2005, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2021, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright (c) 2017, 2020, Chris Fraire <[email protected]>.
  */
 package org.opengrok.indexer.history;
@@ -815,7 +815,14 @@ public void invalidateRepositories(Collection<? extends RepositoryInfo> repos, C
          * run in parallel to speed up the process.
          */
         final CountDownLatch latch = new CountDownLatch(repos.size());
-        final ExecutorService executor = Executors.newFixedThreadPool(env.getIndexingParallelism(),
+        int parallelismLevel;
+        // Both indexer and web app startup should be as quick as possible.
+        if (cmdType.equals(CommandTimeoutType.INDEXER) || cmdType.equals(CommandTimeoutType.WEBAPP_START)) {
+            parallelismLevel = env.getIndexingParallelism();
+        } else {
+            parallelismLevel = env.getRepositoryInvalidationParallelism();
+        }
+        final ExecutorService executor = Executors.newFixedThreadPool(parallelismLevel,
                 runnable -> {
                     Thread thread = Executors.defaultThreadFactory().newThread(runnable);
                     thread.setName("invalidate-repos-" + thread.getId());

opengrok-indexer/src/main/java/org/opengrok/indexer/history/RepositoryFactory.java

@@ -245,7 +245,7 @@ public static Repository getRepository(File file, CommandTimeoutType cmdType, bo
 
                 // If this repository displays tags only for files changed by tagged
                 // revision, we need to prepare list of all tags in advance.
-                if (env.isTagsEnabled() && repo.hasFileBasedTags()) {
+                if (cmdType.equals(CommandTimeoutType.INDEXER) && env.isTagsEnabled() && repo.hasFileBasedTags()) {
                     repo.buildTagList(file, cmdType);
                 }
 

opengrok-web/src/main/java/org/opengrok/web/api/v1/controller/ConfigurationController.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2021, Oracle and/or its affiliates. All rights reserved.
  * Portions Copyright (c) 2017, 2020, Chris Fraire <[email protected]>.
  */
 package org.opengrok.web.api.v1.controller;
@@ -59,7 +59,7 @@ public String get() {
     @PUT
     @Consumes(MediaType.APPLICATION_XML)
     public void set(final String body, @QueryParam("reindex") final boolean reindex) {
-        env.applyConfig(body, reindex, reindex ? CommandTimeoutType.INDEXER : CommandTimeoutType.RESTFUL);
+        env.applyConfig(body, reindex, CommandTimeoutType.RESTFUL);
         suggesterService.refresh();
     }