// If forceNew is true, GetTxn() must return a new transaction.
// In this situation, if current transaction is still in progress,
// there will be an implicit commit and create a new transaction.
func (s *session) GetTxn(forceNew bool) (kv.Transaction, error) {
var err error
if s.txn == nil {
s.resetHistory()
s.txn, err = s.store.Begin()
if err != nil {
return nil, err
}
if !variable.IsAutocommit(s) {
variable.GetSessionVars(s).SetStatusFlag(mysql.ServerStatusInTrans, true)
}
log.Infof("New txn:%s in session:%d", s.txn, s.sid)
return s.txn, nil
}
if forceNew {
err = s.txn.Commit()
variable.GetSessionVars(s).SetStatusFlag(mysql.ServerStatusInTrans, false)
if err != nil {
return nil, err
}
s.resetHistory()
s.txn, err = s.store.Begin()
if err != nil {
return nil, err
}
if !variable.IsAutocommit(s) {
variable.GetSessionVars(s).SetStatusFlag(mysql.ServerStatusInTrans, true)
}
log.Warnf("Force new txn:%s in session:%d", s.txn, s.sid)
}
return s.txn, nil
}
func runStmt(ctx context.Context, s stmt.Statement, args ...interface{}) (rset.Recordset, error) {
var err error
var rs rset.Recordset
// before every execution, we must clear affectedrows.
variable.GetSessionVars(ctx).SetAffectedRows(0)
switch s.(type) {
case *stmts.PreparedStmt:
ps := s.(*stmts.PreparedStmt)
return runPreparedStmt(ctx, ps)
case *stmts.ExecuteStmt:
es := s.(*stmts.ExecuteStmt)
rs, err = runExecute(ctx, es, args...)
if err != nil {
return nil, errors.Trace(err)
}
default:
if s.IsDDL() {
err = ctx.FinishTxn(false)
if err != nil {
return nil, errors.Trace(err)
}
}
stmt.BindExecArgs(ctx, args)
rs, err = s.Exec(ctx)
stmt.ClearExecArgs(ctx)
}
// MySQL DDL should be auto-commit
if err == nil && (s.IsDDL() || variable.IsAutocommit(ctx)) {
err = ctx.FinishTxn(false)
}
return rs, errors.Trace(err)
}
// Plan implements the plan.Planner interface.
// The whole phase for select is
// `from -> where -> lock -> group by -> having -> select fields -> distinct -> order by -> limit -> final`
func (s *SelectStmt) Plan(ctx context.Context) (plan.Plan, error) {
var (
r plan.Plan
err error
)
if s.From != nil {
r, err = s.From.Plan(ctx)
if err != nil {
return nil, err
}
} else if s.Fields != nil {
// Only evaluate fields values.
fr := &rsets.FieldRset{Fields: s.Fields}
r, err = fr.Plan(ctx)
if err != nil {
return nil, err
}
}
if w := s.Where; w != nil {
r, err = (&rsets.WhereRset{Expr: w.Expr, Src: r}).Plan(ctx)
if err != nil {
return nil, err
}
}
lock := s.Lock
if variable.IsAutocommit(ctx) {
// Locking of rows for update using SELECT FOR UPDATE only applies when autocommit
// is disabled (either by beginning transaction with START TRANSACTION or by setting
// autocommit to 0. If autocommit is enabled, the rows matching the specification are not locked.
// See: https://dev.mysql.com/doc/refman/5.7/en/innodb-locking-reads.html
lock = coldef.SelectLockNone
}
r, err = (&rsets.SelectLockRset{Src: r, Lock: lock}).Plan(ctx)
if err != nil {
return nil, err
}
// Get select list for futher field values evaluation.
selectList, err := plans.ResolveSelectList(s.Fields, r.GetFields())
if err != nil {
return nil, errors.Trace(err)
}
var groupBy []expression.Expression
if s.GroupBy != nil {
groupBy = s.GroupBy.By
}
if s.Having != nil {
// `having` may contain aggregate functions, and we will add this to hidden fields.
if err = s.Having.CheckAndUpdateSelectList(selectList, groupBy, r.GetFields()); err != nil {
return nil, errors.Trace(err)
}
}
if s.OrderBy != nil {
// `order by` may contain aggregate functions, and we will add this to hidden fields.
if err = s.OrderBy.CheckAndUpdateSelectList(selectList, r.GetFields()); err != nil {
return nil, errors.Trace(err)
}
}
switch {
case !rsets.HasAggFields(selectList.Fields) && s.GroupBy == nil:
// If no group by and no aggregate functions, we will use SelectFieldsPlan.
if r, err = (&rsets.SelectFieldsRset{Src: r,
SelectList: selectList}).Plan(ctx); err != nil {
return nil, err
}
default:
if r, err = (&rsets.GroupByRset{By: groupBy,
Src: r,
SelectList: selectList}).Plan(ctx); err != nil {
return nil, err
}
}
if s := s.Having; s != nil {
if r, err = (&rsets.HavingRset{
Src: r,
Expr: s.Expr}).Plan(ctx); err != nil {
return nil, err
}
}
if s.Distinct {
if r, err = (&rsets.DistinctRset{Src: r,
SelectList: selectList}).Plan(ctx); err != nil {
return nil, err
}
}
if s := s.OrderBy; s != nil {
if r, err = (&rsets.OrderByRset{By: s.By,
Src: r,
SelectList: selectList}).Plan(ctx); err != nil {
return nil, err
}
}
if s := s.Offset; s != nil {
if r, err = (&rsets.OffsetRset{Count: s.Count, Src: r}).Plan(ctx); err != nil {
return nil, err
}
}
if s := s.Limit; s != nil {
if r, err = (&rsets.LimitRset{Count: s.Count, Src: r}).Plan(ctx); err != nil {
return nil, err
}
}
if r, err = (&rsets.SelectFinalRset{Src: r,
SelectList: selectList}).Plan(ctx); err != nil {
return nil, err
}
return r, nil
}