SQL - transaction log backup frequency

When asking the question of any solution stakeholder: "How much data can we afford to lose?" The answer will almost certainly be "None.". Unfortunately a no-data-loss system would cost millions and in the majority of situations is financially unattainable.

So if a no-data-loss system is not an option, what options do we have? Transaction log backups. Increasing the frequency of transaction log backups does not exponentially increase the load on our database servers as one might first think. Creating an hourly transaction log of 60GB would actually give the server more of a jolt than creating 60 1GB transaction logs taken every minute.

At this point you might think me crazy for suggesting high frequency log backups. However I'm no less crazy than those choosing hourly or even daily transaction log backups. It's really not for us to decide, more for us to implement based on the stakeholders needs.

Of course taking a transaction log backup every minute will create dozens of files. Restoring these files through the GUI would take a long time and is unrealistic in a mission critical outage.

This is where a restore script is essential for your database. It should be created, tested and ready to run at a moment notice. I've provided an example of a restore script below.

USE Master; 
GO  
SET NOCOUNT ON 

-- 1 - Variable declaration 
DECLARE @dbName sysname 
DECLARE @backupPath NVARCHAR(500) 
DECLARE @cmd NVARCHAR(500) 
DECLARE @fileList TABLE (backupFile NVARCHAR(255)) 
DECLARE @lastFullBackup NVARCHAR(500) 
DECLARE @lastDiffBackup NVARCHAR(500) 
DECLARE @backupFile NVARCHAR(500) 

-- 2 - Initialize variables 
SET @dbName = 'Customer' 
SET @backupPath = 'D:\SQLBackups\' 

-- 3 - get list of files 
SET @cmd = 'DIR /b "' + @backupPath + '"'

INSERT INTO @fileList(backupFile) 
EXEC master.sys.xp_cmdshell @cmd 

-- 4 - Find latest full backup 
SELECT @lastFullBackup = MAX(backupFile)  
FROM @fileList  
WHERE backupFile LIKE '%.BAK'  
   AND backupFile LIKE @dbName + '%' 

SET @cmd = 'RESTORE DATABASE [' + @dbName + '] FROM DISK = '''  
       + @backupPath + @lastFullBackup + ''' WITH NORECOVERY, REPLACE' 
PRINT @cmd 

-- 4 - Find latest diff backup 
SELECT @lastDiffBackup = MAX(backupFile)  
FROM @fileList  
WHERE backupFile LIKE '%.DIF'  
   AND backupFile LIKE @dbName + '%' 
   AND backupFile > @lastFullBackup 

-- check to make sure there is a diff backup 
IF @lastDiffBackup IS NOT NULL 
BEGIN 
   SET @cmd = 'RESTORE DATABASE [' + @dbName + '] FROM DISK = '''  
       + @backupPath + @lastDiffBackup + ''' WITH NORECOVERY' 
   PRINT @cmd 
   SET @lastFullBackup = @lastDiffBackup 
END 

-- 5 - check for log backups 
DECLARE backupFiles CURSOR FOR  
   SELECT backupFile  
   FROM @fileList 
   WHERE backupFile LIKE '%.TRN'  
   AND backupFile LIKE @dbName + '%' 
   AND backupFile > @lastFullBackup 

OPEN backupFiles  

-- Loop through all the files for the database  
FETCH NEXT FROM backupFiles INTO @backupFile  

WHILE @@FETCH_STATUS = 0  
BEGIN  
   SET @cmd = 'RESTORE LOG [' + @dbName + '] FROM DISK = '''  
       + @backupPath + @backupFile + ''' WITH NORECOVERY' 
   PRINT @cmd 
   FETCH NEXT FROM backupFiles INTO @backupFile  
END 

CLOSE backupFiles  
DEALLOCATE backupFiles  

-- 6 - put database in a useable state 
SET @cmd = 'RESTORE DATABASE [' + @dbName + '] WITH RECOVERY' 
PRINT @cmd