Performance updating a extra huge table

Question

Hi guys, just an advice. I'm handling table with more than 300 millions rows, sometimes even 800 millions and so far I came up with some good solution but now I really need to be concerned about the performance. I got a table with:
FlyID int, FlyNumber int, SettlDate datetime2, SettlPeriod double, Consumpt dec, Ixl dec, Aunit int
300 millions rows. The settldate is a date , settperiod is an half hour ( so 48 period each day).
The other table is:
BMUnit int,  SettlDate datetime2, SettlPeriod double, Chargefact dec
I'm going to join the two table on bmunit=bmunit, settdate=settdate, settperiod=settperiod and with an insert filling a new table
Fingers crossed and I hope it wors within a reasonable time ( 3 hours...more?)
The real concern is:
I got another table with
FlyID int, Company varchar, CompanyID int, FromDate datetime, ToDate datetime
The logic should be something like this:
Update table1 set 1companyid=dd.companyid , company=company
where table1.flyid=company.flyid
and settlementdate >= fromdate and settlementdate <= todate
but just yesterday I tried something without date and the querr ran for more than seven hours and so I had to killed it. I'm wondering if there is a better way...all this stuff because I'm going to build several cube taking as source a big table. That's
it's going to make the retrievement really fast, so far I cut pratically entire hours but now I need you this more element and before I start to write some code I'd like to hear some your advice..
Thanks

Answer 1

Tables that large are always a problem to do major maintenance.
I would do your update in batches:
DECLARE @cnt int;
SET @cnt = 1;
WHILE @cnt > 0
BEGIN
Update TOP 1000000 table1 set 1companyid=dd.companyid , company=company
where table1.flyid=company.flyid
and settlementdate >= fromdate and settlementdate <= todate
SET @cnt=@@ROWCOUNT
END