sql: ensure the home region savepoint is not broken by pausable portals

[ZhouXing19]

When re-executing a pausable portal, we re-call the connExecutor.execStmtInOpenState(). Originally, the logic in this function is expected to be run only once for each query, so we're not sure if they should be rerun for a portal. This home region savepoint part is an example, and we should confirm its usage.

cockroach/pkg/sql/conn_executor_exec.go

Lines 739 to 768 in d8ea15c

	if enforceHomeRegion && ex.state.mu.txn.IsOpen() && isSelectStmt {
	// Create a savepoint at a point before which rows were read so that we can
	// roll back to it, which will allow the txn to be modified with a
	// historical timestamp (so that the locality-optimized ops used for error
	// reporting can run locally and not incur latency). This is currently only
	// supported for SELECT statements.
	var b strings.Builder
	b.WriteString("enforce_home_region_sp")
	// Add some unprintable ASCII characters to the name of the savepoint to
	// decrease the likelihood of collision with a user-created savepoint.
	b.WriteRune(rune(0x11))
	b.WriteRune(rune(0x12))
	b.WriteRune(rune(0x13))
	enforceHomeRegionSavepointName := tree.Name(b.String())
	s := &tree.Savepoint{Name: enforceHomeRegionSavepointName}
	var event fsm.Event
	var eventPayload fsm.EventPayload
	if event, eventPayload, err = ex.execSavepointInOpenState(ctx, s, res); err != nil {
	return event, eventPayload, err
	}
	r = &tree.ReleaseSavepoint{Savepoint: enforceHomeRegionSavepointName}
	rollbackSP = &tree.RollbackToSavepoint{Savepoint: enforceHomeRegionSavepointName}
	defer func() {
	// The default case is to roll back the internally-generated savepoint
	// after every request. We only need it if a retryable "query has no home
	// region" error occurs.
	ex.execRelease(ctx, r, res)
	}()
	}

Jira issue: CRDB-25869

Epic CRDB-25183