[Tarantool-patches] [PATCH v4 05/16] replication: add META stage to JOIN

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

The new META stage is part of server's response to a join request.
It's marked by IPROTO_JOIN_META and IPROTO_JOIN_SNAPSHOT requests and goes
before the actual snapshot data.

Prerequisite #6034

@TarantoolBot document
Title: new protocol stage during JOIN

A new stage is added to the stream of JOIN rows coming from master.
The stage is marked with a bodyless row with type
IPROTO_JOIN_META = 71
Once all the rows from the stage are sent out, the JOIN continues as
before (as a stream of snapshot rows). The end of META stage is marked
with a row of type IPROTO_JOIN_SNAPSHOT = 72

The stage contains the rows that are necessary for instance
initialization (current Raft term, current state of synchronous
transaction queue), but do not belong to any system space.
---
 src/box/applier.cc         | 17 ++++++++++++++++-
 src/box/box.cc             |  5 +++--
 src/box/iproto_constants.h |  2 ++
 src/box/relay.cc           | 19 ++++++++++++++++++-
 src/box/relay.h            |  4 +++-
 5 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/src/box/applier.cc b/src/box/applier.cc
index 07fe7f5c7..0f81b7cc4 100644
--- a/src/box/applier.cc
+++ b/src/box/applier.cc
@@ -447,12 +447,26 @@ applier_wait_snapshot(struct applier *applier)
 		xrow_decode_vclock_xc(&row, &replicaset.vclock);
 	}
 
+	coio_read_xrow(coio, ibuf, &row);
+	if (row.type == IPROTO_JOIN_META) {
+		/* Read additional metadata. Empty at the moment. */
+		do {
+			coio_read_xrow(coio, ibuf, &row);
+			if (iproto_type_is_error(row.type)) {
+				xrow_decode_error_xc(&row);
+			} else if (row.type != IPROTO_JOIN_SNAPSHOT) {
+				tnt_raise(ClientError, ER_UNKNOWN_REQUEST_TYPE,
+					  (uint32_t)row.type);
+			}
+		} while (row.type != IPROTO_JOIN_SNAPSHOT);
+		coio_read_xrow(coio, ibuf, &row);
+	}
+
 	/*
 	 * Receive initial data.
 	 */
 	uint64_t row_count = 0;
 	while (true) {
-		coio_read_xrow(coio, ibuf, &row);
 		applier->last_row_time = ev_monotonic_now(loop());
 		if (iproto_type_is_dml(row.type)) {
 			if (apply_snapshot_row(&row) != 0)
@@ -477,6 +491,7 @@ applier_wait_snapshot(struct applier *applier)
 			tnt_raise(ClientError, ER_UNKNOWN_REQUEST_TYPE,
 				  (uint32_t) row.type);
 		}
+		coio_read_xrow(coio, ibuf, &row);
 	}
 
 	return row_count;
diff --git a/src/box/box.cc b/src/box/box.cc
index 6d5516682..8c695686e 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -2474,7 +2474,7 @@ box_process_fetch_snapshot(struct ev_io *io, struct xrow_header *header)
 
 	/* Send the snapshot data to the instance. */
 	struct vclock start_vclock;
-	relay_initial_join(io->fd, header->sync, &start_vclock);
+	relay_initial_join(io->fd, header->sync, &start_vclock, 0);
 	say_info("read-view sent.");
 
 	/* Remember master's vclock after the last request */
@@ -2672,7 +2672,8 @@ box_process_join(struct ev_io *io, struct xrow_header *header)
 	 * Initial stream: feed replica with dirty data from engines.
 	 */
 	struct vclock start_vclock;
-	relay_initial_join(io->fd, header->sync, &start_vclock);
+	relay_initial_join(io->fd, header->sync, &start_vclock,
+			   replica_version_id);
 	say_info("initial data sent.");
 
 	/**
diff --git a/src/box/iproto_constants.h b/src/box/iproto_constants.h
index 137bee9da..e913801a8 100644
--- a/src/box/iproto_constants.h
+++ b/src/box/iproto_constants.h
@@ -261,6 +261,8 @@ enum iproto_type {
 	IPROTO_FETCH_SNAPSHOT = 69,
 	/** REGISTER request to leave anonymous replication. */
 	IPROTO_REGISTER = 70,
+	IPROTO_JOIN_META = 71,
+	IPROTO_JOIN_SNAPSHOT = 72,
 
 	/** Vinyl run info stored in .index file */
 	VY_INDEX_RUN_INFO = 100,
diff --git a/src/box/relay.cc b/src/box/relay.cc
index 60f527b7f..4ebe0fb06 100644
--- a/src/box/relay.cc
+++ b/src/box/relay.cc
@@ -392,7 +392,8 @@ relay_set_cord_name(int fd)
 }
 
 void
-relay_initial_join(int fd, uint64_t sync, struct vclock *vclock)
+relay_initial_join(int fd, uint64_t sync, struct vclock *vclock,
+		   uint32_t replica_version_id)
 {
 	struct relay *relay = relay_new(NULL);
 	if (relay == NULL)
@@ -432,6 +433,22 @@ relay_initial_join(int fd, uint64_t sync, struct vclock *vclock)
 	row.sync = sync;
 	coio_write_xrow(&relay->io, &row);
 
+	/*
+	 * Version is present starting with 2.7.3, 2.8.2, 2.9.1
+	 * All these versions know of additional META stage of initial join.
+	 */
+	if (replica_version_id > 0) {
+		/* Mark the beginning of the metadata stream. */
+		row.type = IPROTO_JOIN_META;
+		coio_write_xrow(&relay->io, &row);
+
+		/* Empty at the moment. */
+
+		/* Mark the end of the metadata stream. */
+		row.type = IPROTO_JOIN_SNAPSHOT;
+		coio_write_xrow(&relay->io, &row);
+	}
+
 	/* Send read view to the replica. */
 	engine_join_xc(&ctx, &relay->stream);
 }
diff --git a/src/box/relay.h b/src/box/relay.h
index 615ffb75d..112428ae8 100644
--- a/src/box/relay.h
+++ b/src/box/relay.h
@@ -116,9 +116,11 @@ relay_push_raft(struct relay *relay, const struct raft_request *req);
  * @param fd        client connection
  * @param sync      sync from incoming JOIN request
  * @param vclock[out] vclock of the read view sent to the replica
+ * @param replica_version_id peer's version
  */
 void
-relay_initial_join(int fd, uint64_t sync, struct vclock *vclock);
+relay_initial_join(int fd, uint64_t sync, struct vclock *vclock,
+		   uint32_t replica_version_id);
 
 /**
  * Send final JOIN rows to the replica.
-- 
2.30.1 (Apple Git-130)