fix(handler): optimise snapshot hanlding (#8652)

# Which Problems Are Solved

There are cases where not all statements of multiExec are succeed. This
leads to inconsistent states. One example is [LDAP
IDPs](https://github.com/zitadel/zitadel/issues/7959).

If statements get executed only partially this can lead to inconsistent
states or even break projections for objects which might not were
correctly created in a sub table.

This behaviour is possible because we use
[`SAVEPOINTS`](https://www.postgresql.org/docs/current/sql-savepoint.html)
during each statement of a multiExec.

# How the Problems Are Solved

SAVEPOINTS are only created at the beginning of an exec function not
during every execution like before. Additionally `RELEASE` or `ROLLBACK`
of `SAVEPOINTS` are only used when needed.

# Additional Changes

- refactor some unused parameters

# Additional Context

- closes https://github.com/zitadel/zitadel/issues/7959

internal/eventstore/handler/v2/handler.go

@@ -528,7 +528,7 @@ func (h *Handler) processEvents(ctx context.Context, config *triggerConfig) (add
 		return additionalIteration, err
 	}
 
-	lastProcessedIndex, err := h.executeStatements(ctx, tx, currentState, statements)
+	lastProcessedIndex, err := h.executeStatements(ctx, tx, statements)
 	h.log().OnError(err).WithField("lastProcessedIndex", lastProcessedIndex).Debug("execution of statements failed")
 	if lastProcessedIndex < 0 {
 		return false, err
@@ -600,7 +600,7 @@ func skipPreviouslyReducedStatements(statements []*Statement, currentState *stat
 	return -1
 }
 
-func (h *Handler) executeStatements(ctx context.Context, tx *sql.Tx, currentState *state, statements []*Statement) (lastProcessedIndex int, err error) {
+func (h *Handler) executeStatements(ctx context.Context, tx *sql.Tx, statements []*Statement) (lastProcessedIndex int, err error) {
 	lastProcessedIndex = -1
 
 	for i, statement := range statements {
@@ -608,7 +608,7 @@ func (h *Handler) executeStatements(ctx context.Context, tx *sql.Tx, currentStat
 		case <-ctx.Done():
 			break
 		default:
-			err := h.executeStatement(ctx, tx, currentState, statement)
+			err := h.executeStatement(ctx, tx, statement)
 			if err != nil {
 				return lastProcessedIndex, err
 			}
@@ -618,28 +618,24 @@ func (h *Handler) executeStatements(ctx context.Context, tx *sql.Tx, currentStat
 	return lastProcessedIndex, nil
 }
 
-func (h *Handler) executeStatement(ctx context.Context, tx *sql.Tx, currentState *state, statement *Statement) (err error) {
+func (h *Handler) executeStatement(ctx context.Context, tx *sql.Tx, statement *Statement) (err error) {
 	if statement.Execute == nil {
 		return nil
 	}
 
-	_, err = tx.Exec("SAVEPOINT exec")
+	_, err = tx.ExecContext(ctx, "SAVEPOINT exec_stmt")
 	if err != nil {
 		h.log().WithError(err).Debug("create savepoint failed")
 		return err
 	}
-	var shouldContinue bool
-	defer func() {
-		_, errSave := tx.Exec("RELEASE SAVEPOINT exec")
-		if err == nil {
-			err = errSave
-		}
-	}()
 
 	if err = statement.Execute(tx, h.projection.Name()); err != nil {
 		h.log().WithError(err).Error("statement execution failed")
 
-		shouldContinue = h.handleFailedStmt(tx, failureFromStatement(statement, err))
+		_, rollbackErr := tx.ExecContext(ctx, "ROLLBACK TO SAVEPOINT exec_stmt")
+		h.log().OnError(rollbackErr).Error("rollback to savepoint failed")
+
+		shouldContinue := h.handleFailedStmt(tx, failureFromStatement(statement, err))
 		if shouldContinue {
 			return nil
 		}

internal/eventstore/handler/v2/init.go

@@ -264,11 +264,23 @@ func NewViewCheck(selectStmt string, secondaryTables ...*SuffixedTable) *handler
 }
 
 func execNextIfExists(config execConfig, q query, opts []execOption, executeNext bool) func(handler.Executer, string) (bool, error) {
-	return func(handler handler.Executer, name string) (bool, error) {
-		err := exec(config, q, opts)(handler, name)
-		if isErrAlreadyExists(err) {
-			return executeNext, nil
+	return func(handler handler.Executer, name string) (shouldExecuteNext bool, err error) {
+		_, err = handler.Exec("SAVEPOINT exec_stmt")
+		if err != nil {
+			return false, zerrors.ThrowInternal(err, "V2-U1wlz", "create savepoint failed")
 		}
+		defer func() {
+			if err == nil {
+				return
+			}
+
+			if isErrAlreadyExists(err) {
+				_, err = handler.Exec("ROLLBACK TO SAVEPOINT exec_stmt")
+				shouldExecuteNext = executeNext
+				return
+			}
+		}()
+		err = exec(config, q, opts)(handler, name)
 		return false, err
 	}
 }

internal/eventstore/handler/v2/statement.go

@@ -677,18 +677,6 @@ func exec(config execConfig, q query, opts []execOption) Exec {
 			opt(&config)
 		}
 
-		_, err = ex.Exec("SAVEPOINT stmt_exec")
-		if err != nil {
-			return zerrors.ThrowInternal(err, "CRDB-YdOXD", "create savepoint failed")
-		}
-		defer func() {
-			if err != nil {
-				_, rollbackErr := ex.Exec("ROLLBACK TO SAVEPOINT stmt_exec")
-				logging.OnError(rollbackErr).Debug("rollback failed")
-				return
-			}
-			_, err = ex.Exec("RELEASE SAVEPOINT stmt_exec")
-		}()
 		_, err = ex.Exec(q(config), config.args...)
 		if err != nil {
 			return zerrors.ThrowInternal(err, "CRDB-pKtsr", "exec failed")

internal/query/projection/executer_test.go

@@ -25,7 +25,7 @@ type execution struct {
 type anyArg struct{}
 
 func (e *testExecuter) Exec(stmt string, args ...interface{}) (sql.Result, error) {
-	if stmt == "SAVEPOINT stmt_exec" || stmt == "RELEASE SAVEPOINT stmt_exec" {
+	if stmt == "SAVEPOINT exec_stmt" {
 		return nil, nil
 	}