[Tarantool-patches] [PATCH v4 2/4] replication: hide 0-th vclock components in replication responses

[Serge Petrenko]

If an anonymous replica is promoted to a normal one and becomes
replication master later, its vclock contains a non-empty zero
component, tracking local changes on this replica from the time when it
had been anonymous. No need to pollute joining instance's vclock with
our non-empty 0 component.
When an anonymous replica reports its status to a remote instance it
should also hide its 0-th vclock component.

This is needed for backward compatibility with old instances, which
don't ignore 0th vclock component coming from a remote instance by
default.
Also make sure that new instances ignore 0th vclock component.

Follow-up #3186
Prerequisite #4114
---
 src/box/applier.cc             |  5 ++++-
 src/box/box.cc                 | 12 ++++++++++--
 src/box/relay.cc               |  8 ++++++--
 test/replication/anon.result   |  5 +++++
 test/replication/anon.test.lua |  2 ++
 5 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/src/box/applier.cc b/src/box/applier.cc
index 47a26c366..2e765ca12 100644
--- a/src/box/applier.cc
+++ b/src/box/applier.cc
@@ -173,7 +173,10 @@ applier_writer_f(va_list ap)
 			continue;
 		try {
 			struct xrow_header xrow;
-			xrow_encode_vclock(&xrow, &replicaset.vclock);
+			struct vclock vclock;
+			vclock_copy(&vclock, &replicaset.vclock);
+			vclock_reset(&vclock, 0, 0);
+			xrow_encode_vclock(&xrow, &vclock);
 			coio_write_xrow(&io, &xrow);
 		} catch (SocketError *e) {
 			/*
diff --git a/src/box/box.cc b/src/box/box.cc
index 765d64678..87e836432 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1540,6 +1540,7 @@ box_process_fetch_snapshot(struct ev_io *io, struct xrow_header *header)
 	/* Remember master's vclock after the last request */
 	struct vclock stop_vclock;
 	vclock_copy(&stop_vclock, &replicaset.vclock);
+	vclock_reset(&stop_vclock, 0, 0);
 
 	/* Send end of snapshot data marker */
 	struct xrow_header row;
@@ -1621,7 +1622,9 @@ box_process_register(struct ev_io *io, struct xrow_header *header)
 
 	struct xrow_header row;
 	/* Send end of WAL stream marker */
-	xrow_encode_vclock_xc(&row, &replicaset.vclock);
+	vclock_copy(&vclock, &replicaset.vclock);
+	vclock_reset(&vclock, 0, 0);
+	xrow_encode_vclock_xc(&row, &vclock);
 	row.sync = header->sync;
 	coio_write_xrow(io, &row);
 
@@ -1773,7 +1776,11 @@ box_process_join(struct ev_io *io, struct xrow_header *header)
 	say_info("final data sent.");
 
 	/* Send end of WAL stream marker */
-	xrow_encode_vclock_xc(&row, &replicaset.vclock);
+	struct vclock vclock;
+	vclock_copy(&vclock, &replicaset.vclock);
+	vclock_reset(&vclock, 0, 0);
+	xrow_encode_vclock_xc(&row, &vclock);
+
 	row.sync = header->sync;
 	coio_write_xrow(io, &row);
 
@@ -1905,6 +1912,7 @@ box_process_vote(struct ballot *ballot)
 	ballot->is_loading = is_ro;
 	vclock_copy(&ballot->vclock, &replicaset.vclock);
 	vclock_copy(&ballot->gc_vclock, &gc.vclock);
+	vclock_reset(&ballot->gc_vclock, 0, 0);
 }
 
 /** Insert a new cluster into _schema */
diff --git a/src/box/relay.cc b/src/box/relay.cc
index c634348a4..9abf35fdf 100644
--- a/src/box/relay.cc
+++ b/src/box/relay.cc
@@ -322,7 +322,11 @@ relay_initial_join(int fd, uint64_t sync, struct vclock *vclock)
 
 	/* Respond to the JOIN request with the current vclock. */
 	struct xrow_header row;
-	xrow_encode_vclock_xc(&row, vclock);
+	struct vclock subst_vclock;
+	vclock_copy(&subst_vclock, vclock);
+	/* zero - out 0-th vclock component. */
+	vclock_reset(&subst_vclock, 0, 0);
+	xrow_encode_vclock_xc(&row, &subst_vclock);
 	row.sync = sync;
 	coio_write_xrow(&relay->io, &row);
 
@@ -464,7 +468,7 @@ relay_schedule_pending_gc(struct relay *relay, const struct vclock *vclock)
 		 * the greater signatures is due to changes pulled
 		 * from other members of the cluster.
 		 */
-		if (vclock_compare(&curr->vclock, vclock) > 0)
+		if (vclock_compare_ignore0(&curr->vclock, vclock) > 0)
 			break;
 		stailq_shift(&relay->pending_gc);
 		free(gc_msg);
diff --git a/test/replication/anon.result b/test/replication/anon.result
index 88061569f..cbbeeef09 100644
--- a/test/replication/anon.result
+++ b/test/replication/anon.result
@@ -187,6 +187,11 @@ a > 0
  | ---
  | - true
  | ...
+-- 0-th vclock component isn't propagated across the cluster.
+box.info.vclock[0]
+ | ---
+ | - null
+ | ...
 test_run:cmd('switch default')
  | ---
  | - true
diff --git a/test/replication/anon.test.lua b/test/replication/anon.test.lua
index 8a8d15c18..627dc5c8e 100644
--- a/test/replication/anon.test.lua
+++ b/test/replication/anon.test.lua
@@ -66,6 +66,8 @@ test_run:cmd('switch replica_anon2')
 a = box.info.vclock[1]
 -- The instance did fetch a snapshot.
 a > 0
+-- 0-th vclock component isn't propagated across the cluster.
+box.info.vclock[0]
 test_run:cmd('switch default')
 box.space.test:insert{2}
 test_run:cmd("switch replica_anon2")
-- 
2.21.1 (Apple Git-122.3)