I have written a couple articles showing how to audit database offline events via the default trace as well as via Extended Events. These are great for a more proactive approach. Sometimes the proactive approach is just not plausible for the given circumstances. A good example of this is when you inherit servers (e.g. new client, new project, new job) and there are databases on the server that were taken offline prior to your inheritance.
In a situation like this, you need to find out when the databases were taken offline, but you are somewhat limited by the data available to you for your research purposes. The default trace has rolled beyond the retention point for your server for events that were trapped. Setting up an Extended Events session would be less than helpful given the databases are already offline. So we must find an alternative to finding approximately when the databases were taken offline.
If your predecessor leaves you with a database that has been taken offline and no documentation about it, there is an alternative to find the approximate time it was taken offline – using TSQL. Granted, you could explore the file system and make the same sort of guess based on the file modified date. Data people generally prefer some sort of script and a script that is native to their language (tsql).
So, let’s take a look at a viable option for figuring out the mystery behind your database that has been set offline with no good info surrounding it.
/* requires that the DB have had at least one full backup*/
DECLARE @Numdays INT = 1;
--minute, d for days
d.name AS DBName
, mf.name AS filelogicalname
, mf.differential_base_time AS DBOfflineDate --utc time
FROM sys.master_files mf
INNER JOIN sys.databases d
ON mf.database_id = d.database_id
WHERE mf.differential_base_time < DATEADD(DAY,@Numdays * -1,GETUTCDATE())
AND d.state_desc = 'offline'
ORDER BY mf.differential_base_time;
Running this query, I see the following on my test server:
Note that this query uses GETUTCDATE. The differential_base_time column in sys.master_files is in UTC time. Thus, in order to compare properly, we need to ensure we use a UTC datestamp for comparison. Also, of note, this query doesn’t work if there is no full database backup for the database in question. Who doesn’t backup their databases though, right? No seriously, you really should.
Since this is my test server and I am well prepared, I just so happen to have an XEvent session running that tracks the offline events that I can use to compare the results.
Yes, there is a bit of variance in the actual database offline event and the differential_base_time column. This variance is due to timing of the backup and the actual offline event. Again, this is about finding an approximate time of when the database was taken offline as a viable alternative when other data is not really available.
We all aspire to having a perfect database environment where nothing surprising or unexpected happens. Unfortunately, that is the desire of dreams and fairy tales. The unexpected will happen. A database can be offline at the time that you take over responsibility of the database. You will be asked when it was taken offline. This script will help you get a reasonable deduction for that offline event in the absence of better data.
Extended Events is a powerful tool to help in troubleshooting and tuning your environment. I recommend investing a little time in reading the 60 day series about Extended Events. This is not a short series but is designed to provide an array of topics to help learn the tool over time. Don’t forget to go back and read the companion article showing how to audit these events via the default trace.