Category Archives: SQL Server
Let’s face it: column enlargement is a very sensitive topic. I get thousands of emails every month on this particular topic, although most of them end up in my spam folder. Go figure…
The inconvenient truth is that enlarging a fixed size column is a long and painful operation, that will make you wish there was a magic lotion or pill to use on your column to enlarge it on the spot.
Unfortunately, there is no such magic pill, but turns out you can use some SQL Server features to make the column enlargement less painful for your users.
First, let’s create a table with one smallint column, that we will try to enlarge later.
-- Go to a safe place USE tempdb; GO IF OBJECT_ID('EnlargeTest') IS NOT NULL DROP TABLE EnlargeTest; -- Create test table CREATE TABLE EnlargeTest ( SomeColumn smallint ); -- Insert 1 million rows INSERT INTO EnlargeTest (SomeColumn) SELECT TOP(1000000) 1 FROM master.dbo.spt_values AS A CROSS JOIN master.dbo.spt_values AS B;
If you try to enlarge this column with a straight “ALTER TABLE” command, you will have to wait for SQLServer to go through all the rows and write the new data type. Smallint is a data type that is stored in 2 bytes, while int requires 4 bytes, so SQL Server will have to enlarge each and every row to accommodate 2 extra bytes.
This operation requires some time and also causes a lot of page splits, especially if the pages are completely full.
SET STATISTICS IO, TIME ON; -- Enlarge column ALTER TABLE EnlargeTest ALTER COLUMN SomeColumn int; SET STATISTICS IO, TIME OFF; /* (1000000 rows affected) SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 0 ms. Table 'EnlargeTest'. Scan count 9, logical reads 3001171, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 8, logical reads 2064041, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. SQL Server Execution Times: CPU time = 13094 ms, elapsed time = 11012 ms. */
The worst part of this approach is that, while the ALTER TABLE statement is running, nobody can access the table.
To overcome this inconvenience, there is a magic column enlargement pill that your table can take, and it’s called Row Compression.
Let’s try and revert to the original column size and take the Row Compression pill:
-- Let's revert to smallint ALTER TABLE EnlargeTest ALTER COLUMN SomeColumn smallint; -- Add row compression ALTER TABLE EnlargeTest REBUILD WITH (DATA_COMPRESSION = ROW);
With Row Compression, your fixed size columns can use only the space needed by the smallest data type where the actual data fits. This means that for an int column that contains only smallint data, the actual space usage inside the row is 1 or 2 bytes, not 4.
This is exactly what you need here:
SET STATISTICS IO, TIME ON; -- Let's try to enlarge the column again ALTER TABLE EnlargeTest ALTER COLUMN SomeColumn int; SET STATISTICS IO, TIME OFF; /* SQL Server Execution Times: CPU time = 0 ms, elapsed time = 0 ms. */
Excellent! This time the command completes instantly and the ALTER COLUMN statement is a metadata only change.
The good news is that Row Compression is available in all editions of SQL Server since version 2016 SP1 and compression can be applied by rebuilding indexes ONLINE, with no downtime (yes, you will need Enteprise Edition for this).
The (relatively) bad news is that I tested this method on several versions of SQL Server and it only works on 2016 and above. Previous versions are not smart enough to take the compression options into account when enlarging the columns and they first enlarge and then reduce the columns when executing the ALTER COLUMN command. Another downside to this method is that row compression will refuse to work if the total size of your columns exceeds 8060 bytes, as the documentation states.
Bottom line is: painless column enlargement is possible, if you take the Row Compression pills. Just don’t overdo it: you don’t want to enlarge your columns too much, do you?
Three years ago, I started to work on a project called ExtendedTsqlCollector. I blogged about it multiple times here on spaghettidba.com.
Even if I received positive feedback, I knew that one aspect was slowing down the adoption of the project: the Data Collector. That particular feature of SQL Server has a very bad reputation for being difficult to set up, customize and monitor. ExtendedTSQLCollector tried to address some of those issues, but the damage was already done and I knew that the Data Collector was already on the verge of extinction.
So, how could I preserve the work done for that project and, at the same time, offer DBAs the ability to set up complex actions in response to events? What I aimed to release was a tool capable of streaming events from a session and perform configurable actions in response to those events, mainly writing to a database table and sending alerts. The tool I had in mind should have to be configured in a simple and straightforward way, possibly with a single configuration file.
So, back to the drawing board. The tool I came up with had ditched the data collector, but it kept as much as possible from the previous project.
I am proud to introduce XESmartTarget: the easiest way to interact with extended events sessions without writing a single line of code.
XESmartTarget uses the Extended Events streaming API to connect to a session and execute some actions in response to each event. The actions you perform can be configured in a simple .json file, which controls the Response types and all their properties.
For instance, if you have a session to capture deadlocks, you may want to be notified whenever such an event is captured. All you need to do is configure XESmartTarget to send an email using the EmailResponse class. You can do that by creating a simple .json file with all the parameters needed:
XESmartTarget will connect to your session and will execute an EmailResponse for every event you capture. What will you see? Not much, because XESmartTarget is a console application that you are supposed to run in the background:
What you will actually see is email messages flowing to your inbox:
This is just an example of what XESmartTarget can do: you already have Response types to write events to a database table or replay execution-related events to a target instance. More Response types are in the works as well, but the good news is that XESmartTarget is open source, so you can code your own ad contribute it to the project on GitHub.
What are you waiting for? Download and try XESmartTarget now!
If you’re working for a big company, chances are that your IT already has a strategy and tools for dealing with backups. Many objects need to backed up (files, emails, virtual machines, databases…) and vendors are happy to provide software solutions for all those needs.
Usually, the first type of object that has to be protected is files: every company, even the smaller ones, have file servers with lots of data that has to be regularly backed up, so the data protection solution found in the majority of companies is typically built around the capabilities and features of backup tools designed and engineered for protecting the file system.
The same tools are probably capable of taking backups of different types of objects, by means of “plug-ins” or “agents” for databases, e-mail servers, virtual machines and so on. Unfortunately, those agents are often delusional and fail to deliver what they promise.
With regard to SQL Server database backups, these are the most common issues:
1. Naming things wrong
It’s not surprising that backup tools built for protecting the file system fail to name things properly when it comes down to database backups. What you often find is that transaction log backups are called “incremental backups” or full backups are instead called “snapshots”, according to whichever the naming convention is in the main file system backup process. It’s also not uncommon to find transaction log backups going under the name of “archive log backups”, because this is what they are called like in Oracle. This naming mismatch is potentially dangerous, because it can trick the DBA into choosing the wrong type of backup. The term “DBA” is not used here by accident, which takes us to the next point.
2. Potentially dangerous separation of duties
Backup tools are often run and controlled by windows admins, who may or may not be the same persons responsible for taking care of databases. Well, surprise: if you’re taking backups you’re responsible for them, and backups are the main task of the DBA, so… congrats: you’re the DBA now, like it or not.
If your windows admins are not ok with being the DBA, but at the same time are ok with taking backups, make sure that you discuss who gets accountable for data loss when thing go south. Don’t get fooled: you must not be responsible for restores (which, ultimately, is the reason why you take backups) if you don’t have control over the backup process. Period.
3. One size fits all
Some backup tools won’t allow you to back up individual databases with special schedules and policies, but will try to protect the whole instance as an atomic object, with a “one size fits all” approach. Be careful not to trade safety for simplicity.
4. Missing backup / restore options
Most (if not all) third-party backup tools do not offer the same flexibility that you have with native backups, so you will probably miss some of the backup/restore options. I’m not talking about overly exotic options such as KEEP_REPLICATION or NEW_BROKER: in some cases you may not be able to restore with NORECOVERY. Whether this is going to be a problem or not, only you can tell: go and check the possibilities of your data protection tool, because you might need a feature that is unavailable and you might need it when it’s too late.
5. Dangerous internal workings
Not all backup tools behind the covers are acting as you would expect. For instance, Microsoft Data Protection Manager (DPM) is unable to take transaction log backups streaming them directly to the backup server, but needs to write the backup set to a file first. I bet you can see what’s wrong with this idea: if your transaction log is growing due to an unexpected spike in activity, the only way to stop if from growing and eventually fill the disk is to take a t-log backup, but the backup itself will have to be written to disk. In the worst case, you won’t have enough disk space to perform the backup, so it will simply fail. In a similarly catastrophic scenario, the transaction log file may try to grow again while the log backup is being taken, resulting in failure to allocate disk space.It is incredibly ironic how you need disk space to perform a backup and you need a backup to release disk space, so I am just going to guess that the developers of DPM were simply trying to be funny when they designed this mechanism.
6. Incoherent schedules
Some backup tools are unable to provide a precise schedule and instead of running the backup operation when due, they add it to a queue that will eventually run everything. This may look like a trivial difference, but it is not: if your RPO is, let’s say, 15 minutes, transaction log backups have to occur every 15 minutes at most, so having transaction log backups executed from a queue would probably mean that some of them will exceed the RPO if at least one of the backups takes longer than usual. Detecting this condition is fairly simple: you just have to look at your backupset table in msdb.
7. Sysadmin privileges
All third-party backup applications rely on an API in SQL Server which is called “Virtual Device Interface” (or VDI in short). This API allows SQL Server to treat backup sessions from your data protection tool as devices, and perform backup/restore operations by using these devices as source/destination.
One of the downsides of VDI is that it requires sysadmin privileges on the SQL Server instance and Administrator privileges on the Windows box. In case you’re wondering, no: it’s not strictly necessary to have sysadmin privileges to back up a database.
8. VSS backups
A number of backup tools rely on taking VSS snapshots of the SQL Server databases. SQL Server supports VSS snapshots and has a provider for that. Unfortunately, it’s not impossible to see VSS backups interfering with other types of backups and/or failures initializing the VSS provider, which require a reboot to fix.
9. VM backups
Some backup vendors are more focused on backing up the whole virtual machine rather than the single database / instance that you want to protect. Taking a whole machine backup is different and you have to make sure that you understand what that means, especially compared to taking full, diff or log backups. For instance, did you know that taking VM backups is based on the snapshot feature of the hypervisor, which in turn runs VSS backups of snapshot-aware software, like SQL Server?
10. Interfere with other features
Oftentimes, these enterprise-grade super-expensive backup tools live on the assumption that they’re the only one tool you will ever use, and refuse to play nicely with other SQL Server features. For instance, they will happily try to back up transaction log for databases that are part of log shipping (see point #3), ending up with broken log chains.
All backup tools that take advantage of the VDI API require that you install an agent application locally on the SQL Server machine. While having an agent running on the windows machine is not overly concerning per se, on the other hand this means that the agent itself will have to be patched and upgraded from time to time, often requiring that you restart the machine to apply changes.
This also means that you might run into bugs in the agent that could prevent taking backups until you patch/upgrade the agent itself.
12. Illogical choices
Some data protection tools will force illogical policies and schedules on you for no reason whatsoever. For instance, EMC Networker cannot take transaction log backups of master and model (which must/should be in simple recovery anyway), so when you schedule transaction log backups for all databases on the instance, it won’t skip them, but take a full backup instead. Both databases are usually quite small, but still, taking a full backup every 15 or 5 minutes is less than ideal.
13. Not designed with availability in mind
Backing up the file system is very different from backing up SQL Server databases, as one might expect. One of the key differences is that with SQL Server databases you don’t have to deal with RPO and RTO only, but the way that you back up your databases can have a serious impact on the availability of the databases itself. To put that simply: if you don’t take transaction log backups, nothing truncates your logs, so it keeps growing and growing until space runs out either on the log file (and the database stops working) or on the disk (and the whole instance stops working). Backup operations are critical for RDBMSs: if something or somebody commits to performing backups every x minutes, that commitment MUST be fulfilled. For the record, many backup tools that offer the “one size fits all” approach will try to take full and transaction logs on the same schedule, so they will simply skip transaction log backups while taking full backups. This means that you might be exceeding your RPO, with no clear indication of that happening.
14. No support for SQL Server compression or encryption
A number of backup tools offer their own compression and encryption features (again, because the file system does not offer those), so they will try in each and every possible way to push their shiny-enterprise-expensive features instead of what you already have.
Compression helps keeping the backup and restore times under control, by keeping the size of the backup sets small: this means that the number of bytes that travels across the network will be smaller. Nowadays, the majority of backup solutions supports Data Domain or equivalent solutions: smart storage appliances that offer powerful compression and deduplication features to avoid storing the same information multiple times. These dedupe features can be incredibly effective and reduce immensely the amount of disk space needed for storing backups. Some data domains offer deduplication inside the appliance itself: data has to travel the network and reach the data domain, which takes care of breaking the file in blocks, calculate a hash on the blocks and store only the blocks whose hash was not found inside the data domain. This behavior is already clever enough, but some data domains improved it even further, with host deduplication (DDBoost, to name the most prominent product). Basically, what happens with host deduplication is that the hash of the blocks is calculated on the host and not on the data domain: in this way, all the duplicate blocks do not need to travel across the network, hence reducing the amount of time needed for backup operations.
These dedupe technologies are incredibly useful and also allow backup admins to show to their boss all those shiny charts that depict how cleverly the data domain is reducing disk usage across the board. This is going to be so amazing that the backup admin will not allow you to deteriorate his exceptional dedupe stats by using any backup option that prevents deduplication from happening. The two main enemies of Data Domain efficiency are compression and encryption in the source data. Compression of similar uncompressed files does not produce similar compressed files, so chances of deduplication are much slimmer. Encryption of backups is non-deterministic, which means that two backup sets of the same exact database will be completely different, bringing down deduplication rates close to zero.
While the need for encryption is probably something that your backup admins could live with, they will try in every possible way to make you get rid of backup compression. Letting the data domain take care of compression and deduplication can be acceptable in many cases, but it must not be a hard rule, because of its possible impact on RTO.
The real issue with deduplication can be dramatically evident at restore time: the advantage of deduplication will be lost, because all the blocks that make up your backups will have to travel across the network.
Long story short: at backup time, deduplication can be extremely effective, but, at restore time, backup compression can be much more desirable and can make the difference between meeting and not meeting your RTO.
15. No separation of duties
What often happens with general-purpose backup tools is that management of a single object type is not possible. A number of tools will allow you to be a backup admin on the whole infrastructure or nothing, without the ability to manage database backups only. This may or may not be a problem, depending on how dangerous your windows admins consider your ability to manage the backup schedules of Exchange servers and file servers.
Some tools offer the possibility to create separate tenants and assign resources and schedules to particular tenants, each with its own set of administrators. This feature often comes with limitations, such as the inability to share resources throughout multiple tenants: if tape drives can be assigned to a single tenant and the company only owns a single tape drive, this option obviously goes out of the table.
16. No management tools
Often, the management tools offered by these backup vendors are simply ridiculous. Some use web applications with java applets or similar outdated/insecure technologies. Some offer command line tools but no GUI tools, some the other way around. The main takeaway is: make sure that your backup vendor gives you the tools that you need, which must include a command line or anything that can be automated.
17. Ridiculous RPO/RTO
The developers of some backup tools (DPM, I’m looking at you) decided that forcing a minimum schedule frequency of 15 minutes was a great idea. Well, in case you’re wondering, it’s not.
Other tools manage the internal metadata so dreadfully that loading the list of available backup sets can take forever, hence making restores excruciating exercises, that often fall outside of the requested RTO.
Make sure that tool you are using is able to deliver the RPO and RTO you agreed upon with the owners of the data.
Bottom line is: don’t let your backup vendor impose the policies for backups and restores. Your stakeholders are the owners of the data and everyone else is not entitled to dictate RPOs and RTOs. Make sure that your backup admins understand that your primary task is to perform restores (not backups!) and that the tool they are using with Exchange might not be the best choice for you. Talk to your backup admins, find the best solution together and test it across the board, with or without the use of third party tools, because, yes, native SQL Server backups can be the best choice for you.
One of the things that really annoys me when presenting is the transition between slides and demos. Usually, I try to improve the process as much as possible by having the least minimum amount of windows open while presenting, so that I don’t land on the wrong window. Unfortunately, that is not always easy.
Another thing that I would like to be smoother is the transition itself. The ideal process should be:
- Leave the powerpoint slides open at full screen
- Switch immediately to the virtual machine with the demos
- Go back to the slides, to the exact point where I left
What I usually do is show the desktop with the WIN+D hotkey, then activate the Virtualbox window with my demos, but this shows my desktop for a moment and I don’t really like this extra transition.
I could also use ALT+Tab to switch to the Virtualbox window, but this would briefly show the list of running applications, which is not exactly what I want.
Turns out that Windows 10 has the perfect solution built-in: Virtual Desktops.
Here is the setup described:
- If you press WIN+Tab, you will see a “New desktop” button on the bottom right corner. Use it to create three desktops:
- desktop 3 for the slides
- desktop 2 for the demos
- desktop 1 for the rest
- Press WIN+Tab, find your virtual machine and move it to desktop 2. It is really easy: you just have right click the window you want to send to a different desktop and select which desktop to use.
- Open your presentation and start it by pressing F5. Again, hit WIN+Tab, find the fullscreen window of your PowerPoint presentation and move it to desktop 3.
- In order to transition from one desktop to another, you can use the hotkey CTRL+WIN+Arrow, as shown in this GIF:
Here it is! Perfectly smooth, a nice transition animation and nothing but your slides and your demos shown to the attendees.
A couple of years ago I blogged about Installing the SQL Server 2014 Language Reference Help from disk.
With SQL Server 2016 things changed significantly: we have the new Help Viewer 2.2, which is shipped with the Management Studio setup kit.
However, despite all the changes in the way help works and is shipped, I am still unable to download and install help content from the web, so I resorted to using the same trick that I used for SQL Server 2014.
This time the URLs and the files to download are different:
- Point your browser to http://services.mtps.microsoft.com/ServiceAPI/catalogs/sql2016/en-us
- Download the Language Reference Files:
If you’re a PowerShell person, these three lines will do:
Invoke-WebRequest -Uri "http://packages.mtps.microsoft.com/sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab" ` -OutFile "sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab" Invoke-WebRequest -Uri "http://packages.mtps.microsoft.com/v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab" ` -OutFile "v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab" Invoke-WebRequest -Uri "http://packages.mtps.microsoft.com/v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab" ` -OutFile "v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab"
- Create a text file name HelpContentSetup.msha in the same folder as the .cab files and paste the following html:
<html xmlns="http://www.w3.org/1999/xhtml"> <head /> <body class="vendor-book"> <div class="details"> <span class="vendor">Microsoft</span> <span class="locale">en-us</span> <span class="product">SQL Server 2016</span> <span class="name">Microsoft SQL Server Language Reference</span> </div> <div class="package-list"> <div class="package"> <span class="name">SQL_2016_Branding_en-US</span> <span class="deployed">False</span> <a class="current-link" href="sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab">sql_2016_branding_en-us(1bd6e667-f159-ac3b-f0a5-964c04ca5a13).cab</a> </div> <div class="package"> <span class="name">v2SQL_Shared_Language_Reference_B4621_SQL_130_en-us_1</span> <span class="deployed">False</span> <a class="current-link" href="v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab">v2sql_shared_language_reference_b4621_sql_130_en-us_1(83748a56-8810-751f-d453-00c5accc862d).cab</a> </div> <div class="package"> <span class="name">v2SQL_Shared_Language_Reference_B4621_SQL_130_en-us_2</span> <span class="deployed">False</span> <a class="current-link" href="v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab">v2sql_shared_language_reference_b4621_sql_130_en-us_2(ccc38276-b744-93bd-9008-fe79b294ff41).cab</a> </div> </div> </body> </html>
- First, set the Help Viewer to open help from the local sources:
- Then select the “Add and Remove Help Content” command:
- This command opens the Help Viewer and asks for the content to add.
Browse to the file you created in step 3.
Click “Add” on all the items you wish to add to the library. In this case you will have only 1 item.
When done, click the “Update” button.
- Unfortunately, during the installation phase of the library item, something crashes and the installation won’t proceed until you tell it to ignore or report the error.
- Despite the crash, everything works as expected and you will find the topic installed in your help library:
Here it is, nice and easy. Hope it works for you too.
Today I published the first release of ForumSurfer, a RSS reader designed explicitly to be a tool for the SQL Server online community.
Here is a screenshot:
ForumSurfer has some unique features that will help you help others online:
- it is designed to help you keep an eye on multiple communities through their RSS feeds
- it opens questions in the integrated web browser
- it can update from the feeds much more often than online RSS readers do
- it has built-in support for boilerplate answers
- it supports high-DPI displays, letting you choose the appropriate zoom level for individual sites
- it can import/export OPML files (you can start by importing the OPML file containing all the online SQL Server communities I’m keeping on the radar)
What are you waiting for? Download now the latest release of ForumSurfer and start being helpful!
One of the most popular posts on this bog describes how to enable bitmap scaling is SSMS on high DPI displays, which is a sign that more and more people are starting to use 4K displays and are unhappy with SSMS’s behaviour at high DPI. The solution described in that post is to enable bitmap scaling, which renders graphic objects correctly, at the price of some blurriness.
The good news is that starting with SSMS 16.3 high DPI displays are finally first class citizens and SSMS does its best to scale objects properly. By default, SSMS will keep using bitmap scaling: in order to enable DPI scaling you will have to use a manifest file.
- Merge this key to your registry:
Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide] "PreferExternalManifest"=dword:00000001
- Save this manifest file to “C:\Program Files (x86)\Microsoft SQL Server\130\Tools\Binn\ManagementStudio\Ssms.exe.manifest” using UTF-8 format:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3"> <asmv3:application> <asmv3:windowsSettings xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings"> <dpiAware>True</dpiAware> </asmv3:windowsSettings> </asmv3:application> <dependency> <dependentAssembly> <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="18.104.22.168" processorArchitecture="X86" publicKeyToken="6595b64144ccf1df" language="*" /> </dependentAssembly> </dependency> <dependency> <dependentAssembly> <assemblyIdentity type="win32" name="debuggerproxy.dll" processorArchitecture="X86" version="22.214.171.124"></assemblyIdentity> </dependentAssembly> </dependency> </assembly>
This is a huge improvement over the bitmap scaling solution we had to use up to now: no more blurriness and proper fonts are used in SSMS.
For comparison, this is how bitmap scaling renders in SSMS 2014:
And this is how DPI scaling renders is SSMS 16.3, with scaling set to 200%:
As you can see, it’s not perfect yet (for instance, I had to change the grid font size to 9pt. in order to have readable fonts).
However, the GUI is much more readable now. For instance, look at the difference in object explorer: (click on the image to open fullsize and see the difference)
Now that your favourite tool is working in high DPI displays, nothing is holding you back from buying one of those fancy 4K laptops!
Brent Ozar recently published the feedback he got on his abstract submissions for PASS Summit 2016 and, as he often does, started a trend which some others followed. I think the feedback is interesting and useful for speakers that plan to improve their own submissions for the years to come, so I decided I will publish my feedback as well.
I did not get selected and, obviously, I would be happier if I got selected instead. This doesn’t mean I have problems with the selection process or the reviewers that implemented it. Instead I’m grateful for the enormous amount of work they did for the community, so a huge thank you goes to the committee.
Every year I see people publicly complain about the selection process or getting mad about being rejected. Folks, get over it: organizers have the right to choose whichever sessions they find more suitable for the Summit. It’s their responsibility to put together the best possible agenda and that doesn’t necessarily include your session.
That said, this is my feedback:
Responding to Extended Events in near real-time
Not Accepted: Higher rated session selected.
Category: General Session (75 minutes)
Track: Enterprise Database Administration & Deployment
Topic: Performance Monitoring / Tuning / Extended Events / Waits
Abstract: Extended Events provide deep insight into SQL Server’s behavior and allow us to gather information not available by other means. However, compared to other technologies such as SQL Trace and Event Notifications, a way to react to the events as soon as they happen seems to be lacking.
In this session we will see how the Extended Events streaming API can be used to process events in a near real-time fashion. We will demonstrate how this technology enables new possibilities to solve real world problems, such as capturing and notifying deadlocks or blocking sessions.
Prerequisites: Extended Events basics, C# basics, Powershell basics. The amount of coding required is in line with the average DBA skills.
Goal1: Introduce Extended Events and compare them with other monitoring technologies available in SQL Server
Goal2: Introduce the Extended Events streaming API and demonstrate how it can be used to process the events as soon as they occur, without shredding XML.
Goal3: Demonstrate how the Extended Events streaming API can be used to solve real world problems, such as building a monitoring and alerting solution for deadlocks and blocked sessions.
Needs more specifics in abstract.
A : 4 The abstract digs a little deeper on what’s being offered by XEs, and what needs to be done to efficiently capture events in near real-time without bogging down the system
T : 5 The topic matches with the goals – and many people hesitate capturing large amounts of .xel files fearing shredding the xml. This session offers a new approach to capturing the same using streaming APIs, with C#/PowerShell
S : 5 Prereqs are a little steep, but given the outcome – justified, and will interest people.
Level looks ok for the prereqs and goals. Topic is ok. Abstract is good overall. Only issue is the second sentence reads a little oddly.
Abstract: Well written abstract with strong supportive goals. Topic: Great topic! Subjective: This sounds like a very interesting session. Taking xEvents to the next level. I would attend this session. I think it will be a large draw!
Feedback on comments:
“Needs more specifics in abstract”. What kind of specifics is needed in the abstract? A clue would be helpful here.
A/T/S: what do these letters stand for? I suppose they mean Abstract, Topic, Subjective. What do the numbers stand for? A mark maybe? Again, no explanation.
“The second sentence reads a little oddly”. I really don’t understand grammar or language comments. It’s not a conference on the English language and non-native speakers are already disadvantaged enough without being constantly reminded that their language skills can’t compare to Shakespeare’s. Speakers names are stripped away from the sessions, so the reviewers may not be aware that the session comes from a foreigner. If the topic is good and fits what the organizers are looking for, minor grammar/language mistakes can be fixed. BTW, one of the reviewers told me that when multiple sessions are on a tie, language is the tie breaker. Questionable, but understandable.
The feedback itself is not very useful for improving this submission for next year.
SQL Server Infernals: Worst Practices in Action
Not Accepted: Other sessions selected based on building a balanced program for track coverage, speaker coverage, topic coverage, and session rating.
Category: General Session (75 minutes)
Track: Enterprise Database Administration & Deployment
Topic: Internals: Storage Engine / Query Engine / Compression
Abstract: Let’s face it: Best Practices are too many to really know them all and choose which ones should be applied first. Does your telephone ring all the time? Do your users ask for that “quick report” that instead takes ages and keeps changing every time you think it’s done?
Have you ever thought that in dire times avoiding Worst Practices could be a good starting point and you can leave fine tuning for a better future? If the answer is “yes”, then this session is for you: we will discover together how not to torture a SQL Server instance and we will see how to avoid making choices that in the long run could turn out to be not as smart as they looked initially.
Prerequisites: Basic database design skills, basic development concepts, basic database administration skills.
Goal1: Demonstrate how bad Database Design decisions (irresponsible denormalization, EAV, bad data types, wrong or missing primary keys) can haunt a project through its whole lifetime.
Goal2: Illustrate how bad development practices (SQL Injection, RBAR, poor or no testing) can hurt performance, put security at risk and pose serious threats to the success of our projects.
Goal3: Enumerate and explain the worst installation and administration practices for SQL Server instances, offering the correct alternatives. Topics covered: HW choice, OS policies, security, ongoing administration, monitoring and tuning.
Topic: I like goals
Subjective rating: interesting, but level too low
Abstract: The outline and details of this abstract are well written
Topic: This is a great topic
Subjective: I may attend this session
The outline does not seem to clearly describe the contents of the presentation. The level of detail seems low – more detail might help attendees decide on value of attending. The title may not attract the appropriate attendees – it seems a little vague.
Abstract: Abstract is a little muddled. Goals are clearly laid out. Goals seem to contain the entire gamut of SQL Server. Perhaps a more focused area of SQL Server would help.
Topic: Title is cute.
Subjective: Could be a fun session.
Feedback on comments:
“Level too low”. Level is intentionally low: it’s meant as an introductory session. What to avoid is exactly that: an introductory topic for beginners. Have you ever noticed that basic introductory sessions pack the room? Should we take it as a clue that attendees want 100-level sessions? Apparently not.
“The outline does not seem to clearly describe the contents”. True, I agree. Next time I submit this session I will include in the abstract more details about the contents. It seems that including those details in the goals is not enough.
“Goals seem to contain the entire gamut of SQL Server”. True. I don’t see how this is a bad thing for an introductory session.
This feedback is much more useful than the other ones.
The shape of your Workload: Benchmarking and Baselining
Not Accepted: Higher rated session selected.
Category: General Session (75 minutes)
Track: Enterprise Database Administration & Deployment
Topic: Performance Monitoring / Tuning / Extended Events / Waits
Abstract: The key to optimizing SQL Server performance is to establish a performance baseline and thoroughly analyze the workload on the server. Collecting a baseline is not enough: it is important to analyze the workload in order to intervene effectively exactly where performance issues lie.
In this session we will describe the techniques and tools to analyze SQL Server performance and we will introduce benchmarking techniques that allow us to rate our tuning efforts. We will also introduce some tools included in SQL Server 2014, such as the Distributed Replay, and several third-party applications that come at little or no cost, but provide the highest benefit.
Prerequisites: Basic SQL Server performance tuning techniques (DMVs, Performance Counters), basic monitoring techniques (SQL Trace, Extended Events).
Goal1: Introduce SQL Server performance analysis tools (DMVs, Performance Counters, Data Collector) and demonstrate how to use them to collect a baseline.
Goal2: Introduce workload analysis techniques, using SQL Server and third party tools, including cache analysis queries, RML Utilities and ClearTrace.
Goal3: Demonstrate benchmarking techniques which will allow us to compare performance before and after applying tuning measures, using RML utilities, Distributed Replay and Qure Analyzer.
Needs more specifics in abstract.
A : 5 The abstract clearly spells out the need for baseling, and benchmarking, to identify performance workload.
T : 5 The topic maps well with the session goals – and makes use of the Dist Replay Controller/Client to replay the prod workload on lower environments, and making use of RML utils and ClearTrace
S : 5 The prereqs are not steep, and the session offers a lot to replay prod workload on lower envs.
Topic is a good and relevant choice that appeals to a distinct attendee pool. Level appears good for the prereqs and goals.
Abstract is ok. Some word choices make the sentences difficult to follow (ie. ‘intervene effectively exactly’).
Abstract: Well written abstract with strong, supportive goals. Enough information is provided from which an attendee can make an informed decision on whether or not to attend this session.
Topic: Excellent topic. Likely a 200 level session, not 300.
Subjective: Great session which should draw in attendees. This is a skill every database professional needs.
Feedback on comments:
“Needs more specifics in abstract” and “enough information is provided” in the same feedback. Not very helpful.
“Some word choices make the sentences difficult to follow”. I’ve already said what I think about language comments.
Reading the comments, you would think it made the cut, but it didn’t. What can I say? Competition is tough: there are lots of great speakers with lots of great sessions.
“Likely a 200 level session, not 300”. I disagree: I’ve never seen anyone less than experienced fiddling with RML Utilities or distributed replay.
The comments I received this time are less helpful than the ones I got last year on the same exact sessions. Yep: I submitted the same sessions last year and I got very useful comments that I used to improve my submissions this year. Unfortunately, it will be hard to improve next year.
The level discussion is completely subjective. I was under the impression that here in Europe we tend to rate sessions lower than Americans do, so a 200 session in Europe could easily be a 300 session in USA. Maybe my impression was wrong. However, it’s interesting to see how the session that I proposed with level 100 was deemed to be underrated and the one that I proposed with level 300 was deemed to be overrated. Levels are part of the session: the speaker chooses which level to go for and I would have a really hard time as a reviewer arguing against that decision without having seen the session.
Regarding the reason for rejection, I am not completely sure it can be helpful for improving next year’s submissions. For instance, my session on Extended Events got “Higher rated session selected” as the reason for rejection, but looking at the schedule there is no other session on Extended Events (which is quite surprising) and no other session on monitoring (which is even more surprising and maybe a bit disappointing). This means that the higher rated session does not have to be on the same topic, which makes the other reason for rejection (Other sessions selected based on building a balanced program for track coverage, speaker coverage, topic coverage, and session rating) difficult to decipher.
- You’re selling the abstract, not the session
The reviewers are evaluating your abstract, not your session. All your efforts should be pushed towards perfecting your abstract. Craft it as your masterpiece. Start well in advance, don’t wait for the last minute.
- Take as many shots as you can
Looking at the selection process from the outside it’s really hard to tell how it works, so submitting multiple abstracts can increase your chances of scoring a session. Maybe that session that you don’t like is exactly what the committee is looking for. Again, you’re selling only the abstract and if you get selected you have several months to improve the session.
- There’s a review service offered by PASS. Use it.
There is no guarantee that it is going to be the best feedback you will get, but it’s some feedback at least.
- You have friends in your #sqlfamily: ask for advice.
If you don’t trust the feedback that you get from the PASS review service, trust your friends. If you’re submitting for PASS Summit, chances are that you already have spoken at SQLSaturdays or other community events (if not, maybe you should think twice before submitting: PASS Summit is not for inexperienced speakers). In this case, you got in touch with the community leaders in your chapter, who probably keep scoring sessions at Summit year after year: ask them to review your sessions. I am sure that they will have precious suggestions for you.
- If you’re not an English native speaker, ask a native speaker to proofread it
Sure, your English is great. Sure, the reviewers have something to say about native speakers’ English as well. Sure, language should not be the focus of the reviewers. However, see lesson learned #1.
- Speaker/Abstract separation is a joke
If you read Brent’s feedback, one thing emerges quite clearly: in many cases, the reviewers know exactly whose abstract they are reviewing. This might be because they already have seen the session somewhere else or because the abstract contains some “distinctive features” (sp_AskXXX anyone?). This means that some speakers have an advantage over the average Joe, but rightly so: those speakers are awesome and well known for being awesome. I’m not saying that the “Top Guns” can submit their grocery list: what I’m saying is that they are not selling only their abstracts. Now that Brent has published his abstracts, I wonder what would happen next year if somebody submitted one of his sessions… 🙂
Being selected for speaking at the PASS Summit is damn hard. I hope that sharing my feedback will help you improving your submission next year. I also hope that you will find my advice useful, if you dare accepting advice from somebody who never managed to score a session himself.
The next few months will be crazy for me. I will be travelling a lot around Europe, speaking about SQL Server topics.
Here is where you will find me in the upcoming weeks:
- May 4: SQLNexus
SQLNexus is a new conference in Copenhagen and will be the official launch event in Denmark for SQL Server 2016.
I will speak about “Responding to Extended Events in near Real-Time”.
- May 5: SQLBits
SQLBits doesn’t need to be introduced. It’s the biggest SQL Server event in Europe and it will also be the official SQL Server 2016 launch event in UK.
Again, I will speak about “Responding to Extended Events in near Real-Time”.
- May 16: NTK
NTK is a famous conference in Slovenia, which has been running for many years now. This year it will be held in Portorosz, near the Italian border.
It’s going to be fun: I will speak about “Benchmarking, Baselining and Workload Analysis”.
- June 14: INSIDE-SQL
INSIDE-SQL is also a new event, run this year for the first time. It’s an event focused on in-depth concepts, delivered in 75 minutes sessions, with long breaks between sessions, so that attendees can go to the next session without rushing and can hang out with the speakers and ask questions.
I will deliver two sessions:
“Responding to Extended Events in near Real-Time”
“Advanced T-SQL Techniques”
- June 24: SQL Saturday Paris
Free SQL Server training from the 40th floor of the Tour Montparnasse in Paris.What else can I say?
I will be speaking about “New Security Features in SQL Server 2016”
- September 10: SQL Saturday Cambridge
One of the coolest SQLSats around!
This time I’ll be speaking about “SQL Server Infernals”, AKA “how to torture your SQL Server instances to death with worst practices”. It’s going to be fun!
I hope to see you at these super cool events!
This will be no surprise to those who have been working with SQL Server for a long time, but it can be puzzling at first and actually I was a bit confused myself when I stumbled upon this behavior for the first time.
SQL Server treats windows users in a special way, a way that could lead us to some interesting observations.
First of all, we need a test database and a couple of windows principals to perform our tests:
1. In a command prompt, create a windows group named ‘testGroup’
net localgroup testGroup /ADD
2. In a command prompt, create a windows user named ‘testUser’ and add it to the group
net user testUser "testUser" /ADD net localgroup testGroup testUser /ADD
3. In SSMS, create a test database:
CREATE DATABASE testWindowsUser;
Now that everything is set up, we can start our investigation.
You can create a database user for a Windows user with no corresponding login
When dealing with windows users, you don’t need to create a login in SQL Server in order to create a database user, but you can create it directly:
USE testWindowsUser; GO CREATE USER [XPS13-SQLC\testUser]; GO
We just created a user in the database, without creating a login first and without having to add “WITHOUT LOGIN” to the CREATE USER statement. If you search for a login with the same SID in sys.logins, nothing will turn up:
SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%testUser';
login_name user_name default_schema_name ----------- -------------------- -------------------- NULL XPS13-SQLC\testUser dbo
It is interesting to note that the default schema for the user, if you don’t specify one, will be “dbo”.
At this point, the Windows user cannot log in to SQL Server, but the user can be impersonated to perform operations against the databases, in the same exact way as with any other user without login.
Before we proceed with the investigation, let’s clean up our mess:
DROP USER [XPS13-SQLC\testUser];
You can create a database user for a Windows group with no corresponding login
If we try to do the same thing with a Windows group, we get even more interesting findings.
USE testWindowsUser; GO CREATE USER [XPS13-SQLC\testGroup] GO
Again, we did not have to specify an existing login name and we did not have to add “WITHOUT LOGIN”. Looking at the user data in sys.database_principals and sys.logins shows again that no login is associated with this user, but this time we can see that no default schema was set.
SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%testGroup';
login_name user_name default_schema_name ----------- --------------------- -------------------- NULL XPS13-SQLC\testGroup NULL
As common sense suggests, we cannot impersonate a database user that corresponds to a Windows group. If we try that, we are met with an error message.
EXECUTE AS USER = 'XPS13-SQLC\testGroup'; -- '
Msg 15517, Level 16, State 1, Line 85 Cannot execute as the database principal because the principal "XPS13-SQLC\testGroup" does not exist, this type of principal cannot be impersonated, or you do not have permission.
Windows users are granted access through groups in surprising ways
Now the fun begins. Turns out that you can impersonate a Windows user that is not a user in the database, as long as the Windows user is a member of the group.
Let’s grant some permissions to the group and see what happens:
ALTER ROLE db_owner ADD MEMBER [XPS13-SQLC\testGroup]; GO EXECUTE AS USER = 'XPS13-SQLC\testUser'; -- ' EXEC('CREATE VIEW testView AS SELECT 1 AS one'); REVERT; GO
Surprisingly enough, we were able to impersonate a database principal that doesn’t exist at all. In fact we dropped it right before we started to play with the groups, right? Let’s check again the database principals:
SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%test%'; GO
login_name user_name default_schema_name ----------- --------------------- -------------------- NULL XPS13-SQLC\testGroup NULL NULL XPS13-SQLC\testUser XPS13-SQLC\testUser
Wait, what? Who created that user? Looks like SQL Server creates the database user automatically when it needs to impersonate one of the group members that are not created in the database yet.
Another interesting fact is that the default schema of the newly created user matches the user name. If we don’t like that, we can change it afterwards, but wouldn’t it be cool if we could simply change that on the Windows group and let it propagate to the users created during this process? Let’s try and see if this is possible.
-- First let's drop the user and dependent objects DROP VIEW [XPS13-SQLC\testUser].testView; DROP SCHEMA [XPS13-SQLC\testUser]; DROP USER [XPS13-SQLC\testUser]; GO -- Then let's change the default schema for the group ALTER USER [XPS13-SQLC\testGroup] WITH default_schema = dbo; GO -- Let's re-create the view impersonating the user EXECUTE AS USER = 'XPS13-SQLC\testUser'; -- ' EXEC('CREATE VIEW testView AS SELECT 1 AS One'); REVERT GO -- Check if the view is there SELECT OBJECT_SCHEMA_NAME(object_id) AS schema_name, name FROM sys.views WHERE name = 'testView'; GO -- Check database users: SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%test%'; GO
schema_name name ------------ --------- dbo testView login_name user_name default_schema_name ------------ --------------------- -------------------- NULL XPS13-SQLC\testGroup dbo
This time the view was placed in the “dbo” schema as expected (remember? We set the default schema on the group), but the really weird thing is that no new user was added. Why? I couldn’t find any answer in the documentation. It is even more puzzling that SQL Server was able to impersonate a user that is not present at all. Nevertheless, as far as I can remember it has always been like this, at least starting from SQL Server 2005.
To be sure we’re not imagining things, let’s change again the default schema of the Windows group:
-- Note the weird syntax ALTER USER [XPS13-SQLC\testGroup] WITH default_schema = NULL; GO -- Let's re-create the view impersonating the user EXECUTE AS USER = 'XPS13-SQLC\testUser'; -- ' EXEC('CREATE VIEW testView AS SELECT 1 AS One'); REVERT GO -- Check if the view is there SELECT OBJECT_SCHEMA_NAME(object_id) AS schema_name, name FROM sys.views WHERE name = 'testView'; GO -- Check database users: SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%test%'; GO
schema_name name -------------------- --------------------- dbo testView XPS13-SQLC\testUser testView login_name user_name default_schema_name -------------------- --------------------- -------------------- NULL XPS13-SQLC\testGroup NULL NULL XPS13-SQLC\testUser XPS13-SQLC\testUser
Again, SQL Server creates a new user and assigns it a default schema with the same name. The view was placed in the user’s default schema.
Now let’s revert to a clean database and drop some objects.
DROP VIEW dbo.testView; DROP VIEW [XPS13-SQLC\testUser].testView; DROP SCHEMA [XPS13-SQLC\testUser]; DROP USER [XPS13-SQLC\testUser]; GO
In order to have a complete picture, we can now check what happens if we create a login for the windows user.
CREATE LOGIN [XPS13-SQLC\testUser] FROM WINDOWS; GO EXECUTE AS LOGIN = 'XPS13-SQLC\testUser'; EXEC('CREATE VIEW testView AS SELECT 1 AS One'); REVERT GO -- Check if the view is there SELECT OBJECT_SCHEMA_NAME(object_id) AS schema_name, name FROM sys.views WHERE name = 'testView'; GO -- Check database users: SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%test%'; GO
schema_name name -------------------- --------------------- XPS13-SQLC\testUser testView login_name user_name default_schema_name -------------------- --------------------- -------------------- NULL XPS13-SQLC\testGroup NULL XPS13-SQLC\testUser XPS13-SQLC\testUser XPS13-SQLC\testUser
Again, SQL Server creates a new database user for this login and a schema with the same name. The view gets added to the user’s default schema.
What is interesting to note is that we could access the database by logging in as the Windows user, without having an explicit permission path to allow it. Only after accessing the database an explicit database user is created.
If we try the same thing with the default schema set to “dbo” on the windows group, the behavior matches what we got for the user:
-- let's try again with a default schema on the group ALTER USER [XPS13-SQLC\testGroup] WITH default_schema = dbo; GO -- cleanup DROP VIEW dbo.testView; DROP VIEW [XPS13-SQLC\testUser].testView; DROP SCHEMA [XPS13-SQLC\testUser]; DROP USER [XPS13-SQLC\testUser]; GO EXECUTE AS LOGIN = 'XPS13-SQLC\testUser'; -- ' EXEC('CREATE VIEW testView AS SELECT 1 AS One'); REVERT GO -- Check if the view is there SELECT OBJECT_SCHEMA_NAME(object_id) AS schema_name, name FROM sys.views WHERE name = 'testView'; GO -- Check database users: SELECT svp.name AS login_name, dbp.name AS user_name, dbp.default_schema_name FROM sys.database_principals AS dbp LEFT JOIN sys.server_principals AS svp ON dbp.sid = svp.sid WHERE dbp.name LIKE '%test%'; GO
This means that this behavior has to be taken into account when we’re querying permissions on the databases to see who can access what. In order to know whether a windows user is member of a windows group, we can use the system function IS_MEMBER().
In our case, it would be enough to call the function in this way:
EXECUTE AS LOGIN = 'XPS13-SQLC\testUser'; -- ' SELECT IS_MEMBER('XPS13-SQLC\testGroup'); REVERT GO
Unfortunately, there is no additional parameter available to specify which windows user to test for group membership and the function will always test against the current login. This has two important consequences:
- To test multiple logins, we need to impersonate them one at a time, which is difficult to achieve in scripts.
- There is no way to test database users: impersonating the database user will not be enough to test the windows group membership for the windows user associated to the database user.
Summing it up, this is what we have:
|Windows user impersonated as||Group’s Default Schema set||New user added||New user’s schema|
|Database User||No||Yes||User name|
The dbo user can be mapped to a non-existing Windows User
This is extremely tricky and I was bitten by this behavior recently, wasting countless hours trying to figure out what was happening.
Imagine that a developer creates a database in the development environment, while logged in with Windows authentication. This is a very common scenario, both if you’re using a centralized development server or developers’ workstations.
When development is complete, the developer hands us a database backup to restore in production, because the database already contains some data (built-in values in lookup tables or something else required by the application). We restore the database in production, where the developer does not have a login, confident that he will be unable to access it. Well, that’s not exactly what is going to happen.
Let’s see it with an example:
-- Grant dbcreator permissions to the windows user ALTER SERVER ROLE dbcreator ADD MEMBER [XPS13-SQLC\testUser] GO -- The user creates a database. It may happen in development, right? EXECUTE AS LOGIN = 'XPS13-SQLC\testUser'; CREATE DATABASE testWindowsGroup REVERT GO -- Let's pretend that developers finish working with the database -- and ask to move it from development to production -- He takes a backup and we restore it to production BACKUP DATABASE testWindowsGroup TO DISK = 'c:\temp\testWindowsGroup.bak'; GO -- We don't have two separate servers to test, we will simulate -- the same situation by dropping some objects. Let's drop the database. DROP DATABASE testWindowsGroup; GO -- Now let's drop the associated windows login DROP LOGIN [XPS13-SQLC\testUser] GO -- The database gets restored in production (again, we will use the same instance, -- but the main point is that the login of the database owner is not present). RESTORE DATABASE testWindowsGroup FROM DISK = 'c:\temp\testWindowsGroup.bak' GO -- Who's the owner of the database? You, the DBA. Looking good. SELECT db.name, svp.name FROM sys.databases AS db INNER JOIN sys.server_principals AS svp ON db.owner_sid = svp.sid WHERE database_id = DB_ID('testWindowsGroup');
Everything is set up the way it should: the database is restored to production, the DBA is the database owner, the developer has no access to the database and everybody is happy.
Now imagine that a new totally unrelated database gets added to the production instance, a database where everybody in the company must have read-only access. We create a new login for a Windows group that includes all authorized logins and we grant access to the new database.
Again, let’s see it with an example (using tempdb):
-- Let's add a login for the group and grant permissions on another database -- I will use tempdb here, but it could be any other database. CREATE LOGIN [XPS13-SQLC\testGroup] FROM WINDOWS; GO USE tempdb; GO -- The group gets added to tempdb with read-only permissions CREATE USER [XPS13-SQLC\testGroup] FOR LOGIN [XPS13-SQLC\testGroup]; ALTER ROLE db_datareader ADD MEMBER [XPS13-SQLC\testGroup]; GO -- Let’s go back to the database we restored previously USE testWindowsGroup; GO -- Now see what happens: EXECUTE AS LOGIN = 'XPS13-SQLC\testUser'; -- ' EXEC('CREATE VIEW testView AS SELECT 1 AS One'); REVERT GO
WTF? A windows user that has no matching SQL Server login could create a view in a database where no matching user exists? How could that happen?
-- Let's check the permissions of this user: EXECUTE AS LOGIN = 'XPS13-SQLC\testUser'; -- ' SELECT IS_ROLEMEMBER('db_owner') AS IAmDbOwner, IS_MEMBER('db_owner') AS AgainDbOwner; REVERT GO
IAmDbOwner AgainDbOwner ----------- ------------- 1 1
Weird. The login of the Windows user seems to be the database owner, but we checked upon restore that the DBA is the database owner. Moreover, there is no explicit login in the server for this Windows user and the only Windows group that contains this user does not have access at all to the database: how is this possible?
The answer is buried inside the database principals table:
-- The sid of the dbo user is still the sid of the user that created the database, -- even if the windows user is not a login in SQL Server SELECT sid FROM sys.database_principals WHERE name = 'dbo';
We got access to the database thanks to a windows group added to grant access to a totally unrelated database. The group has no permissions whatsoever on the database, but it allows its members to log in: the actual permissions on the database are granted through the SID of the dbo user.
This can be spotted immediately with the GUI, which is a fact that hides the resolution even more from experienced DBAs that don’t use the GUI at all.
Windows authentication comes handy most of the times and it offers better protection compared to SQL Server authentication, but sometimes the way SQL Server treats Windows users can be puzzling.
Don’t take things for granted and check now if you really understand who has access to your databases: the answer might be very different from what you expect.
P.S. If you’re wondering why I placed a comment with a quote after every “EXECUTE AS” statement, it’s just to fix this WordPress wacky syntax highlighter going nuts.