Re: [Tarantool-patches] [PATCH 05/12] raft: stop using instance_id

[Serge Petrenko <sergepetrenko@tarantool.org>]

17.11.2020 03:02, Vladislav Shpilevoy пишет:
> Raft is being moved to a separate library in src/lib. It means,
> it can't depend on anything from box/.
>
> The patch makes raft stop using instance_id.
>
> Instead, it has a new option 'instance_id'. It is stored inside
> struct raft as 'self', and should be configured using
> raft_cfg_instance_id().
>
> The configuration is done when bootstrap ends and the instance_id
> is either recovered successfully, or the instance is anonymous.
>
> While working on this, I also considered introducing a new
> function raft_boot() instead of raft_cfg_instance_id(). Which I
> would also use to configure vclock later. Raft_boot() would be
> meant to be called only one time with non-dynamic parameters
> instance_id and vclock.
>
> But then I decided to keep adding new raft_cfg_*() functions.
> Because:
>
> - It is more consistent with the existing options;
>
> - Does not require to think about too many different functions
>    like raft_create(), raft_boot(), raft_cfg_*() and in which order
>    to call them;
>
> Also I was thinking to introduce a single raft_cfg() like I did
> in swim with swim_cfg(), to reduce number of raft_cfg_*()
> functions, but decided it would be even worse with so many
> options.
>
> Part of #5303
> ---
LGTM.
>   src/box/box.cc    | 10 +++++-----
>   src/box/raftlib.c | 32 ++++++++++++++++++++------------
>   src/box/raftlib.h |  9 +++++++++
>   3 files changed, 34 insertions(+), 17 deletions(-)
>
> diff --git a/src/box/box.cc b/src/box/box.cc
> index cc0d7b81d..8f5f3558e 100644
> --- a/src/box/box.cc
> +++ b/src/box/box.cc
> @@ -2763,12 +2763,12 @@ box_cfg_xc(void)
>   	 * Fill in leader election parameters after bootstrap. Before it is not
>   	 * possible - there may be relevant data to recover from WAL and
>   	 * snapshot. Also until recovery is done, it is not possible to write
> -	 * new records into WAL. It is also totally safe, because relaying is
> -	 * not started until the box is configured. So it can't happen, that
> -	 * this election-enabled node will try to relay to another
> -	 * election-enabled node without election actually enabled leading to
> -	 * disconnect.
> +	 * new records into WAL. Another reason - before recovery is done,
> +	 * instance_id is not known, so Raft simply can't work.
>   	 */
> +	if (!replication_anon)
> +		raft_cfg_instance_id(box_raft(), instance_id);
> +
>   	if (box_set_election_timeout() != 0)
>   		diag_raise();
>   	/*
> diff --git a/src/box/raftlib.c b/src/box/raftlib.c
> index 0657fa85a..ca1940ba6 100644
> --- a/src/box/raftlib.c
> +++ b/src/box/raftlib.c
> @@ -296,7 +296,7 @@ raft_process_msg(struct raft *raft, const struct raft_request *req,
>   	say_info("RAFT: message %s from %u", raft_request_to_string(req),
>   		 source);
>   	assert(source > 0);
> -	assert(source != instance_id);
> +	assert(source != raft->self);
>   	if (req->term == 0 || req->state == 0) {
>   		diag_set(ClientError, ER_PROTOCOL, "Raft term and state can't "
>   			 "be zero");
> @@ -337,7 +337,7 @@ raft_process_msg(struct raft *raft, const struct raft_request *req,
>   					 raft->leader);
>   				break;
>   			}
> -			if (req->vote == instance_id) {
> +			if (req->vote == raft->self) {
>   				/*
>   				 * This is entirely valid. This instance could
>   				 * request a vote, then become a follower or
> @@ -373,7 +373,7 @@ raft_process_msg(struct raft *raft, const struct raft_request *req,
>   			break;
>   		case RAFT_STATE_CANDIDATE:
>   			/* Check if this is a vote for a competing candidate. */
> -			if (req->vote != instance_id) {
> +			if (req->vote != raft->self) {
>   				say_info("RAFT: vote request is skipped - "
>   					 "competing candidate");
>   				break;
> @@ -382,7 +382,7 @@ raft_process_msg(struct raft *raft, const struct raft_request *req,
>   			 * Vote for self was requested earlier in this round,
>   			 * and now was answered by some other instance.
>   			 */
> -			assert(raft->volatile_vote == instance_id);
> +			assert(raft->volatile_vote == raft->self);
>   			bool was_set = bit_set(&raft->vote_mask, source);
>   			raft->vote_count += !was_set;
>   			if (raft->vote_count < raft->election_quorum) {
> @@ -547,7 +547,7 @@ end_dump:
>   		} else if (raft->leader != 0) {
>   			/* There is a known leader. Wait until it is dead. */
>   			raft_sm_wait_leader_dead(raft);
> -		} else if (raft->vote == instance_id) {
> +		} else if (raft->vote == raft->self) {
>   			/* Just wrote own vote. */
>   			if (raft->election_quorum == 1)
>   				raft_sm_become_leader(raft);
> @@ -561,7 +561,7 @@ end_dump:
>   			raft_sm_wait_election_end(raft);
>   		} else {
>   			/* No leaders, no votes. */
> -			raft_sm_schedule_new_vote(raft, instance_id);
> +			raft_sm_schedule_new_vote(raft, raft->self);
>   		}
>   	} else {
>   		memset(&req, 0, sizeof(req));
> @@ -596,7 +596,7 @@ raft_worker_handle_broadcast(struct raft *raft)
>   	req.vote = raft->vote;
>   	req.state = raft->state;
>   	if (req.state == RAFT_STATE_CANDIDATE) {
> -		assert(raft->vote == instance_id);
> +		assert(raft->vote == raft->self);
>   		req.vclock = &replicaset.vclock;
>   	}
>   	replicaset_foreach(replica)
> @@ -652,7 +652,7 @@ raft_sm_become_leader(struct raft *raft)
>   	assert(raft->is_candidate);
>   	assert(!raft->is_write_in_progress);
>   	raft->state = RAFT_STATE_LEADER;
> -	raft->leader = instance_id;
> +	raft->leader = raft->self;
>   	ev_timer_stop(loop(), &raft->timer);
>   	/* Make read-write (if other subsystems allow that. */
>   	box_update_ro_summary();
> @@ -682,14 +682,14 @@ raft_sm_become_candidate(struct raft *raft)
>   	say_info("RAFT: enter candidate state with 1 self vote");
>   	assert(raft->state == RAFT_STATE_FOLLOWER);
>   	assert(raft->leader == 0);
> -	assert(raft->vote == instance_id);
> +	assert(raft->vote == raft->self);
>   	assert(raft->is_candidate);
>   	assert(!raft->is_write_in_progress);
>   	assert(raft->election_quorum > 1);
>   	raft->state = RAFT_STATE_CANDIDATE;
>   	raft->vote_count = 1;
>   	raft->vote_mask = 0;
> -	bit_set(&raft->vote_mask, instance_id);
> +	bit_set(&raft->vote_mask, raft->self);
>   	raft_sm_wait_election_end(raft);
>   	/* State is visible and it is changed - broadcast. */
>   	raft_schedule_broadcast(raft);
> @@ -736,7 +736,7 @@ raft_sm_schedule_new_election(struct raft *raft)
>   	assert(raft->is_candidate);
>   	/* Everyone is a follower until its vote for self is persisted. */
>   	raft_sm_schedule_new_term(raft, raft->term + 1);
> -	raft_sm_schedule_new_vote(raft, instance_id);
> +	raft_sm_schedule_new_vote(raft, raft->self);
>   	box_update_ro_summary();
>   }
>   
> @@ -783,7 +783,7 @@ raft_sm_wait_election_end(struct raft *raft)
>   	assert(raft->is_candidate);
>   	assert(raft->state == RAFT_STATE_FOLLOWER ||
>   	       (raft->state == RAFT_STATE_CANDIDATE &&
> -		raft->volatile_vote == instance_id));
> +		raft->volatile_vote == raft->self));
>   	assert(raft->leader == 0);
>   	double election_timeout = raft->election_timeout +
>   				  raft_new_random_election_shift(raft);
> @@ -979,6 +979,14 @@ raft_cfg_death_timeout(struct raft *raft, double death_timeout)
>   	}
>   }
>   
> +void
> +raft_cfg_instance_id(struct raft *raft, uint32_t instance_id)
> +{
> +	assert(raft->self == 0);
> +	assert(instance_id != 0);
> +	raft->self = instance_id;
> +}
> +
>   void
>   raft_new_term(struct raft *raft)
>   {
> diff --git a/src/box/raftlib.h b/src/box/raftlib.h
> index c9c13136e..f75ed2567 100644
> --- a/src/box/raftlib.h
> +++ b/src/box/raftlib.h
> @@ -95,6 +95,8 @@ const char *
>   raft_state_str(uint32_t state);
>   
>   struct raft {
> +	/** Instance ID of this node. */
> +	uint32_t self;
>   	/** Instance ID of leader of the current term. */
>   	uint32_t leader;
>   	/** State of the instance. */
> @@ -241,6 +243,13 @@ raft_cfg_election_quorum(struct raft *raft, int election_quorum);
>   void
>   raft_cfg_death_timeout(struct raft *raft, double death_timeout);
>   
> +/**
> + * Configure ID of the given Raft instance. The ID can't be changed after it is
> + * assigned first time.
> + */
> +void
> +raft_cfg_instance_id(struct raft *raft, uint32_t instance_id);
> +
>   /**
>    * Bump the term. When it is persisted, the node checks if there is a leader,
>    * and if there is not, a new election is started. That said, this function can

-- 
Serge Petrenko