proto: Introduce transactional voting phases

Transactional votes currently only contain information about the vote
that we actually want to cast, but it doesn't contain any sort of
metadata which would allow us to more precisely track the nature of a
specific vote. Most importantly, while we already use "preparatory" and
"committing" votes in almost all places, they are only preparatory and
committing votes by convention: there is no metadata which would allow
us to discern these cases.

Amend the voting RPC call to use "phases", which currently knows three
different phases:

    - "unknown": this is the current default which we'll need to support
      until all voting callsites have been converted to use proper
      phases.

    - "prepared": the change has been prepared to be committed. Locks
      have been taken already, but no change has yet been committed to
      disk such that they would be visible to the user.

    - "committed": changes have been committed to disk and are thus both
      persistent and visible to the user.

With these phases, we can eventually build additional logic into
Praefect which makes use of them. This includes creating less
replication jobs if no change was committed, making two-phase voting a
necessity instead of a convention, and potentially others.

Changelog: added

1 files changed, 7 insertions, 0 deletions

diff --git a/ruby/proto/gitaly/transaction_pb.rb b/ruby/proto/gitaly/transaction_pb.rb
index 59c7f5626..01a04bf3c 100644
--- a/ruby/proto/gitaly/transaction_pb.rb
+++ b/ruby/proto/gitaly/transaction_pb.rb
@@ -12,6 +12,12 @@ Google::Protobuf::DescriptorPool.generated_pool.build do
       optional :transaction_id, :uint64, 2
       optional :node, :string, 3
       optional :reference_updates_hash, :bytes, 4
+      optional :phase, :enum, 5, "gitaly.VoteTransactionRequest.Phase"
+    end
+    add_enum "gitaly.VoteTransactionRequest.Phase" do
+      value :UNKNOWN_PHASE, 0
+      value :PREPARED_PHASE, 1
+      value :COMMITTED_PHASE, 2
     end
     add_message "gitaly.VoteTransactionResponse" do
       optional :state, :enum, 1, "gitaly.VoteTransactionResponse.TransactionState"
@@ -32,6 +38,7 @@ end
 
 module Gitaly
   VoteTransactionRequest = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.VoteTransactionRequest").msgclass
+  VoteTransactionRequest::Phase = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.VoteTransactionRequest.Phase").enummodule
   VoteTransactionResponse = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.VoteTransactionResponse").msgclass
   VoteTransactionResponse::TransactionState = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.VoteTransactionResponse.TransactionState").enummodule
   StopTransactionRequest = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("gitaly.StopTransactionRequest").msgclass