Backport schema reload performance fix

go/mysql/flavor.go

@@ -155,6 +155,7 @@ type flavor interface {
 	enableBinlogPlaybackCommand() string
 	disableBinlogPlaybackCommand() string
 
+	baseShowTables() string
 	baseShowTablesWithSizes() string
 
 	supportsCapability(serverVersion string, capability FlavorCapability) (bool, error)
@@ -571,8 +572,13 @@ func (c *Conn) DisableBinlogPlaybackCommand() string {
 	return c.flavor.disableBinlogPlaybackCommand()
 }
 
-// BaseShowTables returns a query that shows tables and their sizes
+// BaseShowTables returns a query that shows tables
 func (c *Conn) BaseShowTables() string {
+	return c.flavor.baseShowTables()
+}
+
+// BaseShowTablesWithSizes returns a query that shows tables and their sizes
+func (c *Conn) BaseShowTablesWithSizes() string {
 	return c.flavor.baseShowTablesWithSizes()
 }
 

go/mysql/flavor_filepos.go

@@ -326,6 +326,11 @@ func (*filePosFlavor) disableBinlogPlaybackCommand() string {
 	return ""
 }
 
+// baseShowTables is part of the Flavor interface.
+func (*filePosFlavor) baseShowTables() string {
+	return mysqlFlavor{}.baseShowTables()
+}
+
 // baseShowTablesWithSizes is part of the Flavor interface.
 func (*filePosFlavor) baseShowTablesWithSizes() string {
 	return TablesWithSize56

go/mysql/flavor_mariadb_binlog_playback.go

@@ -30,6 +30,11 @@ func (mariadbFlavor) disableBinlogPlaybackCommand() string {
 	return ""
 }
 
+// baseShowTables is part of the Flavor interface.
+func (mariadbFlavor) baseShowTables() string {
+	return mysqlFlavor{}.baseShowTables()
+}
+
 // baseShowTablesWithSizes is part of the Flavor interface.
 func (mariadbFlavor101) baseShowTablesWithSizes() string {
 	return TablesWithSize56

go/mysql/flavor_mysql.go

@@ -308,6 +308,11 @@ func (mysqlFlavor) disableBinlogPlaybackCommand() string {
 	return ""
 }
 
+// baseShowTables is part of the Flavor interface.
+func (mysqlFlavor) baseShowTables() string {
+	return "SELECT table_name, table_type, unix_timestamp(create_time), table_comment FROM information_schema.tables WHERE table_schema = database()"
+}
+
 // TablesWithSize56 is a query to select table along with size for mysql 5.6
 const TablesWithSize56 = `SELECT table_name, table_type, unix_timestamp(create_time), table_comment, SUM( data_length + index_length), SUM( data_length + index_length)
 		FROM information_schema.tables WHERE table_schema = database() group by table_name`

go/mysql/flavor_mysqlgr.go

@@ -239,6 +239,10 @@ func (mysqlGRFlavor) primaryStatus(c *Conn) (PrimaryStatus, error) {
 	return mysqlFlavor{}.primaryStatus(c)
 }
 
+func (mysqlGRFlavor) baseShowTables() string {
+	return mysqlFlavor{}.baseShowTables()
+}
+
 func (mysqlGRFlavor) baseShowTablesWithSizes() string {
 	return TablesWithSize80
 }

go/vt/vttablet/tabletserver/connpool/dbconn.go

@@ -442,11 +442,16 @@ func (dbc *DBConn) ID() int64 {
 	return dbc.conn.ID()
 }
 
-// BaseShowTables returns a query that shows tables and their sizes
+// BaseShowTables returns a query that shows tables
 func (dbc *DBConn) BaseShowTables() string {
 	return dbc.conn.BaseShowTables()
 }
 
+// BaseShowTablesWithSizes returns a query that shows tables and their sizes
+func (dbc *DBConn) BaseShowTablesWithSizes() string {
+	return dbc.conn.BaseShowTablesWithSizes()
+}
+
 func (dbc *DBConn) reconnect(ctx context.Context) error {
 	dbc.conn.Close()
 	// Reuse MySQLTimings from dbc.conn.

go/vt/vttablet/tabletserver/query_executor.go

@@ -510,7 +510,15 @@ func (qre *QueryExecutor) execDDL(conn *StatefulConnection) (*sqltypes.Result, e
 	}
 
 	defer func() {
-		if err := qre.tsv.se.Reload(qre.ctx); err != nil {
+		// Call se.Reload() with includeStats=false as obtaining table
+		// size stats involves joining `information_schema.tables`,
+		// which can be very costly on systems with a large number of
+		// tables.
+		//
+		// Instead of synchronously recalculating table size stats
+		// after every DDL, let them be outdated until the periodic
+		// schema reload fixes it.
+		if err := qre.tsv.se.ReloadAtEx(qre.ctx, mysql.Position{}, false); err != nil {
 			log.Errorf("failed to reload schema %v", err)
 		}
 	}()

go/vt/vttablet/tabletserver/schema/engine.go

@@ -194,7 +194,7 @@ func (se *Engine) Open() error {
 	}
 	se.notifiers = make(map[string]notifier)
 
-	if err := se.reload(ctx); err != nil {
+	if err := se.reload(ctx, true); err != nil {
 		return err
 	}
 	if !se.SkipMetaCheck {
@@ -285,6 +285,8 @@ func (se *Engine) EnableHistorian(enabled bool) error {
 
 // Reload reloads the schema info from the db.
 // Any tables that have changed since the last load are updated.
+// The includeStats argument controls whether table size statistics should be
+// emitted, as they can be expensive to calculate for a large number of tables
 func (se *Engine) Reload(ctx context.Context) error {
 	return se.ReloadAt(ctx, mysql.Position{})
 }
@@ -294,25 +296,35 @@ func (se *Engine) Reload(ctx context.Context) error {
 // It maintains the position at which the schema was reloaded and if the same position is provided
 // (say by multiple vstreams) it returns the cached schema. In case of a newer or empty pos it always reloads the schema
 func (se *Engine) ReloadAt(ctx context.Context, pos mysql.Position) error {
+	return se.ReloadAtEx(ctx, pos, true)
+}
+
+// ReloadAtEx reloads the schema info from the db.
+// Any tables that have changed since the last load are updated.
+// It maintains the position at which the schema was reloaded and if the same position is provided
+// (say by multiple vstreams) it returns the cached schema. In case of a newer or empty pos it always reloads the schema
+// The includeStats argument controls whether table size statistics should be
+// emitted, as they can be expensive to calculate for a large number of tables
+func (se *Engine) ReloadAtEx(ctx context.Context, pos mysql.Position, includeStats bool) error {
 	se.mu.Lock()
 	defer se.mu.Unlock()
 	if !se.isOpen {
 		log.Warning("Schema reload called for an engine that is not yet open")
 		return nil
 	}
 	if !pos.IsZero() && se.reloadAtPos.AtLeast(pos) {
-		log.V(2).Infof("ReloadAt: found cached schema at %s", mysql.EncodePosition(pos))
+		log.V(2).Infof("ReloadAtEx: found cached schema at %s", mysql.EncodePosition(pos))
 		return nil
 	}
-	if err := se.reload(ctx); err != nil {
+	if err := se.reload(ctx, includeStats); err != nil {
 		return err
 	}
 	se.reloadAtPos = pos
 	return nil
 }
 
 // reload reloads the schema. It can also be used to initialize it.
-func (se *Engine) reload(ctx context.Context) error {
+func (se *Engine) reload(ctx context.Context, includeStats bool) error {
 	defer func() {
 		se.env.LogError()
 	}()
@@ -332,7 +344,14 @@ func (se *Engine) reload(ctx context.Context) error {
 	if se.SkipMetaCheck {
 		return nil
 	}
-	tableData, err := conn.Exec(ctx, conn.BaseShowTables(), maxTableCount, false)
+
+	var showTablesQuery string
+	if includeStats {
+		showTablesQuery = conn.BaseShowTablesWithSizes()
+	} else {
+		showTablesQuery = conn.BaseShowTables()
+	}
+	tableData, err := conn.Exec(ctx, showTablesQuery, maxTableCount, false)
 	if err != nil {
 		return err
 	}
@@ -353,12 +372,15 @@ func (se *Engine) reload(ctx context.Context) error {
 		tableName := row[0].ToString()
 		curTables[tableName] = true
 		createTime, _ := evalengine.ToInt64(row[2])
-		fileSize, _ := evalengine.ToUint64(row[4])
-		allocatedSize, _ := evalengine.ToUint64(row[5])
-
-		// publish the size metrics
-		se.tableFileSizeGauge.Set(tableName, int64(fileSize))
-		se.tableAllocatedSizeGauge.Set(tableName, int64(allocatedSize))
+		var fileSize, allocatedSize uint64
+
+		if includeStats {
+			fileSize, _ = evalengine.ToUint64(row[4])
+			allocatedSize, _ = evalengine.ToUint64(row[5])
+			// publish the size metrics
+			se.tableFileSizeGauge.Set(tableName, int64(fileSize))
+			se.tableAllocatedSizeGauge.Set(tableName, int64(allocatedSize))
+		}
 
 		// Table schemas are cached by tabletserver. For each table we cache `information_schema.tables.create_time` (`tbl.CreateTime`).
 		// We also record the last time the schema was loaded (`se.lastChange`). Both are in seconds. We reload a table only when:
@@ -372,8 +394,10 @@ func (se *Engine) reload(ctx context.Context) error {
 		//      #1 will not identify the renamed table as a changed one.
 		tbl, isInTablesMap := se.tables[tableName]
 		if isInTablesMap && createTime == tbl.CreateTime && createTime < se.lastChange {
-			tbl.FileSize = fileSize
-			tbl.AllocatedSize = allocatedSize
+			if includeStats {
+				tbl.FileSize = fileSize
+				tbl.AllocatedSize = allocatedSize
+			}
 			continue
 		}
 
@@ -389,8 +413,10 @@ func (se *Engine) reload(ctx context.Context) error {
 			rec.RecordError(vterrors.Wrapf(err, "in Engine.reload(), reading table %s", tableName))
 			continue
 		}
-		table.FileSize = fileSize
-		table.AllocatedSize = allocatedSize
+		if includeStats {
+			table.FileSize = fileSize
+			table.AllocatedSize = allocatedSize
+		}
 		table.CreateTime = createTime
 		changedTables[tableName] = table
 		if isInTablesMap {