如何重复运行SQL Delete语句并缩小事务日志？

Question

I have a customer who is running out of space on their drive, and it's entirely taken up by the SQL DB and transaction log. Unfortunately, moving the DB and log are not an option available to us at the current time, so I need to figure out how to delete lines from 2 massive tables. So far a coworker has spent 4 days trying to do this and has not been able to put a dent in it. There are only 13GB available for the transaction log, and deleting large quantities from these tables wipes that 13GB out really quick. Obviously the quickest thing to do would be to move what we want to keep to a temporary table, truncate the existing tables, then move them back. Unfortunately, this is an extremely busy environment within a hospital, and there are tens of thousands of lines being written to these tables every hour. So, unfortunately, we can't temporarily stop writing to this table to be able to truncate.

So we've been deleting a month of data at a time from each of these tables, then shrinking the transaction log to do it again. I feel like there's got to be a way to just get this to repeat, but I'm not entirely sure what I'm doing... I tried:

delete top (10000)
from Table 1_
where CreationDate_ < '2017-06-01' 

Go

delete top (10000)
from Table2_
where CreationDate_ < '2017-06-01' 

Go

dbcc shrinkfile (SQL_Log,4)

Go 2

Go 2

This appears to remove 10,000 lines from each table, then runs the shrinkfile for the log twice (for some reason it doesn't fully shrink down to the 4224kb size when we only run it twice), but it does not seem to repeat. I've also tried adding () starting at the first delete statement and ending after the first "Go 2" line. When I do that it just says:

Incorrect syntax near "Go"

Anybody have any clue how to do this? If we can get this to work, I plan on increasing the delete statements to a number much larger than 10,000, and increasing the repeat on the script to something much larger than 2, but I need to get it to work before I can actually do that...

Answer 1

You don't need to shrink the log file repeatedly. If the database is in simple recovery mode the log file will not continue to grow, so long as you don't delete too many rows in a single transaction. Once all the rows have been purged you can shrink the log file down to something reasonable for the environment.

Answer 2

You can use a WHILE loop and control the number of iterations using a COUNT of records.

DECLARE @Chunk INT = 10000
DECLARE @Date DATE = '2017-06-01'
DECLARE @Cnt INT = SELECT COUNT(*) FROM Table 1_ WHERE CreationDate_ < @Date
WHILE @Cnt > 0
  BEGIN
    delete top (@Chunk)
    from Table 1_
    where CreationDate_ < @Date
    SET @Cnt = @Cnt - @Chunk
  END
//Move on to the next group
SET @Date = '2017-07-01'
SET @Cnt = SELECT COUNT(*) FROM Table 1_ WHERE CreationDate_ < @Date

WHILE @Cnt > 0
   BEGIN
   // Your delete query
   SET @Cnt = @Cnt - @Chunk
END
//and so on