Re: [tarantool-patches] Re: [PATCH v5 4/4] box: introduce multikey indexes in memtx

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

> 
> How's it going to work in case the field map stored in a tuple is
> greater than field_map_size?
> 
> I think we should calculate the real size of the field map here
> in case the format allows multikey indexes.

Consider this diff (not on branch yet):

diff --git a/src/box/field_map.c b/src/box/field_map.c
index 5d25e3032..a917d4a25 100644
--- a/src/box/field_map.c
+++ b/src/box/field_map.c
@@ -105,12 +105,28 @@ field_map_build(struct field_map_builder *builder, char *buffer)
 		struct field_map_builder_slot_extent *extent =
 						builder->slots[i].extent;
 		/** Retrive memory for the extent. */
-		uint32_t sz = sizeof(struct field_map_builder_slot_extent) +
-			      extent->size * sizeof(uint32_t);
 		field_map[i] =
 			(uint32_t)((char *)extent_wptr - (char *)field_map);
-		memcpy(extent_wptr, extent, sz);
-		extent_wptr += sz;
+		*(uint32_t *)extent_wptr = extent->size;
+		uint32_t extent_offset_sz = extent->size * sizeof(uint32_t);
+		memcpy(&((uint32_t *) extent_wptr)[1], extent->offset,
+			extent_offset_sz);
+		extent_wptr += sizeof(uint32_t) + extent_offset_sz;
 	}
 	assert(extent_wptr == buffer + builder->extents_size);
 }
+
+uint32_t
+field_map_get_size(const uint32_t *field_map, uint32_t format_field_map_sz)
+{
+	uint32_t total = format_field_map_sz;
+	int32_t field_map_items = format_field_map_sz / sizeof(uint32_t);
+	for (int32_t slot = -1; slot >= -field_map_items; slot--) {
+		if ((int32_t)field_map[slot] >= 0)
+			continue;
+		uint32_t *extent = (uint32_t *)((char *)field_map +
+					(int32_t)field_map[slot]);
+		total += (1 + extent[0]) * sizeof(uint32_t);
+	}
+	return total;
+}
diff --git a/src/box/field_map.h b/src/box/field_map.h
index 0fd35c3e1..78c96e4f7 100644
--- a/src/box/field_map.h
+++ b/src/box/field_map.h
@@ -163,6 +163,19 @@ field_map_get_offset(const uint32_t *field_map, int32_t offset_slot,
 	return offset;
 }
 
+/**
+ * Get size of the tuple field_map using
+ * field_map pointer and format root field_map size.
+ *
+ * In case of multikey indexes the real field_map size may be
+ * greater than the size of format root field_map. To calculate
+ * the total size of the field_map extentions, routine relies
+ * on the fact that all field_map slots that has an extention
+ * use negative offset as a marker.
+ */
+uint32_t
+field_map_get_size(const uint32_t *field_map, uint32_t format_field_map_sz);
+
 /**
  * Initialize field_map_builder.
  *
diff --git a/src/box/memtx_engine.c b/src/box/memtx_engine.c
index 65e8804a4..ab4913035 100644
--- a/src/box/memtx_engine.c
+++ b/src/box/memtx_engine.c
@@ -1180,6 +1180,8 @@ memtx_tuple_new(struct tuple_format *format, const char *data, const char *end)
 	char *raw = (char *) tuple + tuple->data_offset;
 	field_map_build(&builder, raw - field_map_size);
 	memcpy(raw, data, tuple_len);
+	assert(field_map_get_size((uint32_t *)raw,
+				  format->field_map_size) == field_map_size);
 	say_debug("%s(%zu) = %p", __func__, tuple_len, memtx_tuple);
 end:
 	region_truncate(region, region_svp);
@@ -1192,8 +1194,9 @@ memtx_tuple_delete(struct tuple_format *format, struct tuple *tuple)
 	struct memtx_engine *memtx = (struct memtx_engine *)format->engine;
 	say_debug("%s(%p)", __func__, tuple);
 	assert(tuple->refs == 0);
-	size_t total = sizeof(struct memtx_tuple) + format->field_map_size +
-		tuple->bsize;
+	const uint32_t *field_map = tuple_field_map(tuple);
+	size_t total = sizeof(struct memtx_tuple) + tuple->bsize +
+		       field_map_get_size(field_map, format->field_map_size);
 	tuple_format_unref(format);
 	struct memtx_tuple *memtx_tuple =
 		container_of(tuple, struct memtx_tuple, base);