[Tarantool-patches] [PATCH v4 1/4] vclock: add an ability to reset individual clock components

[Serge Petrenko <sergepetrenko@tarantool.org>]

Anonymous replicas use 0th vclock component to sign local rows.
vclock_reset will allow to zero-out 0th vclock component when an
anonymous replica is promoted to a normal one and sends out its vclock
to other joining instances, as to not pollute their own 0th vclock
component.

Follow-up #3186
Prerequisite #4114
---
 src/box/vclock.c | 15 +++++++++++++++
 src/box/vclock.h | 13 +++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/box/vclock.c b/src/box/vclock.c
index 90ae27591..ac3e9fccd 100644
--- a/src/box/vclock.c
+++ b/src/box/vclock.c
@@ -37,6 +37,21 @@
 #include "diag.h"
 #include "tt_static.h"
 
+void
+vclock_reset(struct vclock *vclock, uint32_t replica_id, int64_t lsn)
+{
+	assert(lsn >= 0);
+	assert(replica_id < VCLOCK_MAX);
+	vclock->signature -= vclock_get(vclock, replica_id);
+	if (lsn == 0) {
+		vclock->map &= ~(1 << replica_id);
+		return;
+	}
+	vclock->lsn[replica_id] = lsn;
+	vclock->map |= 1 << replica_id;
+	vclock->signature += lsn;
+}
+
 int64_t
 vclock_follow(struct vclock *vclock, uint32_t replica_id, int64_t lsn)
 {
diff --git a/src/box/vclock.h b/src/box/vclock.h
index 79e5a1bc0..aeb8ca66b 100644
--- a/src/box/vclock.h
+++ b/src/box/vclock.h
@@ -211,6 +211,19 @@ vclock_calc_sum(const struct vclock *vclock)
 	return sum;
 }
 
+/**
+ * Set vclock component represented by replica id to the desired
+ * value. Can be used to decrease stored LSN value for the given
+ * replica id while maintaining a valid signature or in the same
+ * manner as vclock_follow.
+ *
+ * @param vclock Vector clock.
+ * @param replica_id Replica identifier.
+ * @param lsn Lsn to set
+ */
+void
+vclock_reset(struct vclock *vclock, uint32_t replica_id, int64_t lsn);
+
 static inline int64_t
 vclock_sum(const struct vclock *vclock)
 {
-- 
2.21.1 (Apple Git-122.3)