Make messages translatable and more sensible.

Summary:
These exception messages & comments didn't quite match reality.
Fixed and added pht() around a couple of them.

Test Plan: I didn't test this :P

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17578

src/applications/search/fulltextstorage/PhabricatorElasticFulltextStorageEngine.php

@@ -303,7 +303,8 @@ class PhabricatorElasticFulltextStorageEngine
         $exceptions[] = $e;
       }
     }
-    throw new PhutilAggregateException('All search hosts failed:', $exceptions);
+    throw new PhutilAggregateException(pht('All Fulltext Search hosts failed:'),
+      $exceptions);
   }
 
   public function indexExists(PhabricatorElasticSearchHost $host = null) {

src/docs/user/cluster/cluster.diviner

@@ -47,6 +47,7 @@ will have on availability, resistance to data loss, and scalability.
 | **SSH Servers** | Minimal | Low | No Risk | Low
 | **Web Servers** | Minimal | **High** | No Risk | Moderate
 | **Notifications** | Minimal | Low | No Risk | Low
+| **Fulltext Search** | Moderate | **High** | Minimal Risk | Moderate
 
 See below for a walkthrough of these services in greater detail.
 
@@ -237,6 +238,33 @@ hosts is unlikely to have much impact on scalability.
 For details, see @{article:Cluster: Notifications}.
 
 
+Cluster: Fulltext Search
+========================
+
+At a certain scale, you may begin to bump up against the limitations of MySQL's
+built-in fulltext search capabilities. We have seen this with very large
+installations with several million objects in the database and very many
+simultaneous requests. At this point you may consider adding Elasticsearch
+hosts to your cluster to reduce the load on your MySQL hosts.
+
+Elasticsearch has the ability to spread the load across multiple hosts and can
+handle very large indexes by sharding.
+
+Search does not involve any risk of data lost because it's always possible to
+rebuild the search index from the original database objects. This process can
+be very time consuming, however, especially when the database grows very large.
+
+With multiple Elasticsearch hosts, you can survive the loss of a single host
+with minimal disruption as Phabricator will detect the problem and direct
+queries to one of the remaining hosts.
+
+Phabricator supports writing to multiple indexing servers. This Simplifies
+Elasticsearch upgrades and makes it possible to recover more quickly from
+problems with the search index.
+
+For details, see @{article:Cluster: Search}.
+
+
 Overlaying Services
 ===================
 

src/infrastructure/cluster/search/PhabricatorSearchService.php

@@ -235,21 +235,20 @@ class PhabricatorSearchService
    * @throws PhutilAggregateException
    */
   public static function executeSearch(PhabricatorSavedQuery $query) {
-    $services = self::getAllServices();
     $exceptions = array();
-    foreach ($services as $service) {
-      $engine = $service->getEngine();
-      // try all hosts until one succeeds
+    // try all services until one succeeds
+    foreach (self::getAllServices() as $service) {
       try {
+        $engine = $service->getEngine();
         $res = $engine->executeSearch($query);
-        // return immediately if we get results without an exception
+        // return immediately if we get results
         return $res;
       } catch (Exception $ex) {
         $exceptions[] = $ex;
       }
     }
-    throw new PhutilAggregateException('All search engines failed:',
-      $exceptions);
+    $msg = pht('All of the configured Fulltext Search services failed.');
+    throw new PhutilAggregateException($msg, $exceptions);
   }
 
 }