From 668f6e4dc186ab81a3831107c8e5f8f63132a1f3 Mon Sep 17 00:00:00 2001
From: eileen <emcnaughton@wikimedia.org>
Date: Wed, 27 Apr 2016 17:20:43 +1200
Subject: [PATCH] CRM-18842 Dedupe query: remove OR join in favour of more
 performant UNION

Unions are much faster than OR joins. This change took the length of the query to get the dedupes on a large database from
'as long as it took for the server to fall over' to less than one second on a small group of contacts

This query is only affecting one path - ie Individuals - at the moment as I can only extend that as fast as I can write tests.
---
 CRM/Dedupe/BAO/QueryBuilder.php               | 24 +++++++++++++++++++
 .../BAO/QueryBuilder/IndividualSupervised.php |  6 ++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/CRM/Dedupe/BAO/QueryBuilder.php b/CRM/Dedupe/BAO/QueryBuilder.php
index 484ce391c64d..3daff16951f3 100644
--- a/CRM/Dedupe/BAO/QueryBuilder.php
+++ b/CRM/Dedupe/BAO/QueryBuilder.php
@@ -22,4 +22,28 @@ public static function internalFilters($rg, $strID1 = 'contact1.id', $strID2 = '
     }
   }
 
+  /**
+   * If a contact list is specified then adjust the query to ensure one contact is in that list.
+   *
+   * Doing an OR join here will lead to a server-killing unindexed query. However, a union will
+   * perform better.
+   *
+   * @param array $contactList
+   * @param string $query
+   * @param string $strID1
+   * @param string $strID2
+   *
+   * @return string
+   */
+  protected static function filterQueryByContactList(array $contactList, $query, $strID1 = 'contact1.id', $strID2 = 'contact2.id') {
+    if (empty($contactList)) {
+      return $query . " AND ($strID1 < $strID2)";
+    }
+    $contactIDs = implode(',', $contactList);
+    return "$query AND $strID1 IN ($contactIDs) AND $strID1 > $strID2
+      UNION $query AND $strID1 > $strID2 AND $strID2 IN ($contactIDs) AND $strID1 NOT IN ($contactIDs)
+    ";
+
+  }
+
 }
diff --git a/CRM/Dedupe/BAO/QueryBuilder/IndividualSupervised.php b/CRM/Dedupe/BAO/QueryBuilder/IndividualSupervised.php
index 806f023e6c48..e150f44fd06a 100644
--- a/CRM/Dedupe/BAO/QueryBuilder/IndividualSupervised.php
+++ b/CRM/Dedupe/BAO/QueryBuilder/IndividualSupervised.php
@@ -53,7 +53,7 @@ public static function record($rg) {
    * @return array
    */
   public static function internal($rg) {
-    $query = "
+    $query = self::filterQueryByContactList($rg->contactIds, "
             SELECT contact1.id as id1, contact2.id as id2, {$rg->threshold} as weight
             FROM civicrm_contact as contact1
               JOIN civicrm_email as email1 ON email1.contact_id=contact1.id
@@ -63,8 +63,8 @@ public static function internal($rg) {
               JOIN civicrm_email as email2 ON
                 email2.contact_id=contact2.id AND
                 email1.email=email2.email
-            WHERE contact1.contact_type = 'Individual'
-              AND " . self::internalFilters($rg);
+            WHERE contact1.contact_type = 'Individual'");
+
     return array(
       "civicrm_contact.{$rg->name}.{$rg->threshold}" => $query,
     );