On each read/write operation praefect requires to know which

gitaly node is a primary. For mutator operations it used to
define from what node the response will be returned back to
the client. For the read operations it is used to redirect request
to or as a fallback option for reads distribution in case it
is enabled. The default strategy for defining the primary is
an 'sql' which means the primary is tracked inside Postgres
database and praefect issues select statement into it each time
it needs to define current primary. It creates a high load
on the database when there are too many read operations (the
outcome of the performance testing).

To resolve this problem we change logic of retrieving set of
up to date storages to return all storages including primary.
So now we don't need to know the current primary and use any
storage that has latest generation of the repository to serve
the requests. As this information is cached by the in-memory
cache praefect won't create a high load on the database anymore.

This change also makes check IsLatestGeneration for the primary
node redundant as it won't be present in the set of consistent
storages if its generation not the latest one.

Closes: https://gitlab.com/gitlab-org/gitaly/-/issues/3337

1 files changed, 5 insertions, 1 deletions

diff --git a/internal/praefect/server_factory_test.go b/internal/praefect/server_factory_test.go
index d1601a566..c87d69140 100644
--- a/internal/praefect/server_factory_test.go
+++ b/internal/praefect/server_factory_test.go
@@ -80,7 +80,11 @@ func TestServerFactory(t *testing.T) {
 	logger := testhelper.DiscardTestEntry(t)
 	queue := datastore.NewMemoryReplicationEventQueue(conf)
 
-	rs := datastore.MockRepositoryStore{}
+	rs := datastore.MockRepositoryStore{
+		GetConsistentStoragesFunc: func(context.Context, string, string) (map[string]struct{}, error) {
+			return map[string]struct{}{conf.VirtualStorages[0].Nodes[0].Storage: {}}, nil
+		},
+	}
 	sp := datastore.NewDirectStorageProvider(rs)
 	nodeMgr, err := nodes.NewManager(logger, conf, nil, rs, sp, &promtest.MockHistogramVec{}, protoregistry.GitalyProtoPreregistered, nil)
 	require.NoError(t, err)