How to loop and/or wait for delay - sql-server

Question

I have imported over 400 million records to a dummy dimension table. I need to take my existing fact table and join to the dummy dimension to perform an update on the fact table. To avoid filling up the transaction logs, somebody suggested I perform a loop to update these records instead of performing an update to hundreds of millions of records at once. I have research loops and researched using a Wait For and Delays, but I am not for sure the best approach on writing the logic out.
Here is the sample update I need to perform:
Update f
set f.value_key = r.value_key
FROM [dbo].[FACT_Table] f
INNER JOIN dbo.dummy_table r ON f.some_key = r.some_Key
and r.calendar_key = f.calendar_key
WHERE f.date_Key > 20130101
AND f.date_key < 20141201
AND f.diff_key = 17
If anybody has a suggestion on the best way to write I would really appreciate it.

Answer 1

To avoid filling up the transaction log you CAN set your recovery model to SIMPLE on your dev machines - that will prevent transaction log bloating when tran log backups aren't done.
ALTER DATABASE MyDB SET RECOVERY SIMPLE;
If you want to perform your update faster use hint ie., (tablock).

Answer 2

Please don't do what the previous person suggested unless you really understand what else will happen. The most important result is that you lose the ability to do a point in time recovery. If you do a full recovery every night and a transaction log recovery every hour (or every 15 minutes) switching to a simple recovery model breaks the chain and you can only recover to the last full recovery time.
If you do it you have to do it (switch to simple) switch back to full and do a full backup and then switch back to doing log backups on a schedule. When the previous person suggest is like driving without bumpers to save on car weight. Sounds great until you hit something.

Answer 3

-- Run this section of code one time to create a global queue containing only the columns needed to identify a unique row to process. Update the SELECT statement as necessary.
IF OBJECT_ID('Tempdb.dbo.##GlobalQueue') IS NOT NULL
DROP TABLE ##GlobalQueue
SELECT diff_key, date_key INTO ##GlobalQueue FROM [dbo].[FACT_Table] f
INNER JOIN dbo.dummy_table r ON f.some_key = r.some_Key
and r.calendar_key = f.calendar_key
WHERE f.date_Key > 20130101
AND f.date_key < 20141201
AND f.diff_key = 17
-- Copy/paste the SQL below to run from multiple sessions/clients if you want to process things faster than the single session. Start with 1 session and move up from there as needed to ramp up processing load.
WHILE 1 = 1
BEGIN
DELETE TOP ( 10000 ) --Feel free to update to a higher number if desired depending on how big of a 'bite' you want it to take each time.
##Queue WITH ( READPAST )
OUTPUT Deleted.*
INTO #RowsToProcess
IF ##ROWCOUNT > 0
BEGIN
Update f
set f.value_key = r.value_key
FROM [dbo].[FACT_Table] f
INNER JOIN dbo.dummy_table r ON f.some_key = r.some_Key
INNER JOIN #RowsToProcess RTP ON r.some_key = RTP.diff_key
and f.calendar_key = RTP.calendar_key
DELETE FROM #RowsToProcess
--WAITFOR DELAY '00:01' --(Commented out 1 minute delay as running multiple sessions to process the records eliminates the need for that). Here just for demonstration purposes as it may be useful in other situations.
END
ELSE
BREAK
END

Answer 4

use top and <>
in an update you must use top (#)
while 1 = 1
begin
update top (100) [test].[dbo].[Table_1]
set lname = 'bname'
where lname <> 'bname'
if ##ROWCOUNT = 0 break
end
while 1 = 1
begin
Update top (100000) f
set f.value_key = r.value_key
FROM [dbo].[FACT_Table] f
INNER JOIN dbo.dummy_table r
ON f.some_key = r.some_Key
and r.calendar_key = f.calendar_key
AND f.date_Key > 20130101
AND f.date_key < 20141201
AND f.diff_key = 17
AND f.value_key <> r.value_key
if ##ROWCOUNT = 0 break
end