commit c7078ab07caab7f4c2b5340db99c5a1abdb031c4
author Dave Borowitz <dborowitz@google.com> Mon Apr 24 13:42:19 2017 +0200
committer Dave Borowitz <dborowitz@google.com> Tue Apr 25 14:40:37 2017 +0200
tree 5747f518e1f3e1a658880a3b4e4d17239f7eec81
parent ecd4831c732a656d68830d51fc9448af6f7e8e45

Don't fuse code and meta ref updates if it won't be atomic

Prior to fusing updates in Ia5b34bae, BatchUpdate ensured that code
refs updated in updateRepo were all updated before meta refs in
updateChange. Fusing them is safe when BatchRefUpdate is an atomic
transaction in the underlying storage, but it's actually a regression
when the storage doesn't support atomic multi-ref operations. This is
because all updates in the batch can fail independently, so we can end
up with a meta ref update succeeding but the corresponding code update
failing.

To handle this case, temporarily resurrect the old NoteDbBatchUpdate
implementation from 3915d7baa, switching between the fused/unfused
implementations based on a new config option. It's an error to try to
execute a FusedNoteDbBatchUpdate on a repository that doesn't support
atomic transactions, but due to the way BatchUpdate.Factory works, we
have to decide which type of update to instantiate before we have
opened any repos. So we need to have a separate config option to signal
this; add a new NoteDbMode FUSED to run tests in this case.

To keep our tests realistic, use the atomic feature of
InMemoryRepository only if we are running in FUSED mode. Setting this
reveals a latent issue where we need to setAtomic(false), so fix that
as well.

Ideally this workaround of having multiple backends is a temporary
measure until RefDirectory gains the ability to perform multi-ref
transactions[1]. Long term we would like to be able to eliminate this.
This somewhat depends, however, on if there are other RefDatabase
implementations in the wild that people are likely to use with NoteDb
that don't support atomic transactions.

[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=515678

Change-Id: I8e67dc88c7ca7d59ef3157cfb6194571a0521828