TSQL Tuesday #60: Something Learned This Way Comes

Comments: 4 Comments
Published on: November 11, 2014

TSQL2sDay150x150It is once again time to come together as a community and talk about a common theme.  This monthly gathering of the community has just reached it’s 5th anniversary.  Yes, that’s right.  We have been doing this for 60 months or five years at this point.  That is pretty cool.

This month Chris Yates (blog | twitter) has taken the helm to lead us in our venture to discuss all the wonderful things that we have learned.  Well, maybe not all the things we have learned, but at least to discuss something we have learned.

Here are some details from the actual invite that you can read here.

Why do we come to events, webinars, sessions, networking? The basic fundamental therein is to learn; community. With that said here is this month’s theme. You have to discuss one thing, few things, or many things on something new you’ve learned recently. It could be from a webinar, event, conference, or colleague. The idea is for seasoned vets to new beginners to name at least one thing; in doing so it might just help one of your fellow SQL friends within the community.

The topic is straight forward but can be a bit difficult at times.  This is a pretty good topic to try and discuss.  I know I have been struggling for content for the topic.  Which makes it that much better because it provides a prime example of how to think about and discuss some pretty important things, while trying to compile that into a recap of one’s personal progress.

Let’s think about the topic for a bit and the timing of the topic.  This comes to us right on the heels of PASS Summit 2014 and in the middle of SQL Intersections in Las Vegas.  We might as well throw in there all of the other things like SQL Saturdays that have been happening leading up to and following those major conferences.

There has been ample opportunity over the past few weeks to learn technical content.  When networking with people there are ample opportunities at these major conferences to also learn about other people and about one’s self.  A good example of that can be seen in a blog post I wrote while attending PASS Summit, which you can read here.

The biggest learning opportunity that evolved from PASS Summit 2014 for me was the constant prodding in various sessions to break out the debugger and become more familiar with what is happening in various cases.  I saw the debugger used in three of the sessions I attended.  There are some great opportunities to learn more about SQL Server by taking some trinket of information from a session and trying to put it to use in your development environment.  This is where learning becomes internalized and gives a deeper understanding.

I hope you have been able to pick up on some tidbit that can be used to your advantage to get a deeper understanding of SQL Server.

Summit 2014 – Next Impressions

Comments: 4 Comments
Published on: November 7, 2014

As Summit 2014 begins to wind down, it is time for some more impressions from the week.  The week has been good so far.  It has been very busy and also can be quite a drain mentally and physically from everything that has transpired.

If you are interested, I have written about some of my other impressions from the week, here.

Several years ago, I blogged about an incident with plagiarism with both an original post and a follow-up.  I bring that up, not to rehash the negative, but instead to discuss an impression from this week.  If you read the follow-up, you will see that I had a chat, at that time, with Steinar (twitter) about the problem and how to resolve it.  I met Steinar for the first time this week.  And to be honest, I had forgotten about the conflict and had removed the RSS feed since the original domain had gone down.

Anyway, Steinar and I had the chance to chat for the first time face to face this week.  Steinar, in my opinion, is a pretty cool guy that made a simple RSS mistake.  The impression is that he remembered me for how I treated him several years ago and was very appreciative of that.  How cool is that?  I really appreciate the opportunity to chat with him and that something I did left a positive impact on him.

Another opportunity is to be able to perform random acts of kindness or service while at Summit.  Much like helping Paul White learn how to use a smart phone, I had the even more rare opportunity to help Kalen Delaney (blog | twitter) out of a sticky situation.  It was a minor but frustrating thing that all of us run into from time to time.  The zipper on her Surface case had become stuck, so I helped her with that.  It’s a little thing but it is the type of thing that, if you are watching, you will see happening all over the place during the week of PASS Summit.

So, the next time you are at Summit, and while back in your local communities after the week has ended for Summit, keep an eye out for those little acts of kindness.  But at the same time, keep an eye out for those that might be watching you.  What kind of impression are you leaving for them or for the SQL Community?

Summit 2014 – Early Impressions

Categories: News, Professional, SSC
Comments: 3 Comments
Published on: November 5, 2014

Summit 2014 is upon us.  Unless you are still under a rock, you probably know that.  And if you are under that rock, I am curious how you are reading this.

While it is early on in the week for the PASS Summit, things have really been going since Sunday for many.  A lot has happened.  A lot has already been learned.  And yes, some new people have already been met.  So far so good.

Now is a good time for me to just jot down some of my early impressions from the week.

It has been nice to receive a couple of compliments this week from a few people on various things.  It is waaaaay cool to hear things such as the following from community members.  Here are some samples.

“You taught me something.” Paul Randal (blog | twitter) in reference to a recent blog post that you can read here.  It is great to hear somebody learned something.  That is a primary driver for putting up content on the web and trying to help in the community where possible.

“Your index script has saved my bacon several times!” Stuart Ainsworth (blog | twitter) talking about my missing index script here.  Again, totally cool.  I am happy to hear about successes from code that I have put out there.

Those are two big impressions that would be great takeaways for the week.

But then we have to start throwing in the learning that is part of the week is.  I have attended a couple of sessions and found myself inspired by some of the content as well as hopeful by some of the other content.

By attending a session about Extended Events, I learned about an API that can expose some XE data via powershell to extend the possibilities and uses of XE.  Since the referenced blog does not contain any of the proposed material (slides or demos) it is hard to do much more with it just yet.  I will continue to check the referenced site as well as the session information on the Summit website.

By attending another session, I learned about a new feature called the Query Store.  It is basically a “Hammer that can make a lot of things look like nails!”  That session was presented by Conor Cunningham.  And while the Query Store has some extended events that are exposed in 2014, the XEs are useless and do nothing until SQL v.Next.  It would be totally awesome to have it back ported but that has no chance of happening.

And to top all of it off, it was great to sit down and get a couple of client issues fixed during the lunch break.

This is what Summit is, a huge chance to recharge, learn and to get excited about the technology and what is coming.  Oh and every now and again, one might get the chance to teach Paul White how to use a smart phone.

Ghosts – an eXtrasensory Experience

ghostrip_fireThis is the last article in a mini-series diving into the existence of ghosts and how to find them within your database.

So far this has been a fun and rewarding dive into Elysium to see and chat with these entities.  We have unearthed some means to be able to see these things manifesting themselves in the previous articles.  You can take a look at the previous articles here.

For this article, I had planned to discuss another undocumented method to look into the ghost records and their existence based on what was said on an msdn blog.  But after a lot of research, testing and finally reaching out to Paul Randal, I determined that won’t work.  So that idea was flushed all the way to Tartarus.

Let it be made very clear that DBTABLE does not offer a means to see the ghosts.  Paul and I agree that the other article that mentioned DBTABLE really should have been referring to DBCC Page instead.

Despite flushing the idea to Tartarus, it was not a fruitless dive.  It just was meaningless for the purpose of showing ghosts via that DBCC command.  I still gained value from the dive!!

All of that said, the remainder of the plan still applies and it should be fun.

Really, at this point what is there that hasn’t been done about the ghosts?  Well, if you are well tuned to these apparitions, you may have received the urge to explore them with Extended Events – sometimes called XE for short.

As has been done in the past, before we board Charon’s boat to cross the River Styx to Hades to find these ghosts in Elysium, one really needs to run the setup outlined here.

With the framework in place, you are now ready to explore with XE.

Look at that! There are several possible events that could help us track these ghosts.  Or at the least we could get to know how these ghosts are handled deep down in the confines of Hades, err I mean the database engine.

Ghost_XE

 

From these possible events, I opted to work with ghost_cleanup and ghost_cleanup_task_process_pages_for_db_packet.  The sessions I defined to trap our ghost tracks are as follows.

You can see there are two sessions defined for this trip down the Styx.  Each session aptly named for our journey.  The first (GhostHunt) is defined to trap ghost_cleanup and sends that information to a histogram target.  The second (SoulSearch) is defined to use the other event, and is configured to send to the ring_buffer.  Since the second event has a “count” field defined as a part of the event, it will work fine to just send it to the ring buffer for later evaluation.

Once I have the traps, I mean event sessions defined, I can now resume the test harness from the delete step as was previously done in previous articles.  The following Delete is what I will use.

Prior to running that delete though, I checked the Event Session data to confirm a starting baseline.  Prior to the delete, I had the following in my histogram target.

 

predelete_count

 

After running the delete, and checking my histogram again, I see the following results.

post_count

 

You can see from this that in addition to the 25 pre-existing ghosts, we had another 672 ghosts (666 of which were from the delete).

This is how I was able to investigate the GhostHunt Extended Event Histogram.

But what about looking at the other event session?

Let’s look at how we can go and investigate that session first and then look at some of the output data.

ghostclean

 

Cool!  Querying the SoulSearch session has produced some information for various ghosts in the database.  Unlike the histogram session that shows how many ghosts have been cleaned, this session shows us some page ids that could contain some ghosts – in the present.  I can take page 1030111 for instance and examine the page with DBCC PAGE as follows.

 

 

pagealtLook at that page and result!! We have found yet another poltergeist.

RIP

Once again we have been able to journey to the depths of the Database engine and explore the ghosts that might be there.  This just happens to illustrate a possible means to investigate those ghosts.  That said, I would not necessarily run these types of event sessions on a persistent basis.  I would only run these sessions if there seems to be an issue with the Ghost cleanup or if you have a strong penchant to learn (on a sandbox server).

Some good information can be learned.  It can also give a little insight into how much data is being deleted on a routine basis from your database.  As a stretch, you could even possibly use something like this to get a handle on knowing the data you support.  Just be cautious with the configuration of the XE and understand that there could be a negative impact on a very busy server.  And certainly proceed at your own risk.

Database Ghosts

phantasmripRecently you may have seen my first article on this topic over at SQL Solutions Group.  If not, here is the link so you can read that article first before proceeding here.  This article is intended as a first of two part follow-up to that article.

Now that you have read that other article, we can recap it a little bit.

You will recall that in that article, I discussed the presence of Ghosts in your database.  I also discussed that those ghosts are a good thing.  They have some benefits to them, of which is a bit of a performance boost for some operations like the rollback of a delete.

In that article I discussed one method with which you could see these ghost records.  In this article, I would like to share an alternate method to be able to see these ghosts.

In order to explore this alternate means, let’s go ahead and follow the first few steps from the other article to get the setup complete so our second ghost hunting foray can begin.

Now with the setup complete, we should once again confirm that we have appropriate data available for the hunt.  Once again a simple query can suffice to show the data.

Upon execution of the check script, we should see something similar to the following data-set.

datasample

 

Great, the data is confirmed and we should have a wonderful chance to find some ghosts once again.  In the previous attempt, we needed an additional plasma blaster in the form of a trace flag.  In this attempt we will hunt these ghosts without that tool and see what we can find.  Why attempt it in this way?  Well, it is simply because I’d rather not use a trace flag if it is not necessary.  If you recall, that trace flag had a couple of noted effects.  One of the effects was that it turned off the ghost cleanup process.  If I can avoid it, I’d rather leave the containment unit in tact.

Now, due to that clerical error of putting Halloween on the wrong date, we need to follow the prescribed policy to delete records prior to creating the proper records.

Notice that we issued the delete in a transaction this time around.  We are going to leave that transaction open for a bit while we hunt those ghosts.

The first step is to verify that some ghosts might be present.  To do that we should run a query such as the following.

From that query we should see something like the following.

idxstats_ghosts

Once again we are on the right track.  We can further confirm the existence of these ghosts through a little more investigation and monitoring.  Let’s try the trick with the dblog function again.

With that query, we should see something like the following result set.

dblog_ghosts

 

Very cool.  We once again can see that these phantasms are in the database.  We have enough information that we can proceed on to the next stage.  We can pass the PageID into DBCC PAGE in order to investigate the ghosts on the page.  If we use the PageID that is circled with the green in the preceding result set, we can get a better feel for these specters.

And we may see results such as the following.

page_ghosts2

Recall that the log says this page has ghost records on it.  When we check the page with DBCC PAGE we can definitely see that there are ghosts on the page.  This is very cool.  Now, had we tried to check for ghost records on the PFS page we would not be able to see the ghost count like we were able to see by enabling the TF.

Once again we have been able to display the existence of ghosts in the database.  In order to get these ghosts to move on from the database to their afterlife, we merely need to commit the transaction or roll back the transaction.

Stay tuned for the next article in this mini-series about ghosts.  Who knows, we may even have a bonus Halloween article since this is Halloween month.

Part III of the series can now be found here.

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