Get rid of EphemeralFile::ephemeral_files_id

[problame]

Do we need a separate ephemeral file ID and page cache file ID, or could they be the same?

Originally posted by @hlinnaka in #4994 (comment)

[Reminiscent]

Hi, I'd like to try this issue.

[hlinnaka]

@problame commented at #4994 (comment):

This PR maintains the separate IDs for the sole purpose of file names: e0b8785

I'd prefer if we don't intermingle these.

Hmm, looking at the code as it is in 'main' now, I don't see a separate "ephemeral file id" anymore. I guess that you renamed it NEXT_FILENAME counter. I think that helped to reduce the confusion already.

We could replace NEXT_FILENAME with the page cache file ID. Might be handy during debugging that you could see the file ID directly in the filename. But doesn't really matter much.

[Reminiscent]

@hlinnaka Thanks for your explanation. I think you are right. I'll try other issues.

[koivunej]

@problame could you update this to reflect current state and perhaps restore good_first_issue, or close?