[PATCH v3 7/7] box: introduce multikey indexes in memtx

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

- In the case of multikey index arises an ambiguity: which key
  should be used in the comparison. The previously introduced
  comparison hints act as an non-negative numeric index of key
  to use,
- Memtx B+ tree replace and build_next methods have been
  patched to insert the same tuple multiple times by different
  logical indexes of the key in the array,
- Map fields have been expanded service areas "extent" that
  contain an offset of multikey index keys by additional logical
  index.

Part of #1257

@TarantoolBot document
Title: introduce multikey indexes in memtx
Any JSON index in which at least one partition contains "[*]"
- array index placeholder sign is called "Multikey".
Such indexes allows you to automatically index set of documents
having same document structure.

Multikey indexes design have a number of restrictions that must
be taken into account:
 - it cannot be primary because of the ambiguity arising from
   it's definition (primary index requires the one unique key
   that identify tuple),
 - if some node in the JSON tree of all defined indexes contains
   an array index placeholder [*], no other JSON path can use an
   explicit JSON index on it's nested field.
 - it support "unique" semantics, but it's uniqueness a little
   different from conventional indexes: you may insert a tuple
   in which the same key occurs multiple times in a unique
   multikey index, but you cannot insert a tuple when any of its
   keys is in some other tuple stored in space,
 - the unique multikey index "duplicate" conflict occurs when
   the sets of extracted keys have a non-empty logical
   intersection
 - to identify the different keys by which a given data tuple is
   indexed, each key is assigned a logical sequence number in
   the array defined with array index placeholder [*] in index
   (such array is called multikey index root),
 - no index partition can contain more than one array index
   placeholder sign [*] in it's JSON path,
 - all parts containing JSON paths with array index placeholder
   [*] must have the same (in terms of json tokens) prefix
   before this placeholder sign.

Example:
s = box.schema.space.create('withdata')
pk = s:create_index('pk')
parts = {
	{2, 'str', path = 'data[*].name'},
        {2, 'str', path = 'data[*].extra.phone'}
}
idx = s:create_index('idx', {parts = parts})
s:insert({1, {data = {{name="A", extra={phone="111"}},
                      {name="B", extra={phone="111"}}},
             garbage = 1}}
idx:get({'A', '111'})
---
 src/box/errcode.h             |   1 +
 src/box/field_map.c           |  68 +++++++-
 src/box/field_map.h           | 137 ++++++++++++++--
 src/box/index_def.c           |   5 +
 src/box/key_def.c             | 112 +++++++++----
 src/box/key_def.h             |  34 ++++
 src/box/memtx_space.c         |  18 ++
 src/box/memtx_tree.c          | 180 +++++++++++++++++---
 src/box/sql.c                 |   3 +-
 src/box/tuple.c               |  28 +++-
 src/box/tuple.h               |  81 +++++++--
 src/box/tuple_compare.cc      | 150 ++++++++++++++---
 src/box/tuple_extract_key.cc  |  41 ++++-
 src/box/tuple_format.c        | 117 +++++++++++--
 src/box/tuple_format.h        |  32 ++++
 src/box/vinyl.c               |   5 +
 test/box/misc.result          |   1 +
 test/engine/json.result       |  13 --
 test/engine/json.test.lua     |   7 -
 test/engine/multikey.result   | 298 ++++++++++++++++++++++++++++++++++
 test/engine/multikey.test.lua |  88 ++++++++++
 21 files changed, 1262 insertions(+), 157 deletions(-)
 create mode 100644 test/engine/multikey.result
 create mode 100644 test/engine/multikey.test.lua

diff --git a/src/box/errcode.h b/src/box/errcode.h
index 3f8cb8e0e..ea992a6b2 100644
--- a/src/box/errcode.h
+++ b/src/box/errcode.h
@@ -246,6 +246,7 @@ struct errcode_record {
 	/*191 */_(ER_SQL_PARSER_LIMIT,		"%s %d exceeds the limit (%d)") \
 	/*192 */_(ER_INDEX_DEF_UNSUPPORTED,	"%s are prohibited in an index definition") \
 	/*193 */_(ER_CK_DEF_UNSUPPORTED,	"%s are prohibited in a CHECK constraint definition") \
+	/*194 */_(ER_INDEX_MULTIKEY_INVALID,	"Multikey index is invalid: %s") \
 
 /*
  * !IMPORTANT! Please follow instructions at start of the file
diff --git a/src/box/field_map.c b/src/box/field_map.c
index 690aa461d..ae6c5be5f 100644
--- a/src/box/field_map.c
+++ b/src/box/field_map.c
@@ -37,6 +37,8 @@ field_map_builder_create(struct field_map_builder *builder,
 			 uint32_t minimal_field_map_size,
 			 struct region *region)
 {
+	builder->region = region;
+	builder->extents_size = 0;
 	builder->slot_count = minimal_field_map_size / sizeof(uint32_t);
 	if (minimal_field_map_size == 0) {
 		builder->slots = NULL;
@@ -53,9 +55,71 @@ field_map_builder_create(struct field_map_builder *builder,
 	return 0;
 }
 
+/**
+ * Get size of extention (in bytes) by count of items it
+ * must contain.
+ */
+static uint32_t
+field_map_ext_size(uint32_t items)
+{
+	return sizeof(struct field_map_ext) + items * sizeof(uint32_t);
+}
+
+struct field_map_ext *
+field_map_builder_ext_get(struct field_map_builder *builder,
+			  int32_t offset_slot, uint32_t extent_items)
+{
+	struct field_map_ext *extent;
+	if (builder->slots[offset_slot].has_extent) {
+		extent = builder->slots[offset_slot].extent;
+		assert(extent != NULL);
+		assert(extent->items == extent_items);
+		return extent;
+	}
+	uint32_t sz = field_map_ext_size(extent_items);
+	extent = region_alloc(builder->region, sz);
+	if (extent == NULL) {
+		diag_set(OutOfMemory, sz, "region", "extent");
+		return NULL;
+	}
+	memset(extent, 0, sz);
+	extent->items = extent_items;
+	builder->slots[offset_slot].extent = extent;
+	builder->slots[offset_slot].has_extent = true;
+	builder->extents_size += sz;
+	return extent;
+}
+
 void
 field_map_build(struct field_map_builder *builder, char *buffer)
 {
-	uint32_t field_map_size = field_map_build_size(builder);
-	memcpy(buffer, (char *)builder->slots - field_map_size, field_map_size);
+	/*
+	 * To initialize the field map and its extents, prepare
+	 * the following memory layout with pointers:
+	 *
+	 *                      offset
+	 *            +---------------------+
+	 *            |                     |
+	 * [extentK]..[extent1][[slotN]..[slot2][slot1]]
+	 *            |        |extent_wptr            |field_map
+	 *            <-       <-                     <-
+	 *
+	 * The buffer size is assumed to be sufficient to write
+	 * field_map_build_size(builder) bytes there.
+	 */
+	uint32_t *field_map =
+		(uint32_t *)(buffer + field_map_build_size(builder));
+	char *extent_wptr = buffer + builder->extents_size;
+	for (int32_t i = -1; i >= -(int32_t)builder->slot_count; i--) {
+		if (!builder->slots[i].has_extent) {
+			field_map[i] = builder->slots[i].offset;
+			continue;
+		}
+		struct field_map_ext *extent = builder->slots[i].extent;
+		/** Retrive memory for the extent. */
+		uint32_t sz = field_map_ext_size(extent->items);
+		extent_wptr -= sz;
+		field_map[i] = (char *)field_map - (char *)extent_wptr;
+		memcpy(extent_wptr, extent, sz);
+	}
 }
diff --git a/src/box/field_map.h b/src/box/field_map.h
index 47ecbd009..af578ec6b 100644
--- a/src/box/field_map.h
+++ b/src/box/field_map.h
@@ -34,6 +34,7 @@
 #include <stdint.h>
 
 struct region;
+struct field_map_builder_slot;
 
 /**
  * A field map is a special area is reserved before tuple's
@@ -46,13 +47,15 @@ struct region;
  * offset_slot(s) is performed on tuple_format creation on index
  * create or alter (see tuple_format_create()).
  *
- *              4b          4b       MessagePack data.
- *           +------+----+------+---------------------------+
- *    tuple: | offN | .. | off1 | header ..|key1|..|keyN|.. |
- *           +--+---+----+--+---+---------------------------+
- *           |     ...    |                 ^       ^
- *           |            +-----------------+       |
- *           +--------------------------------------+
+ *        4b   4b      4b          4b       MessagePack data.
+ *       +-----------+------+----+------+------------------------+
+ *tuple: |cnt|off1|..| offN | .. | off1 | header ..|key1|..|keyN||
+ *       +-----+-----+--+---+----+--+---+------------------------+
+ * ext1  ^     |        |   ...     |                 ^       ^
+ *       +-----|--------+           |                 |       |
+ * indirection |                    +-----------------+       |
+ *             +----------------------------------------------+
+ *             (offset_slot = N, extent_slot = 1) --> offset
  *
  * This field_map_builder class is used for tuple field_map
  * construction. It encapsulates field_map build logic and size
@@ -60,19 +63,88 @@ struct region;
  *
  * Each field offset is a positive number, except the case when
  * a field is not in the tuple. In this case offset is 0.
+ *
+ * Some slots may store an offset of the field_map_ext structure,
+ * which contains an additional sequence of offsets of size
+ * defined above(see field_map_ext layout). The caller needs to
+ * be aware of when the slot is an offset of the data and when
+ * it is the offset of the field_map_ext.
+ *
+ * Now these extents are used to organize a multikey index.
+ * The count of keys in the multikey index imposes the count of
+ * items in extent while the i-th extent's slot contains the
+ * offset of the i-th key field.
  */
 struct field_map_builder {
 	/**
-	 * The pointer to the end of filed_map allocation.
+	 * The pointer to the end of field_map_builder_slot(s)
+	 * allocation.
 	 * Its elements are accessible by negative indexes
 	 * that coinciding with offset_slot(s).
 	 */
-	uint32_t *slots;
+	struct field_map_builder_slot *slots;
 	/**
 	 * The count of slots in field_map_builder::slots
 	 * allocation.
 	 */
 	uint32_t slot_count;
+	/**
+	 * Total size of memory is allocated for field_map
+	 * extentions.
+	 */
+	uint32_t extents_size;
+	/**
+	 * Region to use to perform memory allocations.
+	 */
+	struct region *region;
+};
+
+/**
+ * Internal stucture representing field_map extent.
+ * (see field_map_builder description).
+ */
+struct field_map_ext {
+	/** Count of field_map_ext::offset[] elements. */
+	uint32_t items;
+	/** Data offset in tuple array. */
+	uint32_t offset[0];
+};
+
+/**
+ * Internal function to get or allocate field map extent
+ * by offset_slot, and count of items.
+ */
+struct field_map_ext *
+field_map_builder_ext_get(struct field_map_builder *builder,
+			  int32_t offset_slot, uint32_t extent_items);
+
+/**
+ * Instead of using uint32_t offset slots directly the
+ * field_map_builder uses this structure as a storage atom.
+ * When there is a need to initialize an extent, the
+ * field_map_builder allocates a new memory chunk and sets
+ * field_map_builder_slot::pointer (instead of real field_map
+ * reallocation).
+ *
+ * On field_map_build, all of the extents are dumped to the same
+ * memory chunk that the regular field_map slots and corresponding
+ * slots represent relative field_map_ext offset instead of
+ * field data offset.
+ *
+ * The allocated memory is accounted for in extents_size.
+ */
+struct field_map_builder_slot {
+	/**
+	 * True when this slot must be interpret as
+	 * extention pointer.
+	 */
+	bool has_extent;
+	union {
+		/** Data offset in tuple. */
+		uint32_t offset;
+		/** Pointer to field_map_ext extention. */
+		struct field_map_ext *extent;
+	};
 };
 
 /**
@@ -82,9 +154,22 @@ struct field_map_builder {
  * When a field is not in the data tuple, its offset is 0.
  */
 static inline uint32_t
-field_map_get_offset(const uint32_t *field_map, int32_t offset_slot)
+field_map_get_offset(const uint32_t *field_map, int32_t offset_slot,
+		     int multikey_idx)
 {
-	return field_map[offset_slot];
+	uint32_t offset;
+	if (multikey_idx >= 0) {
+		assert(field_map[offset_slot] != 0);
+		struct field_map_ext *extent =
+			(struct field_map_ext *)((char *)field_map -
+						 field_map[offset_slot]);
+		if ((uint32_t)multikey_idx >= extent->items)
+			return 0;
+		offset = extent->offset[multikey_idx];
+	} else {
+		offset = field_map[offset_slot];
+	}
+	return offset;
 }
 
 /**
@@ -116,7 +201,32 @@ field_map_builder_set_slot(struct field_map_builder *builder,
 {
 	assert(offset_slot < 0);
 	assert(offset > 0);
-	builder->slots[offset_slot] = offset;
+	builder->slots[offset_slot].offset = offset;
+}
+
+/**
+ * Set data offset in field map extent (by given offset_slot,
+ * extent_slot and extent_items) for a field identified by
+ * unique offset_slot.
+ *
+ * The offset_slot argument must be negative and offset must be
+ * positive (by definition).
+ */
+static inline int
+field_map_builder_set_extent_slot(struct field_map_builder *builder,
+				  int32_t offset_slot, int32_t extent_slot,
+				  uint32_t extent_items, uint32_t offset)
+{
+	assert(offset_slot < 0);
+	assert(offset > 0);
+	assert(extent_slot >= 0 && extent_items > 0);
+	struct field_map_ext *extent =
+		field_map_builder_ext_get(builder, offset_slot, extent_items);
+	if (extent == NULL)
+		return -1;
+	assert(extent->items == extent_items);
+	extent->offset[extent_slot] = offset;
+	return 0;
 }
 
 /**
@@ -125,7 +235,8 @@ field_map_builder_set_slot(struct field_map_builder *builder,
 static inline uint32_t
 field_map_build_size(struct field_map_builder *builder)
 {
-	return builder->slot_count * sizeof(uint32_t);
+	return builder->slot_count * sizeof(uint32_t) +
+	       builder->extents_size;
 }
 
 /**
diff --git a/src/box/index_def.c b/src/box/index_def.c
index c743d12ce..8c9a99551 100644
--- a/src/box/index_def.c
+++ b/src/box/index_def.c
@@ -269,6 +269,11 @@ index_def_is_valid(struct index_def *index_def, const char *space_name)
 			 space_name, "too many key parts");
 		return false;
 	}
+	if (index_def->iid == 0 && key_def_is_multikey(index_def->key_def)) {
+		diag_set(ClientError, ER_MODIFY_INDEX, index_def->name,
+			 space_name, "primary key cannot be multikey");
+		return false;
+	}
 	for (uint32_t i = 0; i < index_def->key_def->part_count; i++) {
 		assert(index_def->key_def->parts[i].type < field_type_MAX);
 		if (index_def->key_def->parts[i].fieldno > BOX_INDEX_FIELD_MAX) {
diff --git a/src/box/key_def.c b/src/box/key_def.c
index 55dcf1eb5..4d36560e0 100644
--- a/src/box/key_def.c
+++ b/src/box/key_def.c
@@ -138,7 +138,57 @@ key_def_set_func(struct key_def *def)
 	key_def_set_extract_func(def);
 }
 
-static void
+static int
+key_def_set_part_path(struct key_def *def, uint32_t part_no, const char *path,
+		      uint32_t path_len, char **path_pool)
+{
+	struct key_part *part = &def->parts[part_no];
+	if (path == NULL) {
+		part->path = NULL;
+		part->path_len = 0;
+		return 0;
+	}
+	assert(path_pool != NULL);
+	part->path = *path_pool;
+	*path_pool += path_len;
+	memcpy(part->path, path, path_len);
+	part->path_len = path_len;
+
+	/*
+	 * Test whether this key_part has array index
+	 * placeholder [*] (i.e. is a part of multikey index
+	 * definition).
+	 */
+	int multikey_path_len =
+		json_path_multikey_offset(path, path_len, TUPLE_INDEX_BASE);
+	if (multikey_path_len < 0)
+		return 0;
+
+	/*
+	 * In case of multikey index key_parts must have the
+	 * same JSON prefix.
+	 */
+	if (!key_def_is_multikey(def)) {
+		/*
+		 * Keep the index of the first multikey key_part
+		 * and the length of JSON path substring to the
+		 * array index placeholder sign [*].
+		 */
+		def->multikey_path = part->path;
+		def->multikey_fieldno = part->fieldno;
+		def->multikey_path_len = (uint32_t)multikey_path_len;
+	} else if (json_path_cmp(path, multikey_path_len, def->multikey_path,
+				 def->multikey_path_len,
+				 TUPLE_INDEX_BASE) != 0) {
+		diag_set(ClientError, ER_WRONG_INDEX_OPTIONS,
+			 part_no + TUPLE_INDEX_BASE,
+			 "incompatable multikey index path");
+		return -1;
+	}
+	return 0;
+}
+
+static int
 key_def_set_part(struct key_def *def, uint32_t part_no, uint32_t fieldno,
 		 enum field_type type, enum on_conflict_action nullable_action,
 		 struct coll *coll, uint32_t coll_id,
@@ -158,17 +208,8 @@ key_def_set_part(struct key_def *def, uint32_t part_no, uint32_t fieldno,
 	def->parts[part_no].sort_order = sort_order;
 	def->parts[part_no].offset_slot_cache = offset_slot;
 	def->parts[part_no].format_epoch = format_epoch;
-	if (path != NULL) {
-		assert(path_pool != NULL);
-		def->parts[part_no].path = *path_pool;
-		*path_pool += path_len;
-		memcpy(def->parts[part_no].path, path, path_len);
-		def->parts[part_no].path_len = path_len;
-	} else {
-		def->parts[part_no].path = NULL;
-		def->parts[part_no].path_len = 0;
-	}
 	column_mask_set_fieldno(&def->column_mask, fieldno);
+	return key_def_set_part_path(def, part_no, path, path_len, path_pool);
 }
 
 struct key_def *
@@ -203,10 +244,14 @@ key_def_new(const struct key_part_def *parts, uint32_t part_count)
 			coll = coll_id->coll;
 		}
 		uint32_t path_len = part->path != NULL ? strlen(part->path) : 0;
-		key_def_set_part(def, i, part->fieldno, part->type,
-				 part->nullable_action, coll, part->coll_id,
-				 part->sort_order, part->path, path_len,
-				 &path_pool, TUPLE_OFFSET_SLOT_NIL, 0);
+		if (key_def_set_part(def, i, part->fieldno, part->type,
+				     part->nullable_action, coll, part->coll_id,
+				     part->sort_order, part->path, path_len,
+				     &path_pool, TUPLE_OFFSET_SLOT_NIL,
+				     0) != 0) {
+			key_def_delete(def);
+			return NULL;
+		}
 	}
 	assert(path_pool == (char *)def + sz);
 	key_def_set_func(def);
@@ -256,11 +301,12 @@ box_key_def_new(uint32_t *fields, uint32_t *types, uint32_t part_count)
 	key_def->unique_part_count = part_count;
 
 	for (uint32_t item = 0; item < part_count; ++item) {
-		key_def_set_part(key_def, item, fields[item],
-				 (enum field_type)types[item],
-				 ON_CONFLICT_ACTION_DEFAULT,
-				 NULL, COLL_NONE, SORT_ORDER_ASC, NULL, 0,
-				 NULL, TUPLE_OFFSET_SLOT_NIL, 0);
+		if (key_def_set_part(key_def, item, fields[item],
+				     (enum field_type)types[item],
+				     ON_CONFLICT_ACTION_DEFAULT, NULL,
+				     COLL_NONE, SORT_ORDER_ASC, NULL, 0, NULL,
+				     TUPLE_OFFSET_SLOT_NIL, 0) != 0)
+			unreachable();
 	}
 	key_def_set_func(key_def);
 	return key_def;
@@ -685,11 +731,13 @@ key_def_merge(const struct key_def *first, const struct key_def *second)
 	part = first->parts;
 	end = part + first->part_count;
 	for (; part != end; part++) {
-		key_def_set_part(new_def, pos++, part->fieldno, part->type,
-				 part->nullable_action, part->coll,
-				 part->coll_id, part->sort_order, part->path,
-				 part->path_len, &path_pool,
-				 part->offset_slot_cache, part->format_epoch);
+		if (key_def_set_part(new_def, pos++, part->fieldno, part->type,
+				     part->nullable_action, part->coll,
+				     part->coll_id, part->sort_order,
+				     part->path, part->path_len, &path_pool,
+				     part->offset_slot_cache,
+				     part->format_epoch) != 0)
+			unreachable();
 	}
 
 	/* Set-append second key def's part to the new key def. */
@@ -698,11 +746,15 @@ key_def_merge(const struct key_def *first, const struct key_def *second)
 	for (; part != end; part++) {
 		if (!key_def_can_merge(first, part))
 			continue;
-		key_def_set_part(new_def, pos++, part->fieldno, part->type,
-				 part->nullable_action, part->coll,
-				 part->coll_id, part->sort_order, part->path,
-				 part->path_len, &path_pool,
-				 part->offset_slot_cache, part->format_epoch);
+		if (key_def_set_part(new_def, pos++, part->fieldno, part->type,
+				     part->nullable_action, part->coll,
+				     part->coll_id, part->sort_order,
+				     part->path, part->path_len, &path_pool,
+				     part->offset_slot_cache,
+				     part->format_epoch) != 0) {
+			key_def_delete(new_def);
+			return NULL;
+		}
 	}
 	assert(path_pool == (char *)new_def + sz);
 	key_def_set_func(new_def);
diff --git a/src/box/key_def.h b/src/box/key_def.h
index 288cf7270..3adf20453 100644
--- a/src/box/key_def.h
+++ b/src/box/key_def.h
@@ -234,6 +234,34 @@ struct key_def {
 	bool has_optional_parts;
 	/** Key fields mask. @sa column_mask.h for details. */
 	uint64_t column_mask;
+	/**
+	 * In case of the multikey index, a pointer to the
+	 * JSON path string, the path to the root node of
+	 * multikey index that contains the array having
+	 * index placeholder sign [*].
+	 *
+	 * This pointer duplicates the JSON path of some key_part.
+	 * This path is not 0-terminated. Moreover, it is only
+	 * JSON path subpath so key_def::multikey_path_len must be
+	 * directly used in all cases.
+	 *
+	 * This field is not NULL iff this is multikey index
+	 * key definition.
+	 */
+	const char *multikey_path;
+	/**
+	 * The length of the key_def::multikey_path.
+	 * Valid when key_def_is_multikey(key_def) is true,
+	 * undefined otherwise.
+	 */
+	uint32_t multikey_path_len;
+	/**
+	 * The index of the root field of the multikey JSON
+	 * path index key_def::multikey_path.
+	 * Valid when key_def_is_multikey(key_def) is true,
+	 * undefined otherwise.
+	*/
+	uint32_t multikey_fieldno;
 	/** The size of the 'parts' array. */
 	uint32_t part_count;
 	/** Description of parts of a multipart index. */
@@ -472,6 +500,12 @@ key_def_is_sequential(const struct key_def *key_def)
 	return true;
 }
 
+static inline bool
+key_def_is_multikey(const struct key_def *key_def)
+{
+	return key_def->multikey_path != NULL;
+}
+
 /**
  * Return true if @a key_def defines has fields that requires
  * special collation comparison.
diff --git a/src/box/memtx_space.c b/src/box/memtx_space.c
index d8529fe0e..ca5f7426d 100644
--- a/src/box/memtx_space.c
+++ b/src/box/memtx_space.c
@@ -638,6 +638,12 @@ memtx_space_check_index_def(struct space *space, struct index_def *index_def)
 				 "HASH index must be unique");
 			return -1;
 		}
+		if (key_def_is_multikey(index_def->key_def)) {
+			diag_set(ClientError, ER_MODIFY_INDEX,
+				 index_def->name, space_name(space),
+				 "HASH index cannot be multikey");
+			return -1;
+		}
 		break;
 	case TREE:
 		/* TREE index has no limitations. */
@@ -661,6 +667,12 @@ memtx_space_check_index_def(struct space *space, struct index_def *index_def)
 				 "RTREE index field type must be ARRAY");
 			return -1;
 		}
+		if (key_def_is_multikey(index_def->key_def)) {
+			diag_set(ClientError, ER_MODIFY_INDEX,
+				 index_def->name, space_name(space),
+				 "RTREE index cannot be multikey");
+			return -1;
+		}
 		/* no furter checks of parts needed */
 		return 0;
 	case BITSET:
@@ -683,6 +695,12 @@ memtx_space_check_index_def(struct space *space, struct index_def *index_def)
 				 "BITSET index field type must be NUM or STR");
 			return -1;
 		}
+		if (key_def_is_multikey(index_def->key_def)) {
+			diag_set(ClientError, ER_MODIFY_INDEX,
+				 index_def->name, space_name(space),
+				 "BITSET index cannot be multikey");
+			return -1;
+		}
 		/* no furter checks of parts needed */
 		return 0;
 	default:
diff --git a/src/box/memtx_tree.c b/src/box/memtx_tree.c
index fe037c54a..fa8a04664 100644
--- a/src/box/memtx_tree.c
+++ b/src/box/memtx_tree.c
@@ -584,6 +584,77 @@ memtx_tree_index_replace(struct index *base, struct tuple *old_tuple,
 	return 0;
 }
 
+static int
+memtx_tree_index_replace_multikey(struct index *base, struct tuple *old_tuple,
+				  struct tuple *new_tuple,
+				  enum dup_replace_mode mode,
+				  struct tuple **result)
+{
+	struct memtx_tree_index *index = (struct memtx_tree_index *)base;
+	struct key_def *cmp_def = memtx_tree_cmp_def(&index->tree);
+	if (new_tuple != NULL) {
+		int errcode = 0, tree_res = 0;
+		struct memtx_tree_data new_data, dup_data;
+		new_data.tuple = new_tuple;
+		int multikey_idx = 0;
+		uint32_t items = tuple_field_multikey_items(new_tuple, cmp_def);
+		for (; (uint32_t)multikey_idx < items; multikey_idx++) {
+			new_data.hint = multikey_idx;
+			dup_data.tuple = NULL;
+			tree_res = memtx_tree_insert(&index->tree, new_data,
+						     &dup_data);
+			if (tree_res != 0) {
+				diag_set(OutOfMemory, MEMTX_EXTENT_SIZE,
+					 "memtx_tree_index", "replace");
+				break;
+			}
+			errcode = new_tuple == dup_data.tuple ? 0 :
+				  replace_check_dup(old_tuple, dup_data.tuple,
+						    mode);
+			if (errcode != 0) {
+				memtx_tree_delete(&index->tree, new_data);
+				if (dup_data.tuple != NULL) {
+					/* Rollback replace. */
+					memtx_tree_insert(&index->tree,
+							  dup_data, NULL);
+				}
+				struct space *sp =
+					space_cache_find(base->def->space_id);
+				if (sp != NULL) {
+					diag_set(ClientError, errcode,
+						 base->def->name,
+						 space_name(sp));
+				}
+				break;
+			}
+		}
+		if (tree_res != 0 || errcode != 0) {
+			multikey_idx--;
+			for (; multikey_idx >= 0; multikey_idx--) {
+				new_data.hint = multikey_idx;
+				memtx_tree_delete(&index->tree, new_data);
+			}
+			return -1;
+		}
+		if (dup_data.tuple != NULL) {
+			*result = dup_data.tuple;
+			return 0;
+		}
+	}
+	if (old_tuple != NULL) {
+		struct memtx_tree_data old_data;
+		old_data.tuple = old_tuple;
+		uint32_t items = tuple_field_multikey_items(old_tuple, cmp_def);
+		for (uint32_t multikey_idx = 0; multikey_idx < items;
+		     multikey_idx++) {
+			old_data.hint = multikey_idx;
+			memtx_tree_delete(&index->tree, old_data);
+		}
+	}
+	*result = old_tuple;
+	return 0;
+}
+
 static struct iterator *
 memtx_tree_index_create_iterator(struct index *base, enum iterator_type type,
 				 const char *key, uint32_t part_count)
@@ -656,34 +727,42 @@ memtx_tree_index_reserve(struct index *base, uint32_t size_hint)
 }
 
 static int
-memtx_tree_index_build_next(struct index *base, struct tuple *tuple)
+memtx_tree_index_build_array_realloc(struct memtx_tree_index *index,
+				     uint32_t items)
 {
-	struct memtx_tree_index *index = (struct memtx_tree_index *)base;
-	struct key_def *cmp_def = memtx_tree_cmp_def(&index->tree);
+	bool need_realloc = false;
 	if (index->build_array == NULL) {
-		index->build_array = malloc(MEMTX_EXTENT_SIZE);
-		if (index->build_array == NULL) {
-			diag_set(OutOfMemory, MEMTX_EXTENT_SIZE,
-				 "memtx_tree_index", "build_next");
-			return -1;
-		}
-		index->build_array_alloc_size =
-			MEMTX_EXTENT_SIZE / sizeof(index->build_array[0]);
+		index->build_array_alloc_size = MEMTX_EXTENT_SIZE /
+						sizeof(index->build_array[0]);
+		need_realloc = true;
 	}
-	assert(index->build_array_size <= index->build_array_alloc_size);
-	if (index->build_array_size == index->build_array_alloc_size) {
-		index->build_array_alloc_size = index->build_array_alloc_size +
-					index->build_array_alloc_size / 2;
-		struct memtx_tree_data *tmp =
-			realloc(index->build_array,
-				index->build_array_alloc_size * sizeof(*tmp));
-		if (tmp == NULL) {
-			diag_set(OutOfMemory, index->build_array_alloc_size *
-				 sizeof(*tmp), "memtx_tree_index", "build_next");
-			return -1;
-		}
-		index->build_array = tmp;
+	uint32_t build_array_new_size = index->build_array_size + items;
+	if (build_array_new_size > index->build_array_alloc_size) {
+		index->build_array_alloc_size +=
+			MAX(index->build_array_alloc_size / 2,
+			    build_array_new_size - index->build_array_alloc_size);
+		need_realloc = true;
+	}
+	if (!need_realloc)
+		return 0;
+	struct memtx_tree_data *tmp = realloc(index->build_array,
+			index->build_array_alloc_size * sizeof(*tmp));
+	if (tmp == NULL) {
+		diag_set(OutOfMemory, index->build_array_alloc_size *
+			 sizeof(*tmp), "memtx_tree_index", "build_next");
+		return -1;
 	}
+	index->build_array = tmp;
+	return 0;
+}
+
+static int
+memtx_tree_index_build_next(struct index *base, struct tuple *tuple)
+{
+	struct memtx_tree_index *index = (struct memtx_tree_index *)base;
+	struct key_def *cmp_def = memtx_tree_cmp_def(&index->tree);
+	if (memtx_tree_index_build_array_realloc(index, 1) != 0)
+		return -1;
 	struct memtx_tree_data *elem =
 		&index->build_array[index->build_array_size++];
 	elem->tuple = tuple;
@@ -691,6 +770,24 @@ memtx_tree_index_build_next(struct index *base, struct tuple *tuple)
 	return 0;
 }
 
+static int
+memtx_tree_index_build_next_multikey(struct index *base, struct tuple *tuple)
+{
+	struct memtx_tree_index *index = (struct memtx_tree_index *)base;
+	struct key_def *cmp_def = memtx_tree_cmp_def(&index->tree);
+	uint32_t items = tuple_field_multikey_items(tuple, cmp_def);
+	if (memtx_tree_index_build_array_realloc(index, items) != 0)
+		return -1;
+	for (uint32_t multikey_idx = 0; multikey_idx < items; multikey_idx++) {
+		struct memtx_tree_data *elem =
+			&index->build_array[index->build_array_size++];
+		assert(index->build_array_size <= index->build_array_alloc_size);
+		elem->tuple = tuple;
+		elem->hint = multikey_idx;
+	}
+	return 0;
+}
+
 static void
 memtx_tree_index_end_build(struct index *base)
 {
@@ -793,6 +890,36 @@ static const struct index_vtab memtx_tree_index_vtab = {
 	/* .end_build = */ memtx_tree_index_end_build,
 };
 
+static const struct index_vtab memtx_tree_index_multikey_vtab = {
+	/* .destroy = */ memtx_tree_index_destroy,
+	/* .commit_create = */ generic_index_commit_create,
+	/* .abort_create = */ generic_index_abort_create,
+	/* .commit_modify = */ generic_index_commit_modify,
+	/* .commit_drop = */ generic_index_commit_drop,
+	/* .update_def = */ memtx_tree_index_update_def,
+	/* .depends_on_pk = */ memtx_tree_index_depends_on_pk,
+	/* .def_change_requires_rebuild = */
+		memtx_index_def_change_requires_rebuild,
+	/* .size = */ memtx_tree_index_size,
+	/* .bsize = */ memtx_tree_index_bsize,
+	/* .min = */ generic_index_min,
+	/* .max = */ generic_index_max,
+	/* .random = */ memtx_tree_index_random,
+	/* .count = */ memtx_tree_index_count,
+	/* .get = */ memtx_tree_index_get,
+	/* .replace = */ memtx_tree_index_replace_multikey,
+	/* .create_iterator = */ memtx_tree_index_create_iterator,
+	/* .create_snapshot_iterator = */
+		memtx_tree_index_create_snapshot_iterator,
+	/* .stat = */ generic_index_stat,
+	/* .compact = */ generic_index_compact,
+	/* .reset_stat = */ generic_index_reset_stat,
+	/* .begin_build = */ memtx_tree_index_begin_build,
+	/* .reserve = */ memtx_tree_index_reserve,
+	/* .build_next = */ memtx_tree_index_build_next_multikey,
+	/* .end_build = */ memtx_tree_index_end_build,
+};
+
 struct index *
 memtx_tree_index_new(struct memtx_engine *memtx, struct index_def *def)
 {
@@ -803,8 +930,11 @@ memtx_tree_index_new(struct memtx_engine *memtx, struct index_def *def)
 			 "malloc", "struct memtx_tree_index");
 		return NULL;
 	}
+	const struct index_vtab *vtab = key_def_is_multikey(def->key_def) ?
+					&memtx_tree_index_multikey_vtab :
+					&memtx_tree_index_vtab;
 	if (index_create(&index->base, (struct engine *)memtx,
-			 &memtx_tree_index_vtab, def) != 0) {
+			 vtab, def) != 0) {
 		free(index);
 		return NULL;
 	}
diff --git a/src/box/sql.c b/src/box/sql.c
index 7d5c3a8e0..be2212ef1 100644
--- a/src/box/sql.c
+++ b/src/box/sql.c
@@ -788,7 +788,8 @@ tarantoolsqlIdxKeyCompare(struct BtCursor *cursor,
 			} else {
 				uint32_t field_offset =
 					field_map_get_offset(field_map,
-							     field->offset_slot);
+							     field->offset_slot,
+							     -1);
 				p = base + field_offset;
 			}
 		}
diff --git a/src/box/tuple.c b/src/box/tuple.c
index 570e4c192..8c2cd7611 100644
--- a/src/box/tuple.c
+++ b/src/box/tuple.c
@@ -130,7 +130,7 @@ tuple_validate_raw(struct tuple_format *format, const char *tuple)
 	int rc = tuple_field_map_create(&builder, format, tuple, true);
 	region_truncate(region, region_svp);
 	assert(rc != 0 ||
-	       field_map_build_size(&builder) == format->field_map_size);
+	       field_map_build_size(&builder) >= format->field_map_size);
 	return rc;
 }
 
@@ -455,7 +455,8 @@ tuple_field_go_to_key(const char **field, const char *key, int len)
 }
 
 int
-tuple_go_to_path(const char **data, const char *path, uint32_t path_len)
+tuple_go_to_path(const char **data, const char *path, uint32_t path_len,
+		 int multikey_idx)
 {
 	int rc;
 	struct json_lexer lexer;
@@ -463,6 +464,10 @@ tuple_go_to_path(const char **data, const char *path, uint32_t path_len)
 	json_lexer_create(&lexer, path, path_len, TUPLE_INDEX_BASE);
 	while ((rc = json_lexer_next_token(&lexer, &token)) == 0) {
 		switch (token.type) {
+		case JSON_TOKEN_ANY:
+			assert(multikey_idx >= 0);
+			token.num = multikey_idx;
+			FALLTHROUGH;
 		case JSON_TOKEN_NUM:
 			rc = tuple_field_go_to_index(data, token.num);
 			break;
@@ -532,7 +537,24 @@ tuple_field_raw_by_full_path(struct tuple_format *format, const char *tuple,
 	}
 	return tuple_field_raw_by_path(format, tuple, field_map, fieldno,
 				       path + lexer.offset,
-				       path_len - lexer.offset, NULL);
+				       path_len - lexer.offset, NULL, -1);
+}
+
+uint32_t
+tuple_field_raw_multikey_items(struct tuple_format *format, const char *data,
+			       const uint32_t *field_map,
+			       struct key_def *key_def)
+{
+	assert(key_def_is_multikey(key_def));
+	const char *array_raw =
+		tuple_field_raw_by_path(format, data, field_map,
+					key_def->multikey_fieldno,
+					key_def->multikey_path,
+					key_def->multikey_path_len, NULL, -1);
+	if (array_raw == NULL)
+		return 0;
+	assert(mp_typeof(*array_raw) == MP_ARRAY);
+	return mp_decode_array(&array_raw);
 }
 
 /* }}} tuple_field_* getters */
diff --git a/src/box/tuple.h b/src/box/tuple.h
index da4085bcf..99753c8d5 100644
--- a/src/box/tuple.h
+++ b/src/box/tuple.h
@@ -508,14 +508,19 @@ tuple_field_count(const struct tuple *tuple)
  *                      with NULL.
  * @param path The path to process.
  * @param path_len The length of the @path.
+ * @param multikey_idx The multikey index hint - index of
+ *                     document to retrieve when array index
+ *                     placeholder "[*]" is met.
  * @retval 0 On success.
  * @retval -1 In case of error in JSON path.
  */
 int
-tuple_go_to_path(const char **data, const char *path, uint32_t path_len);
+tuple_go_to_path(const char **data, const char *path, uint32_t path_len,
+		 int multikey_idx);
 
 /**
- * Get tuple field by field index and relative JSON path.
+ * Get tuple field by field index, relative JSON path and
+ * multikey_idx.
  * @param format Tuple format.
  * @param tuple MessagePack tuple's body.
  * @param field_map Tuple field map.
@@ -528,12 +533,15 @@ tuple_go_to_path(const char **data, const char *path, uint32_t path_len);
  *                         access data in a single operation.
  *                         Else it is initialized with offset_slot
  *                         of format field by path.
+ * @param multikey_idx The multikey index hint - index of
+ *                     document to retrieve when array index
+ *                     placeholder "[*]" is met.
  */
 static inline const char *
 tuple_field_raw_by_path(struct tuple_format *format, const char *tuple,
 			const uint32_t *field_map, uint32_t fieldno,
 			const char *path, uint32_t path_len,
-			int32_t *offset_slot_hint)
+			int32_t *offset_slot_hint, int multikey_idx)
 {
 	int32_t offset_slot;
 	if (offset_slot_hint != NULL &&
@@ -560,7 +568,8 @@ tuple_field_raw_by_path(struct tuple_format *format, const char *tuple,
 			*offset_slot_hint = offset_slot;
 offset_slot_access:
 		/* Indexed field */
-		offset = field_map_get_offset(field_map, offset_slot);
+		offset = field_map_get_offset(field_map, offset_slot,
+					      multikey_idx);
 		if (offset == 0)
 			return NULL;
 		tuple += offset;
@@ -574,8 +583,8 @@ parse:
 		for (uint32_t k = 0; k < fieldno; k++)
 			mp_next(&tuple);
 		if (path != NULL &&
-		    unlikely(tuple_go_to_path(&tuple, path,
-						    path_len) != 0))
+		    unlikely(tuple_go_to_path(&tuple, path, path_len,
+					      multikey_idx) != 0))
 			return NULL;
 	}
 	return tuple;
@@ -597,7 +606,7 @@ tuple_field_raw(struct tuple_format *format, const char *tuple,
 		const uint32_t *field_map, uint32_t field_no)
 {
 	return tuple_field_raw_by_path(format, tuple, field_map, field_no,
-				       NULL, 0, NULL);
+				       NULL, 0, NULL, -1);
 }
 
 /**
@@ -636,16 +645,19 @@ tuple_field_raw_by_full_path(struct tuple_format *format, const char *tuple,
 			     uint32_t path_len, uint32_t path_hash);
 
 /**
- * Get a tuple field pointed to by an index part.
+ * Get a tuple field pointed to by an index part and multikey
+ * index hint.
  * @param format Tuple format.
- * @param tuple A pointer to MessagePack array.
+ * @param data A pointer to MessagePack array.
  * @param field_map A pointer to the LAST element of field map.
  * @param part Index part to use.
+ * @param multikey_idx A multikey index hint.
  * @retval Field data if the field exists or NULL.
  */
 static inline const char *
-tuple_field_raw_by_part(struct tuple_format *format, const char *data,
-			const uint32_t *field_map, struct key_part *part)
+tuple_field_raw_by_part_multikey(struct tuple_format *format, const char *data,
+				 const uint32_t *field_map,
+				 struct key_part *part, int multikey_idx)
 {
 	if (unlikely(part->format_epoch != format->epoch)) {
 		assert(format->epoch != 0);
@@ -658,7 +670,23 @@ tuple_field_raw_by_part(struct tuple_format *format, const char *data,
 	}
 	return tuple_field_raw_by_path(format, data, field_map, part->fieldno,
 				       part->path, part->path_len,
-				       &part->offset_slot_cache);
+				       &part->offset_slot_cache, multikey_idx);
+}
+
+/**
+ * Get a tuple field pointed to by an index part.
+ * @param format Tuple format.
+ * @param data A pointer to MessagePack array.
+ * @param field_map A pointer to the LAST element of field map.
+ * @param part Index part to use.
+ * @retval Field data if the field exists or NULL.
+ */
+static inline const char *
+tuple_field_raw_by_part(struct tuple_format *format, const char *data,
+			const uint32_t *field_map, struct key_part *part)
+{
+	return tuple_field_raw_by_part_multikey(format, data, field_map,
+						part, -1);
 }
 
 /**
@@ -674,6 +702,35 @@ tuple_field_by_part(const struct tuple *tuple, struct key_part *part)
 				       tuple_field_map(tuple), part);
 }
 
+/**
+ * Get count of documents in tuple by given multikey index
+ * definition.
+ * @param format Tuple format.
+ * @param data A pointer to MessagePack array.
+ * @param field_map A pointer to the LAST element of field map.
+ * @param key_def Index key_definition.
+ * @retval Count of documents in the multikey index.
+ */
+uint32_t
+tuple_field_raw_multikey_items(struct tuple_format *format, const char *data,
+			       const uint32_t *field_map,
+			       struct key_def *key_def);
+
+/**
+ * Get count of documents in tuple by given multikey index
+ * definition.
+ * @param tuple Tuple to get the count of documents from.
+ * @param key_def Index key_definition.
+ * @retval Count of documents in the multikey index.
+ */
+static inline uint32_t
+tuple_field_multikey_items(struct tuple *tuple, struct key_def *key_def)
+{
+	return tuple_field_raw_multikey_items(tuple_format(tuple),
+					      tuple_data(tuple),
+					      tuple_field_map(tuple), key_def);
+}
+
 /**
  * @brief Tuple Interator
  */
diff --git a/src/box/tuple_compare.cc b/src/box/tuple_compare.cc
index 93756365b..bf3a23097 100644
--- a/src/box/tuple_compare.cc
+++ b/src/box/tuple_compare.cc
@@ -375,6 +375,29 @@ mp_compare_scalar_coll(const char *field_a, const char *field_b,
 	return mp_compare_scalar_with_type(field_a, type_a, field_b, type_b);
 }
 
+static inline int
+tuple_compare_stub(const struct tuple *tuple_a, const struct tuple *tuple_b,
+		   struct key_def *key_def)
+{
+	(void)tuple_a;
+	(void)tuple_b;
+	(void)key_def;
+	unreachable();
+	return 0;
+}
+
+static inline int
+tuple_compare_with_key_stub(const struct tuple *tuple, const char *key,
+			    uint32_t part_count, struct key_def *key_def)
+{
+	(void) tuple;
+	(void) key;
+	(void) part_count;
+	(void) key_def;
+	unreachable();
+	return 0;
+}
+
 /**
  * @brief Compare two fields parts using a type definition
  * @param field_a field
@@ -445,7 +468,8 @@ tuple_compare_field_with_type(const char *field_a, enum mp_type a_type,
 	}
 }
 
-template<bool is_nullable, bool has_optional_parts, bool has_json_paths>
+template<bool is_nullable, bool has_optional_parts, bool has_json_paths,
+	 bool is_multikey>
 static inline int
 tuple_compare_slowpath_hinted(const struct tuple *tuple_a, hint_t tuple_a_hint,
 			      const struct tuple *tuple_b, hint_t tuple_b_hint,
@@ -455,8 +479,10 @@ tuple_compare_slowpath_hinted(const struct tuple *tuple_a, hint_t tuple_a_hint,
 	assert(!has_optional_parts || is_nullable);
 	assert(is_nullable == key_def->is_nullable);
 	assert(has_optional_parts == key_def->has_optional_parts);
-	int rc = hint_cmp(tuple_a_hint, tuple_b_hint);
-	if (rc != 0)
+	assert(key_def_is_multikey(key_def) == is_multikey);
+	assert(!is_multikey || is_multikey == has_json_paths);
+	int rc = 0;
+	if (!is_multikey && (rc = hint_cmp(tuple_a_hint, tuple_b_hint)) != 0)
 		return rc;
 	struct key_part *part = key_def->parts;
 	const char *tuple_a_raw = tuple_data(tuple_a);
@@ -499,7 +525,14 @@ tuple_compare_slowpath_hinted(const struct tuple *tuple_a, hint_t tuple_a_hint,
 		end = part + key_def->part_count;
 
 	for (; part < end; part++) {
-		if (has_json_paths) {
+		if (is_multikey) {
+			field_a = tuple_field_raw_by_part_multikey(format_a,
+					tuple_a_raw, field_map_a, part,
+					(int)tuple_a_hint);
+			field_b = tuple_field_raw_by_part_multikey(format_b,
+					tuple_b_raw, field_map_b, part,
+					(int)tuple_b_hint);
+		} else if (has_json_paths) {
 			field_a = tuple_field_raw_by_part(format_a, tuple_a_raw,
 							  field_map_a, part);
 			field_b = tuple_field_raw_by_part(format_b, tuple_b_raw,
@@ -556,7 +589,14 @@ tuple_compare_slowpath_hinted(const struct tuple *tuple_a, hint_t tuple_a_hint,
 	 */
 	end = key_def->parts + key_def->part_count;
 	for (; part < end; ++part) {
-		if (has_json_paths) {
+		if (is_multikey) {
+			field_a = tuple_field_raw_by_part_multikey(format_a,
+					tuple_a_raw, field_map_a, part,
+					(int)tuple_a_hint);
+			field_b = tuple_field_raw_by_part_multikey(format_b,
+					tuple_b_raw, field_map_b, part,
+					(int)tuple_b_hint);
+		} else if (has_json_paths) {
 			field_a = tuple_field_raw_by_part(format_a, tuple_a_raw,
 							  field_map_a, part);
 			field_b = tuple_field_raw_by_part(format_b, tuple_b_raw,
@@ -586,11 +626,12 @@ tuple_compare_slowpath(const struct tuple *tuple_a, const struct tuple *tuple_b,
 		       struct key_def *key_def)
 {
 	return tuple_compare_slowpath_hinted
-		<is_nullable, has_optional_parts, has_json_paths>
+		<is_nullable, has_optional_parts, has_json_paths, false>
 		(tuple_a, HINT_NONE, tuple_b, HINT_NONE, key_def);
 }
 
-template<bool is_nullable, bool has_optional_parts, bool has_json_paths>
+template<bool is_nullable, bool has_optional_parts, bool has_json_paths,
+	 bool is_multikey>
 static inline int
 tuple_compare_with_key_slowpath_hinted(const struct tuple *tuple,
 		hint_t tuple_hint, const char *key, uint32_t part_count,
@@ -602,8 +643,10 @@ tuple_compare_with_key_slowpath_hinted(const struct tuple *tuple,
 	assert(has_optional_parts == key_def->has_optional_parts);
 	assert(key != NULL || part_count == 0);
 	assert(part_count <= key_def->part_count);
-	int rc = hint_cmp(tuple_hint, key_hint);
-	if (rc != 0)
+	assert(key_def_is_multikey(key_def) == is_multikey);
+	assert(!is_multikey || is_multikey == has_json_paths);
+	int rc = 0;
+	if (!is_multikey && (rc = hint_cmp(tuple_hint, key_hint)) != 0)
 		return rc;
 	struct key_part *part = key_def->parts;
 	struct tuple_format *format = tuple_format(tuple);
@@ -612,7 +655,11 @@ tuple_compare_with_key_slowpath_hinted(const struct tuple *tuple,
 	enum mp_type a_type, b_type;
 	if (likely(part_count == 1)) {
 		const char *field;
-		if (has_json_paths) {
+		if (is_multikey) {
+			field = tuple_field_raw_by_part_multikey(format,
+					tuple_raw, field_map, part,
+					(int)tuple_hint);
+		} else if (has_json_paths) {
 			field = tuple_field_raw_by_part(format, tuple_raw,
 							field_map, part);
 		} else {
@@ -642,7 +689,11 @@ tuple_compare_with_key_slowpath_hinted(const struct tuple *tuple,
 	struct key_part *end = part + part_count;
 	for (; part < end; ++part, mp_next(&key)) {
 		const char *field;
-		if (has_json_paths) {
+		if (is_multikey) {
+			field = tuple_field_raw_by_part_multikey(format,
+					tuple_raw, field_map, part,
+					(int)tuple_hint);
+		} else if (has_json_paths) {
 			field = tuple_field_raw_by_part(format, tuple_raw,
 							field_map, part);
 		} else {
@@ -684,7 +735,7 @@ tuple_compare_with_key_slowpath(const struct tuple *tuple, const char *key,
 				uint32_t part_count, struct key_def *key_def)
 {
 	return tuple_compare_with_key_slowpath_hinted
-		<is_nullable, has_optional_parts, has_json_paths>
+		<is_nullable, has_optional_parts, has_json_paths, false>
 		(tuple, HINT_NONE, key, part_count, HINT_NONE, key_def);
 }
 
@@ -1314,6 +1365,16 @@ static const comparator_with_key_signature cmp_wk_arr[] = {
 /* {{{ tuple_hint */
 
 /**
+ * Hints are now used for two purposes - passing the index of the
+ * key used in the case of multikey index and to speed up the
+ * comparators.
+ *
+ * Scenario I. Pass the multikey index of the key to comparator.
+ * In the case of multikey index arises an ambiguity: which key
+ * should be used in the comparison. Hints act as an non-negative
+ * numeric index of key to use.
+ *
+ * Scenario II. Speed up comparators.
  * A comparison hint is an unsigned integer number that has
  * the following layout:
  *
@@ -1611,12 +1672,35 @@ tuple_hint(const struct tuple *tuple, struct key_def *key_def)
 	return field_hint<type, is_nullable>(field, key_def->parts->coll);
 }
 
+static hint_t
+key_hint_stub(const char *key, uint32_t part_count, struct key_def *key_def)
+{
+	(void) key;
+	(void) part_count;
+	(void) key_def;
+	return HINT_NONE;
+}
+
+static hint_t
+tuple_hint_stub(const struct tuple *tuple, struct key_def *key_def)
+{
+	(void) tuple;
+	(void) key_def;
+	unreachable();
+	return HINT_NONE;
+}
+
 template<enum field_type type, bool is_nullable>
 static void
 key_def_set_hint_func(struct key_def *def)
 {
-	def->key_hint = key_hint<type, is_nullable>;
-	def->tuple_hint = tuple_hint<type, is_nullable>;
+	if (key_def_is_multikey(def)) {
+		def->key_hint = key_hint_stub;
+		def->tuple_hint = tuple_hint_stub;
+	} else {
+		def->key_hint = key_hint<type, is_nullable>;
+		def->tuple_hint = tuple_hint<type, is_nullable>;
+	}
 }
 
 template<enum field_type type>
@@ -1710,7 +1794,7 @@ key_def_set_compare_func_fast(struct key_def *def)
 			tuple_compare_slowpath<false, false, false>;
 		cmp_hinted = is_sequential ?
 			tuple_compare_sequential_hinted<false, false> :
-			tuple_compare_slowpath_hinted<false, false, false>;
+			tuple_compare_slowpath_hinted<false, false, false, false>;
 	}
 	if (cmp_wk == NULL) {
 		cmp_wk = is_sequential ?
@@ -1718,7 +1802,8 @@ key_def_set_compare_func_fast(struct key_def *def)
 			tuple_compare_with_key_slowpath<false, false, false>;
 		cmp_wk_hinted = is_sequential ?
 			tuple_compare_with_key_sequential_hinted<false, false> :
-			tuple_compare_with_key_slowpath_hinted<false, false, false>;
+			tuple_compare_with_key_slowpath_hinted<false, false,
+							       false, false>;
 	}
 
 	def->tuple_compare = cmp;
@@ -1746,12 +1831,13 @@ key_def_set_compare_func_plain(struct key_def *def)
 		def->tuple_compare = tuple_compare_slowpath
 				<is_nullable, has_optional_parts, false>;
 		def->tuple_compare_hinted = tuple_compare_slowpath_hinted
-				<is_nullable, has_optional_parts, false>;
+				<is_nullable, has_optional_parts, false, false>;
 		def->tuple_compare_with_key = tuple_compare_with_key_slowpath
 				<is_nullable, has_optional_parts, false>;
 		def->tuple_compare_with_key_hinted =
 					tuple_compare_with_key_slowpath_hinted
-					<is_nullable, has_optional_parts, false>;
+					<is_nullable, has_optional_parts,
+					 false, false>;
 	}
 }
 
@@ -1760,15 +1846,25 @@ static void
 key_def_set_compare_func_json(struct key_def *def)
 {
 	assert(def->has_json_paths);
-	def->tuple_compare = tuple_compare_slowpath
-			<is_nullable, has_optional_parts, true>;
-	def->tuple_compare_hinted = tuple_compare_slowpath_hinted
-			<is_nullable, has_optional_parts, true>;
-	def->tuple_compare_with_key = tuple_compare_with_key_slowpath
-			<is_nullable, has_optional_parts, true>;
-	def->tuple_compare_with_key_hinted =
-			tuple_compare_with_key_slowpath_hinted
-			<is_nullable, has_optional_parts, true>;
+	if (key_def_is_multikey(def)) {
+		def->tuple_compare = tuple_compare_stub;
+		def->tuple_compare_hinted = tuple_compare_slowpath_hinted
+				<is_nullable, has_optional_parts, true, true>;
+		def->tuple_compare_with_key = tuple_compare_with_key_stub;
+		def->tuple_compare_with_key_hinted =
+				tuple_compare_with_key_slowpath_hinted
+				<is_nullable, has_optional_parts, true, true>;
+	} else {
+		def->tuple_compare = tuple_compare_slowpath
+				<is_nullable, has_optional_parts, true>;
+		def->tuple_compare_hinted = tuple_compare_slowpath_hinted
+				<is_nullable, has_optional_parts, true, false>;
+		def->tuple_compare_with_key = tuple_compare_with_key_slowpath
+				<is_nullable, has_optional_parts, true>;
+		def->tuple_compare_with_key_hinted =
+				tuple_compare_with_key_slowpath_hinted
+				<is_nullable, has_optional_parts, true, false>;
+	}
 }
 
 void
diff --git a/src/box/tuple_extract_key.cc b/src/box/tuple_extract_key.cc
index 836d4e565..081677ff6 100644
--- a/src/box/tuple_extract_key.cc
+++ b/src/box/tuple_extract_key.cc
@@ -30,6 +30,29 @@ key_def_contains_sequential_parts(const struct key_def *def)
 	return false;
 }
 
+static inline char *
+tuple_extract_key_stub(const struct tuple *tuple, struct key_def *key_def,
+		       uint32_t *key_size)
+{
+	(void) tuple;
+	(void) key_def;
+	(void) key_size;
+	unreachable();
+	return NULL;
+}
+
+static char *
+tuple_extract_key_raw_stub(const char *data, const char *data_end,
+			   struct key_def *key_def, uint32_t *key_size)
+{
+	(void) data;
+	(void) data_end;
+	(void) key_def;
+	(void) key_size;
+	unreachable();
+	return NULL;
+}
+
 /**
  * Optimized version of tuple_extract_key_raw() for sequential key defs
  * @copydoc tuple_extract_key_raw()
@@ -310,7 +333,7 @@ tuple_extract_key_slowpath_raw(const char *data, const char *data_end,
 		const char *src_end = field_end;
 		if (has_json_paths && part->path != NULL) {
 			if (tuple_go_to_path(&src, part->path,
-						   part->path_len) != 0) {
+					     part->path_len, -1) != 0) {
 				/*
 				 * The path must be correct as
 				 * it has already been validated
@@ -349,6 +372,7 @@ static void
 key_def_set_extract_func_plain(struct key_def *def)
 {
 	assert(!def->has_json_paths);
+	assert(!key_def_is_multikey(def));
 	if (key_def_is_sequential(def)) {
 		assert(contains_sequential_parts || def->part_count == 1);
 		def->tuple_extract_key = tuple_extract_key_sequential
@@ -369,11 +393,16 @@ static void
 key_def_set_extract_func_json(struct key_def *def)
 {
 	assert(def->has_json_paths);
-	def->tuple_extract_key = tuple_extract_key_slowpath
-					<contains_sequential_parts,
-					 has_optional_parts, true>;
-	def->tuple_extract_key_raw = tuple_extract_key_slowpath_raw
-					<has_optional_parts, true>;
+	if (!key_def_is_multikey(def)) {
+		def->tuple_extract_key = tuple_extract_key_slowpath
+						<contains_sequential_parts,
+						has_optional_parts, true>;
+		def->tuple_extract_key_raw = tuple_extract_key_slowpath_raw
+						<has_optional_parts, true>;
+	} else {
+		def->tuple_extract_key = tuple_extract_key_stub;
+		def->tuple_extract_key_raw = tuple_extract_key_raw_stub;
+	}
 }
 
 void
diff --git a/src/box/tuple_format.c b/src/box/tuple_format.c
index 9a643b700..33d6db420 100644
--- a/src/box/tuple_format.c
+++ b/src/box/tuple_format.c
@@ -194,6 +194,50 @@ tuple_format_field_by_id(struct tuple_format *format, uint32_t id)
 	return NULL;
 }
 
+/**
+ * Check if child_field may be attached to parent_field,
+ * update the parent_field container type if required.
+ */
+static int
+tuple_format_field_update_type(struct tuple_field *parent_field,
+			       struct tuple_field *child_field)
+{
+	enum field_type expected_type =
+		child_field->token.type == JSON_TOKEN_STR ?
+		FIELD_TYPE_MAP : FIELD_TYPE_ARRAY;
+	if (child_field->token.type == JSON_TOKEN_ANY &&
+	    !json_token_is_multikey(&parent_field->token) &&
+	    !json_token_is_leaf(&parent_field->token)) {
+		assert(expected_type == FIELD_TYPE_ARRAY);
+		diag_set(ClientError, ER_INDEX_MULTIKEY_INVALID,
+			 tt_sprintf("field %s is already refer to document by "
+				    "identifier and cannot use array index "
+				    "placeholder [*]",
+				    tuple_field_path(parent_field)));
+		return -1;
+	}
+	if (json_token_is_multikey(&parent_field->token) &&
+		child_field->token.type != JSON_TOKEN_ANY) {
+		assert(expected_type == FIELD_TYPE_ARRAY);
+		diag_set(ClientError, ER_INDEX_MULTIKEY_INVALID,
+			 tt_sprintf("field %s is already used with array index "
+				    "placeholder [*] and cannot refer to "
+				    "document by identifier",
+				    tuple_field_path(parent_field)));
+		return -1;
+	}
+	if (field_type1_contains_type2(parent_field->type, expected_type)) {
+		parent_field->type = expected_type;
+	} else {
+		diag_set(ClientError, ER_INDEX_PART_TYPE_MISMATCH,
+			 tuple_field_path(parent_field),
+			 field_type_strs[parent_field->type],
+			 field_type_strs[expected_type]);
+		return -1;
+	}
+	return 0;
+}
+
 /**
  * Given a field number and a path, add the corresponding field
  * to the tuple format, allocating intermediate fields if
@@ -228,29 +272,16 @@ tuple_format_add_field(struct tuple_format *format, uint32_t fieldno,
 	*path_pool += path_len;
 
 	int rc = 0;
-	uint32_t token_count = 0;
+	uint32_t token_count = 0, json_token_any_count = 0;
 	struct json_tree *tree = &format->fields;
 	struct json_lexer lexer;
 	json_lexer_create(&lexer, path, path_len, TUPLE_INDEX_BASE);
 	while ((rc = json_lexer_next_token(&lexer, &field->token)) == 0 &&
 	       field->token.type != JSON_TOKEN_END) {
-		if (field->token.type == JSON_TOKEN_ANY) {
-			diag_set(ClientError, ER_UNSUPPORTED,
-				"Tarantool", "multikey indexes");
+		if (tuple_format_field_update_type(parent, field) != 0)
 			goto fail;
-		}
-		enum field_type expected_type =
-			field->token.type == JSON_TOKEN_STR ?
-			FIELD_TYPE_MAP : FIELD_TYPE_ARRAY;
-		if (field_type1_contains_type2(parent->type, expected_type)) {
-			parent->type = expected_type;
-		} else {
-			diag_set(ClientError, ER_INDEX_PART_TYPE_MISMATCH,
-				 tuple_field_path(parent),
-				 field_type_strs[parent->type],
-				 field_type_strs[expected_type]);
-			goto fail;
-		}
+		if (field->token.type == JSON_TOKEN_ANY)
+			json_token_any_count++;
 		struct tuple_field *next =
 			json_tree_lookup_entry(tree, &parent->token,
 					       &field->token,
@@ -268,6 +299,18 @@ tuple_format_add_field(struct tuple_format *format, uint32_t fieldno,
 			if (field == NULL)
 				goto fail;
 		}
+		if (json_token_is_multikey(&parent->token) &&
+		    parent->offset_slot == TUPLE_OFFSET_SLOT_NIL) {
+			/**
+			 * Allocate offset slot for array is used
+			 * in multikey index. This is required to
+			 * quickly extract its size.
+			 * @see tuple_field_multikey_items()
+			 */
+			assert(parent->type == FIELD_TYPE_ARRAY);
+			*current_slot = *current_slot - 1;
+			parent->offset_slot = *current_slot;
+		}
 		parent->is_key_part = true;
 		parent = next;
 		token_count++;
@@ -280,6 +323,13 @@ tuple_format_add_field(struct tuple_format *format, uint32_t fieldno,
 	assert(parent != NULL);
 	/* Update tree depth information. */
 	format->fields_depth = MAX(format->fields_depth, token_count + 1);
+	if (json_token_any_count > 1) {
+		assert(path_len > 0);
+		diag_set(ClientError, ER_INDEX_MULTIKEY_INVALID,
+			 "no more than one array index placeholder [*] is "
+			 "allowed in JSON path");
+		goto fail;
+	}
 cleanup:
 	tuple_field_delete(field);
 end:
@@ -847,7 +897,16 @@ tuple_field_map_create(struct field_map_builder *builder,
 			return -1;
 		}
 		/* Initialize field_map with data offset. */
-		if (field->offset_slot != TUPLE_OFFSET_SLOT_NIL) {
+		int multikey_idx = tuple_parse_iterator_multikey_idx(&it);
+		if (field->offset_slot != TUPLE_OFFSET_SLOT_NIL &&
+		    multikey_idx >= 0) {
+			int multikey_items =
+				tuple_parse_iterator_multikey_items(&it);
+			if (field_map_builder_set_extent_slot(builder,
+					field->offset_slot, multikey_idx,
+					multikey_items, pos - tuple) != 0)
+				return -1;
+		} else if (field->offset_slot != TUPLE_OFFSET_SLOT_NIL) {
 			field_map_builder_set_slot(builder, field->offset_slot,
 						   pos - tuple);
 		}
@@ -966,6 +1025,7 @@ tuple_parse_iterator_create(struct tuple_parse_iterator *it,
 	it->parent = &format->fields.root;
 	it->format = format;
 	it->pos = data;
+	it->multikey_frame = NULL;
 	return 0;
 }
 
@@ -986,6 +1046,14 @@ tuple_parse_iterator_advice(struct tuple_parse_iterator *it,
 		mp_stack_pop(&it->stack);
 		if (mp_stack_is_empty(&it->stack))
 			return rc;
+		if (json_token_is_multikey(it->parent)) {
+			/*
+			 * As we leave the multikey branch,
+			 * we need to reset the pointer to
+			 * multikey_frame.
+			 */
+			it->multikey_frame = NULL;
+		}
 		it->parent = it->parent->parent;
 	}
 	/*
@@ -1038,6 +1106,19 @@ tuple_parse_iterator_advice(struct tuple_parse_iterator *it,
 				mp_decode_array(&it->pos) :
 				mp_decode_map(&it->pos);
 		mp_stack_push(&it->stack, type, size);
+		if (json_token_is_multikey(&(*field)->token)) {
+			/**
+			 * Keep a pointer to the frame that
+			 * describes an array with index
+			 * placeholder [*]. The "current" item
+			 * of this frame matches the logical
+			 * index of document in multikey index
+			 * and is equal to multikey index
+			 * comparison hint.
+			 */
+			assert(type == MP_ARRAY);
+			it->multikey_frame = mp_stack_top(&it->stack);
+		}
 		it->parent = &(*field)->token;
 	} else {
 		mp_next(&it->pos);
diff --git a/src/box/tuple_format.h b/src/box/tuple_format.h
index 88f03d5eb..d07ca91eb 100644
--- a/src/box/tuple_format.h
+++ b/src/box/tuple_format.h
@@ -437,6 +437,12 @@ struct tuple_parse_iterator {
 	 * pointer accordingly.
 	 */
 	struct mp_stack stack;
+	/**
+	 * The pointer to the stack frame representing an array
+	 * filed that has JSON_TOKEN_ANY child, i.e. the root
+	 * of the multikey index.
+	 */
+	struct mp_frame *multikey_frame;
 	/** The current read position in msgpack. */
 	const char *pos;
 };
@@ -479,6 +485,32 @@ tuple_parse_iterator_advice(struct tuple_parse_iterator *it,
 			    struct tuple_field **field, const char **data,
 			    const char **data_end);
 
+/**
+ * Returns non-negative multikey index comparison hint when
+ * the iterator's position in the format::fields subtree
+ * corresponds to the multikey subtree and -1 otherwise.
+ */
+static inline int
+tuple_parse_iterator_multikey_idx(struct tuple_parse_iterator *it)
+{
+	if (it->multikey_frame == NULL)
+		return -1;
+	return it->multikey_frame->curr;
+}
+
+/**
+ * Returns positive number - a count of document's in multikey
+ * index for when the iterator's position in the format::fields
+ * subtree corresponds to the multikey subtree and -1 otherwise.
+ */
+static inline int
+tuple_parse_iterator_multikey_items(struct tuple_parse_iterator *it)
+{
+	if (it->multikey_frame == NULL)
+		return -1;
+	return it->multikey_frame->count;
+}
+
 #if defined(__cplusplus)
 } /* extern "C" */
 #endif /* defined(__cplusplus) */
diff --git a/src/box/vinyl.c b/src/box/vinyl.c
index da8910255..c2860098a 100644
--- a/src/box/vinyl.c
+++ b/src/box/vinyl.c
@@ -699,6 +699,11 @@ vinyl_space_check_index_def(struct space *space, struct index_def *index_def)
 			return -1;
 		}
 	}
+	if (key_def_is_multikey(index_def->key_def)) {
+		diag_set(ClientError, ER_UNSUPPORTED,
+			 "Vinyl", "multikey indexes");
+		return -1;
+	}
 	return 0;
 }
 
diff --git a/test/box/misc.result b/test/box/misc.result
index e2b618c9c..b89a7ed2f 100644
--- a/test/box/misc.result
+++ b/test/box/misc.result
@@ -522,6 +522,7 @@ t;
   191: box.error.SQL_PARSER_LIMIT
   192: box.error.INDEX_DEF_UNSUPPORTED
   193: box.error.CK_DEF_UNSUPPORTED
+  194: box.error.INDEX_MULTIKEY_INVALID
 ...
 test_run:cmd("setopt delimiter ''");
 ---
diff --git a/test/engine/json.result b/test/engine/json.result
index 09c704963..6ccfe92b7 100644
--- a/test/engine/json.result
+++ b/test/engine/json.result
@@ -705,16 +705,3 @@ s:replace({4, {"d1", name='D1'}, "test"})
 s:drop()
 ---
 ...
---
--- gh-1260: Multikey indexes
---
-s = box.schema.space.create('withdata')
----
-...
-idx = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
----
-- error: Tarantool does not support multikey indexes
-...
-s:drop()
----
-...
diff --git a/test/engine/json.test.lua b/test/engine/json.test.lua
index 5c235e1ba..05c64ea93 100644
--- a/test/engine/json.test.lua
+++ b/test/engine/json.test.lua
@@ -201,10 +201,3 @@ idx0 = s:create_index('idx0', {parts = {{2, 'str', path = 'name'}, {3, "str"}}})
 s:insert({4, {"d", name='D'}, "test"})
 s:replace({4, {"d1", name='D1'}, "test"})
 s:drop()
-
---
--- gh-1260: Multikey indexes
---
-s = box.schema.space.create('withdata')
-idx = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
-s:drop()
diff --git a/test/engine/multikey.result b/test/engine/multikey.result
new file mode 100644
index 000000000..dd6487383
--- /dev/null
+++ b/test/engine/multikey.result
@@ -0,0 +1,298 @@
+test_run = require('test_run').new()
+---
+...
+engine = test_run:get_cfg('engine')
+---
+...
+--
+-- gh-1260: Multikey indexes
+--
+s = box.schema.space.create('withdata', {engine = 'vinyl'})
+---
+...
+pk = s:create_index('pk')
+---
+...
+-- Vinyl's space can't be multikey (yet).
+_ = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
+---
+- error: Vinyl does not support multikey indexes
+...
+s:drop()
+---
+...
+s = box.schema.space.create('withdata', {engine = 'memtx'})
+---
+...
+-- Primary index must be unique so it can't be multikey.
+_ = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}}})
+---
+- error: 'Can''t create or modify index ''idx'' in space ''withdata'': primary key
+    cannot be multikey'
+...
+pk = s:create_index('pk')
+---
+...
+-- Only tree index type may be mutlikey.
+_ = s:create_index('idx', {type = 'hash', unique = true, parts = {{3, 'str', path = '[*].fname'}}})
+---
+- error: 'Can''t create or modify index ''idx'' in space ''withdata'': HASH index
+    cannot be multikey'
+...
+_ = s:create_index('idx', {type = 'bitset', unique = false, parts = {{3, 'str', path = '[*].fname'}}})
+---
+- error: 'Can''t create or modify index ''idx'' in space ''withdata'': BITSET index
+    cannot be multikey'
+...
+_ = s:create_index('idx', {type = 'rtree', unique = false, parts = {{3, 'array', path = '[*].fname'}}})
+---
+- error: 'Can''t create or modify index ''idx'' in space ''withdata'': RTREE index
+    cannot be multikey'
+...
+-- Test incompatible multikey index parts.
+_ = s:create_index('idx3', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '["data"][*].sname'}}})
+---
+- error: 'Wrong index options (field 2): incompatable multikey index path'
+...
+_ = s:create_index('idx2', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname[*].a'}}})
+---
+- error: 'Multikey index is invalid: no more than one array index placeholder [*]
+    is allowed in JSON path'
+...
+idx0 = s:create_index('idx0', {parts = {{3, 'str', path = '[1].fname'}}})
+---
+...
+_ = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
+---
+- error: 'Multikey index is invalid: field 3 is already refer to document by identifier
+    and cannot use array index placeholder [*]'
+...
+idx0:drop()
+---
+...
+-- Unique multikey index.
+idx = s:create_index('idx', {unique = true, parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
+---
+...
+_ = s:create_index('idx2', {parts = {{3, 'str', path = '[1].fname'}, {3, 'str', path = '[1].sname'}}})
+---
+- error: 'Multikey index is invalid: field 3 is already used with array index placeholder
+    [*] and cannot refer to document by identifier'
+...
+s:insert({1, {1, 2, 3}, {{fname='James', sname='Bond'}, {fname='Vasya', sname='Pupkin'}}})
+---
+- [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+s:insert({2, {3, 4, 5}, {{fname='Ivan', sname='Ivanych'}}})
+---
+- [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+...
+_ = s:create_index('arr_idx', {unique = true, parts = {{2, 'unsigned', path = '[*]'}}})
+---
+- error: Duplicate key exists in unique index 'arr_idx' in space 'withdata'
+...
+-- Non-unique multikey index; two multikey indexes per space.
+arr_idx = s:create_index('arr_idx', {unique = false, parts = {{2, 'unsigned', path = '[*]'}}})
+---
+...
+arr_idx:select()
+---
+- - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+...
+idx:get({'James', 'Bond'})
+---
+- [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+idx:get({'Ivan', 'Ivanych'})
+---
+- [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+...
+idx:get({'Vasya', 'Pupkin'})
+---
+- [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+idx:select()
+---
+- - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+s:insert({3, {1, 2}, {{fname='Vasya', sname='Pupkin'}}})
+---
+- error: Duplicate key exists in unique index 'idx' in space 'withdata'
+...
+s:insert({4, {1}, {{fname='James', sname='Bond'}}})
+---
+- error: Duplicate key exists in unique index 'idx' in space 'withdata'
+...
+idx:select()
+---
+- - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+-- Duplicates in multikey parts.
+s:insert({5, {1, 1, 1}, {{fname='A', sname='B'}, {fname='C', sname='D'}, {fname='A', sname='B'}}})
+---
+- [5, [1, 1, 1], [{'fname': 'A', 'sname': 'B'}, {'fname': 'C', 'sname': 'D'}, {'fname': 'A',
+      'sname': 'B'}]]
+...
+arr_idx:select({1})
+---
+- - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [5, [1, 1, 1], [{'fname': 'A', 'sname': 'B'}, {'fname': 'C', 'sname': 'D'}, {
+        'fname': 'A', 'sname': 'B'}]]
+...
+s:delete(5)
+---
+- [5, [1, 1, 1], [{'fname': 'A', 'sname': 'B'}, {'fname': 'C', 'sname': 'D'}, {'fname': 'A',
+      'sname': 'B'}]]
+...
+-- Check that there is no garbage in index
+arr_idx:select({1})
+---
+- - [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+idx:get({'A', 'B'})
+---
+...
+idx:get({'C', 'D'})
+---
+...
+idx:delete({'Vasya', 'Pupkin'})
+---
+- [1, [1, 2, 3], [{'fname': 'James', 'sname': 'Bond'}, {'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+s:insert({6, {1, 2}, {{fname='Vasya', sname='Pupkin'}}})
+---
+- [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+s:insert({7, {1}, {{fname='James', sname='Bond'}}})
+---
+- [7, [1], [{'fname': 'James', 'sname': 'Bond'}]]
+...
+arr_idx:select({1})
+---
+- - [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [7, [1], [{'fname': 'James', 'sname': 'Bond'}]]
+...
+idx:select()
+---
+- - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [7, [1], [{'fname': 'James', 'sname': 'Bond'}]]
+  - [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+-- Snapshot & recovery.
+box.snapshot()
+---
+- ok
+...
+test_run:cmd("restart server default")
+s = box.space["withdata"]
+---
+...
+idx = s.index["idx"]
+---
+...
+arr_idx = s.index["arr_idx"]
+---
+...
+s:select()
+---
+- - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [7, [1], [{'fname': 'James', 'sname': 'Bond'}]]
+...
+idx:select()
+---
+- - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [7, [1], [{'fname': 'James', 'sname': 'Bond'}]]
+  - [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+...
+arr_idx:select()
+---
+- - [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [7, [1], [{'fname': 'James', 'sname': 'Bond'}]]
+  - [6, [1, 2], [{'fname': 'Vasya', 'sname': 'Pupkin'}]]
+  - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+  - [2, [3, 4, 5], [{'fname': 'Ivan', 'sname': 'Ivanych'}]]
+...
+s:drop()
+---
+...
+-- Assymetric multikey index paths.
+s = box.schema.space.create('withdata')
+---
+...
+pk = s:create_index('pk')
+---
+...
+idx = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].extra.sname', is_nullable = true}}})
+---
+...
+s:insert({1, 1, {{fname='A1', extra={sname='A2'}}, {fname='B1'}, {fname='C1', extra={sname='C2'}}}})
+---
+- [1, 1, [{'fname': 'A1', 'extra': {'sname': 'A2'}}, {'fname': 'B1'}, {'fname': 'C1',
+      'extra': {'sname': 'C2'}}]]
+...
+s:drop()
+---
+...
+-- Unique multikey index peculiar properties
+s = box.schema.space.create('withdata')
+---
+...
+pk = s:create_index('pk')
+---
+...
+idx0 = s:create_index('idx0', {parts = {{2, 'int', path = '[*]'}}})
+---
+...
+s:insert({1, {1, 1, 1}})
+---
+- [1, [1, 1, 1]]
+...
+s:insert({2, {2, 2}})
+---
+- [2, [2, 2]]
+...
+s:insert({3, {3, 3, 2, 2, 1, 1}})
+---
+- error: Duplicate key exists in unique index 'idx0' in space 'withdata'
+...
+idx0:get(2)
+---
+- [2, [2, 2]]
+...
+idx0:get(1)
+---
+- [1, [1, 1, 1]]
+...
+idx0:get(3)
+---
+...
+idx0:select()
+---
+- - [1, [1, 1, 1]]
+  - [2, [2, 2]]
+...
+idx0:delete(2)
+---
+- [2, [2, 2]]
+...
+idx0:get(2)
+---
+...
+idx0:select()
+---
+- - [1, [1, 1, 1]]
+...
+s:drop()
+---
+...
diff --git a/test/engine/multikey.test.lua b/test/engine/multikey.test.lua
new file mode 100644
index 000000000..71fc82a5f
--- /dev/null
+++ b/test/engine/multikey.test.lua
@@ -0,0 +1,88 @@
+test_run = require('test_run').new()
+engine = test_run:get_cfg('engine')
+
+--
+-- gh-1260: Multikey indexes
+--
+s = box.schema.space.create('withdata', {engine = 'vinyl'})
+pk = s:create_index('pk')
+-- Vinyl's space can't be multikey (yet).
+_ = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
+s:drop()
+
+s = box.schema.space.create('withdata', {engine = 'memtx'})
+-- Primary index must be unique so it can't be multikey.
+_ = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}}})
+pk = s:create_index('pk')
+-- Only tree index type may be mutlikey.
+_ = s:create_index('idx', {type = 'hash', unique = true, parts = {{3, 'str', path = '[*].fname'}}})
+_ = s:create_index('idx', {type = 'bitset', unique = false, parts = {{3, 'str', path = '[*].fname'}}})
+_ = s:create_index('idx', {type = 'rtree', unique = false, parts = {{3, 'array', path = '[*].fname'}}})
+-- Test incompatible multikey index parts.
+_ = s:create_index('idx3', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '["data"][*].sname'}}})
+_ = s:create_index('idx2', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname[*].a'}}})
+idx0 = s:create_index('idx0', {parts = {{3, 'str', path = '[1].fname'}}})
+_ = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
+idx0:drop()
+-- Unique multikey index.
+idx = s:create_index('idx', {unique = true, parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].sname'}}})
+_ = s:create_index('idx2', {parts = {{3, 'str', path = '[1].fname'}, {3, 'str', path = '[1].sname'}}})
+s:insert({1, {1, 2, 3}, {{fname='James', sname='Bond'}, {fname='Vasya', sname='Pupkin'}}})
+s:insert({2, {3, 4, 5}, {{fname='Ivan', sname='Ivanych'}}})
+_ = s:create_index('arr_idx', {unique = true, parts = {{2, 'unsigned', path = '[*]'}}})
+-- Non-unique multikey index; two multikey indexes per space.
+arr_idx = s:create_index('arr_idx', {unique = false, parts = {{2, 'unsigned', path = '[*]'}}})
+arr_idx:select()
+idx:get({'James', 'Bond'})
+idx:get({'Ivan', 'Ivanych'})
+idx:get({'Vasya', 'Pupkin'})
+idx:select()
+s:insert({3, {1, 2}, {{fname='Vasya', sname='Pupkin'}}})
+s:insert({4, {1}, {{fname='James', sname='Bond'}}})
+idx:select()
+-- Duplicates in multikey parts.
+s:insert({5, {1, 1, 1}, {{fname='A', sname='B'}, {fname='C', sname='D'}, {fname='A', sname='B'}}})
+arr_idx:select({1})
+s:delete(5)
+-- Check that there is no garbage in index
+arr_idx:select({1})
+idx:get({'A', 'B'})
+idx:get({'C', 'D'})
+idx:delete({'Vasya', 'Pupkin'})
+s:insert({6, {1, 2}, {{fname='Vasya', sname='Pupkin'}}})
+s:insert({7, {1}, {{fname='James', sname='Bond'}}})
+arr_idx:select({1})
+idx:select()
+-- Snapshot & recovery.
+box.snapshot()
+test_run:cmd("restart server default")
+s = box.space["withdata"]
+idx = s.index["idx"]
+arr_idx = s.index["arr_idx"]
+s:select()
+idx:select()
+arr_idx:select()
+s:drop()
+
+-- Assymetric multikey index paths.
+s = box.schema.space.create('withdata')
+pk = s:create_index('pk')
+idx = s:create_index('idx', {parts = {{3, 'str', path = '[*].fname'}, {3, 'str', path = '[*].extra.sname', is_nullable = true}}})
+s:insert({1, 1, {{fname='A1', extra={sname='A2'}}, {fname='B1'}, {fname='C1', extra={sname='C2'}}}})
+s:drop()
+
+-- Unique multikey index peculiar properties
+s = box.schema.space.create('withdata')
+pk = s:create_index('pk')
+idx0 = s:create_index('idx0', {parts = {{2, 'int', path = '[*]'}}})
+s:insert({1, {1, 1, 1}})
+s:insert({2, {2, 2}})
+s:insert({3, {3, 3, 2, 2, 1, 1}})
+idx0:get(2)
+idx0:get(1)
+idx0:get(3)
+idx0:select()
+idx0:delete(2)
+idx0:get(2)
+idx0:select()
+s:drop()
-- 
2.21.0