[PATCH 06/10] ddl: restore sequence value if drop is rolled back

[Vladimir Davydov <vdavydov.dev@gmail.com>]

A sequence isn't supposed to roll back to the old value if the
transaction it was used in is aborted for some reason. However,
if a sequence is dropped, we do want to restore the original
value on rollback so that we don't lose it on an unsuccessful
attempt to drop the sequence.
---
 src/box/alter.cc           | 24 ++++++++++++++++++++++++
 test/box/sequence.result   | 21 +++++++++++++++++++++
 test/box/sequence.test.lua | 10 ++++++++++
 3 files changed, 55 insertions(+)

diff --git a/src/box/alter.cc b/src/box/alter.cc
index 89ab9c65..4f046ef6 100644
--- a/src/box/alter.cc
+++ b/src/box/alter.cc
@@ -3460,6 +3460,20 @@ on_replace_dd_sequence(struct trigger * /* trigger */, void *event)
 	trigger_run_xc(&on_alter_sequence, seq);
 }
 
+/** Restore the old sequence value on rollback. */
+static void
+on_drop_sequence_data_rollback(struct trigger *trigger, void * /* event */)
+{
+	struct tuple *tuple = (struct tuple *)trigger->data;
+	uint32_t id = tuple_field_u32_xc(tuple, BOX_SEQUENCE_DATA_FIELD_ID);
+	int64_t val = tuple_field_i64_xc(tuple, BOX_SEQUENCE_DATA_FIELD_VALUE);
+
+	struct sequence *seq = sequence_by_id(id);
+	assert(seq != NULL);
+	if (sequence_set(seq, val) != 0)
+		panic("Can't restore sequence value");
+}
+
 /**
  * A trigger invoked on replace in space _sequence_data.
  * Used to update a sequence value.
@@ -3483,6 +3497,16 @@ on_replace_dd_sequence_data(struct trigger * /* trigger */, void *event)
 		if (sequence_set(seq, value) != 0)
 			diag_raise();
 	} else {					/* DELETE */
+		/*
+		 * A sequence isn't supposed to roll back to the old
+		 * value if the transaction it was used in is aborted
+		 * for some reason. However, if a sequence is dropped,
+		 * we do want to restore the original sequence value
+		 * on rollback.
+		 */
+		struct trigger *on_rollback = txn_alter_trigger_new(
+				on_drop_sequence_data_rollback, old_tuple);
+		txn_on_rollback(txn, on_rollback);
 		sequence_reset(seq);
 	}
 }
diff --git a/test/box/sequence.result b/test/box/sequence.result
index 99eed0ec..91795290 100644
--- a/test/box/sequence.result
+++ b/test/box/sequence.result
@@ -2249,3 +2249,24 @@ sq:drop()
 s:drop()
 ---
 ...
+--
+-- Check that if a deletion from _sequence_data is rolled back,
+-- the sequence state is restored.
+--
+sq = box.schema.sequence.create('test')
+---
+...
+sq:next() -- 1
+---
+- 1
+...
+box.begin() box.space._sequence_data:delete{sq.id} box.rollback()
+---
+...
+sq:next() -- 2
+---
+- 2
+...
+sq:drop()
+---
+...
diff --git a/test/box/sequence.test.lua b/test/box/sequence.test.lua
index 9615c447..b0ec020e 100644
--- a/test/box/sequence.test.lua
+++ b/test/box/sequence.test.lua
@@ -761,3 +761,13 @@ s:insert{box.NULL} -- ok
 s.index.pk:alter{sequence = false}
 sq:drop()
 s:drop()
+
+--
+-- Check that if a deletion from _sequence_data is rolled back,
+-- the sequence state is restored.
+--
+sq = box.schema.sequence.create('test')
+sq:next() -- 1
+box.begin() box.space._sequence_data:delete{sq.id} box.rollback()
+sq:next() -- 2
+sq:drop()
-- 
2.11.0