I am adding some 2m record in a table with database in Full Recovery but my log file size is not increasing from the default assigned when database was created.What can be the possible reason?
One of two things is happening (possibly both):
The log file is already sized to be sufficient for the activity that you're putting against it.
There are periodic transaction log backups running.
Log size doesn't increase just because there has been a transaction. It increases because the current log file doesn't have enough free space for the transaction.
In other words, 2-million-row transaction is small enough, and with your backup schedule, the system sees no need to increase the physical log file size.
Why this happens is due to backup. When a log backup is taken, the log is truncated. This doesn't mean that the log file will be shrunk. Rather, the unused space will be freed for future transaction while the physical size remain unchanged. This is useful because excessive and repeated increase would take up the system resource unnecessarily. In other words, if your log file is, say 500MB, then it's likely that that's how much space your database typically needs. So shrinking it to 1 MB only have it quickly grown to 500 MB would be likely to affect performance negatively.
To see this in action, observe the log file information by running DBCC SQLPERF(Logspace) in the database you are interested in. INSERT and BACKUP LOG will change the number(s).
Further reading:
Log Truncation
Log Size Management
Related
MSSQL V18.7.1
Transaction log on databases is back-upped every hour.
Size from this databaselog is auto-grow with 128Mb max 5Gb
This runs smoothly but sometimes we do get an error in our application:
'The transaction log for database Borculo is full due to 'LOG_BACKUP'
This message we got 8.15AM while on 8.01AM de log-backup was done (and emptied).
I would really like it if I had a script or command to check what caused this exponential growth.
We could backup more often (ever 30 minutes) or change size but the problem is not solved then.
Basically this problem should not occur with the number of transactions we have.
Probably some task is running (in our ERP) which causes this.
This does not happen every day but in the last month this is the 2nd time.
The transaction-log is a back-upped one to get info from. Not the active one.
Can anyone point me in the right direction?
Thanks
An hourly transaction log backup means in case of a disaster you could lose up to an hour's worth of data.
It is usually advised to keep you transaction log backups as frequent as possible.
Every 15 mins is usually a good starting point. But if it is a business critical database consider a transaction log backup every minute.
Also why would you limit the size for your transaction log file? If you have more space available on the disk, allow your file to grow if it needs to grow.
It is possible that the transaction log file is getting full because there is some maintenance task running (Index/Statistics maintenance etc) and because the log file is not backed up for an entire hour, the logs doesn't get truncated for and hour and the file reaches 5GB in size. Hence the error message.
Things I would do, to sort this out.
Remove the file size limit, or at least increase the limit to allow it to grow bigger than 5 GB.
Take transaction Log backups more frequently, maybe every 5 minutes.
Set the log file growth increment to at least 1 GB from 128MB (to reduce the number of VLFs)
Monitor closely what is running on the server when the log file gets full, it is very likely to be a maintenance task (or maybe a bad hung connection).
Instead of setting max limit on the log file size, setup some alerts to inform you when the log file is growing too much, this will allow you to investigate the issue without any interference or even potential downtime for the end users.
I have a database with log file size of 700 MB. Now I have fixed its max file size to 1 GB.
When it reaches 1 GB,transaction failed the reason for the same is that "The transaction log for database is full. To find out why space in the log cannot be reused, see the log_reuse_wait_desc column in sys.databases"
This is same case if I uncheck Autogrowth for log file.
When I checked log_reuse_wait_desc column in sys.databases it says "Active_Transaction".
I am not able to understand why Sql server is not maintaining the max file size limit.Why it cannot delete old logs or something like that to maintain the max file size.
How does it work.
What I want is to limit the log file size that not to exceed 1 GB in any case.
There are a few things you need to consider here, especially if you want to restrict the log file size to 1GB.
as already mentioned, you need to understand the difference
between the three recovery models. Taking log backups is a key task
when using the full recovery model. However this is only part of the
problem; log backups only truncate the inactive part of the log,
therefore a transaction could fill the log file with 1GB+ of data,
and then you are in the same position you are in now... even if you are in simple recovery model (a log backup will not help you here!).
In an ideal situation, you would not restrict the log file in such a way, because of this problem. if possible you want to allow it to auto-grow so, in theory, it could fill the disk.
Transaction log management is a science in itself. Kimberly Tripp has some very good advice on how to manage transaction log throughput here
understanding VLF's will allow you to better manage your transaction log, and could help towards better proportioning your log file for large transactions.
If, after everything you have read, you are still required to limit the transaction log growth, then you will need to consider batch updating large result sets. this will allow you to update, say, 1000 rows at a time, meaning that only 1000 records are written to the log. SQL Server uses write-ahead logging, so in order to complete a transaction, you first need to have enough space in the transaction log to write all the details. If using a simple recovery model, this write-ahead logging is automatically truncated, meaning you don't need to backup the log. Therefore, writing 1000 records at a time (for example) will causing less of a problem than a huge 1,000,000 record insert (say)
Redgate provide a free e-book to help you on your way!
EDIT:
P.s. I've just read your comment above... If you are in full recovery model you MUST do log backups, otherwise sql server WILL NOT recover the space from the log, and will continue to write to the log causing it to expand! However note, you MUST have a full backup for transaction log backups to take effect. SQL Server cannot backup the log if it doesn't have an initial restore point (i.e. the full backup).
After deploying a project on the client's machine, the sql db log file has grown to up to 450G, although the db size is less than 100MB, The logging mode is set to Simple mode, and the transactions are send from a windows service that send insertion and updating transaction every 30 seconds.
my question is, how to know the reason of db log file growth?
I would like to know how to monitor the log file to know what is the exact transaction that causes the problem.
should i debug the front end ? or there is away that expose the transactions that cause db log file growth.
Thank you.
Note that a simple recovery model does not allow for log backups since it keeps the least amount of information and relies on CHECKPOINT, so if this is a critical database, consider protecting the client by use of a FULL RECOVERY plan. Yes, you have to use more space, but disk space is cheap and you can have greater control over the point in time recovery and managing your log files. Trying to be concise:
A) Your database in Simple Mode will only truncate transactions in your transaction log as when a CHECKPOINT is created.
B) Unfortunately, large/lots of uncommitted transactions, including BACKUP, creation of SNAPSHOT, and LOG SCANs, among other things will stop your database from creating those checkpoints and your database will be left unprotected until those transactions are completed.
Your current system relies on having the right edition of your .bak file, which depending on the size may mean hours of potential loss.
In other words, it is that ridiculous size because your database is not able to create a CHECKPOINT to truncate these transactions often enough....
a little note on log files
Foremost, Log files are not automatically truncated every time a transaction is committed (otherwise, you would only have the last committed transaction to go back to). Taking frequent log backups will ensure pertinent changes are kept (point in time) and SHRINKFILE will squeeze the log file to the smallest size available/size specified.
Use DBCC SQLPERF(logspace) to see how much of your log file is in use and how large it is. Once you perform a full backup, the log file will be truncated to the remaining uncommitted/active transactions. (Do not confuse this with shrinking the size)
Some suggestions on researching your transactions:
You can use the system tables to see the most expensive cache, frequent, and active plans.
You can search the log file using an undocumented extended stored procedure, fn_dblog.
Pinal has great info on this topic that you can read at this webpage and link:
Beginning Reading Transaction Log
A Log File is text, and depending on your log levels and how many errors and messages you receive these files can grow very quickly.
You need to rotate your logs with something like logrotate although from your question it sounds like you're using Windows so not sure what the solution for that would be.
The basics of log rotation are taking daily/weekly versions of the logs, and compressing them with gzip or similar and trashing the uncompressed version.
As it is text with a lot of repetition this will make the files very very small in comparison, and should solve your storage issues.
log file space won't be reused ,if there is open transaction..You can verify the reason for log space reuse using below DMV..
select log_reuse_wait_desc,database_id from sys.databases
In your case,your database is set to simple and database is 100 MB..but the log has grown upto 450 GB..which is very huge..
My theory is that ,there may be some open transactions ,which prevented log space reuse..log file won't shrink back,once it grew..
As of know you can run above DMV and see ,what is preventing log space reuse at this point,you can't go back in time to know what prevented log space reuse
We are using SQL Server 2008 with full recovery model, the database size is 10 GB and the log file is 172 GB, we want to clear up the space of the log file internally ,we did transaction log file backup it should be clear up, but it still 172 GB ,what to do?
shrink the DB after doing the following task :
/*Perform a full backup of your database.
Change the backup method of your database to "Simple"
Open a query window and enter "checkpoint" and execute
Perform another backup of the database
Perform a final full backup of the database.*/
To understand this, you need to understand the difference between file shrinkage and truncation.
Shrinking means physically shrinking the size of the file on disk. Truncation means logically freeing up space to be used by new data, but with NO impact on the size of the file on disk.
In layman's terms for instance, if your log file is 100 GB in size and you've never backed it up, 100GB of that size is USED. If you then back up the log / database, it will be truncated, meaning the 100GB will be reserved for future use... basically meaning it's freed up for SQL Server, but still uses up the same space on disk as before. You can actually see this with the following query for instance.
DBCC SQLPERF(logspace) WITH NO_INFOMSGS
The result will show on a DB basis how large the log file is, and how much of the log file is actually used. If you now shrink that file, it will free up the reserved portion of the file on disk.
This same logic applies to all files in SQL Server (including primary and partition files, as well as log files for tempdb, user databases etc), even on table-level. For instance if you run this code
sp_spaceused 'myTableName'
You will see how much of that table is reserved and used for various things, where the "unused" column will show how much is reserved but NOT used.
So as a conclusion, you can NOT free up space on disk without shrinking it. The real question here is why exactly are you not allowed to shrink the log? The typical reason for the recommendation to not shrink log files is because it will naturally grow to its normal size anyway, so there's no point. But if you're only stepping into the recommended practice of backing up the log anyway, it only makes sense to start by shrinking the oversized log first so that in the future your maintenance backups will keep it in its natural, comparatively smaller size.
Another EXTREMELY IMPORTANT point about shrinking, is that shrinking data files is another matter entirely. If you shrink a data file, you will be severely fragmenting all indexes and statistics on the database, making it mandatory to rebuild practically all the indexes on the entire database to avoid catastrophic degradation in performance. So do NOT shrink data files, ever, without consulting someone who knows what they're doing and is prepared to deal with the consequences. Log files are a lot safer in this regard since the fragmentation doesn't apply there.
I have seen that our database has the full recovery model and has a 3GB transaction log.
As the log gets larger, how will this affect the performance of the database and the performance of the applications that accesses the database?
The recommended best practice is to assign a SQL Server Transaction log file its’ very own disk or LUN.
This is to avoid fragmentation of the transaction log file on disk, as other posters have mentioned, and to also avoid/minimise disk contention.
The ideal scenario is to have your DBA allocate sufficient log space for your database environment ahead of time i.e. to allocate say x GB of data in one go. On a dedicated disk this will create a contiguous allocation, thereby avoiding fragmentation.
If you need to grow your transaction log, again you should endeavour to do so in sizeable chunks in order to endeavour to allocate contiguously.
You should also look to NOT shrink your transaction log file as, repeated shrinking and auto growth can lead to fragmentation of the data file on disk.
I find it best to think of the autogrowth database property as a failsafe i.e. your DBA should proactively monitor transaction log space (perhaps by setting up alerts) so that they can increase the transaction log file size accordingly to support your database usage requirements but the autogrowth property can be in place to ensure that your database can continue to operate normally should unexpected growth occur.
A larger transaction log file in itself if not detrimental to performance as SQL server writes to the log sequentially, so provided you are managing your overall log size and allocation of additional space appropriately you should not be concerned.
In a couple of ways.
If your system is configured to auto-grow the transaction log, as the file gets bigger, your SQL server will need to do more work and you will potentially get slowed down. When you finally do run out of space, you're out of luck and your database will stop taking new transactions.
You need to get with your DBA (or maybe you are the DBA?) and perform frequent, periodic log backups. Save them off your server onto another dedicated backup system. As you back up the log, the space in your existing log file will be reclaimed, preventing the log from getting much bigger. Backing up the transaction log will also allow you to restore your database to a specific point in time after your last full or differential backup, which significantly cuts your data losses in the event of a server failure.
If the log gets fragmented or needs to grow it will slow down the application.
If you don't clear the transaction log periodically by performing backups, the log will get full and consume the entire available disk space.
If the log file growths larger in small steps you will end up with a lot of virtual log files
these virtual log files will slow down the database startups, restore and backup operations.
here is an article that shows how to fix this:
http://www.sqlserveroptimizer.com/2013/02/how-to-speed-up-sql-server-log-file-by-reducing-number-of-virtual-log-file/
For increasing performance it's nice to separate SQL server log file from sql server data file in order to optimize I/O efficiency.
The writing method to the data file is Random but SQL Server writes to the transaction log sequentially.
With Sequential I/O ,SQL Server can read/write data without re-positioning the disk head.