MDL-39725 database: Add statistics collection functions

lib/dml/moodle_database.php

@@ -2126,6 +2126,15 @@ public function sql_regex($positivematch=true) {
         return '';
     }
 
+    /**
+     * Analyze the data in temporary tables to force statistics collection after bulk data loads.
+     *
+     * @return void
+     */
+    public function update_temp_table_stats() {
+        $this->temptables->update_stats();
+    }
+
     /**
      * Checks and returns true if transactions are supported.
      *

lib/dml/moodle_temptables.php

@@ -22,6 +22,7 @@
  *
  *   - databases not retrieving temp tables from information schema tables (mysql)
  *   - databases using a different name schema for temp tables (like mssql).
+ *   - databases that don't collect planner stats for temp tables (like PgSQL).
  *
  * Basically it works as a simple store of created temporary tables, providing
  * some simple getters/setters methods. Each database can extend it for its own
@@ -31,9 +32,6 @@
  * and the sql_generator, so both are able to use its facilities, with the final goal
  * of doing temporary tables support 100% cross-db and transparent within the DB API.
  *
- * Only drivers needing it will use this store. Neither moodle_database (abstract) or
- * databases like postgres need this, because they don't lack any temp functionality.
- *
  * @package    core_dml
  * @copyright  2009 onwards Eloy Lafuente (stronk7) {@link http://stronk7.com}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
@@ -119,6 +117,17 @@ public function get_correct_name($tablename) {
         return null;
     }
 
+    /**
+     * Analyze the data in temporary tables to force statistics collection after bulk data loads.
+     * The database class detects all temporary tables and will automatically analyze all created tables
+     *
+     * @return void
+     */
+    public function update_stats() {
+        // By default most databases do automatic on temporary tables, PgSQL does not.
+        // As a result, update_stats call immediately return for non-interesting database types.
+    }
+
     /**
      * Dispose the temptables stuff, checking for wrong situations, informing and recovering from them
      */

lib/dml/pgsql_native_moodle_temptables.php

@@ -29,5 +29,16 @@
 require_once(__DIR__.'/moodle_temptables.php');
 
 class pgsql_native_moodle_temptables extends moodle_temptables {
-    // I love these classes :-P
+    /**
+     * Analyze the data in temporary tables to force statistics collection after bulk data loads.
+     * PostgreSQL does not natively support automatic temporary table stats collection, so we do it.
+     *
+     * @return void
+     */
+    public function update_stats() {
+        $temptables = $this->get_temptables();
+        foreach ($temptables as $temptablename) {
+            $this->mdb->execute("ANALYZE {".$temptablename."}");
+        }
+    }
 }