rdbms: avoid lag estimates in getLagFromPtHeartbeat ruined by snapshots

[lhc/web/wiklou.git] / includes / libs / rdbms / database / DatabaseMysqlBase.php

diff --git a/includes/libs/rdbms/database/DatabaseMysqlBase.php b/includes/libs/rdbms/database/DatabaseMysqlBase.php
index 286d658..bc4beba 100644 (file)
--- a/includes/libs/rdbms/database/DatabaseMysqlBase.php
+++ b/includes/libs/rdbms/database/DatabaseMysqlBase.php
@@ -749,6 +749,7 @@ abstract class DatabaseMysqlBase extends Database {
        protected function getLagFromSlaveStatus() {
                $res = $this->query( 'SHOW SLAVE STATUS', __METHOD__ );
                $row = $res ? $res->fetchObject() : false;
+               // If the server is not replicating, there will be no row
                if ( $row && strval( $row->Seconds_Behind_Master ) !== '' ) {
                        return intval( $row->Seconds_Behind_Master );
                }
@@ -762,6 +763,17 @@ abstract class DatabaseMysqlBase extends Database {
        protected function getLagFromPtHeartbeat() {
                $options = $this->lagDetectionOptions;
 
+               if ( $this->trxLevel ) {
+                       // Avoid returning higher and higher lag value due to snapshot age
+                       // given that the isolation level will typically be REPEATABLE-READ
+                       $this->queryLogger->warning(
+                               "Using cached lag value for {db_server} due to active transaction",
+                               $this->getLogContext( [ 'method' => __METHOD__ ] )
+                       );
+
+                       return $this->getTransactionLagStatus()['lag'];
+               }
+
                if ( isset( $options['conds'] ) ) {
                        // Best method for multi-DC setups: use logical channel names
                        $data = $this->getHeartbeatData( $options['conds'] );
@@ -856,7 +868,8 @@ abstract class DatabaseMysqlBase extends Database {
                        // Note: this would use "TIMESTAMPDIFF(MICROSECOND,ts,UTC_TIMESTAMP(6))" but the
                        // percision field is not supported in MySQL <= 5.5.
                        $res = $this->query(
-                               "SELECT ts FROM heartbeat.heartbeat WHERE $whereSQL ORDER BY ts DESC LIMIT 1"
+                               "SELECT ts FROM heartbeat.heartbeat WHERE $whereSQL ORDER BY ts DESC LIMIT 1",
+                               __METHOD__
                        );
                        $row = $res ? $res->fetchObject() : false;
                } finally {