We are seeing some odd behaviour on our SSAS instances. We process our cubes as part of an overnight job on different environments, on our prod environment we process the cube on a separate server and then sync it out to a set of user facing servers. We are however seeing this behaviour even on environments where we process and query on a single instance.
The first user that hits any environment with fresh data seems to trigger a reload of the cube data from disk. Given we have 2 cubes that run to some 20Gb this takes a while. During this we are seeing low CPU utilisation, but, we can see the memory footprint of the SSAS instance spooling up, this is very visible if the instance has just been started as it seems to start using a couple of hundred Mb initially and then spool up to 22Gb at which point is becomes responsive for end users. During the spool up DAX stuiod/Excel/SSMS all seem to hang a far as the end user is concerned. Profiler isn't showing anything usfeul other than very slow responses to META data discover requests.
Is there a setting somewhere that can change this? Or do I have to run some DAX against the cube to "prewarm" it?
Is this something I've missed in the past because all my models were pretty small (sub 1Gb)
This is SQL 2016 SP2 running Tab Models at compat 1200.
Many thanks
Steve
I see that you are suffering from an acute OLAP cube cold. :)
You need to get it warmer (as you've guessed it, you need to issue a command against it, after (re)starting the service).
What you want to do, is issue a discover command - a query like this one should be enough:
SELECT * FROM $System.DBSCHEMA_CATALOGS
If you want the full story, and a detailed explanation on how to automate this warming, you can find my post here: https://fundatament.com/2018/11/07/moments-before-disaster-ssas-tabular-is-not-responding-after-a-server-restart/
Hope it helps.
Have fun. :)
Related
We are using a SQL Server Tabular model which we use for self-service BI purposes. At monthly basis we have some 90 distinct persons who are using the model. Recently we encountered some issues/errors in the client tools(Excel and Power BI) that are connecting to the Tabular model. See screenshots. We did not make any significant changes to the model the past period.
We noticed that the errors keep showing up after our incremental load, i.e. a full process of a number of partitions we process these partitions every 15 minutes. The process is kicked of by a SSIS job which is scheduled every 15 minutes and processes 5 partitions in 3 tables.
Edit: After some research I figured out that the problem lies in the perspectives. Everytime I do a full process on any object. The error appears. This does not happen on the default model view. Still not found a solution though.
The error occurs when you make a change to the power bi report or the excel file. For example when you do a refresh, or when you click a filter. If you press refresh multiple times the connection comes back and everything works as it is supposed to. It seems like the clients lose their connection to the model. After 15 minutes the problem occurs again.
This is very aggravating for the users. Especially when they are in the middle of a presentation.
This is what we tried:
We tried searching Google for a solution
Checked that we have the latest SQL Server 2016 update (13.0.5149.0)
SSAS Builds from Visual Studio(2015 en 2017)
No full process on tables, only on
partitions.
Upgrading the server from 4 to 8 cpu cores.
I hope somebody can help us.
You shouldn't have the error that you are seeing with just a full process of a partition or even the full table. We do this every hour for a number of core tables and we do not see any issues like this (and we would)
I am starting from the hypothesis that
Your 15 minute process is doing more than just processing the partitions with a refresh command
Something else is happening on the environment (either scheduled or not). Who has permissions to change the schema? Could it be users / developers deliberately or not making changes?
The only things that should cause that kind of error would be Alter, Delete or CreateOrReplace TMSL commands
So unless that triggers your own ideas on a diagnostic process I would do the following steps
Note: I presume that your users also see this issue on your test environment when you run your 15 min processing routine on that. You should do the following on that test environment where nothing else is running to eliminate the possibility of someone else interfering with the experiment. If you don't have a representative test environment then you will have to do on live but I would do this out of hours or under some kind of change control process with your 15 minute refresh turned off and admin permissions to the cube heavily locked down to ensure that nothing can interfere with your experiment.
First prove that you can reproduce this issue with the 15 minute routine
Get your sample PowerBI report that is known to present the error (I'd prefer Power BI for a repro as it is slightly simpler than Excel)
Refresh your PowerBI and explore the data to prove that the error doesn't occur
Run your 15 minute process
You should now see the problem reported. If you do, great, you have a reproduceable issue! If you don't then it is not quite as you thought it was and you need to find the way of reliably reproducing these errors. (perhaps something else is happening that isn't the 15 minute process)
So now you are sure how you can reproduce the issue, you need to isolate whether it is really the processing that is causing the problem
Refresh your PowerBI and explore the data to prove that the error doesn't occur
Execute (via SSMS) your XMLA that processes the entire database for one of your tables
it should look something like this
{
"refresh": {
"type": "full",
"objects": [
{
"database": "yourdbname"
}
]
}
}
Do the thing that your users do when they see the issue.
If you too see the issue, then I would raise to Microsoft Support as this shouldn't happen
If you don't see the issue then you can refine this processing to just be the partition for a single table. But as we have done a process for the entire db above if shouldn't change the result
If you still don't see the issue then it isn't the processing that is causing this issue (which I suspect) and it is something else in the 15 minute routine that is causing it. Look deeper into that process and understand what else it is doing.
Alongside this checking the logs should show if there are any other processing tasks or types of XMLA happening.
I hope these ideas get you closer to finding the actual activity that is causing this experience for your users. It would be great if you could post with how you got on and what you found.
I have the same problem here if I install the latest CU on my SQL Server 2017. My production environment is still running with CU3 (Jan/2018) due to this problem.
Knowing that I would suggest reverting your installation to a previous release. Maybe 13.0.5026.0 (SP2) or even to the 13.0.4466.4 (Jan/2018).
I am facing the same issue with SQL Server 2017 CU 11 installed.
The issue indeed occurs in case of a 'full refresh' in combination with the use of a 'perspective' in an existing connection. The workaround to use the default 'Model' in the connection does indeed 'solve' the issue.
This is the error I get from the Log while trying to process a SQL Server 2012 MOLAP Cube.
"Time-out occurred while waiting for buffer latch type 3 for page (1:2044928) database ID 2.; 42000." Source="Microsoft SQL Server 2012 Analysis Services" HelpFile="Error ErrorCode="3240034318" Description="Errors in the OLAP storage engine: An error occurred while processing the 'Measurement' partition of the measure group for the 'PE cube' cube from the Cube database."
I have scripted the processing task in XMLA and execute the processing via a SSAS Command in an Agent Job.
The first step is to Process Update all dimensions and this succeeds, but when I want to Process Data of the cube the load fails and this error pops up.
I first tried processing with an SSIS package, but this caused the whole server to crash instead of just the job failing. This leads me to believe this a performance issue, but the machine running the job is an Azure VM with 16 processors and 112 GB RAM so I don't know where to look. I also tried running the job without any other activities on the server, but that did not help.
The disk containing the SSAS Instance still has 500GB Free.
The measure group is querying a table containing 180 million records.
While processing the cube on a Dev server with way less data there are no issues. I once succeeded to Process Full the whole cube while processing the SSAS cube directly within SSAS, but via DTEXEC, SSISDB or using SSDT the processing results in a server crash.
Earlier I got different time-out errors, but after adjusting the SSAS ExternalCommandTimeOut, ExternalConnectionTimeOut and ForceCommitTimeout properties to 0 this did not occur anymore.
I have tried multiple processing settings, but because I think it is a performance issue I tried to make the processing as low as possible on performance.
Processing Settings:
Object: Cube; Option: Process Data;
Processing Order: Sequential with Seperate Transactions.
Writeback Table Option: Use Existing;
Do not process affected objects.
Update:
I have processed the measure which triggered the error on its own, this did not finish and in the Activity Monitor I saw a lot of Wait_Type IO_Completion and CXPacket. And when querying the sys.dm_exe_requests I see a Select with wait_type IO_Completion which is already running for a long time and a lot of reads.
Last night I tried to process all measurements excluding the measuregroup which triggered the error earlier, but unfortunately the whole server crashed again...
Update2:
We have looked into upgrading to premium storage, but this means we have to switch from A11 to a DS or GS serie. Meaning we need to resize the whole VM which contains live solutions resulting in down-time and effort to restore the VHDS and replacing the current OS disk which contains parts of live solutions.
Another option we identified is applying partitioning or improving the underlying queries from the measures. Unfortunately way more effort than anticipated, a quick work-around for now would help a lot in selling a long-term solution improvement.
Update3:
We have had contact with Microsoft and they advice to migrate from an A11 VM to a D14 V2 and upgrade to premium storage disks. This will be our next step and will be executed upcoming friday. After the migration I will update or close this post.
If you miss information, please let me know. Any suggestions that would help me pin-point the situation would be much appreciated!
The upgrade to a VM better suitable for the situation (DS14 V2) and upgrade to P30 premium storage disks have resolved the occuring issues. The issue was not in the way the cube was being processed or configured, but in the hardware used.
My application contains a pivot grid that is connected to several cubes in Analysis Services (SQL Server 2014). When enough time has passed (maybe a couple of hours, I haven't timed it), the next time I use the pivot grid, I experience an increased lag time of 5 - 10 seconds compared to subsequent uses. Basically, my first call to SSAS is always slow, all the next ones are fast.
I'm unable to find any documentation or article about why I'm experiencing a slow response time for my application's first call to Analysis Services. Can anyone shed some light on this issue?
Edit:
I should mention that this is for a web application, so long load times are no good. It seems like SSAS goes to sleep after awhile and I'd like to keep it "awake" if it's possible.
At our shop, in the job that processes the SSAS database, we follow that step with some steps that run typical queries against SSAS to "warm the cache".
Seems to work for us.
I'm starting to assess our company using RavenDB for storing some stuff that doesn't really belong in a relational database (we're traditionally a SQL Server shop). I installed RavenDB locally on my machine, created a database, added a document. Nice!
Being a DBA, I decided to see how backups/restores work. I backed up my database, deleted it, then restored it from the backup. After refreshing my admin screen, I saw my database. I clicked on it, and got a message that the database doesn't exist.
After a couple hours, I tried again. Still doesn't exist. A full day later, I walk into work, and try again. This time the database works. I've had similar situations with updating documents. The update seems to take anywhere between 1 second - several hours to show an update...
Is this normal for RavenDB?? Am I completely misconfigured?? I run SQL Server on my local machine and it's lightning-fast, so I can't imagine updating a single document could take that long. As-is, I can't imagine recommending we use RavenDB for anything.
Are you querying using indexes or getting documents by ID? Documents should be updated immediately (ACID). If indexes are slow to update (check their status using RavenDB Studio), it could be a configuration problem or something external like an anti-virus software can cause them to update slowly.
Apparently, at least for the document-update latency, the default for caching in queries is enabled, so I was getting cached results.
Jeffery,
No, that isn't normal by a long short. You should be able to immediately see what was changed.
Note that certain AV products will interfere with the HTTP pipeline and can affect RavenDB's usage. The studio will also auto update things only every 5 seconds (to reduce UI jitter), but that is about it.
Restoring a database (from the same machine), should take only as long as it take to copy the files (pure I/O bound operation).
If this is from another machine using a different version of Windows, we might need to run a check on the file, which can take a bit of time, but that doesn't sound like your scenario
I decided I wanted to try out Microsoft SQL Azure, as many people have talked very highly about it. It should be fast, flexible, cheap and many other things.
I got it up and running, migrated my data to Azure and hooked up the connectionstring. I tried to run some queries on the database, and was shocked about how slow even simple queries were. A "SELECT *" from a table with 700 rows took 7 seconds. My page also seems extremely slow, compared to when I used a localhost managent studio or a database on a shared hosting.
Now, when I setup my server, I couldn't pick a physical position. However, I live in Denmark, and I can see the server is the "South Central US". This might be the issue.
I don't use any stored procedures (so I guess no parameter sniffing).. I can also see my indexes is transfered succesfully.
Any ideas on what to do? Any performance things I am missing?
I ran into this very issue the last few days. Change your database tier from basic to standard and you will see a HUGE increase in performance. I am working on a query intensive dashboard at the moment, it took a 20 sec response time down to 2 sec response.
I've used Azure now for the last many years, and my original question is pretty much solved.
My main take-aways after dealing with Azure databases for a while:
It's extremely important that your application and database is placed in the same region. If not, then you will have a slow application. Recently I had an API and app running on two different regions - it took ~1 second for every response.. After moving it to same, it was instant
If your application has a high load, it's often a good idea to upgrade. This happens earlier than you might expect
Pick the nearest region - it really matters