Experiencing CLR error on SQL Azure DB Out of nowhere we started seeing this error and it seems to occur fairly frequently when making calls to the database or any other database in our Elastic Pool. The DTUs aren't being maxed out and the resource dmvs don't seem bad.


  Failed to enter Common Language Runtime (CLR) with HRESULT 
  0x80131022. This may be due to low resource conditions. (db)


Here's what I got from the system resource governor pool

Resource Pool Name           cache_memory (MB)   used_memory (MB)
internal                     104.773437          1577.125000
default                      37.609375           38.796875
SloSecSharedPool             2.914062            8.156250
InMemBackupRestorePool       26.210937           101.437500
InMemDmvCollectorPool        186.195312          203.406250
InMemMetricsDownloaderPool   2.234375            2.250000
InMemDTAPool                 0.000000            0.000000
SloHkPool                    0.000000            0.031250
InMemQueryStorePool          22.453125           35.304687
InMemWIAutoTuningPool        3.312500            4.062500
InMemXdbLoginPool            3.976562            6.250000
PVSCleanerPool               0.000000            0.000000
InMemTdeScanPool             0.000000            0.000000
SloSharedPool1               1108.890625         1234.312500


From the sys.dm_os_performance_counters this is what it looks like for the past 3 hours.

cpu%    data_io%   log_write%   memory_usage%   max_worker%   sessions%
22.37   73.51      16.54        41.56           5.50          0.43


This doesn't seem like a common error for SQL Azure as I cannot find anything that pertains to this happening past SQL Server 2008. Any help would be appreciated.

Update:

We got a response from the Microsoft support rep and it looks like our memory usage was completely capped out. 



After moving the elastic pool up a tier the error has gone away. We have ~56GB of memory instead of the ~28GB we had previously and the error ceased. This would have probably also moved us to a different server on Azure which may have fixed the problem for now. The site has been running at around 78% on memory usage with the buffer cache hit ratio @ 8588 and PLE of 87332. Now it's operating at usage under 2% across the board for CPU, Workers, DataIO, etc. during normal load which seems like a huge waste. 

We could not definitively identify what was causing the errors but we assume it was the complete memory usage as the site is running fine for now...
While Azure SQL Database (not the new Managed Instance) does not support custom SQLCLR Assemblies (i.e. the "CLR enabled" server-level configuration option), CLR is still used internally for the following features:


CLR datatypes:


Geometry
Geography
Hierarchyid

Built-in functions:


introduced in SQL Server 2012:


FORMAT
PARSE
TRY_PARSE

introduced in SQL Server 2016:


AT TIME ZONE
COMPRESS
DECOMPRESS
sys.time_zone_info

maybe others

SSIS (Fuzzy Lookup / sp_FuzzyLookupTableMaintenanceInvoke, etc)
Change Data Capture (CDC)
Replication
Master Data Services
Policy Based Managemen (PBM; originally named "Dynamic Management Framework (DMF)" )
External Tables (including External Data Sources and possibly External File Formats): This functionality is new as of SQL Server 2016, and this functionality using CLR internally has been mentioned in other answers here by Joe and Henrik. Both Joe and Henrik indicate being told by Microsoft that External Tables rely upon CLR, and while I have not been able to confirm this directly (by seeing the system App Domain get created when using any of this functionality), I was at least able to confirm that when "Lightweight Pooling" mode is enabled, all 3 of these components fail with the following error:


  Msg 7432, Level 16, State 0, Line XXXXX
  Heterogeneous queries and use of OLEDB providers are not supported in fiber mode.

maybe others


Of course, this does not point to what would be hogging memory. But it should help identify the affected area(s).