Zero instance doesn't run ValueLog GC

[jarifibrahim]

As of commit 4c5abce, the zero instance doesn't run Value Log GC .

Even though the amount of data written by zero is very less, we should run GC for it otherwise the zw will grow without any bounds.

Original post - https://discuss.dgraph.io/t/dgraph-is-not-calling-badger-vlog-gc-for-zw-directory/5861

Looks like the user has too many vlog files because of missing garbage collection https://discuss.dgraph.io/t/dgraph-is-not-calling-badger-vlog-gc-for-zw-directory/5861/3?u=ibrahim

[jarifibrahim]

This looks like a serious issue to me. Bumping up the priority to P1.

[lgalatin]

Fixed by: #4716