Back in 2010s in my first job I've seen a bug caused by too many files in one directory. I don't remember the exact details, but it was making me crazy. Basica

Back in 2010s in my first job I've seen a bug caused by too many files in one directory. I don't remember the exact details, but it was making me crazy. Basically we wrote temporary files into one big directory and later printed them. And sometimes our code returned "File not found" errors despite the fact that ls filename had showed the file is there and has correct permissions. And when I tried to cat filename from shell - it also caused the same error :) But if you created another file with a different name in the same directory - it worked correctly :) There was also space on the disk, and the number of files was high, but not crazy high (a few hundred thousand I think)? It turns out this particular filesystem (it was ext2 or ext3 with specific parameters IIRC) can behave like that when there's too many similarly-named files in one directory, because there's some metadata with hash of filenames in the filesystem and there can be collisions and it only can handle so many of them before failing. The solution was to remove the files after printing them of course, so that they don't accumulate forever.