code: func (s *SessionVars) WithdrawAllPreparedStmt() {
  	psCount := len(s.PreparedStmts)
  	if psCount == 0 {
  		return
  	}
  	afterMinus := atomic.AddInt64(&preparedStmtCount, -int64(psCount))
  	metrics.PreparedStmtGauge.Set(float64(afterMinus))
  }
docs: // WithdrawAllPreparedStmt remove all preparedStmt in current session and decrease count in global.