BrowserMetrics

1. Edge seems to clean up these files upon launch. It knows how to do that.
2. Edge behaves differently depending on version
   1. For me, it occurs in:
      1. Edge Stable: Version 89.0.774.63 (Official build) (64-bit)
      2. Edge Canary: Version 91.0.837.0 (Official build) (64-bit)
   2. It does not occur in:
      1. Edge Beta: Version 90.0.818.22 (Official build) beta (64-bit)
   3. Therefore, it seems there is either
      1. a regression between 90.0.918 and 91.0.837, or
      2. a difference in 'feature flag' or other configuration
   4. I did notice that the Beta version ran with the following command line argument that was absent from the Stable version
      1. "--monitor-self"
3. At first I thought Edge might be losing a 'race condition' with Windows Defender Real Time Protection (RTP); that is, Defender locks the file and Edge can't delete it  (see detail [1] below)
4. That seems unlikely, though, since the Beta ring works fine with Defender
5. Instead, it appears that the Stable version (and possibly the Canary one as well) aren't even _trying_ to delete the old files until after the next time Edge is completely closed and re-opened (... which for some people can be hours to weeks!) (see detail [2] below)
6. Perhaps unrelated, there was a mention of this in one of the file access traces - perhaps it is another lead for the devs:

   1. msedge.dll - RelaunchChromeBrowserWithNewCommandLineIfNeeded

1. Edge creates the 4.0 MiB PMA (Persistent Memory Access) file named "BrowserMetrics-spare.pma" in the "%LocalAppData%\Microsoft\Edge\User Data" directory.
2. Edge moves that file to the "%LocalAppData%\Microsoft\Edge\User Data\BrowserMetrics" directory and renames it.
3. Edge loads that re-named file as a memory-mapped file
   
   1. After some time, the 'spare' file from step 1 is re-created
4. If Windows Defender is running,
   1. writes to this file are sometimes / always accessed filtered through the Defender (MsMpEng.exe) process (Synchronous Paging I/O)
5. If Windows Defender ATP (Advanced Threat Protection) is running,
   1. that process (MsSense.exe) requests an 'opportunistic lock (oplock)' [FSCTL_REQUEST_OPLOCK IOCTL (winioctl.h)] while it is scanning
   2. Before that scan is complete (and therefore the oplock is released), Edge (msedge.exe) closes the file

Beta - Version 90.0.818.22 (Official build) beta (64-bit)

  --> Normal (working) process, that prevents build-up of "BrowserMetrics-hhhhhhhh-hhhhh.pma" files:

  CreateFile                                              Desired Access: Generic Read/Write, Disposition: OpenIf, 
                                                            Options: Synchronous IO Non-Alert, Non-Directory File, 
                                                            Attributes: n/a, ShareMode: Read, Write, Delete, 
                                                            AllocationSize: 0, OpenResult: Created
  CreateFileMapping                                       SyncType: SyncTypeCreateSection, 
                                                            PageProtection: PAGE_EXECUTE_READWRITE
                    Result: FILE LOCKED WITH WRITERS
  QueryStandardInformationFile                            AllocationSize: 0, EndOfFile: 0, NumberOfLinks: 1, 
                                                            DeletePending: False, Directory: False
  SetEndOfFileInformationFile                             EndOfFile: 4,194,304
  CreateFileMapping                                       SyncType: SyncTypeOther
  ReadFile                                                Offset: 0, Length: 32,768, I/O Flags: Non-cached, Paging I/O, 
                                                            Synchronous Paging I/O, Priority: Normal
	...
  CreateFile                    IRP_MJ_CREATE
  QueryAttributeTagFile         IRP_MJ_QUERY_INFORMATION  Type: QueryAttributeTagFile, Attributes: AC, ReparseTag: 0x0
  SetDispositionInformationEx   IRP_MJ_SET_INFORMATION    FILE_DISPOSITION_DELETE, FILE_DISPOSITION_POSIX_SEMANTICS, 
                                                            FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK
                                IRP_MJ_CLEANUP
  CloseFile                     IRP_MJ_CLOSE