diff --git a/admin/tool/log/store/database/classes/log/store.php b/admin/tool/log/store/database/classes/log/store.php
index c394d0b8add..0bbffb2950f 100644
--- a/admin/tool/log/store/database/classes/log/store.php
+++ b/admin/tool/log/store/database/classes/log/store.php
@@ -25,7 +25,7 @@
 namespace logstore_database\log;
 defined('MOODLE_INTERNAL') || die();
 
-class store implements \tool_log\log\writer, \core\log\sql_select_reader {
+class store implements \tool_log\log\writer, \core\log\sql_reader {
     use \tool_log\helper\store,
         \tool_log\helper\reader,
         \tool_log\helper\buffered_writer {
@@ -173,28 +173,71 @@ class store implements \tool_log\log\writer, \core\log\sql_select_reader {
         $records = $this->extdb->get_records_select($dbtable, $selectwhere, $params, $sort, '*', $limitfrom, $limitnum);
 
         foreach ($records as $data) {
-            $extra = array('origin' => $data->origin, 'realuserid' => $data->realuserid, 'ip' => $data->ip);
-            $data = (array)$data;
-            $id = $data['id'];
-            $data['other'] = unserialize($data['other']);
-            if ($data['other'] === false) {
-                $data['other'] = array();
-            }
-            unset($data['origin']);
-            unset($data['ip']);
-            unset($data['realuserid']);
-            unset($data['id']);
-
-            $event = \core\event\base::restore($data, $extra);
-            // Add event to list if it's valid.
-            if ($event) {
-                $events[$id] = $event;
+            if ($event = $this->get_log_event($data)) {
+                $events[$data->id] = $event;
             }
         }
 
         return $events;
     }
 
+    /**
+     * Fetch records using given criteria returning a Traversable object.
+     *
+     * Note that the traversable object contains a moodle_recordset, so
+     * remember that is important that you call close() once you finish
+     * using it.
+     *
+     * @param string $selectwhere
+     * @param array $params
+     * @param string $sort
+     * @param int $limitfrom
+     * @param int $limitnum
+     * @return \core\dml\recordset_walk|\core\event\base[]
+     */
+    public function get_events_select_iterator($selectwhere, array $params, $sort, $limitfrom, $limitnum) {
+        if (!$this->init()) {
+            return array();
+        }
+
+        if (!$dbtable = $this->get_config('dbtable')) {
+            return array();
+        }
+
+        $sort = self::tweak_sort_by_id($sort);
+
+        $recordset = $this->extdb->get_recordset_select($dbtable, $selectwhere, $params, $sort, '*', $limitfrom, $limitnum);
+
+        return new \core\dml\recordset_walk($recordset, array($this, 'get_log_event'));
+    }
+
+    /**
+     * Returns an event from the log data.
+     *
+     * @param stdClass $data Log data
+     * @return \core\event\base
+     */
+    public function get_log_event($data) {
+
+        $extra = array('origin' => $data->origin, 'ip' => $data->ip, 'realuserid' => $data->realuserid);
+        $data = (array)$data;
+        $id = $data['id'];
+        $data['other'] = unserialize($data['other']);
+        if ($data['other'] === false) {
+            $data['other'] = array();
+        }
+        unset($data['origin']);
+        unset($data['ip']);
+        unset($data['realuserid']);
+        unset($data['id']);
+
+        if (!$event = \core\event\base::restore($data, $extra)) {
+            return null;
+        }
+
+        return $event;
+    }
+
     /**
      * Get number of events present for the given select clause.
      *
diff --git a/admin/tool/log/store/legacy/classes/log/store.php b/admin/tool/log/store/legacy/classes/log/store.php
index 846e4ab0f93..7aa205689f1 100644
--- a/admin/tool/log/store/legacy/classes/log/store.php
+++ b/admin/tool/log/store/legacy/classes/log/store.php
@@ -26,7 +26,7 @@ namespace logstore_legacy\log;
 
 defined('MOODLE_INTERNAL') || die();
 
-class store implements \tool_log\log\store, \core\log\sql_select_reader {
+class store implements \tool_log\log\store, \core\log\sql_reader {
     use \tool_log\helper\store,
         \tool_log\helper\reader;
 
@@ -47,7 +47,7 @@ class store implements \tool_log\log\store, \core\log\sql_select_reader {
     const CRUD_REGEX = "/(crud).*?(<>|=|!=).*?'(.*?)'/s";
 
     /**
-     * This method contains mapping required for Moodle core to make legacy store compatible with other sql_select_reader based
+     * This method contains mapping required for Moodle core to make legacy store compatible with other sql_reader based
      * queries.
      *
      * @param string $selectwhere Select statment
@@ -104,7 +104,7 @@ class store implements \tool_log\log\store, \core\log\sql_select_reader {
         $events = array();
 
         foreach ($records as $data) {
-            $events[$data->id] = \logstore_legacy\event\legacy_logged::restore_legacy($data);
+            $events[$data->id] = $this->get_log_event($data);
         }
 
         $records->close();
@@ -112,6 +112,48 @@ class store implements \tool_log\log\store, \core\log\sql_select_reader {
         return $events;
     }
 
+    /**
+     * Fetch records using given criteria returning a Traversable object.
+     *
+     * Note that the traversable object contains a moodle_recordset, so
+     * remember that is important that you call close() once you finish
+     * using it.
+     *
+     * @param string $selectwhere
+     * @param array $params
+     * @param string $sort
+     * @param int $limitfrom
+     * @param int $limitnum
+     * @return \Traversable|\core\event\base[]
+     */
+    public function get_events_select_iterator($selectwhere, array $params, $sort, $limitfrom, $limitnum) {
+        global $DB;
+
+        $sort = self::tweak_sort_by_id($sort);
+
+        // Replace the query with hardcoded mappings required for core.
+        list($selectwhere, $params, $sort) = self::replace_sql_legacy($selectwhere, $params, $sort);
+
+        try {
+            $recordset = $DB->get_recordset_select('log', $selectwhere, $params, $sort, '*', $limitfrom, $limitnum);
+        } catch (\moodle_exception $ex) {
+            debugging("error converting legacy event data " . $ex->getMessage() . $ex->debuginfo, DEBUG_DEVELOPER);
+            return new \EmptyIterator;
+        }
+
+        return new \core\dml\recordset_walk($recordset, array($this, 'get_log_event'));
+    }
+
+    /**
+     * Returns an event from the log data.
+     *
+     * @param stdClass $data Log data
+     * @return \core\event\base
+     */
+    public function get_log_event($data) {
+        return \logstore_legacy\event\legacy_logged::restore_legacy($data);
+    }
+
     public function get_events_select_count($selectwhere, array $params) {
         global $DB;
 
diff --git a/admin/tool/log/store/legacy/tests/store_test.php b/admin/tool/log/store/legacy/tests/store_test.php
index e571a235991..7fb6353b64d 100644
--- a/admin/tool/log/store/legacy/tests/store_test.php
+++ b/admin/tool/log/store/legacy/tests/store_test.php
@@ -50,7 +50,7 @@ class logstore_legacy_store_testcase extends advanced_testcase {
         $this->assertEquals(array('logstore_legacy'), array_keys($stores));
         $store = $stores['logstore_legacy'];
         $this->assertInstanceOf('logstore_legacy\log\store', $store);
-        $this->assertInstanceOf('core\log\sql_select_reader', $store);
+        $this->assertInstanceOf('core\log\sql_reader', $store);
         $this->assertTrue($store->is_logging());
 
         $logs = $DB->get_records('log', array(), 'id ASC');
diff --git a/admin/tool/log/store/standard/classes/log/store.php b/admin/tool/log/store/standard/classes/log/store.php
index 44c66dea4b4..fe93ff58fbc 100644
--- a/admin/tool/log/store/standard/classes/log/store.php
+++ b/admin/tool/log/store/standard/classes/log/store.php
@@ -26,7 +26,7 @@ namespace logstore_standard\log;
 
 defined('MOODLE_INTERNAL') || die();
 
-class store implements \tool_log\log\writer, \core\log\sql_internal_reader {
+class store implements \tool_log\log\writer, \core\log\sql_internal_table_reader {
     use \tool_log\helper\store,
         \tool_log\helper\buffered_writer,
         \tool_log\helper\reader;
@@ -75,22 +75,8 @@ class store implements \tool_log\log\writer, \core\log\sql_internal_reader {
         $records = $DB->get_recordset_select('logstore_standard_log', $selectwhere, $params, $sort, '*', $limitfrom, $limitnum);
 
         foreach ($records as $data) {
-            $extra = array('origin' => $data->origin, 'ip' => $data->ip, 'realuserid' => $data->realuserid);
-            $data = (array)$data;
-            $id = $data['id'];
-            $data['other'] = unserialize($data['other']);
-            if ($data['other'] === false) {
-                $data['other'] = array();
-            }
-            unset($data['origin']);
-            unset($data['ip']);
-            unset($data['realuserid']);
-            unset($data['id']);
-
-            $event = \core\event\base::restore($data, $extra);
-            // Add event to list if it's valid.
-            if ($event) {
-                $events[$id] = $event;
+            if ($event = $this->get_log_event($data)) {
+                $events[$data->id] = $event;
             }
         }
 
@@ -99,6 +85,57 @@ class store implements \tool_log\log\writer, \core\log\sql_internal_reader {
         return $events;
     }
 
+    /**
+     * Fetch records using given criteria returning a Traversable object.
+     *
+     * Note that the traversable object contains a moodle_recordset, so
+     * remember that is important that you call close() once you finish
+     * using it.
+     *
+     * @param string $selectwhere
+     * @param array $params
+     * @param string $sort
+     * @param int $limitfrom
+     * @param int $limitnum
+     * @return \core\dml\recordset_walk|\core\event\base[]
+     */
+    public function get_events_select_iterator($selectwhere, array $params, $sort, $limitfrom, $limitnum) {
+        global $DB;
+
+        $sort = self::tweak_sort_by_id($sort);
+
+        $recordset = $DB->get_recordset_select('logstore_standard_log', $selectwhere, $params, $sort, '*', $limitfrom, $limitnum);
+
+        return new \core\dml\recordset_walk($recordset, array($this, 'get_log_event'));
+    }
+
+    /**
+     * Returns an event from the log data.
+     *
+     * @param stdClass $data Log data
+     * @return \core\event\base
+     */
+    public function get_log_event($data) {
+
+        $extra = array('origin' => $data->origin, 'ip' => $data->ip, 'realuserid' => $data->realuserid);
+        $data = (array)$data;
+        $id = $data['id'];
+        $data['other'] = unserialize($data['other']);
+        if ($data['other'] === false) {
+            $data['other'] = array();
+        }
+        unset($data['origin']);
+        unset($data['ip']);
+        unset($data['realuserid']);
+        unset($data['id']);
+
+        if (!$event = \core\event\base::restore($data, $extra)) {
+            return null;
+        }
+
+        return $event;
+    }
+
     public function get_events_select_count($selectwhere, array $params) {
         global $DB;
         return $DB->count_records_select('logstore_standard_log', $selectwhere, $params);
diff --git a/admin/tool/log/store/standard/tests/store_test.php b/admin/tool/log/store/standard/tests/store_test.php
index 08d70d43069..0ff4f6a1df0 100644
--- a/admin/tool/log/store/standard/tests/store_test.php
+++ b/admin/tool/log/store/standard/tests/store_test.php
@@ -218,4 +218,59 @@ class logstore_standard_store_testcase extends advanced_testcase {
             $this->assertContains($expectedreport, $reports);
         }
     }
+
+    /**
+     * Test sql_reader::get_events_select_iterator.
+     * @return void
+     */
+    public function test_events_traversable() {
+        global $DB;
+
+        $this->resetAfterTest();
+        $this->preventResetByRollback();
+        $this->setAdminUser();
+
+        set_config('enabled_stores', 'logstore_standard', 'tool_log');
+
+        $manager = get_log_manager(true);
+        $stores = $manager->get_readers();
+        $store = $stores['logstore_standard'];
+
+        $events = $store->get_events_select_iterator('', array(), '', 0, 0);
+        $this->assertFalse($events->valid());
+
+        // Here it should be already closed, but we should be allowed to
+        // over-close it without exception.
+        $events->close();
+
+        $user = $this->getDataGenerator()->create_user();
+        for ($i = 0; $i < 1000; $i++) {
+            \core\event\user_created::create_from_userid($user->id)->trigger();
+        }
+        $store->flush();
+
+        // Check some various sizes get the right number of elements.
+        $this->assertEquals(1, iterator_count($store->get_events_select_iterator('', array(), '', 0, 1)));
+        $this->assertEquals(2, iterator_count($store->get_events_select_iterator('', array(), '', 0, 2)));
+
+        $iterator = $store->get_events_select_iterator('', array(), '', 0, 500);
+        $this->assertInstanceOf('\core\event\base', $iterator->current());
+        $this->assertEquals(500, iterator_count($iterator));
+        $iterator->close();
+
+        // Look for non-linear memory usage for the iterator version.
+        $mem = memory_get_usage();
+        $events = $store->get_events_select('', array(), '', 0, 0);
+        $delta1 = memory_get_usage() - $mem;
+        $events = $store->get_events_select_iterator('', array(), '', 0, 0);
+        $delta2 = memory_get_usage() - $mem;
+        $this->assertInstanceOf('\Traversable', $events);
+        $events->close();
+
+        $this->assertLessThan($delta1 / 10, $delta2);
+
+        set_config('enabled_stores', '', 'tool_log');
+        get_log_manager(true);
+    }
+
 }
diff --git a/lib/tablelib.php b/lib/tablelib.php
index 2e6960f7730..134671adc3b 100644
--- a/lib/tablelib.php
+++ b/lib/tablelib.php
@@ -1345,7 +1345,7 @@ class table_sql extends flexible_table {
      */
     public $sql = NULL;
     /**
-     * @var array Data fetched from the db.
+     * @var array|\Traversable Data fetched from the db.
      */
     public $rawdata = NULL;
 
@@ -1374,14 +1374,27 @@ class table_sql extends flexible_table {
      * processing each col using either col_{columnname} method or other_cols
      * method or if other_cols returns NULL then put the data straight into the
      * table.
+     *
+     * @return void
      */
     function build_table() {
-        if ($this->rawdata) {
-            foreach ($this->rawdata as $row) {
-                $formattedrow = $this->format_row($row);
-                $this->add_data_keyed($formattedrow,
-                        $this->get_row_class($row));
-            }
+
+        if ($this->rawdata instanceof \Traversable && !$this->rawdata->valid()) {
+            return;
+        }
+        if (!$this->rawdata) {
+            return;
+        }
+
+        foreach ($this->rawdata as $row) {
+            $formattedrow = $this->format_row($row);
+            $this->add_data_keyed($formattedrow,
+                $this->get_row_class($row));
+        }
+
+        if ($this->rawdata instanceof \core\dml\recordset_walk ||
+                $this->rawdata instanceof moodle_recordset) {
+            $this->rawdata->close();
         }
     }
 
diff --git a/report/log/classes/table_log.php b/report/log/classes/table_log.php
index 8df6db9285d..25ac3df0154 100644
--- a/report/log/classes/table_log.php
+++ b/report/log/classes/table_log.php
@@ -36,7 +36,11 @@ class report_log_table_log extends table_sql {
     /** @var array list of user fullnames shown in report */
     private $userfullnames = array();
 
-    /** @var array list of course short names shown in report */
+    /**
+     * @deprecated since Moodle 2.9 MDL-48595 - please do not use this argument any more.
+     * @todo MDL-49291 This will be deleted in 3.1
+     * @var array list of course short names shown in report.
+     */
     private $courseshortnames = array();
 
     /** @var array list of context name shown in report */
@@ -54,7 +58,7 @@ class report_log_table_log extends table_sql {
      *     - int userid: user id
      *     - int|string modid: Module id or "site_errors" to view site errors
      *     - int groupid: Group id
-     *     - \core\log\sql_select_reader logreader: reader from which data will be fetched.
+     *     - \core\log\sql_reader logreader: reader from which data will be fetched.
      *     - int edulevel: educational level.
      *     - string action: view action
      *     - int date: Date from which logs to be viewed.
@@ -94,10 +98,15 @@ class report_log_table_log extends table_sql {
     /**
      * Generate the course column.
      *
+     * @deprecated since Moodle 2.9 MDL-48595 - please do not use this function any more.
+     * @todo MDL-49291 This will be deleted in 3.1
      * @param stdClass $event event data.
      * @return string HTML for the course column.
      */
     public function col_course($event) {
+
+        debugging('col_course() is deprecated, there is no such column', DEBUG_DEVELOPER);
+
         if (empty($event->courseid) || empty($this->courseshortnames[$event->courseid])) {
             return '-';
         } else {
@@ -105,6 +114,39 @@ class report_log_table_log extends table_sql {
         }
     }
 
+    /**
+     * Gets the user full name.
+     *
+     * This function is useful because, in the unlikely case that the user is
+     * not already loaded in $this->userfullnames it will fetch it from db.
+     *
+     * @since Moodle 2.9
+     * @param int $userid
+     * @return string|false
+     */
+    protected function get_user_fullname($userid) {
+        global $DB;
+
+        if (!empty($this->userfullnames[$userid])) {
+            return $this->userfullnames[$userid];
+        }
+
+        // We already looked for the user and it does not exist.
+        if ($this->userfullnames[$userid] === false) {
+            return false;
+        }
+
+        // If we reach that point new users logs have been generated since the last users db query.
+        list($usql, $uparams) = $DB->get_in_or_equal($userid);
+        $sql = "SELECT id," . get_all_user_name_fields(true) . " FROM {user} WHERE id " . $usql;
+        if (!$user = $DB->get_records_sql($sql, $uparams)) {
+            return false;
+        }
+
+        $this->userfullnames[$userid] = fullname($user);
+        return $this->userfullnames[$userid];
+    }
+
     /**
      * Generate the time column.
      *
@@ -129,25 +171,29 @@ class report_log_table_log extends table_sql {
         // Add username who did the action.
         if (!empty($logextra['realuserid'])) {
             $a = new stdClass();
-            $params = array('id' => $logextra['realuserid']);
-            if ($event->courseid) {
-                $params['course'] = $event->courseid;
+            if (!$a->realusername = $this->get_user_fullname($logextra['realuserid'])) {
+                $a->realusername = '-';
+            }
+            if (!$a->asusername = $this->get_user_fullname($event->userid)) {
+                $a->asusername = '-';
             }
-            $a->realusername = $this->userfullnames[$logextra['realuserid']];
-            $a->asusername = $this->userfullnames[$event->userid];
             if (empty($this->download)) {
+                $params = array('id' => $logextra['realuserid']);
+                if ($event->courseid) {
+                    $params['course'] = $event->courseid;
+                }
                 $a->realusername = html_writer::link(new moodle_url('/user/view.php', $params), $a->realusername);
                 $params['id'] = $event->userid;
                 $a->asusername = html_writer::link(new moodle_url('/user/view.php', $params), $a->asusername);
             }
             $username = get_string('eventloggedas', 'report_log', $a);
-        } else if (!empty($event->userid) && !empty($this->userfullnames[$event->userid])) {
-            $params = array('id' => $event->userid);
-            if ($event->courseid) {
-                $params['course'] = $event->courseid;
-            }
-            $username = $this->userfullnames[$event->userid];
+
+        } else if (!empty($event->userid) && $username = $this->get_user_fullname($event->userid)) {
             if (empty($this->download)) {
+                $params = array('id' => $event->userid);
+                if ($event->courseid) {
+                    $params['course'] = $event->courseid;
+                }
                 $username = html_writer::link(new moodle_url('/user/view.php', $params), $username);
             }
         } else {
@@ -164,13 +210,12 @@ class report_log_table_log extends table_sql {
      */
     public function col_relatedfullnameuser($event) {
         // Add affected user.
-        if (!empty($event->relateduserid) && isset($this->userfullnames[$event->relateduserid])) {
-            $params = array('id' => $event->relateduserid);
-            if ($event->courseid) {
-                $params['course'] = $event->courseid;
-            }
-            $username = $this->userfullnames[$event->relateduserid];
+        if (!empty($event->relateduserid) && $username = $this->get_user_fullname($event->relateduserid)) {
             if (empty($this->download)) {
+                $params = array('id' => $event->relateduserid);
+                if ($event->courseid) {
+                    $params['course'] = $event->courseid;
+                }
                 $username = html_writer::link(new moodle_url('/user/view.php', $params), $username);
             }
         } else {
@@ -463,26 +508,43 @@ class report_log_table_log extends table_sql {
             $this->pageable(false);
         }
 
-        $this->rawdata = $this->filterparams->logreader->get_events_select($selector, $params, $this->filterparams->orderby,
-                $this->get_page_start(), $this->get_page_size());
+        // Get the users and course data.
+        $this->rawdata = $this->filterparams->logreader->get_events_select_iterator($selector, $params,
+            $this->filterparams->orderby, $this->get_page_start(), $this->get_page_size());
+
+        // Update list of users which will be displayed on log page.
+        $this->update_users_used();
+
+        // Get the events. Same query than before; even if it is not likely, logs from new users
+        // may be added since last query so we will need to work around later to prevent problems.
+        // In almost most of the cases this will be better than having two opened recordsets.
+        $this->rawdata = $this->filterparams->logreader->get_events_select_iterator($selector, $params,
+            $this->filterparams->orderby, $this->get_page_start(), $this->get_page_size());
 
         // Set initial bars.
         if ($useinitialsbar && !$this->is_downloading()) {
             $this->initialbars($total > $pagesize);
         }
 
-        // Update list of users and courses list which will be displayed on log page.
-        $this->update_users_and_courses_used();
     }
 
     /**
      * Helper function to create list of course shortname and user fullname shown in log report.
+     *
      * This will update $this->userfullnames and $this->courseshortnames array with userfullname and courseshortname (with link),
      * which will be used to render logs in table.
+     *
+     * @deprecated since Moodle 2.9 MDL-48595 - please do not use this function any more.
+     * @todo MDL-49291 This will be deleted in 3.1
+     * @see self::update_users_used()
      */
     public function update_users_and_courses_used() {
         global $SITE, $DB;
 
+        debugging('update_users_and_courses_used() is deprecated, please use update_users_used() instead.', DEBUG_DEVELOPER);
+
+        // We should not call self::update_users_used() as would have to iterate twice around the list of logs.
+
         $this->userfullnames = array();
         $this->courseshortnames = array($SITE->id => $SITE->shortname);
         $userids = array();
@@ -491,14 +553,14 @@ class report_log_table_log extends table_sql {
         // Get list of userids and courseids which will be shown in log report.
         foreach ($this->rawdata as $event) {
             $logextra = $event->get_logextra();
-            if (!empty($event->userid) && !in_array($event->userid, $userids)) {
-                $userids[] = $event->userid;
+            if (!empty($event->userid) && empty($userids[$event->userid])) {
+                $userids[$event->userid] = $event->userid;
             }
-            if (!empty($logextra['realuserid']) && !in_array($logextra['realuserid'], $userids)) {
-                $userids[] = $logextra['realuserid'];
+            if (!empty($logextra['realuserid']) && empty($userids[$logextra['realuserid']])) {
+                $userids[$logextra['realuserid']] = $logextra['realuserid'];
             }
-            if (!empty($event->relateduserid) && !in_array($event->relateduserid, $userids)) {
-                $userids[] = $event->relateduserid;
+            if (!empty($event->relateduserid) && empty($userids[$event->relateduserid])) {
+                $userids[$event->relateduserid] = $event->relateduserid;
             }
 
             if (!empty($event->courseid) && ($event->courseid != $SITE->id) && !in_array($event->courseid, $courseids)) {
@@ -506,6 +568,12 @@ class report_log_table_log extends table_sql {
             }
         }
 
+        // Closing it just in case, we can not rewind moodle recordsets anyway.
+        if ($this->rawdata instanceof \core\dml\recordset_walk ||
+                $this->rawdata instanceof moodle_recordset) {
+            $this->rawdata->close();
+        }
+
         // Get user fullname and put that in return list.
         if (!empty($userids)) {
             list($usql, $uparams) = $DB->get_in_or_equal($userids);
@@ -513,6 +581,13 @@ class report_log_table_log extends table_sql {
                     $uparams);
             foreach ($users as $userid => $user) {
                 $this->userfullnames[$userid] = fullname($user);
+                unset($userids[$userid]);
+            }
+
+            // We fill the array with false values for the users that don't exist anymore
+            // in the database so we don't need to query the db again later.
+            foreach ($userids as $userid) {
+                $this->userfullnames[$userid] = false;
             }
         }
 
@@ -537,4 +612,53 @@ class report_log_table_log extends table_sql {
             }
         }
     }
+
+    /**
+     * Helper function to create list of user fullnames shown in log report.
+     *
+     * This will update $this->userfullnames array with userfullname,
+     * which will be used to render logs in table.
+     *
+     * @since   Moodle 2.9
+     * @return  void
+     */
+    protected function update_users_used() {
+        global $DB;
+
+        $this->userfullnames = array();
+        $userids = array();
+
+        // For each event cache full username.
+        // Get list of userids which will be shown in log report.
+        foreach ($this->rawdata as $event) {
+            $logextra = $event->get_logextra();
+            if (!empty($event->userid) && empty($userids[$event->userid])) {
+                $userids[$event->userid] = $event->userid;
+            }
+            if (!empty($logextra['realuserid']) && empty($userids[$logextra['realuserid']])) {
+                $userids[$logextra['realuserid']] = $logextra['realuserid'];
+            }
+            if (!empty($event->relateduserid) && empty($userids[$event->relateduserid])) {
+                $userids[$event->relateduserid] = $event->relateduserid;
+            }
+        }
+        $this->rawdata->close();
+
+        // Get user fullname and put that in return list.
+        if (!empty($userids)) {
+            list($usql, $uparams) = $DB->get_in_or_equal($userids);
+            $users = $DB->get_records_sql("SELECT id," . get_all_user_name_fields(true) . " FROM {user} WHERE id " . $usql,
+                    $uparams);
+            foreach ($users as $userid => $user) {
+                $this->userfullnames[$userid] = fullname($user);
+                unset($userids[$userid]);
+            }
+
+            // We fill the array with false values for the users that don't exist anymore
+            // in the database so we don't need to query the db again later.
+            foreach ($userids as $userid) {
+                $this->userfullnames[$userid] = false;
+            }
+        }
+    }
 }