Group Contact Cache problem

[Eileen]

We were getting catastrophic performance on the group contact cache problem but it was fixed by the below  - I'd be keen to see if any else gets performance increase from this - or can suggest why it is faster! Creating the temp table and then inserting into it wasn't faster which was mysterious. I can't rule out some config issue is involved

diff --git a/CRM/Contact/BAO/GroupContactCache.php b/CRM/Contact/BAO/GroupContactCache.php
index e8e2ab0..4abee2f 100644
--- a/CRM/Contact/BAO/GroupContactCache.php
+++ b/CRM/Contact/BAO/GroupContactCache.php
@@ -113,14 +113,19 @@
     // sort the values so we put group IDs in front and hence optimize
     // mysql storage (or so we think) CRM-9493
     sort($values);
-
+ $tempTable = 'civicrm_temp_group_contact_cache' . rand(0,2000);
     // to avoid long strings, lets do BULK_INSERT_COUNT values at a time
     while (!empty($values)) {
       $processed = TRUE;
       $input = array_splice($values, 0, CRM_Core_DAO::BULK_INSERT_COUNT);
       $str = implode(',', $input);
- $sql = "INSERT IGNORE INTO civicrm_group_contact_cache (group_id,contact_id) VALUES $str;";
+ $sql = "CREATE TEMPORARY TABLE $tempTable $str;";
       CRM_Core_DAO::executeQuery($sql);
+ CRM_Core_DAO::executeQuery(
+ "INSERT IGNORE INTO civicrm_group_contact_cache (contact_id, group_id)
+ SELECT DISTINCT id, group_id FROM $tempTable
+ ");
+ CRM_Core_DAO::executeQuery(" DROP TABLE $tempTable");
     }
     self::updateCacheTime($groupID, $processed);
   }
@@ -336,15 +341,21 @@
 
     $groupIDs = array($groupID);
     self::remove($groupIDs);
-
+ $tempTable = 'civicrm_temp_group_contact_cache' . rand(0,2000);
     foreach (array($sql, $sqlB) as $selectSql) {
       if (!$selectSql) {
         continue;
       }
- $insertSql = "INSERT IGNORE INTO civicrm_group_contact_cache (group_id,contact_id) ($selectSql);";
+ $insertSql = "CREATE TEMPORARY TABLE $tempTable ($selectSql);";
       $processed = TRUE; // FIXME
       $result = CRM_Core_DAO::executeQuery($insertSql);
+ CRM_Core_DAO::executeQuery(
+ "INSERT IGNORE INTO civicrm_group_contact_cache (contact_id, group_id)
+ SELECT DISTINCT id, group_id FROM $tempTable
+ ");
+ CRM_Core_DAO::executeQuery(" DROP TABLE $tempTable");
     }
+
     self::updateCacheTime($groupIDs, $processed);
 
     if ($group->children) {