Re: [Tarantool-patches] [PATCH v2 01/11] applier: store instance_id in struct applier

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

The patch was reworked from the scratch. It appeared, that we can't
rely on getting an id when an applier is assigned to a struct replica.
Because that moment is not clearly defined. Sometimes applier starts
serving rows, but still wasn't assigned to a struct replica.

Then I realized, that SUBSCRIBE response contains replica_id of the
sender. It is sent in box_process_subscribe(). So I started fetching
that ID in applier_subscribe().

====================
    applier: store instance_id in struct applier
    
    Applier is going to need its numeric ID in order to tell the
    future Raft module who is a sender of a Raft message. An
    alternative would be to add sender ID to each Raft message, but
    this looks like a crutch. Moreover, applier still needs to know
    its numeric ID in order to notify Raft about heartbeats from the
    peer node.
    
    Needed for #1146

diff --git a/src/box/applier.cc b/src/box/applier.cc
index e272a7af6..1a0b55640 100644
--- a/src/box/applier.cc
+++ b/src/box/applier.cc
@@ -1118,6 +1118,7 @@ applier_subscribe(struct applier *applier)
 		vclock_create(&applier->remote_vclock_at_subscribe);
 		xrow_decode_subscribe_response_xc(&row, &cluster_id,
 					&applier->remote_vclock_at_subscribe);
+		applier->instance_id = row.replica_id;
 		/*
 		 * If master didn't send us its cluster id
 		 * assume that it has done all the checks.
diff --git a/src/box/applier.h b/src/box/applier.h
index 6e979a806..15ca1fcfd 100644
--- a/src/box/applier.h
+++ b/src/box/applier.h
@@ -95,6 +95,8 @@ struct applier {
 	ev_tstamp lag;
 	/** The last box_error_code() logged to avoid log flooding */
 	uint32_t last_logged_errcode;
+	/** Remote instance ID. */
+	uint32_t instance_id;
 	/** Remote instance UUID */
 	struct tt_uuid uuid;
 	/** Remote URI (string) */