How to shrink a SQL Server Log file with Mirroring enabled?

Question

I have several databases for my applications that use SQL Server 2005 mirroring to keep a nice copy of the data somewhere else. Works like a charm, however, the log file just seems to be growing and growing, one is at 15GB for a 3GB database.

Normally, I can just shrink it - however an error pops up that this specifically cannot be done. But, it seems eventually if unchecked would just expand to use all the space on the drive.

I see that I can set a maximum file size for the log file, is that the answer here? Will the log just roll when it hits the max, or will the DB just stop functioning?

Thanks

Answer 1

We ran into the same issue after switching from log shipping to mirroring. You have to create a job that regularly backs up the transaction log (every 15 or 30 minutes or so) to keep the log size from getting out of hand.

If it is already out of hand, run BACKUP LOG TO DISK = 'Nul', then run a DBCC SHRINKFILE command. Then you can get your job set up.

Note that The 'Nul' is not a misspelling, it is an old DOS trick that behaves as if you are writing a file, but really just dumps the information off into the ether so it doesn't take up space on the machine.

Also, your log will grow until you run out of space, then the whole thing stops working. Your app will receive an error that the transaction log is full.

EDIT: David correctly pointed out that this action will break the log chain and reduce the ability to recover from failure. Be sure to use the backup log to 'nul' command as a last resort. If you have space on the drive, you should take a proper log backup and setup your log backup plan. Make sure you also include regular full backups and a cleanup task to remove old files.

Answer 2

I would look at why your logfile is growing, then you can define a strategy for solving your issue. It might be worth checking your mirroring state

When a principal database is exposed, it is active with user connections and processing transactions. However, no log records are being sent to the mirror database, and if the principal should fail, the mirror will not have any of the transactions from the principal from the point the principal entered the exposed state. Also, the principal's transaction log cannot be truncated, so the log file will be growing indefinitely. ref http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx

Answer 3

I had the same problem on mirrored databases the log file grew 40GB where main Db file was around 700 Mb I found this solution In microsoft it works but only shrinked my Database about 4 percent

1- just execute this to create a stored procedure

   use master
   go
   if object_id ('sp_shrink_mirrored_database', 'P') is not null 
     drop proc sp_shrink_mirrored_database 
   go
   create procedure sp_shrink_mirrored_database @dbname sysname, @target_percent int = null
   as
   begin
     declare @filename sysname
     declare @filesize int
     declare @sql nvarchar(4000)

     if @target_percent is null
       dbcc shrinkdatabase (@dbname)
     else 
       dbcc shrinkdatabase (@dbname, @target_percent)
     declare c cursor for 
     select [name], [size] from sys.master_files where type=0 and database_id = db_id (@dbname)
     open c
     fetch next from c into @filename, @filesize
     while @@fetch_status=0
     begin
       set @filesize=(@filesize+1)*8
       set @sql='alter database [' + @dbname + '] modify file ( name=' 
         + @filename + ', size=' + cast(@filesize as nvarchar) + 'kb )'
       execute sp_executesql @sql
       fetch next from c into @filename, @filesize
     end
     close c
     deallocate c
   end
   go

2- execute the stored procedure like this in a new query window For example, if you want to shrink the mydb database, run the following statement.

  EXEC sp_shrink_mirrored_database 'mydb'

Answer 4

http://support.microsoft.com/kb/937531

The shrink operation is not duplicated on the mirror database when you use database mirroring in SQL Server 2005

CAUSE
Database mirroring will change the physical file sizes only after a checkpoint.

WORKAROUND
Method 1
To work around this problem, run the following statements to create a new stored procedure in the master database. Then, use this stored procedure to shrink the principal database instead of running the DBCC SHRINKDATABASE statement or the DBCC SHRINKFILE statement.
[stored procedure too long to post here]

Method 2
Issue a manual checkpoint after shrinking the files on the principal.

Answer 5

Some good ideas can be found here: http://yukonspace ... transaction-log-growth .

From my experience with full-recovery mode databases (should behave in somewhat similar way) you need to make regular full backups at least, otherwise logs only grow.

Answer 6

Simply you can shrink the log file by using the following command

USE DBNAME
GO
DBCC SHRINKFILE(DBNAME_log, 1)
BACKUP LOG DBNAME WITH TRUNCATE_ONLY
DBCC SHRINKFILE(DBNAME_log, 1)
GO

Answer 7

Are you sure the Mirror did not fall behind? The principal server instance can't truncate the log until they have been successfully applied to the mirror. After a certain point I believe you may have to backup the transaction log and apply it to the mirror and restart mirroring.

Answer 8

要收缩事务文件，必须执行备份，因为存在活动虚拟日志文件： http ： //www.xoowiki.com/Article/SQL-Server/tronquer-journal-de-log-sur-base-en-miroir-499的.aspx

Answer 9

1. You have to backup the log regularly otherwise your log file will grow indefinitely. If you can't write to the log (ie out of disk space or hit max size) the DB will fail
2. SQL Server 2005 has an issue where the shrink isn't reflected on the mirror side. The solution is here http://support.microsoft.com/kb/937531

This article has some good info on How Log Files work, you should also read Factors that can delay log truncation

Answer 10

Configure Transaction Log backup and create a job or run direct the following command.

use DatabaseName GO DBCC SHRINKFILE (LogicalFileName_log, 1); GO

and if you want to shrink a Data file then follow the bellow steps.

1. go to your database properties.
2. select option in the left.
3. change auto Shrink property to true, by default it is false. and wait for sql server to shrink it automatically.

I hope it will resolve both log and data file shrining problem.

Yousaf Khan.

Answer 11

Please make sure to perform a full backup after performing log backup with TRUNCATE_ONLY. This breaks the log backup chain.