service/share: Implement parallelisation for GetSharesByNamespace

[renaynay]

Implement parallelisation for GetSharesByNamespace when there are multiple rows that contain the given namespace.ID.

[vgonkivs]

Hi @renaynay , may I take this one?

[renaynay]

Hey @vgonkivs we are currently debugging an issue with ipld + bitswap, so will wait on @Wondertan for further notice. But after that bug is fixed, that would be great!

[vgonkivs]

Ok, then I will wait until the bug will be fixed.

[renaynay]

It's been fixed! @vgonkivs

[vgonkivs]

Great. So If I understand correctly, rowRootCIDs and namespacedShares in GetSharesByNamespace should fill concurrently, right? Since appending is not a thread safe operation, should I protect it by adding a local mutex or mutex should be added to service ?

[renaynay]

I would say the best approach is:

step 1: figure out which rows (rowRootCIDs) contain the given nID
step 2: loop over the rowRootCIDs and spawn a go routine on each row to return the namespacedShares from that row
step 3: if even 1 error occurs, return nil, err.

step 2 is the only one that should be happening concurrently.