Arvados

• All observed failures are in the n=8 iteration (lots of goroutines operating on 8 different dirs in the same collection) -- no failures when running concurrent goroutines on 1, 2, or 4 different dirs
• All observed failures return 409 for "PUT dirN/fileN"
• The only case where the webdav handler returns 409 for PUT is when the parent directory does not exist
• The test case has a barrier between MKCOL dirN and PUT dirN/fileN
• In the attached log, PUT i=0/j=0,1,2,3,4,5,6 fail, then PUT i=0/j=7 succeeds

This seems to indicate that the side effect of MKCOL is reliably preserved, but calling collectionDir.Sync() at the end of MKCOL is not enough to guarantee that the created directory is visible during a future request.

The fact that we only see the problem with n=8 hints that the problem is a race between concurrent collectionDir.Sync() calls for different directories in the same collection.