Tag: administration

One of the things that I think is extremely important for DBAs and really anyone that has to administer a SQL Server instance is a set of alerts on various items that might occur.

I ran across Glenn Berry’s article on Provisioning SQL Server and there’s a section in there that is titled “Setting Up SQL Server Agent Alerts”. It assumes you have Agent running (and you should), and includes a series of alerts that you can set to inform you when certain things occur.

Glenn has alerts for severity errors 19-25, which are important, and then includes an alert for Error 825.  This error is indicative of possible corruption and at least some I/O issue with your storage. It’s important to have this error trapped, but in addition, I’d also recommend setting alerts for 823 and 824 errors.

I would recommend modifying Glenn’s code to include this T-SQL as well.

-- Error 823: Read Write Request Failure
DECLARE @Error823AlertName SYSNAME = N'I/O Alert - Error 823: Read or Write request failure';

EXEC msdb.dbo.sp_add_alert @name = @Error823AlertName,
              @message_id=823,
              @Severity=0,
              @enabled=1,
              @delay_between_responses=900,
              @include_event_description_in=1,
              @category_name=N'[Uncategorized]',
              @job_id=N'00000000-0000-0000-0000-000000000000';

EXEC msdb.dbo.sp_add_notification @alert_name = @Error823AlertName,
@operator_name=@OperatorName, @notification_method = 1;
GO
-- Error 824: Read Write Request Failure
DECLARE @Error824AlertName SYSNAME = N'I/O Alert - Error 824: Logical Consistency I/O Error';

EXEC msdb.dbo.sp_add_alert @name = @Error824AlertName,
              @message_id=824,
              @Severity=0,
              @enabled=1,
              @delay_between_responses=900,
              @include_event_description_in=1,
              @category_name=N'[Uncategorized]',
              @job_id=N'00000000-0000-0000-0000-000000000000';

EXEC msdb.dbo.sp_add_notification @alert_name = @Error824AlertName,
@operator_name=@OperatorName, @notification_method = 1;
GO

In one of my presentations recently I was recommending DBCC CHECKDB on every database every day. I realize that isn’t always possible or practical, so I noted that if you don’t have resources on your production server, or enough spare hardware, you should at least run it on every database once a month. At least on the database you care about.

Someone in the audience asked if they could just script DBCC PAGE on every page in the database instead. I wasn’t sure if that was accurate, but I didn’t think it was. So I asked THE MAN, and he confirmed this doesn’t equate to a DBCC CHECKDB.

I won’t attempt to give a complete explanation, mostly because I’m sure I’d miss something or be incorrect, but I will tell you how I feel about this, based on what I know.

CHECKDB performs an extensive evaluation of not only all objects (and hence their pages), but also their linkages. It performs a more complete check by default, but you can add the PHYSICAL_ONLY flag to speed things up and limit the checks to just the physical structures and allocations. PHYSICAL_ONLY also skips Filestream checks.

The DBCC PAGE command, undocumented, works, but it doesn’t really examine if the links and relationships between pages are correct.

I can’t say that DBCC PAGE couldn’t be use to detect corruption or find issues, but I wouldn’t depend on it. YMMV, but I wouldn’t use this as a substitute for CHECKDB.