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In Microsoft SQL Server I should take log backup twice to free up LDF space. Why did this happen?
Can anyone help me?
In fact, I use full model recovery and have a full backup.
I want to say that I am sure that full model recovery is active. But when I take a log backup from the database, the space of the LDF file is not freed, until I take a log backup for the second time in a row, and the space is freed.
When you take a log backup, only inactive Virtual Log Files (VLFs) within the LDF can be backed up and truncated - therefore, if you have an active/open transaction consuming a VLF near the end of the file, the file cannot be truncated.
This document provides some common reasons truncation might be delayed:
Factors that can delay log truncation
Related
My DB Admin advised that I should regularly take backup of .ldf files. Fine, this SQL post here explains this beautifully.
Consider that a transaction is being done in SQL Server. And at the same time, a scheduled process tries to access the .ldf file for backing it up.
What happens ? How this works ?
You must read Article Understanding SQL Server backup by Paul Randal. That is the best I can see which is available and can explain you in details various aspects.
Coming to your question a transaction log backup includes all information from previous transaction log back or full backup that started the log chain. Backup simply means reading information froma file(data or log) and writing it to destination disk. The transaction any would work independed of log backup running. A transaction follow a WAL(write ahead logging) protocol, for practical purposes all transaction information is first written in log file and then changes are later made to data file. So when transaction is running it would not be affected by transaction log backup job which is running both are doing different task and are muttually exclusive events. Current backup would try to backup all logs which are marked as committed and would truncate the logs if no transaction requires it. If any portion of log is committed after log backup has read that portion it would not come in current log backup but would come under further log backup.
Transacion log backup has important role in crash recovery it helps in determining what all operations has to be roll forwared and what has to be rolled back. Without transaction log backup or transaction log crash recovery is not possible
You must also read Logging and recovery in SQL Server to know about life cycle of a transaction.
The excat answer as to what acctual steps happens inside is beyond scope of discussion as nobody can exactly tell you what would happen but reading the article would give you a good idea.
Please let me know if you have any further questions.
I am dealing with someone else's backup Maintenance Plan and have an issue with the log file, I have a database that sits on one drive with a size of 31 GB and a log file that sits on another server with a size of 20 GB, the database is in Full Recovery Model. There is a maintenance plan that runs once a day to do a complete backup and a second plan that does a backup of the log file every 15 minutes. I have checked and the drive that the log file gets backed up to and there is still plenty of room but the log file never gets smaller after the backup, is there something missing from the maintenance plan?
Thanks in advance
The situation as you describe it seems fine.
A transaction log backup does not shrink the log file. However, it does truncate the log, file, which means that space can be reused:
From Books Online (Transaction Log Truncation):
Log truncation automatically frees space in the logical log for reuse
by the transaction log.
Also, from Managing the Transaction Log:
Log truncation, which is automatic under the simple recovery model, is
essential to keep the log from filling. The truncation process reduces
the size of the logical log file by marking as inactive the virtual
log files that do not hold any part of the logical log.
This means that each time the transaction log backup occurs in your scenario, it's creating free space in the file which can be used by subsequent transactions.
Leading on from this, should you shrink the file as well? Generally speaking, the answer is no. Assuming your database does not suddenly have massive one-off spikes in usage, the transaction log will have grown to a size to accommodate the typical workload.
This means if you start shrinking the log, SQL Server will just need to grow it again... This is a resource intensive operation, affecting server performance, and no transactions can complete while the log is growing.
The current plan and file sizes all seem reasonable to me.
I don't know if this applies to your situation, but earlier versions of SQL Server 2012 have a bug that crops up when model is set to Simple recovery model. For any database created with model set to Simple, log files will continue to grow in an attempt to reach the 2,097,152 MB limit. This still applies if you alter to Full afterwards. KB article 2830400 states that altering to Full, then altering back to Simple is a workaround -- that was not my experience. Running CU 7 for SP1 was the only trick that worked for me.
The article provides links for the first updates that resolved this bug: "Cumulative Update 4 for SQL Server 2012 SP1", as well as, "Cumulative Update 7 for SQL Server 2012" (if you haven't installed SP1).
If you change the recovery to full and then back to simple, the shrink will work successfully.
I have an SQL Server 2005 instance whose full backup (.BAK) failed due to low disk space. However half hourly transaction log backups continue (.TRN). Assuming I have an older full backup, could these continuing transaction logs be used to restore the database?
i.e. do the transaction log backups only run from the last successful backup and ingore any intermediate failed full backups?
I would have thought the failed backup would be rolled back, so the ongoing transaction log backups plus a full database restore prior to these, should be sufficient to restore a database.
Having said that, I would fix this issue as soon as possible, it's not a good position to be in.
You will need ALL the logs taken since the last full Backup.
You cannot roll forward a log if you have lost a previous log.
Have a look here to determine the LSNs and status of your failed backup.
I went in and checked my Transaction log the other day and it was something crazy like 15GB. I ran the following code:
USE mydb
GO
BACKUP LOG mydb WITH TRUNCATE_ONLY
GO
DBCC SHRINKFILE(mydb_log,8)
GO
Which worked fine, shrank it down to 8MB...but the DB in question is a Log Shipping Publisher, and the log is already back up to some 500MB and growing quick.
Is there any way to automate this log shrinking, outside of creating a custom "Execute T-SQL Statement Task" Maintenance Plan Task, and hooking it on to my log backup task? If that's the best way then fine...but I was just thinking that SQL Server would have a better way of dealing with this. I thought it was supposed to shrink automatically whenever you took a log backup, but that's not happening (perhaps because of my log shipping, I don't know).
Here's my current backup plan:
Full backups every night
Transaction log backups once a day, late morning (maybe hook the Log shrinking onto this...doesn't need to be shrank every day though)
Or maybe I just run it once a week, after I run a full backup task? What do you all think?
If you file grows every night at 500 MB there is only one correct action: pre-grow the file to 500MB and leave it there. Shrinking the log file is damaging. Having the log file auto-grow is also damaging.
you hit the file growth zero fill initialization during normal operations, reducing performance
your log grows in small increments creating many virtual log files, resulting in poorer operational performance
your log gets fragmented during shrinkage. While not as bad as a data file fragmentation, log file fragmentation still impact performance
one day the daily growth of 500MB will run out of disk space and you'd wish the file was pre-grown
You don't have to take my word for it, you can read on some of the MVP blogs what they have to say about the practice of log and file shrinkage on a regular basis:
Auto-shrink – turn it OFF!
Oh, the horror! Please stop telling people they should shrink their log files!
Why you want to be restrictive with shrink of database files
Don't Touch that Shrink Button!
Do not truncate your ldf files!
There are more, I just got tired of linking them.
Every time you shrink a log file, a fairy loses her wings.
I'd think more frequent transaction log backups.
I think what you suggest in your question is the right approach. That is, "hook the Log shrinking onto" your nightly backup/maintenance task process. The main thing is that you are regularly doing transaction log backups, which will allow the database to be shrunk when you do the shrink task. The key thing to keep in mind is that this is a two-step process: 1) backup your transaction log, which automatically "truncates" your log file; 2) run a shrink against your log file. "truncate" doesn't necessarily (or ever?) mean that the file will shrink...shrinking it is a separate step you must do.
for SQL Server 2005
DBCC SHRINKFILE ( Database_log_file_name , NOTRUNCATE)
This statement don't break log shipping. But, you may need to run more than one. For each run, the log shipping backup, copy, and restored to run after again run this statement.
Shrink and truncate are different.
My experiences:
AA db, 6.8GB transaction log
first run: 6.8 GB
log shipping backup, copy, restore after second run: 1.9 GB
log shipping backup, copy, restore after third run: 1.7 GB
log shipping backup, copy, restore after fourth run: 1 GB
BB db, 50GB transaction log
first run: 39 GB
log shipping backup, copy, restore after second run: 1 GB
Creating a transaction log backup doesn't mean that the online transaction log file size will be reduced. The file size remains the same. When a transaction is backuped up, in the online transaction log it's marked for overwriting. It;s not automatically removed, and no spaces is freed, therefore, the size remains the same.
Once you set the LDF file size, maintain its size by setting the right transaction log backup frequency.
Paul Randal provides details here:
Understanding Logging and Recovery in SQL Server
Understanding SQL Server Backups
Based on Microsoft recommendation Before you intend to Shrink log file you should first try to perform the following capabilities:
Freeing disk space so that the log can automatically grow.
Moving the log file to a disk drive with sufficient space.
Increasing the size of a log file.
Adding a log file on a different disk.
Turn on auto growth by using the ALTER DATABASE statement to set a non-zero growth increment for the FILEGROWTH option.
ALTER DATABASE EmployeeDB MODIFY FILE ( NAME = SharePoint_Config_log, SIZE = 2MB, MAXSIZE = 200MB, FILEGROWTH = 10MB );
Also, you should be aware of shrink operation via maintenance plan will effect on *.mdf file and *.ldf file. so you need to create a maintenance plan with SQL job task and write the following command to can only shrink *.ldf file to your appropriate target size.
use sharepoint_config
go
alter database sharepoint_config set recovery simple
go
dbcc shrinkfile('SharePoint_Config_log',100)
go
alter database sharepoint_config set recovery FUll
go
Note: 100 is called the target_size for the file in megabytes, expressed as an integer. If not specified, DBCC SHRINKFILE reduces the size to the default file size. The default size is the size specified when the file was created.
In my humble opinion, It’s not recommended to perform the shrink operation periodically! Only in some circumstances that you need to reduce the physical size.
You can also check this useful guide to Shrink a transaction log file Maintenance Plan in SQL Server
This morning I truncated my transaction before it's hourly backup. Since I truncated the transaction log, the backup failed. The error code I got was 0xC002F210. Any ideas why this happened?
The problem is caused by not having done a full backup before switching the data into SIMPLE recovery mode, shrinking the log file and then switching back to FULL recovery mode.
Why did you truncate the log instead of just backing it up? If you were running out of space you could have backed up the log and then shrunk the file, instead of truncating. Truncating messes with the backup chain and forces you to start over (by taking a new, full backup).
This is one of the reasons BACKUP LOG WITH TRUNCATE_ONLY has been deprecated, and actually won't run in SQL Server 2008. For some background reading:
http://sqlserverpedia.com/blog/sql-server-backup-and-restore/backup-log-with-truncate_only-like-a-bear-trap/
https://sqlblog.org/2009/07/27/oh-the-horror-please-stop-telling-people-they-should-shrink-their-log-files