How to fix being stuck on Indexing forever loop of death on multi million file DBs after db crash

Well it happened again... out of nowhere with no major changes, syncing forever with no reason why, just never finishing I tried my usual tricks and nothing

Using resmon to see if any files where open by some app that were holding up the sync?

Nope

Using resmon to check for disk activity to see what files were being written or read that could be causing the problem?

Nope

Checking the folders to see what folder had the "sync" blue icon and figured one huge file was syncing?

Nope

Suspend and wait for re-indexing to do a re-index and find out if that fixes it?

Nope

I was running out of ideas and I came across this post:

https://www.dropboxforum.com/t5/Apps-and-Installations/Desktop-client-stuck-a-quot-Syncing-quot/td-p/434215

And I figured could it be that easy?

so I went to the Dropbox\.dropbox.cache\old_files\ folder and sure enough a 15 gig file was there, I deleted it and like magic the problem plaguing me for more than a week fixed itself.

So if you tried my previous solutions and the sync issue still persists try this one

For those that care:

The reason this happens is every time you right click and select a file or folder to convert to "online-only" dropbox doesn't just automatically delete it, it moves it to a temporary location for further processing.

Basically what dropbox does when you do this is it moves the file immediately to Dropbox\.dropbox.cache\old_files\ under a random generic number and puts an online only link where the file was before as a placeholder, then once it does this it starts hashing out the file, meaning it reads it all completely, then creates a hash of it, then compares it to the hash on the server, if the hashes match, then it deletes it for real, if it doesn't match, it uploads the file and then deletes it, this ensures the online only'ed file is always the most up to date version.

This has two benefits:

The first, as described above if the file were to be different it would correct the situation by uploading it.

Second, if you accidentally hit online only, on these files, you have until dropbox does this process to "undo" your mistake without having to redownload the files again, so its kinda useful.

I'm guessing what happened is something borked up on the dropbox hashing routine, making it never be able to hash the file, since it never hashed it couldn't be deleted, since it was not deleted the sync icon just stayed there forever.

Deleting the file causes dropbox to "error" out saying "file not found" and skipping the hashing procedure, just assuming the last file he has on the server is the newest one, and leaving it at that.

This causes the sync to finally finish

So now you know, if it happens to you, try this, it might fix it.