diff --git a/config-dist.php b/config-dist.php
index ec68c6b2c87..3febb696075 100644
--- a/config-dist.php
+++ b/config-dist.php
@@ -105,8 +105,9 @@ $CFG->dboptions = array(
       'latency' => 0.5,      // Set read-only slave sync latency in seconds.
                              // When 'latency' seconds have lapsed after an update to a table
                              // it is deemed safe to use readonly slave for reading from the table.
-                             // It is optional. If omitted once written to a table it will always
-                             // use master handle for reading.
+                             // It is optional, defaults to 1 second. If you want once written to a table
+                             // to always use master handle for reading set it to something ridiculosly big,
+                             // eg 10.
                              // Lower values increase the performance, but setting it too low means
                              // missing the master-slave sync.
       'exclude_tables' => [  // Tables to exclude from read-only slave feature.
diff --git a/lib/dml/moodle_read_slave_trait.php b/lib/dml/moodle_read_slave_trait.php
index cba970ed624..2e99699d9de 100644
--- a/lib/dml/moodle_read_slave_trait.php
+++ b/lib/dml/moodle_read_slave_trait.php
@@ -43,8 +43,8 @@ defined('MOODLE_INTERNAL') || die();
  * - It supports multiple 'instance' entries, in case one is not accessible,
  *   but only one (first connectable) instance is used.
  * - 'latency' option: master -> slave sync latency in seconds (will probably
- *   be a fraction of a second). If specified, a table being written to is
- *   deemed fully synced and suitable for slave read.
+ *   be a fraction of a second). A table being written to is deemed fully synced
+ *   after that period and suitable for slave read. Defaults to 1 sec.
  * - 'exclude_tables' option: a list of tables that never go to the slave for
  *   querying. The feature is meant to be used in emergency only, so the
  *   readonly feature can still be used in case there is a rogue query that
@@ -54,8 +54,8 @@ defined('MOODLE_INTERNAL') || die();
  *
  * Choice of the database handle is based on following:
  * - SQL_QUERY_INSERT, UPDATE and STRUCTURE record table from the query
- *   in the $written array and microtime() the event if the 'latency' option
- *   is set. For those queries master write handle is used.
+ *   in the $written array and microtime() the event. For those queries master
+ *   write handle is used.
  * - SQL_QUERY_AUX queries will always use the master write handle because they
  *   are used for transactionstart/end, locking etc. In that respect, query_start() and
  *   query_end() *must not* be used during the connection phase.
@@ -63,11 +63,9 @@ defined('MOODLE_INTERNAL') || die();
  *   -- any of the tables involved is a temp table
  *   -- any of the tables involved is listed in the 'exclude_tables' option
  *   -- any of the tables involved is in the $written array:
- *      * If the 'latency' option is set then the microtime() is compared to
- *        the write microrime, and if more then latency time has passed the slave
- *        handle is used.
- *      * Otherwise (not enough time passed or 'latency' option not set)
- *        we choose the master write handle
+ *      * current microtime() is compared to the write microrime, and if more than
+ *        latency time has passed the slave handle is used
+ *      * otherwise (not enough time passed) we choose the master write handle
  *   If none of the above conditions are met the slave instance is used.
  *
  * A 'latency' example:
@@ -92,7 +90,7 @@ trait moodle_read_slave_trait {
 
     private $wantreadslave = false;
     private $readsslave = 0;
-    private $slavelatency = 0;
+    private $slavelatency = 1;
 
     private $written = []; // Track tables being written to.
     private $readexclude = []; // Tables to exclude from using dbhreadonly.
@@ -324,23 +322,27 @@ trait moodle_read_slave_trait {
                     }
 
                     if (isset($this->written[$tablename])) {
-                        if ($this->slavelatency) {
-                            $now = $now ?: microtime(true);
-                            if ($now - $this->written[$tablename] < $this->slavelatency) {
-                                return false;
-                            }
-                            unset($this->written[$tablename]);
-                        } else {
+                        $now = $now ?: microtime(true);
+                        // Paranoid check.
+                        if ($this->written[$tablename] === true) {
+                            debugging(
+                                "$tablename last written set to true outside transaction - should not happen!",
+                                DEBUG_DEVELOPER
+                            );
+                            $this->written[$tablename] = $now;
                             return false;
                         }
+                        if ($now - $this->written[$tablename] < $this->slavelatency) {
+                            return false;
+                        }
+                        unset($this->written[$tablename]);
                     }
                 }
 
                 return true;
             case SQL_QUERY_INSERT:
             case SQL_QUERY_UPDATE:
-                // If we are in transaction we cannot set the written time yet.
-                $now = $this->slavelatency && !$this->transactions ? microtime(true) : true;
+                $now = $this->transactions ? true : microtime(true);
                 foreach ($this->table_names($sql) as $tablename) {
                     $this->written[$tablename] = $now;
                 }
@@ -364,23 +366,15 @@ trait moodle_read_slave_trait {
      * @throws dml_transaction_exception Creates and throws transaction related exceptions.
      */
     public function commit_delegated_transaction(moodle_transaction $transaction) {
-        parent::commit_delegated_transaction($transaction);
-
-        if ($this->transactions) {
-            return;
-        }
-
-        if (!$this->slavelatency) {
-            return;
-        }
-
-        $now = null;
-        foreach ($this->written as $tablename => $when) {
-            if ($when === true) {
-                $now = $now ?: microtime(true);
+        if ($this->written) {
+            // Adjust the written time.
+            $now = microtime(true);
+            foreach ($this->written as $tablename => $when) {
                 $this->written[$tablename] = $now;
             }
         }
+
+        parent::commit_delegated_transaction($transaction);
     }
 
     /**
diff --git a/lib/dml/tests/dml_mysqli_read_slave_test.php b/lib/dml/tests/dml_mysqli_read_slave_test.php
index af55928f384..60924169de4 100644
--- a/lib/dml/tests/dml_mysqli_read_slave_test.php
+++ b/lib/dml/tests/dml_mysqli_read_slave_test.php
@@ -21,8 +21,11 @@
  * @category   dml
  * @copyright  2018 Srdjan Janković, Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @coversDefaultClass \mysqli_native_moodle_database
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/fixtures/read_slave_moodle_database_mock_mysqli.php');
@@ -35,7 +38,7 @@ require_once(__DIR__.'/fixtures/read_slave_moodle_database_mock_mysqli.php');
  * @copyright  2018 Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class core_dml_mysqli_read_slave_testcase extends base_testcase {
+class dml_mysqli_read_slave_test extends \base_testcase {
     /**
      * Test readonly handle is not used for reading from special pg_*() call queries,
      * pg_try_advisory_lock and pg_advisory_unlock.
@@ -80,7 +83,7 @@ class core_dml_mysqli_read_slave_testcase extends base_testcase {
             'connecttimeout' => 1
         ];
 
-        $db2 = moodle_database::get_driver_instance($cfg->dbtype, $cfg->dblibrary);
+        $db2 = \moodle_database::get_driver_instance($cfg->dbtype, $cfg->dblibrary);
         $db2->connect($cfg->dbhost, $cfg->dbuser, $cfg->dbpass, $cfg->dbname, $cfg->prefix, $cfg->dboptions);
         $this->assertTrue(count($db2->get_records('user')) > 0);
     }
diff --git a/lib/dml/tests/dml_pgsql_read_slave_test.php b/lib/dml/tests/dml_pgsql_read_slave_test.php
index b1f24ebbf9f..1ad15bf77f8 100644
--- a/lib/dml/tests/dml_pgsql_read_slave_test.php
+++ b/lib/dml/tests/dml_pgsql_read_slave_test.php
@@ -21,8 +21,11 @@
  * @category   dml
  * @copyright  2018 Srdjan Janković, Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @coversDefaultClass \pgsql_native_moodle_database
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/fixtures/read_slave_moodle_database_mock_pgsql.php');
@@ -35,7 +38,7 @@ require_once(__DIR__.'/fixtures/read_slave_moodle_database_mock_pgsql.php');
  * @copyright  2018 Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class core_dml_pgsql_read_slave_testcase extends base_testcase {
+class dml_pgsql_read_slave_test extends \base_testcase {
     /**
      * Test correct database handles are used for cursors
      *
@@ -135,12 +138,12 @@ class core_dml_pgsql_read_slave_testcase extends base_testcase {
         }
 
         // Get a separate disposable db connection handle with guaranteed 'readonly' config.
-        $db2 = moodle_database::get_driver_instance($cfg->dbtype, $cfg->dblibrary);
+        $db2 = \moodle_database::get_driver_instance($cfg->dbtype, $cfg->dblibrary);
         $db2->connect($cfg->dbhost, $cfg->dbuser, $cfg->dbpass, $cfg->dbname, $cfg->prefix, $cfg->dboptions);
 
         $dbman = $db2->get_manager();
 
-        $table = new xmldb_table('silly_test_table');
+        $table = new \xmldb_table('silly_test_table');
         $table->add_field('id', XMLDB_TYPE_INTEGER, 10, null, XMLDB_NOTNULL, XMLDB_SEQUENCE);
         $table->add_field('msg', XMLDB_TYPE_CHAR, 255);
         $table->add_key('primary', XMLDB_KEY_PRIMARY, ['id']);
@@ -155,7 +158,7 @@ class core_dml_pgsql_read_slave_testcase extends base_testcase {
         $db2->get_records('silly_test_table');
         $this->assertEquals($reads, $db2->perf_get_reads_slave());
 
-        $table2 = new xmldb_table('silly_test_table2');
+        $table2 = new \xmldb_table('silly_test_table2');
         $table2->add_field('id', XMLDB_TYPE_INTEGER, 10, null, XMLDB_NOTNULL, XMLDB_SEQUENCE);
         $table2->add_field('msg', XMLDB_TYPE_CHAR, 255);
         $table2->add_key('primary', XMLDB_KEY_PRIMARY, ['id']);
@@ -193,7 +196,7 @@ class core_dml_pgsql_read_slave_testcase extends base_testcase {
             'connecttimeout' => 1
         ];
 
-        $db2 = moodle_database::get_driver_instance($cfg->dbtype, $cfg->dblibrary);
+        $db2 = \moodle_database::get_driver_instance($cfg->dbtype, $cfg->dblibrary);
         $db2->connect($cfg->dbhost, $cfg->dbuser, $cfg->dbpass, $cfg->dbname, $cfg->prefix, $cfg->dboptions);
         $this->assertTrue(count($db2->get_records('user')) > 0);
     }
diff --git a/lib/dml/tests/dml_read_slave_test.php b/lib/dml/tests/dml_read_slave_test.php
index 4ee6fc9c620..f9b5b070a94 100644
--- a/lib/dml/tests/dml_read_slave_test.php
+++ b/lib/dml/tests/dml_read_slave_test.php
@@ -21,12 +21,16 @@
  * @category   dml
  * @copyright  2018 Srdjan Janković, Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @coversDefaultClass \moodle_temptables
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/fixtures/read_slave_moodle_database_table_names.php');
 require_once(__DIR__.'/fixtures/read_slave_moodle_database_special.php');
+require_once(__DIR__.'/../../tests/fixtures/event_fixtures.php');
 
 /**
  * DML read/read-write database handle use tests
@@ -36,10 +40,12 @@ require_once(__DIR__.'/fixtures/read_slave_moodle_database_special.php');
  * @copyright  2018 Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class core_dml_read_slave_testcase extends base_testcase {
+class dml_read_slave_test extends \base_testcase {
 
     /** @var float */
     static private $dbreadonlylatency = 0.8;
+    /** @var float */
+    static private $defaultlatency = 1;
 
     /**
      * Instantiates a test database interface object.
@@ -223,18 +229,27 @@ class core_dml_read_slave_testcase extends base_testcase {
         $this->assertEquals('test_rw::test:test', $handle);
         $this->assertEquals(0, $DB->perf_get_reads_slave());
 
-        sleep(1);
         $handle = $DB->get_records('table');
         $this->assertEquals('test_rw::test:test', $handle);
         $this->assertEquals(0, $DB->perf_get_reads_slave());
 
-        $handle = $DB->get_records('table2');
+        $handle = $DB->get_records_sql("SELECT * FROM {table2} JOIN {table}");
+        $this->assertEquals('test_rw::test:test', $handle);
+        $this->assertEquals(0, $DB->perf_get_reads_slave());
+
+        sleep(1);
+
+        $handle = $DB->get_records('table');
         $this->assert_readonly_handle($handle);
         $this->assertEquals(1, $DB->perf_get_reads_slave());
 
+        $handle = $DB->get_records('table2');
+        $this->assert_readonly_handle($handle);
+        $this->assertEquals(2, $DB->perf_get_reads_slave());
+
         $handle = $DB->get_records_sql("SELECT * FROM {table2} JOIN {table}");
-        $this->assertEquals('test_rw::test:test', $handle);
-        $this->assertEquals(1, $DB->perf_get_reads_slave());
+        $this->assert_readonly_handle($handle);
+        $this->assertEquals(3, $DB->perf_get_reads_slave());
     }
 
     /**
@@ -278,12 +293,15 @@ class core_dml_read_slave_testcase extends base_testcase {
      * so the latency parameter is applied properly.
      *
      * @return void
+     * @covers ::can_use_readonly
+     * @covers ::commit_delegated_transaction
      */
-    public function test_transaction() : void {
+    public function test_transaction(): void {
         $DB = $this->new_db(true);
 
         $this->assertNull($DB->get_dbhwrite());
 
+        $skip = false;
         $transaction = $DB->start_delegated_transaction();
         $now = microtime(true);
         $handle = $DB->get_records_sql("SELECT * FROM {table}");
@@ -304,11 +322,92 @@ class core_dml_read_slave_testcase extends base_testcase {
 
             // Make sure enough time passes.
             sleep(1);
+        } else {
+            $skip = true;
         }
 
         // Exceeded latency time, use ro handle.
         $handle = $DB->get_records_sql("SELECT * FROM {table}");
         $this->assert_readonly_handle($handle);
+
+        if ($skip) {
+            $this->markTestSkipped("Delay too long to test write handle immediately after transaction");
+        }
+    }
+
+    /**
+     * Test readonly handle is not used with events
+     * when the latency parameter is applied properly.
+     *
+     * @return void
+     * @covers ::can_use_readonly
+     * @covers ::commit_delegated_transaction
+     */
+    public function test_transaction_with_events(): void {
+        $this->with_global_db(function () {
+            global $DB;
+
+            $DB = $this->new_db(true, ['test_ro'], read_slave_moodle_database_special::class);
+            $DB->set_tables([
+                'config_plugins' => [
+                    'columns' => [
+                        'plugin' => (object)['meta_type' => ''],
+                    ]
+                ]
+            ]);
+
+            $this->assertNull($DB->get_dbhwrite());
+
+            $this->_called = false;
+            $transaction = $DB->start_delegated_transaction();
+            $now = microtime(true);
+
+            $observers = [
+                [
+                    'eventname'   => '\core_tests\event\unittest_executed',
+                    'callback'    => function (\core_tests\event\unittest_executed $event) use ($DB, $now) {
+                        $this->_called = true;
+                        $this->assertFalse($DB->is_transaction_started());
+
+                        // This condition should always evaluate true, however we need to
+                        // safeguard from an unaccounted delay that can break this test.
+                        if (microtime(true) - $now < 1 + self::$dbreadonlylatency) {
+                            // Not enough time passed, use rw handle.
+                            $handle = $DB->get_records_sql_p("SELECT * FROM {table}");
+                            $this->assertEquals('test_rw::test:test', $handle);
+
+                            // Make sure enough time passes.
+                            sleep(1);
+                        } else {
+                            $this->markTestSkipped("Delay too long to test write handle immediately after transaction");
+                        }
+
+                        // Exceeded latency time, use ro handle.
+                        $handle = $DB->get_records_sql_p("SELECT * FROM {table}");
+                        $this->assertEquals('test_ro::test:test', $handle);
+                    },
+                    'internal'    => 0,
+                ],
+            ];
+            \core\event\manager::phpunit_replace_observers($observers);
+
+            $handle = $DB->get_records_sql_p("SELECT * FROM {table}");
+            // Use rw handle during transaction.
+            $this->assertEquals('test_rw::test:test', $handle);
+
+            $handle = $DB->insert_record_raw('table', array('name' => 'blah'));
+            // Introduce delay so we can check that table write timestamps
+            // are adjusted properly.
+            sleep(1);
+            $event = \core_tests\event\unittest_executed::create([
+                'context' => \context_system::instance(),
+                'other' => ['sample' => 1]
+            ]);
+            $event->trigger();
+            $transaction->allow_commit();
+
+            $this->assertTrue($this->_called);
+        });
     }
 
     /**
diff --git a/lib/dml/tests/fixtures/read_slave_moodle_database.php b/lib/dml/tests/fixtures/read_slave_moodle_database.php
index 982dbad135d..db41bd977d2 100644
--- a/lib/dml/tests/fixtures/read_slave_moodle_database.php
+++ b/lib/dml/tests/fixtures/read_slave_moodle_database.php
@@ -23,6 +23,8 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/test_moodle_database.php');
@@ -37,7 +39,7 @@ require_once(__DIR__.'/../../moodle_read_slave_trait.php');
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class read_slave_moodle_database extends test_moodle_database {
-    use moodle_read_slave_trait;
+    use \moodle_read_slave_trait;
 
     /** @var string */
     protected $handle;
@@ -58,7 +60,7 @@ class read_slave_moodle_database extends test_moodle_database {
         $this->prefix = $prefix;
 
         if ($dbhost == 'test_ro_fail') {
-            throw new dml_connection_exception($dbhost);
+            throw new \dml_connection_exception($dbhost);
         }
 
         return true;
diff --git a/lib/dml/tests/fixtures/read_slave_moodle_database_mock_mysqli.php b/lib/dml/tests/fixtures/read_slave_moodle_database_mock_mysqli.php
index 29165f6b3ba..e1b5d0a93b9 100644
--- a/lib/dml/tests/fixtures/read_slave_moodle_database_mock_mysqli.php
+++ b/lib/dml/tests/fixtures/read_slave_moodle_database_mock_mysqli.php
@@ -23,6 +23,8 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/../../mysqli_native_moodle_database.php');
@@ -36,7 +38,7 @@ require_once(__DIR__.'/test_moodle_read_slave_trait.php');
  * @copyright  2018 Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class read_slave_moodle_database_mock_mysqli extends mysqli_native_moodle_database {
+class read_slave_moodle_database_mock_mysqli extends \mysqli_native_moodle_database {
     use test_moodle_read_slave_trait;
 
     /**
diff --git a/lib/dml/tests/fixtures/read_slave_moodle_database_mock_pgsql.php b/lib/dml/tests/fixtures/read_slave_moodle_database_mock_pgsql.php
index 60367fdd5f4..a59573b35c1 100644
--- a/lib/dml/tests/fixtures/read_slave_moodle_database_mock_pgsql.php
+++ b/lib/dml/tests/fixtures/read_slave_moodle_database_mock_pgsql.php
@@ -23,6 +23,8 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/../../pgsql_native_moodle_database.php');
@@ -36,6 +38,6 @@ require_once(__DIR__.'/test_moodle_read_slave_trait.php');
  * @copyright  2018 Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class read_slave_moodle_database_mock_pgsql extends pgsql_native_moodle_database {
+class read_slave_moodle_database_mock_pgsql extends \pgsql_native_moodle_database {
     use test_moodle_read_slave_trait;
 }
diff --git a/lib/dml/tests/fixtures/read_slave_moodle_database_special.php b/lib/dml/tests/fixtures/read_slave_moodle_database_special.php
index f34491935ee..be09eba0b43 100644
--- a/lib/dml/tests/fixtures/read_slave_moodle_database_special.php
+++ b/lib/dml/tests/fixtures/read_slave_moodle_database_special.php
@@ -23,10 +23,11 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/read_slave_moodle_database.php');
-require_once(__DIR__.'/read_slave_moodle_recordset_special.php');
 
 /**
  * Database driver mock test class that uses read_slave_moodle_recordset_special
@@ -50,6 +51,19 @@ class read_slave_moodle_database_special extends read_slave_moodle_database {
         return [];
     }
 
+    /**
+     * Returns read_slave_moodle_database::get_records_sql()
+     * For the tests where we need both fake result and dbhandle info.
+     * @param string $sql the SQL select query to execute.
+     * @param array $params array of sql parameters
+     * @param int $limitfrom return a subset of records, starting at this point (optional).
+     * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
+     * @return string $handle handle property
+     */
+    public function get_records_sql_p($sql, array $params = null, $limitfrom = 0, $limitnum = 0) {
+        return parent::get_records_sql($sql, $params);
+    }
+
     /**
      * Returns fake recordset
      * @param string $sql
@@ -74,3 +88,46 @@ class read_slave_moodle_database_special extends read_slave_moodle_database {
         return 1;
     }
 }
+
+/**
+ * Database recordset mock test class
+ *
+ * @package    core
+ * @category   dml
+ * @copyright  2018 Catalyst IT
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class read_slave_moodle_recordset_special extends \moodle_recordset {
+    /**
+     * Iterator interface
+     * @return void
+     */
+    public function close() {
+    }
+    /**
+     * Iterator interface
+     * @return stdClass
+     */
+    public function current() {
+        return new stdClass();
+    }
+    /**
+     * Iterator interface
+     * @return void
+     */
+    public function next() {
+    }
+    /**
+     * Iterator interface
+     * @return mixed
+     */
+    public function key() {
+    }
+    /**
+     * Iterator interface
+     * @return bool
+     */
+    public function valid() {
+        return false;
+    }
+}
diff --git a/lib/dml/tests/fixtures/read_slave_moodle_database_table_names.php b/lib/dml/tests/fixtures/read_slave_moodle_database_table_names.php
index a0a199c8716..b676b11c33d 100644
--- a/lib/dml/tests/fixtures/read_slave_moodle_database_table_names.php
+++ b/lib/dml/tests/fixtures/read_slave_moodle_database_table_names.php
@@ -23,6 +23,8 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/read_slave_moodle_database.php');
diff --git a/lib/dml/tests/fixtures/test_moodle_database.php b/lib/dml/tests/fixtures/test_moodle_database.php
index 54f41c0b4d3..90238958ff6 100644
--- a/lib/dml/tests/fixtures/test_moodle_database.php
+++ b/lib/dml/tests/fixtures/test_moodle_database.php
@@ -23,6 +23,8 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/../../moodle_database.php');
@@ -38,7 +40,7 @@ require_once(__DIR__.'/test_sql_generator.php');
  * @copyright  2018 Catalyst IT
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-abstract class test_moodle_database extends moodle_database {
+abstract class test_moodle_database extends \moodle_database {
 
     /** @var string */
     private $error;
@@ -53,7 +55,7 @@ abstract class test_moodle_database extends moodle_database {
     public function __construct($external = false) {
         parent::__construct($external);
 
-        $this->temptables = new moodle_temptables($this);
+        $this->temptables = new \moodle_temptables($this);
     }
 
     /**
diff --git a/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php b/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php
index 530e71a9816..087e6e94f4c 100644
--- a/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php
+++ b/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php
@@ -23,9 +23,7 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
-defined('MOODLE_INTERNAL') || die();
-
-require_once(__DIR__.'/../../pgsql_native_moodle_database.php');
+namespace core;
 
 /**
  * Read slave helper that exposes selected moodle_read_slave_trait metods
@@ -55,7 +53,7 @@ trait test_moodle_read_slave_trait {
         $this->dbhreadonly = $ro;
         $this->set_db_handle($this->dbhwrite);
 
-        $this->temptables = new moodle_temptables($this);
+        $this->temptables = new \moodle_temptables($this);
     }
 
     /**
diff --git a/lib/dml/tests/fixtures/test_sql_generator.php b/lib/dml/tests/fixtures/test_sql_generator.php
index a1a42aa9de9..edf06f34455 100644
--- a/lib/dml/tests/fixtures/test_sql_generator.php
+++ b/lib/dml/tests/fixtures/test_sql_generator.php
@@ -23,6 +23,8 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+namespace core;
+
 defined('MOODLE_INTERNAL') || die();
 
 require_once(__DIR__.'/../../../ddl/sql_generator.php');
@@ -36,7 +38,7 @@ require_once(__DIR__.'/../../../ddl/sql_generator.php');
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  *
  */
-class test_sql_generator extends sql_generator {
+class test_sql_generator extends \sql_generator {
     // phpcs:disable moodle.NamingConventions.ValidFunctionName.LowercaseMethod
 
     /**