Sitecore Commerce 8.2.1 MSCS_Admin Database & the Tyranny of SQLOLEDB.1

Disclaimer: this is a journey of discovery and not a manual on database best practices for Sitecore Commerce 8.2.1.

You don’t see a lot of talk about disaster recovery and Sitecore Commerce — getting the regular implementation to work well is enough of a challenge that DR and Sitecore Commerce feels like a mythical Phase 5 of a project with only 4 Phases.

I want to write-up some notes and exploratory digging I did recently on the topic of disaster recover and Sitecore Commerce 8.2.1. You could even consider it a poor man’s option for database high availability that doesn’t incur the licensing costs of SQL Server Always On . . . but it’s probably best if you forget I ever mentioned that. Just because something can be done, doesn’t mean it should be done. I get in trouble sometimes presenting cans when I should just stick to the shoulds, but sometimes there’s real opportunity in those cans so I just can’t resist. Reader: beware.

Enough preamble. To simplify the scope of this post, I’m going to focus on database disaster recovery since it’s distinct for Sitecore Commerce 8 from “regular” Sitecore without Commerce. It’s because Commerce has a decade (or two!?) of COM code and legacy architectures that are way down deep in the Sitecore Commerce 8.2.1 system.

The crux of the challenge I was tasked with addressing was the inability to identify a SQL Mirror as part of a Sitecore Commerce 8.2.1 project. Many customers have used SQL Server database “Mirroring” as the high availability option for Sitecore databases for a long time because it was the only one officially supported by Sitecore. As this documentation explains, only since Sitecore 8.2 has “Always On” been an option for an officially supported Sitecore implementation. I know — many projects are successful with newer SQL Server approaches or RDS on AWS etc, but in my role at Rackspace, we have to walk the line of what Sitecore officially supports from top to bottom to ensure clean lines of escalation in the event of any issue; this is appealing to risk-averse customers, those with aggressive SLAs, etc.

To use SQL Server Mirroring one must identify a failover partner in each of your SQL Server database connections defined in ConnectionStrings.config like:

FailoverPartner

In Sitecore Commerce 8.2.1, however, this is the interface you have to manage a database connection for the MSCS_Admin database . . . there is a single endpoint (server name) and no provision for a failover partner. It comes down to a limit of the SQLOLEDB.1 provider, I believe. It’s fine for a SQL Server Availability Group listener where you get a service to route requests between the Always On SQL Server nodes, but this Commerce UI is incompatible with SQL Server Database Mirroring:

DRCommerce

I set to digging and found some old documentation on a Windows Registry key for Commerce Server 2007 edition and the MSCS_Admin database. I’ll assume you understand the primacy of the MSCS_Admin database for Sitecore Commerce 8.2.1 — if that’s not the case, you can review this material for background, but trust when I explain that MSCS_Admin is the administrative heart of Sitecore Commerce 8.2.1. This SQL query shows how the ResourceProps table in MSCS_Admin stores all the dependent database connections for Inventory, Catalog, Profiles, etc:

Now, the old documentation I found mentions an encrypted registry key named ADMINDBPS that is where Commerce Server Manager, the desktop tool, reads and writes the actual database connection string for the MSCS_Admin database. Since I can’t insert a DB Mirroring Failover Partner into the desktop tool, I figured I could engineer a work around using this registry key as leverage.

The problem, however, is this documentation I was reading was from 2006 and no longer reflected reality. It also mentioned how this approach wasn’t supported by Microsoft and came with every cautionary disclaimer. Sounds like fun, right? The Windows Registry Key schema had changed, but not the overall approach and after doing some digging I found HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\CommerceServer was where this newer version of Sitecore Commerce had reorganized the Registry state and that’s where ADMINDBPS was hiding!

admindbps

The connection string to MSCS_Admin was still encrypted . . . sure . . . but nothing the .Net System.Security.Cryptography namespace couldn’t resolve.

The connection string to MSCS_Admin was still buried in the Windows Registry . . . sure . . . but nothing the .Net Microsoft.Win32 namespace couldn’t resolve.

Here’s the code I used to read this value:

RegWork

Since we’re getting this value, we might as well just add the set logic too, right?

RegWork2

Yes, let the Registry edits flow through you!

I told you this was a reader: beware type of post.

Taking a step back, remember my original challenge was finding a way to weave support for SQL Server DB Mirroring into Sitecore Commerce 8.2.1 and I found the MSCS_Admin database connection to be my focus? We can wrap the above c# code into a command line tool that can be run in a database failover situation to update the MSCS_Admin database connection automatically — changing to the intended failover partner defined as part of the conventional SQL Server Database Mirroring. We could schedule this c# logic to run once every 30 seconds in Windows Task Scheduler, for example, conditionally changing the MSCS_Admin database connection in the event of a failover scenario. The MSCS_Admin database connection string could update automatically. I’m not going to present this as a viable alternative to SQL Server Always On for many many reasons, but you achieve some semblance of it with robust enough PowerShell.

If you’re scratching your head here because I work with customers who are risk averse or have critical Sitecore SLAs that would still rely on the above Registry hacks, you’re not quite getting my point. I’m sharing this because it’s possible, it’s interesting to know how the guts of Sitecore Commerce 8.2.1 are working, and others may also learn from this. While it’s theoretically an option to introduce some automated failover logic through this method, it’s an uncomfortable hack. Based on my testing, though, it works.

Honestly, this technique is most appropriate in a disaster recovery scenario where a set of database servers are unavailable (and then this can apply whether using SQL Server  Always On or DB Mirroring — doesn’t really matter). Instead of considering this a high availability solution, it’s a DR solution.

I spoke with some on the Sitecore Commerce technical team about this and they agreed this was a bit crazy, but it works (and also I shouldn’t quote them directly). They also pointed out how you don’t have to store MSCS_Admin connections in the Windows Registry and that as part of the PaaS support evolving through Sitecore Commerce there was a “Registry Free” deployment option for Sitecore Commerce 8.2.1 that I didn’t know about for this version. With this technique, you can use a ConnectionString defined like the others for Sitecore (see some details here)

<connectionStrings>
 <add name="ADMINDBPS" connectionString="<your MSCS_Admin connection string" />
</connectionStrings>

I haven’t experimented with the Registry Free deployment for Commerce 8.2.1 but I’d like to see if it avoids the tyranny of the SQLOLEDB.1 provider and would let us add the Failover Partner logic to a connection string. I think this blog post may have a Part 2 . . . but I’m not sure how much further down this rabbit hole it’s worth tunneling.

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The case of the Inventory gotcha with Azure SQL and Sitecore Commerce 8.2.1

I only recently discovered comments to this blog were going into an unmonitored spam folder — my apologies if anybody had their hearts set on a response to their comment!  In scanning some of those comments, I thought a proper response was warranted to one note on a piece I wrote about a hard to find Sitecore Commerce configuration setting.

I started that post by writing:

After recently swapping the backing store from Azure SQL to SQL Server (due to an interesting Inventory gotcha with the Reference Storefront that I’ll maybe share at some other time), I’m finding nooks and crannies of configuration I never knew existed with the Commerce product until now.

This post discusses the interesting Inventory gotcha with the Sitecore Commerce storefront implementation. I should point out this is relevant to Sitecore Commerce 8 and I’ve not tested this specifically with Sitecore Commerce 9, but I assume it’s been addressed in version 9 by either not using the same Reference Storefront for Commerce (in version 9 you’d be steered to an SXA UI instead of the older “Reference Storefront”) or by the general platform improvements in Sitecore Commerce 9.  I guess you can stay tuned for Sitecore Commerce 9 news on this front!

The Problem Scenario

This is IaaS VMs running Sitecore 8 (conventional IIS, not PaaS) and using the Sitecore Commerce 8.2.1 release in a scaled Sitecore environment. Azure SQL was chosen as the database technology for a variety of reasons I need not go into. This implementation used separate Commerce catalogs for CM servers and CD servers, to provide the “publish workflow” behavior Sitecore uses for marketing content; this is accomplished for Commerce via the Staging Service.

One tricky area when using multiple Commerce catalogs is Inventory. A late-breaking customer requirement was the need for inventory updates to flow real-time between content management and content delivery servers, so nobody sees stale inventory data. Don’t you love those late-breaking customer requirements?

This can be handled in different ways, but the method appropriate to this project was to use a single Inventory database that both Sitecore CM and CD environments would reference for inventory data.  Commerce Server Manager presents this in the UI as the “Inventory” resource under the Commerce site:

commerceInventory

It’s smart to have separate databases for product catalog and inventory, and we set this solution up to have multiple catalogs (one for CM and one for CD) with a shared Inventory database so that data was always realtime.

The crux of the problem was the mechanism Sitecore’s Reference Storefront uses to coordinate Inventory queries between the two Commerce catalog databases — it’s called Cross Database Query and it’s not supported the same way in Azure SQL as it is in conventional SQL Server.  You can do cross database queries with Azure SQL, just not the way the Reference Storefront for Sitecore Commerce depends on it.

The exception we would see was as follows:

SqlException (0x80131904): Reference to database and/or server name in ‘CFSolutionStorefrontSite_productcatalog.dbo.Habitat_Inventory_InventorySkus’ is not supported in this version of SQL Server.

The above was followed by a fair amount of StackTrace such as:

System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) +3189408
 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) +753
 System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) +5042
 System.Data.SqlClient.SqlDataReader.TryConsumeMetaData() +87
 System.Data.SqlClient.SqlDataReader.get_MetaData() +101
 System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption) +590

You get the idea.

What We Considered

After considering our Sitecore Commerce configuration and confirming it was solid, the exception next had us examining Azure SQL compatibility settings, but that wasn’t the issue.

We determined we could do an import/export of Inventory data.  Maybe the Sitecore publish:end event could push inventory changes to the CD servers, where they store inventory in an XML file and on publish:end:remote we could import that XML data into the Content Delivery servers.

We could remove publishing from the equation and use a scheduled <agent> to move Inventory data around.

What We Actually Did

The import/export options were never going to be truly realtime, at least not sufficiently “real” for our project and their inventory requirements. So we swapped out the database back-end and used SQL Server in IaaS VMs instead. Cross database query worked as expected, and we could use a central Inventory database with multiple Commerce Catalog databases for CM and CD sites. It worked as it should.

This concludes the tale of the interesting Inventory gotcha around Sitecore Commerce 8.2.1 — this should close the loop with the initial post from a few months ago, I hope this helps out somebody else!

Sitecore 9 SIF – WebDeploy Gets What WebDeploy Wants

I’ve been doing a lot with Sitecore 9 lately as we work to retrofit automation processes into the new Sitecore Installation Framework (SIF) paradigm.  It will be nice to have Sitecore’s approved way of provisioning a Sitecore environment with JSON and PowerShell . . . but it’s a shame we’ve spent years investing in our own libraries doing the same thing with essentially the same technologies 🙂

That may sound like sour grapes from me, but that’s not really the case.  It’s just not trivial to master the SIF specifics at the same time as one is digesting the whole of Sitecore 9 with xConnect, Sitecore PaaS, and Sitecore 9 for Commerce coming any day now.  Taking a step back, I’m now in the process of crafting PowerShell to automate the prequisites for Sitecore 9 SIF — and if that strikes you as ironic, I think you get my point.  Can a publicly available Sitecore 9 bootstrapper be that far away?  Lets just hope it’s not a custom miasma of JSON with PowerShell and with it’s very own prerequisites to perpetuate the cycle!

Just an aside: I think many of us are doing the same thing, just refer to this effort around Solr or this GUI to layer on top of Sitecore’s new framework.  Both these efforts, and many others, are excellent, but illustrate how Sitecore 9 SIF feels unfinished.

With that all off my chest . . . I thought I’d share a gotcha with SIF that I haven’t seen documented elsewhere in case it helps others.  Categorize this as a self-inflicted Sitecore 9 SIF wound, I can’t really blame the framework here — the exception message is actually very helpful.  While the WebDeploy task was running with any Sitecore 9 SIF installation, I would get this error every time from a few of our servers:

Could not deploy package.
Internal Error. The database platform service with type Microsoft.Data.Tools.Schema.Sql.Sql130DatabaseSchemaProvider is not valid. You must make sure the service is loaded, or you must provide the full type name
of a valid database platform service.

Here’s how it looks in situ as part of the InstallWDP : WebDeploy task with SIF:

scriptdom2

This didn’t happen on development environments, but on some build servers or new virtual machines.

I reviewed the Sitecore installation documentation but couldn’t see anything explicitly speaking to this, and I verified the SQL Server DAC fx was consistent with the installation docs.  My initial solution was to install SQL Server Management Studio (SSMS) as that package includes the key dependencies for automating SQL Server 2016 the way SIF expects.  Then I realized it’s probably encompassed in this line item tucked into the Installation Guide:

scriptdom

The link https://msdn.microsoft.com/en-us/dn864412 reads more like VS.Net integration tooling when I glanced at it, so I initially dismissed it for my use-case . . . but WebDeploy gets what WebDeploy wants, and to get Sitecore 9 SIF running you’ll need these libraries one way or the other.

This explains why development machines or other servers that had been around a while wouldn’t exhibit this problem — they already had the SQL tooling installed through one means or another.

For posterity, here’s the output from my console in case it helps a web searcher find their resolution . . .

InstallWDP : WebDeploy 
[WebDeploy]:[Path] C:\Program Files\iis\Microsoft Web Deploy V3\msdeploy.exe
Info: Adding MsDeploy.Site (MsDeploy.Site).
Info: Adding database (user id=sqlUserNotTelling;data source=SC9Run482-SQL;initial catalog=xp0482_Processing.Pools)
Info: Initializing deployment: Pending.
Info: Analyzing deployment plan: Pending.
Info: Updating database: Pending.
Info: Creating deployment plan: Pending.
Info: Verifying deployment plan: Pending.
Info: Deploying package to database: Pending.
Info: Creating deployment plan: Running.
Info: Initializing deployment: Running.
Info: Initializing deployment (Start)
Info: Initializing deployment: Faulted.
Info: Initializing deployment (Failed)
Info: Creating deployment plan: Faulted.
Info: Verifying deployment plan: Faulted.
Info: Deploying package to database: Faulted.
msdeploy.exe : Error Code: ERROR_EXECUTING_METHOD
At C:\Program Files\WindowsPowerShell\Modules\SitecoreInstallFramework\1.1.0\Public\Tasks\Invoke-CommandTask.ps1:31 char:13
+ & $Path $Arguments | Out-Default
+ ~~~~~~~~~~~~~~~~~~
 + CategoryInfo : NotSpecified: (Error Code: ERROR_EXECUTING_METHOD:String) [], RemoteException
 + FullyQualifiedErrorId : NativeCommandError
 
More Information: Could not deploy package.
Internal Error. The database platform service with type Microsoft.Data.Tools.Schema.Sql.Sql130DatabaseSchemaProvider is not valid. You must make sure the service is loaded, or you must provide the full type name
 of a valid database platform service.

Sitecore Commerce 8.2.1 Firewalls & Azure SQL Notes

I know Sitecore Commerce 9 is just around the corner, but I know many projects are under way with the current Sitecore Commerce 8.2.1 and I wanted to share some notes we’ve collected on how to work with the technology.

This is from lessons our team at Rackspace has collected, including some exceptionally talented “sales weasels” who have really dug into the Commerce platform with us to determine perf benchmarcks etc — score 1 for the talented sales weasels ξ(^◒^)ξ !

These two links are the key pillars of online documentation for getting started with the product:

http://commercesdn.sitecore.net/SitecoreCommerce/DeploymentGuide/en-us/index.html

http://commercesdn.sitecore.net/SitecoreCommerce/DevOpsGuide/en-us/index.html

As a complement to the above, I’d like to share the following tips we’ve learned on a few Sitecore Commerce 8.2.1 projects . . .

Firewall Settings

We’ve run into issues with both the Sitecore Commerce Staging software and the Profile system; the exceptions are logged to the Windows Event log or the Sitecore logs and can report an ugly COM error such as the following . . .

don't panic
Don’t panic

. . . it turns out that the current documentation doesn’t mention Firewall rules for these two services to operate.  After some investigation we realized we needed to open up ports.  Prior versions of Sitecore Commerce have this article, http://commercesdn.sitecore.net/SCpbCS82/SitecoreCommerceDeploymentGuide/en-us/FirewallPorts.html, and it turns out port ranges 5000-5030 and 507 can be important to proper communications in a distributed Sitecore Comemrce build.

Azure SQL

Everyone is price conscious and Azure SQL can save customers a lot of money over conventional SQL Server.  Documentation online for 8.2 states Azure SQL is supported, but the installation documentation doesn’t treat it as a first-class citizen.  There is this great link, http://commercesdn.sitecore.net/SCpbCS81/SitecoreCommerceDeploymentGuide/en-us/c_UsingAzureSQLwithCS.html, with notes on Azure SQL specific provisioning for Sitecore Commerce — but it’s organized under a PaaS installation topic which hides it from our IaaS Sitecore Commerce eyes.

Generally speaking, the Initialize-CSSite script modifies the SQL database schemas and does not work if you use Azure SQL.  The authentication assumptions are invalid (using an App Pool user isn’t going to fly with Azure SQL).

This can be worked around (mostly), but we learned the hard way that the Sitecore Commerce Reference Storefront application is not compatible with Azure SQL in the reliance on Cross-Database queries for certain key operations; in our case, trying to use a central Commerce Inventory Azure SQL database was ultimately untenable.  Azure SQL does offer Cross-Database queries, but the syntax is different and the Reference Storefront code has non-trivial dependencies on the IaaS SQL Server understanding of querying between databases.

There are a lot of nooks and crannies with Sitecore Commerce 8.2.1.  I know everyone is excited about a fresh start with Sitecore Commerce 9 that doesn’t include the legacy COM and thick-client dependencies; this write-up summarizes a few of the Commerce highlights on the horizon.  For now, however, there are Commerce 8.2.1 builds in the wild that require our attention and I hope the above notes help others to be successful.

How a 13 year old archived list serv helped me out with Sitecore Commerce

Sitecore Commerce is an interesting landscape — it’s never a dull moment.  After recently swapping the backing store from Azure SQL to SQL Server (due to an interesting Inventory gotcha with the Reference Storefront that I’ll maybe share at some other time), I’m finding nooks and crannies of configuration I never knew existed with the Commerce product until now.

After I migrated to Azure IaaS SQL Server VMs from Azure SQL, I thought I had everything tidied up.

  • Commerce Server Manager references?  ✔
  • Sitecore application connection strings?  ✔
  • Bootstrap configuration (I posted this gist on manipulating those files to make this easier)? 

I updated the Azure SQL database credentials to prove that I had no lingering connections to Azure SQL.  I encountered an exception at Sitecore start-up related to initialization of the profile service, however, and had to start digging.  CommerceProfileSystemException was the exception type and the stacktrace started as follows:

Exception type: CommerceProfileSystemException 
 Exception message: Failed to initialize profile service handle.
 at CommerceServer.Core.Runtime.Profiles.ProfileContext..ctor(String profileServiceConnectionString, String providerConnectionString, String bdaoConnectionString, DebugContext debugContext)
 at CommerceServer.Core.Runtime.CommerceContextFactory.CreateProfileContext()
 at CommerceServer.Core.Runtime.CommerceContextFactory.get_ProfileContextSingleton()
 at CommerceServer.Core.Runtime.Profiles.CommerceProfileModule.get_ModuleProfileContext()
 at CommerceServer.Core.Runtime.Profiles.CommerceProfileModule.get_ProfileContext()

The Commerce Server Manager encapsulates the connection strings, and I thought I had them all updated to the SQL Server VM equivalents, even going so far as to inspect MSCS_Admin in SQL Server with a query like this:

SELECT [i_ResourceID]
 ,[s_PropertyName]
 ,[s_Value]
 FROM [MSCS_Admin].[dbo].[ResourceProps]
 where f_IsConnStr=1
 ORDER BY 1

While interesting to find where this information is stored (may or may not be permanent, though — tough to tell with Commerce!), this output didn’t shed light on what might be going on, though:

Eventually I stumbled across some 13 year old documentation on Commerce Server discussing updating the ProfileService data source in some detail (http://microsoft.public.commerceserver.general.narkive.com/NPLMLusv/commerce-2002sp3-on-windows-2003-can-t-change-profiles-data-source).  It turns out, this 13 year old solution was completely applicable to my 2017 Sitecore Commerce predicament.

Succinctly, within Commerce Server manager you should do the following:

  1. Expand the Commerce Server “Global Resources” node, then “Profiles” node, then “Profile Catalog” node, then “Data Sources” node, and finally expand the “ProfileService_SQLSource” node
  2. Click on the Partitions node:
  3. In the right pane, there’s a SQLSource element you right-click and choose “Properties”
  4. Select the Partitions Tab, then “Edit” the connection string
  5. Make your connection string modifications here.  This is where my elusive reference to Azure SQL was hiding and causing Sitecore to fail to initialize.

The more work I do with Sitecore Commerce, the more I’m appreciating the value of the older documentation targeting previous editions of the product.  The catch is, it’s not 100% relevant to the modern experience with Sitecore Commerce . . . and knowing what is and isn’t applicable to the Sitecore Commerce 8.2.1 world is a challenge.  I think we’re getting there, a little bit at a time!

Encrypting Sitecore connection strings for Sitecore Commerce, Azure SQL, and beyond

There’s been a lot of Sitecore Commerce on my plate this Summer, and sadly one limitation of using that product for some customers is the requirement for SQL Server authentication instead of Active Directory and Windows Auth; I won’t get into why they need SQL auth at this point, but trust that in many use-cases this is a necessity.

In an effort to always deliver a secured platform for customers, at Rackspace we encrypt the App_Config/connectionStrings.config file to avoid having plaintext usernames and passwords on disk.    This is a link to our Rackspace GitHub “gist” performing such encryption with the ASP.Net tool aspnet_regiis.exe.  The logic is also there to un-encrypt, in case that’s necessary.

Encryption success
You can update the $configLocation variable at the top of the script to point to where your Sitecore installation is located; you then run this script using PowerShell, and you’ll get an output like this.

Once you’ve run the script, your connectionStrings.config file will resemble this:

Before you get too excited, for Sitecore Commerce in the current incarnation, there are several other plaintext passwords on disk in the \CommerceAuthoring\wwwroot\data\Environments and related .json files for both SQL and Sitecore.  The PowerShell I’ve shared doesn’t address those areas.  The Sitecore Commerce documentation does a good job of cataloging where to find these references, at least, but this still leaves a lot to be desired in terms of security.

I’m not going to go too far down this path, since I mostly wanted to post the PowerShell we use to automate SQL Server connection string encryption.  This technique can be useful for a variety of projects, not just for Sitecore Commerce — although this is the use case we’re repeatedly seeing right now.  If I have time, I’ll share some other Sitecore Commerce tips around Azure SQL friendly deployments (Sitecore’s documentation is a decent start, but lacking in some respects).

Here’s the script to encrypt/decrypt those Sitecore connectionStrings.config file:

Sitecore Session Persistence Notes

I’ve neglected this blog of late, being focused on a number of “not easily blogged about” scenarios across several Sitecore projects.  It’s too bad, because the work is very interesting, but it doesn’t lend itself to a page or two write-up with a digestible take-away for the general Sitecore community out there.

I do want to keep in the habit of blogging, though, so I’m going to mention this ongoing discussion I’ve been a part of about session management with regards to Sitecore.  There are a few options for managing HTTP session state with Sitecore covered in https://doc.sitecore.net/sitecore_experience_platform/setting_up_and_maintaining/xdb/session_state/session_state: SQL Server, MongoDB, and Redis.  Those three technologies are really just the tip of the mountain, as implementation details for each can get quite detailed.  For the discerning Sitecore implementation, it can be useful to understand the nuances of each session state provider.  While not an exhaustive look at any one of these solutions, I wanted to post some notes on each one given the current state of Sitecore architecture (June 2017):

SQL Server

This is often the default session provider we gravitate to.  The SQL Server “Boost” script from Sitecore is something we’ve used on implementations (see “Optimize SQL Server performance” on that link), but it is not without it’s rough edges (see our Rackspace write-up on how to alter permissions so TempDB is reliably available across service restarts).

You’ll notice the approach for improving SQL Server performance with session state is all about getting session state “in-memory” to the furthest extent possible.  Remember this when we examine the other two providers below . . .

I will say that, generally speaking, SQL Server is easy to administer as it’s a well-known technology and updating it, scaling it, managing fail-overs, etc is simple compared with the alternatives.  SQL Server has been part of the Windows dev stack for ages, now, so it’s often the default session provider one gravitates to.

MongoDB

With MongoDB serving as the persistence layer for Sitecore’s xDB, it became a fully supported and viable option for HTTP session state with Sitecore at the same time.  The comparative performance between MongoDB and SQL Server is up for debate (Redis too, for that matter!), and it usually comes down to testing based on how the specific implementation is using session with Sitecore etc; I’m not going to hazard any generalizations on relative perf, as that’s not really the point of this post.

Instead, I’d like to point out how MongoDB does not come in just a single flavor.  The two most common flavors, or “storage engines,” are MMAP and WiredTiger, but there are still others designed to serve specific use cases.  Take, for example, the Percona Server for MongoDB hosted by ObjectRocket that has a posted option for the RocksDB storage engine.  RocksDB with MongoDB may not be a great fit for Sitecore session state (RocksDB is tuned for write-heavy work loads — and, in some cases, if you’re making extensive use of TTL indexes for Sitecore then RocksDB fits those scenarios in certain appealing ways), but it does open the door to MongoDB being more than just a one-size-fits-all data repository (read more about RocksDB and it’s Facebook pedigree here).  One MongoDB storage engine option that is easily overlooked is for WiredTiger “in-memory” that will force data to be stored in RAM . . . and this is perfect for HTTP Session State for most Sitecore builds.

In fact, if you consider the SQL Server “boost” approach that uses TempDB to store session state for Sitecore . . . WiredTiger “in-memory” is attacking the problem from the same direction.  Store everything in RAM!  This is why one must be cautious with general comparisons between SQL Server and MongoDB, the devil is always in the details: a far better comparison would be “boosted” SQL Server for Sitecore using TempDB vs MongoDB WiredTiger “in-memory” storage engine.  And note the network latency . . . and the size of the session objects . . . and you’re getting the point, I trust.  To really answer the SQL Server vs MongoDB question for Sitecore sessions, one has to develop a matrix of performance evaluations and level assumptions across the board.  “It depends” is the only honest answer that doesn’t come with a list of caveats.

If you’re curious on this MongoDB topic for your project, go to http://objectrocket.com/docs/mongodb_plans.html and spin up a WT 3.2 storage engine plan for 5 GB of storage (this allows 1.5 GB for RAM).  1.5 GB for RAM is going to be overkill for most small/medium Sitecore implementations — but again, you’ll want to test with your specific session data set to see!  Furthermore, network latency of 10 ms or less is going to help make the most of an ObjectRocket hosted MongoDB service like this — otherwise, the network latency may not make it worth the money.  Let me know if you pursue this with ObjectRocket, as there are some benchmarking measures we want to do but we haven’t had a real implementation to try it out on.  So if you feel like being a guinea pig, please let me know at grant.killian [at] rackspace.com.  It would be great to have real world metrics to prove this all out.

Redis

If the way to get the best session management perf out of SQL Server and MongoDB is to find in-memory solutions, Redis looks like the slam dunk since it’s just an in-memory storage solution.  We find most clients aren’t interested in managing Redis infrastructure, so again a hosted option such as ObjectRocket has appeal.

Sitecore relies on the StackExchange.Redis assembly, which doesn’t support Redis Sentinel — it’s a bit of a saga at https://github.com/StackExchange/StackExchange.Redis/pull/406;  therefore there’s not a great high availability story with the self-hosted Redis and Sitecore right now.  How concerned one should be with HA of fairly transient HTTP Session State for Sitecore, however, is an open question.  I usually wouldn’t worry about it too much.  Honestly, Redis is a technology that we’re just now starting to get really serious about at Rackspace so our sophistication in this space will improve dramatically in the months to come.  Between Azure Redis and all the Sitecore PaaS movement we’re seeing, it’s become a key player in a lot of Sitecore architectures.