[SuperStar88]

Переписал так, без промежуточного буфера, всё равно долго

ttsbegin;
    while select forupdate rowQuota
    {
        monthDiff = intvNo(rowQuota.DateTo, rowQuota.DateFrom, IntvScale::Month);
        dayDiff = intvNo(rowQuota.DateTo, rowQuota.DateFrom, IntvScale::Day);

        if(rowQuota.UsagePeriod <= monthDiff && dayDiff > 0)
        {
            do
            {
                rowQuota.DateFrom = dateMthFwd(rowQuota.DateFrom, rowQuota.UsagePeriod);
                rowQuota.DatePotreb = rowQuota.DateFrom;
                rowQuota.insert();

                monthDiff = intvNo(rowQuota.DateTo, rowQuota.DateFrom, IntvScale::Month);
                dayDiff = intvNo(rowQuota.DateTo, rowQuota.DateFrom, IntvScale::Day);
            }
            while(rowQuota.UsagePeriod <= monthDiff && dayDiff > 0);
        }
    }
ttscommit;