validating table structure on applier and migrator

- reading column list on applier
- comparing original table on applier and migrator, expecting exact column list
- or else bailing out

build.sh

@@ -2,7 +2,7 @@
 #
 #
 
-RELEASE_VERSION="1.0.23"
+RELEASE_VERSION="1.0.26"
 
 function build {
     osname=$1

go/base/context.go

@@ -147,6 +147,7 @@ type MigrationContext struct {
 	UserCommandedUnpostponeFlag            int64
 	PanicAbort                             chan error
 
+	OriginalTableColumnsOnApplier    *sql.ColumnList
 	OriginalTableColumns             *sql.ColumnList
 	OriginalTableUniqueKeys          [](*sql.UniqueKey)
 	GhostTableColumns                *sql.ColumnList

go/logic/applier.go

@@ -67,6 +67,9 @@ func (this *Applier) InitDBConnections() (err error) {
 	} else {
 		this.connectionConfig.ImpliedKey = impliedKey
 	}
+	if err := this.readTableColumns(); err != nil {
+		return err
+	}
 	return nil
 }
 
@@ -95,6 +98,16 @@ func (this *Applier) validateAndReadTimeZone() error {
 	return nil
 }
 
+// readTableColumns reads table columns on applier
+func (this *Applier) readTableColumns() (err error) {
+	log.Infof("Examining table structure on applier")
+	this.migrationContext.OriginalTableColumnsOnApplier, err = mysql.GetTableColumns(this.db, this.migrationContext.DatabaseName, this.migrationContext.OriginalTableName)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // showTableStatus returns the output of `show table status like '...'` command
 func (this *Applier) showTableStatus(tableName string) (rowMap sqlutils.RowMap) {
 	rowMap = nil

go/logic/inspect.go

@@ -8,6 +8,7 @@ package logic
 import (
 	gosql "database/sql"
 	"fmt"
+	"reflect"
 	"strings"
 	"sync/atomic"
 
@@ -83,7 +84,7 @@ func (this *Inspector) InspectTableColumnsAndUniqueKeys(tableName string) (colum
 	if len(uniqueKeys) == 0 {
 		return columns, uniqueKeys, fmt.Errorf("No PRIMARY nor UNIQUE key found in table! Bailing out")
 	}
-	columns, err = this.getTableColumns(this.migrationContext.DatabaseName, tableName)
+	columns, err = mysql.GetTableColumns(this.db, this.migrationContext.DatabaseName, tableName)
 	if err != nil {
 		return columns, uniqueKeys, err
 	}
@@ -99,9 +100,15 @@ func (this *Inspector) InspectOriginalTable() (err error) {
 	return nil
 }
 
-// InspectOriginalAndGhostTables compares original and ghost tables to see whether the migration
+// inspectOriginalAndGhostTables compares original and ghost tables to see whether the migration
 // makes sense and is valid. It extracts the list of shared columns and the chosen migration unique key
-func (this *Inspector) InspectOriginalAndGhostTables() (err error) {
+func (this *Inspector) inspectOriginalAndGhostTables() (err error) {
+	originalNamesOnApplier := this.migrationContext.OriginalTableColumnsOnApplier.Names()
+	originalNames := this.migrationContext.OriginalTableColumns.Names()
+	if !reflect.DeepEqual(originalNames, originalNamesOnApplier) {
+		return fmt.Errorf("It seems like table structure is not identical between master and replica. This scenario is not supported.")
+	}
+
 	this.migrationContext.GhostTableColumns, this.migrationContext.GhostTableUniqueKeys, err = this.InspectTableColumnsAndUniqueKeys(this.migrationContext.GetGhostTableName())
 	if err != nil {
 		return err
@@ -478,31 +485,6 @@ func (this *Inspector) CountTableRows() error {
 	return nil
 }
 
-// getTableColumns reads column list from given table
-func (this *Inspector) getTableColumns(databaseName, tableName string) (*sql.ColumnList, error) {
-	query := fmt.Sprintf(`
-		show columns from %s.%s
-		`,
-		sql.EscapeName(databaseName),
-		sql.EscapeName(tableName),
-	)
-	columnNames := []string{}
-	err := sqlutils.QueryRowsMap(this.db, query, func(rowMap sqlutils.RowMap) error {
-		columnNames = append(columnNames, rowMap.GetString("Field"))
-		return nil
-	})
-	if err != nil {
-		return nil, err
-	}
-	if len(columnNames) == 0 {
-		return nil, log.Errorf("Found 0 columns on %s.%s. Bailing out",
-			sql.EscapeName(databaseName),
-			sql.EscapeName(tableName),
-		)
-	}
-	return sql.NewColumnList(columnNames), nil
-}
-
 // applyColumnTypes
 func (this *Inspector) applyColumnTypes(databaseName, tableName string, columnsLists ...*sql.ColumnList) error {
 	query := `

go/logic/migrator.go

@@ -26,7 +26,7 @@ import (
 type ChangelogState string
 
 const (
-	TablesInPlace              ChangelogState = "TablesInPlace"
+	GhostTableMigrated         ChangelogState = "GhostTableMigrated"
 	AllEventsUpToLockProcessed                = "AllEventsUpToLockProcessed"
 )
 
@@ -58,7 +58,7 @@ type Migrator struct {
 	migrationContext *base.MigrationContext
 
 	firstThrottlingCollected   chan bool
-	tablesInPlace              chan bool
+	ghostTableMigrated         chan bool
 	rowCopyComplete            chan bool
 	allEventsUpToLockProcessed chan bool
 
@@ -76,7 +76,7 @@ func NewMigrator() *Migrator {
 	migrator := &Migrator{
 		migrationContext:           base.GetMigrationContext(),
 		parser:                     sql.NewParser(),
-		tablesInPlace:              make(chan bool),
+		ghostTableMigrated:         make(chan bool),
 		firstThrottlingCollected:   make(chan bool, 1),
 		rowCopyComplete:            make(chan bool),
 		allEventsUpToLockProcessed: make(chan bool),
@@ -182,9 +182,9 @@ func (this *Migrator) onChangelogStateEvent(dmlEvent *binlog.BinlogDMLEvent) (er
 	}
 	changelogState := ChangelogState(dmlEvent.NewColumnValues.StringColumn(3))
 	switch changelogState {
-	case TablesInPlace:
+	case GhostTableMigrated:
 		{
-			this.tablesInPlace <- true
+			this.ghostTableMigrated <- true
 		}
 	case AllEventsUpToLockProcessed:
 		{
@@ -291,14 +291,14 @@ func (this *Migrator) Migrate() (err error) {
 		return err
 	}
 
-	log.Infof("Waiting for tables to be in place")
-	<-this.tablesInPlace
-	log.Debugf("Tables are in place")
+	log.Infof("Waiting for ghost table to be migrated")
+	<-this.ghostTableMigrated
+	log.Debugf("ghost table migrated")
 	// Yay! We now know the Ghost and Changelog tables are good to examine!
 	// When running on replica, this means the replica has those tables. When running
 	// on master this is always true, of course, and yet it also implies this knowledge
 	// is in the binlogs.
-	if err := this.inspector.InspectOriginalAndGhostTables(); err != nil {
+	if err := this.inspector.inspectOriginalAndGhostTables(); err != nil {
 		return err
 	}
 	// Validation complete! We're good to execute this migration
@@ -926,12 +926,13 @@ func (this *Migrator) initiateApplier() error {
 		log.Errorf("Unable to create ghost table, see further error details. Perhaps a previous migration failed without dropping the table? Bailing out")
 		return err
 	}
+
 	if err := this.applier.AlterGhost(); err != nil {
 		log.Errorf("Unable to ALTER ghost table, see further error details. Bailing out")
 		return err
 	}
 
-	this.applier.WriteChangelogState(string(TablesInPlace))
+	this.applier.WriteChangelogState(string(GhostTableMigrated))
 	go this.applier.InitiateHeartbeat()
 	return nil
 }

go/mysql/utils.go

@@ -10,6 +10,8 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/github/gh-ost/go/sql"
+
 	"github.com/outbrain/golib/log"
 	"github.com/outbrain/golib/sqlutils"
 )
@@ -149,3 +151,28 @@ func GetInstanceKey(db *gosql.DB) (instanceKey *InstanceKey, err error) {
 	err = db.QueryRow(`select @@global.hostname, @@global.port`).Scan(&instanceKey.Hostname, &instanceKey.Port)
 	return instanceKey, err
 }
+
+// GetTableColumns reads column list from given table
+func GetTableColumns(db *gosql.DB, databaseName, tableName string) (*sql.ColumnList, error) {
+	query := fmt.Sprintf(`
+		show columns from %s.%s
+		`,
+		sql.EscapeName(databaseName),
+		sql.EscapeName(tableName),
+	)
+	columnNames := []string{}
+	err := sqlutils.QueryRowsMap(db, query, func(rowMap sqlutils.RowMap) error {
+		columnNames = append(columnNames, rowMap.GetString("Field"))
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	if len(columnNames) == 0 {
+		return nil, log.Errorf("Found 0 columns on %s.%s. Bailing out",
+			sql.EscapeName(databaseName),
+			sql.EscapeName(tableName),
+		)
+	}
+	return sql.NewColumnList(columnNames), nil
+}