Set default space free in sql log

Question

We have a database that needs 40% free in the log files at all times or we get an alert. I cannot find a way to set growth when a limit is reached.

Of course we can set autogrowth to a certain limit but then we would have to go into it weekly to add 40% based on last growth.

Any ideas? SQL 2012

Answer 1

I agree with Brent about this being not a fantastic idea; I prefer to manage log file sizes manually with intention.

Having said that, you can use SQL Server Agent alerts to accomplish what you want.

DECLARE @jobid uniqueidentifier;
DECLARE @cmd nvarchar(max);
SET @cmd = N'DECLARE @cmd nvarchar(max);
DECLARE @size int;
DECLARE @newSize int;
SET @size = (SELECT size * 8192E0 / 1048576 
             FROM sys.master_files mf 
             WHERE mf.name = ''templog'');
SET @newSize = @size + (@size * 0.40);
SET @cmd = N''ALTER DATABASE tempdb 
              MODIFY FILE (name = ''''templog''''
                 , SIZE = '' + CONVERT(nvarchar(max), @newSize) + N''MB'''');'';
EXEC master.sys.sp_executesql @cmd;';

IF EXISTS (SELECT 1 
             FROM msdb.dbo.sysjobs sj 
             WHERE sj.name = N'tempdb log size increase')
BEGIN
    EXEC msdb.dbo.sp_delete_job @job_name = N'tempdb log size increase';
END
EXEC msdb.dbo.sp_add_job @job_name = N'tempdb log size increase'
    , @enabled = 1
    , @description = N'increases the size of tempdb log file by 40%'
    , @start_step_id = 1
    , @owner_login_name = 'sa'
    , @job_id = @jobid OUT;

EXEC msdb.dbo.sp_add_jobstep @job_id = @jobid
    , @step_id = 1
    , @step_name = N'increase log size'
    , @subsystem = N'TSQL'
    , @command = @cmd;

EXEC msdb.dbo.sp_add_jobserver @job_id = @jobid, @server_name = N'(local)';

IF EXISTS (SELECT 1 
             FROM msdb.dbo.sysalerts sa 
             WHERE sa.name = N'tempdb 80pct Tx Log Alert')
BEGIN
    EXEC msdb.dbo.sp_delete_alert @name = N'tempdb 80pct Tx Log Alert';
END
EXEC msdb.dbo.sp_add_alert @name = N'tempdb 80pct Tx Log Alert' 
        , @message_id = 0 
        , @severity = 0 
        , @enabled = 1 
        , @delay_between_responses = 300 
        , @include_event_description_in = 7 
        , @category_name = N'[Uncategorized]' 
        , @performance_condition = N'MSSQL$MV2016:Databases|Percent Log Used|tempdb|>|60' 
        , @job_id = @jobid;

You'll need to modify the code above to reflect the name of the server in the @performance_condition parameter. If your server is a named instance, you'll need to change MV2016 to the name of your instance. If you're using an unnamed instance then @performance_condition would simply be:

@performance_condition = N'MSSQL:Databases|Percent Log Used|tempdb|>|60' 

This alert will fire whenever the tempdb log file crosses 60% full. When the alert fires, it automatically runs a job which increases the size of the tempdb log by 40%.

Answer 2

SQL Server doesn't have this functionality built in, but you could start with this DBA.se question:

Query to report disk space allocation and used space

Then based on the output, grow the log files appropriately.

I'll be honest though: I'm decent with T-SQL, and it'd take me longer to write that than it would to just change the threshold in my monitoring software so that it's more appropriate. Because here's the problem: if you start growing your log files like crazy, next thing you know, your monitoring software is going to be complaining about having less than 40% free space on your drives, hahaha.