http://www.sqlservercentral.com/blogs/sqlrnnr/2011/10/31/haunting-a-database-near-you/

Printed 2014/10/30 11:01PM

Haunting a Database Near You

By Jason Brimhall, 2011/10/31

Today, we have a special Halloween edition.  For me, Halloween and computer geek go quite well together.  And thinking about it, I wanted to try to better understand if there was a correlation.  As a DBA, have you wondered the same thing?

Well, I have a short list of five things that may help you to correlate your affinity for Halloween with your love for Databases.

Tombstones

Did you know that a tombstone is a legitimate thing in SQL Server?

Tombstones are replica related.  They are deleted items in the replica and are used to make sure the deleted item doesn’t get put back in the replica inadvertently.

You can read a lot more about tombstones from the msdn article here.

Tombstones are not unique to SQL Server.  These are commonplace in Active Directory as well.

 

Ghosts

Not all rows that are deleted move on to the afterlife quickly like they should.  Some like to hang around due to unfinished business.

The unfinished business in this case is the server running a cleanup thread.  This has to be done when the server is not too busy and has enough free resources to help these records move on to the afterlife.

You can see the evidence of these ghosts with specialized equipment.  By the use of a DMO, we can see the ghost record count on a per index basis.  The DMO is sys.dm_db_index_physical_stats.  Take a look at the ghost_record_count column in the returned record set.

With more specialized equipment, the engine takes care of the cleanup and removal of these ghosts.  Here is an in-depth foray into the world of SQL ghost hunting.  Whatever you do, don’t cross the streams.

Zombies

It’s alive!!

No, I killed it!!

It can’t be…How is it still alive?

The transaction will not commit and may get rolled back.  The zombie has reared its’ ugly head.  A transaction that cannot commit but keeps going (or rolls back) due to an unrecoverable error is a zombie transaction.

From MSDN, here is a more specific definition of a zombie.

Rowsets can become zombies if the internal resource on which they depend goes away because a transaction aborts.

Spawn

The spawn of SQL server is not so much like the Spawn character of the comics.  Nor is it much like the spawn shown to the right.

That is unless it is not managed very well.  SQL can spawn multiple threads if the optimizer deems it necessary for a query.  This is also known as parallelism.

Parallelism can be a good thing or it can be a bad thing.  Understanding it can help keep it on the good side.  You might want to check out some of Paul White’s articles on the topic.

Children of the Corn

Well, this one is not really something in SQL server.  That said, every time I think of orphaned users in SQL server – children of the corn comes to mind.

An orphaned user is one in which the login SID does not match for one reason or another.  This makes it so that the user can no longer log in to SQL server.

If you don’t know about these kids, they can really make for a frustrating day.  Read more here.

Bonus

I have just covered five things in SQL server that correlate quite closely to Halloween.  But this by no means is an exhaustive list.  For instance, an obvious correlation is the “KILL” command.  Another good one is the monster known as the Blob (read more about that monster here and here).

With the opportunity to have Halloween every day, it’s no wonder I like being a DBA.

Happy Halloween


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