[Tarantool-patches] [PATCH 13/16] tx: introduce txm_story

[Aleksandr Lyapunov <alyapunov@tarantool.org>]

---
 src/box/txn.c | 725 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/box/txn.h | 127 ++++++++++
 2 files changed, 851 insertions(+), 1 deletion(-)

diff --git a/src/box/txn.c b/src/box/txn.c
index b9f1737..78c542f 100644
--- a/src/box/txn.c
+++ b/src/box/txn.c
@@ -36,13 +36,44 @@
 #include "xrow.h"
 #include "errinj.h"
 #include "iproto_constants.h"
+#include "small/mempool.h"
+
+static uint32_t
+txm_story_key_hash(const struct tuple *a)
+{
+	uintptr_t u = (uintptr_t)a;
+	if (sizeof(uintptr_t) <= sizeof(uint32_t))
+		return u;
+	else
+		return u ^ (u >> 32);
+}
+
+#define mh_name _history
+#define mh_key_t struct tuple *
+#define mh_node_t struct txm_story *
+#define mh_arg_t int
+#define mh_hash(a, arg) (txm_story_key_hash((*(a))->tuple))
+#define mh_hash_key(a, arg) (txm_story_key_hash(a))
+#define mh_cmp(a, b, arg) ((*(a))->tuple != (*(b))->tuple)
+#define mh_cmp_key(a, b, arg) ((a) != (*(b))->tuple)
+#define MH_SOURCE
+#include "salad/mhash.h"
 
 struct tx_manager
 {
 	/** Last prepare-sequence-number that was assigned to preped TX. */
 	int64_t last_psn;
+	/** Mempools for tx_story objects with difference index count. */
+	struct mempool txm_story_pool[BOX_INDEX_MAX];
+	/** Hash table tuple -> txm_story of that tuple. */
+	struct mh_history_t *history;
+	/** List of all txm_story objects. */
+	struct rlist all_stories;
+	/** Iterator that sequentially traverses all txm_story objects. */
+	struct rlist *traverse_all_stories;
 };
 
+/** The one and only instance of tx_manager. */
 static struct tx_manager txm;
 
 struct tx_conflict_tracker {
@@ -120,6 +151,9 @@ txn_stmt_new(struct region *region)
 	stmt->space = NULL;
 	stmt->old_tuple = NULL;
 	stmt->new_tuple = NULL;
+	stmt->add_story = NULL;
+	stmt->del_story = NULL;
+	stmt->next_in_del_list = NULL;
 	stmt->engine_savepoint = NULL;
 	stmt->row = NULL;
 	stmt->has_triggers = false;
@@ -1047,11 +1081,23 @@ txn_on_yield(struct trigger *trigger, void *event)
 void
 tx_manager_init()
 {
+	for (size_t i = 0; i < BOX_INDEX_MAX; i++) {
+		size_t item_size = sizeof(struct txm_story) +
+			i * sizeof(struct txm_story_link);
+		mempool_create(&txm.txm_story_pool[i],
+			       cord_slab_cache(), item_size);
+	}
+	txm.history = mh_history_new();
+	rlist_create(&txm.all_stories);
+	txm.traverse_all_stories = &txm.all_stories;
 }
 
 void
 tx_manager_free()
 {
+	mh_history_delete(txm.history);
+	for (size_t i = 0; i < BOX_INDEX_MAX; i++)
+		mempool_destroy(&txm.txm_story_pool[i]);
 }
 
 int
@@ -1095,4 +1141,681 @@ txm_cause_conflict(struct txn *wreaker, struct txn *victim)
 	rlist_add(&wreaker->conflict_list, &tracker->in_conflict_list);
 	rlist_add(&wreaker->conflicted_by_list, &tracker->in_conflicted_by_list);
 	return 0;
-}
\ No newline at end of file
+}
+
+struct txm_story *
+txm_story_new(struct tuple *tuple, uint32_t index_count)
+{
+	assert(!tuple->is_dirty);
+	assert(index_count < BOX_INDEX_MAX);
+	struct mempool *pool = &txm.txm_story_pool[index_count];
+	struct txm_story *story = (struct txm_story *)mempool_alloc(pool);
+	if (story == NULL) {
+		size_t item_size = sizeof(struct txm_story) +
+			index_count * sizeof(struct txm_story_link);
+		diag_set(OutOfMemory, item_size,
+			 "tx_manager", "tx story");
+		return story;
+	}
+	story->tuple = tuple;
+
+	const struct txm_story **put_story = (const struct txm_story **)&story;
+	struct txm_story **empty = NULL;
+	mh_int_t pos = mh_history_put(txm.history, put_story, &empty, 0);
+	if (pos == mh_end(txm.history)) {
+		mempool_free(pool, story);
+		diag_set(OutOfMemory, pos + 1,
+			 "tx_manager", "tx history hash table");
+		return NULL;
+	}
+	tuple->is_dirty = true;
+	tuple_ref(tuple);
+
+	story->index_count = index_count;
+	story->add_stmt = NULL;
+	story->add_psn = 0;
+	story->del_stmt = NULL;
+	story->del_psn = 0;
+	rlist_create(&story->reader_list);
+	rlist_add(&txm.all_stories, &story->in_all_stories);
+	memset(story->link, 0, sizeof(story->link[0]) * index_count);
+	return story;
+}
+
+static struct txm_story *
+txm_story_new_add_stmt(struct tuple *tuple, struct txn_stmt *stmt)
+{
+	struct txm_story *res = txm_story_new(tuple, stmt->space->index_count);
+	if (res == NULL)
+		return NULL;
+	res->add_stmt = stmt;
+	assert(stmt->add_story == NULL);
+	stmt->add_story = res;
+	return res;
+}
+
+static struct txm_story *
+txm_story_new_del_stmt(struct tuple *tuple, struct txn_stmt *stmt)
+{
+	struct txm_story *res = txm_story_new(tuple, stmt->space->index_count);
+	if (res == NULL)
+		return NULL;
+	res->del_stmt = stmt;
+	assert(stmt->del_story == NULL);
+	stmt->del_story = res;
+	return res;
+}
+
+static void
+txm_story_delete_add_stmt(struct txm_story *story)
+{
+	story->add_stmt->add_story = NULL;
+	story->add_stmt = NULL;
+	txm_story_delete(story);
+}
+
+static void
+txm_story_delete_del_stmt(struct txm_story *story)
+{
+	story->del_stmt->del_story = NULL;
+	story->del_stmt = NULL;
+	txm_story_delete(story);
+}
+
+
+static struct txm_story *
+txm_story_get(struct tuple *tuple)
+{
+	assert(tuple->is_dirty);
+
+	mh_int_t pos = mh_history_find(txm.history, tuple, 0);
+	assert(pos != mh_end(txm.history));
+	return *mh_history_node(txm.history, pos);
+}
+
+static struct tuple *
+txm_story_older_tuple(struct txm_story_link *link)
+{
+	return link->older.is_story ? link->older.story->tuple
+				    : link->older.tuple;
+}
+
+static void
+txm_story_link_story(struct txm_story *story, struct txm_story *older_story,
+		     uint32_t index)
+{
+	assert(older_story != NULL);
+	struct txm_story_link *link = &story->link[index];
+	/* Must be unlinked. */
+	assert(!link->older.is_story);
+	assert(link->older.tuple == NULL);
+	link->older.is_story = true;
+	link->older.story = older_story;
+	older_story->link[index].newer_story = story;
+}
+
+static void
+txm_story_link_tuple(struct txm_story *story, struct tuple *older_tuple,
+                     uint32_t index)
+{
+	struct txm_story_link *link = &story->link[index];
+	/* Must be unlinked. */
+	assert(!link->older.is_story);
+	assert(link->older.tuple == NULL);
+	if (older_tuple == NULL)
+		return;
+	if (older_tuple->is_dirty) {
+		txm_story_link_story(story, txm_story_get(older_tuple), index);
+		return;
+	}
+	tusp_setNT(&link->older.tuple, older_tuple);
+}
+
+static void
+txm_story_unlink(struct txm_story *story, uint32_t index)
+{
+	struct txm_story_link *link = &story->link[index];
+	if (link->older.is_story)
+		link->older.story->link[index].newer_story = NULL;
+	else
+		tusp_setUN(&link->older.tuple, NULL);
+	link->older.is_story = false;
+	link->older.tuple = NULL;
+}
+
+static bool
+txm_story_is_visible(struct txm_story *story, struct txn *txn,
+		      struct tuple **visible_tuple, bool prepared_ok,
+		     bool *own_change)
+{
+	*own_change = false;
+	struct txn_stmt *dels = story->del_stmt;
+	while (dels != NULL) {
+		if (dels->txn == txn) {
+			/* deleted by us. */
+			*visible_tuple = NULL;
+			*own_change = true;
+			return true;
+		}
+		dels = dels->next_in_del_list;
+	}
+	if (prepared_ok && story->del_psn != 0) {
+		/* deleted by at least prepared TX. */
+		*visible_tuple = NULL;
+		return true;
+	}
+	if (story->del_psn != 0 && story->del_stmt == NULL) {
+		/* deleted by committed TX. */
+		*visible_tuple = NULL;
+		return true;
+	}
+
+	if (story->add_stmt != NULL && story->add_stmt->txn == txn) {
+		/* added by us. */
+		*visible_tuple = story->tuple;
+		*own_change = true;
+		return true;
+	}
+	if (prepared_ok && story->add_psn != 0) {
+		/* added by at least prepared TX. */
+		*visible_tuple = story->tuple;
+		return true;
+	}
+	if (story->add_psn != 0 && story->add_stmt == NULL) {
+		/* added by committed TX. */
+		*visible_tuple = story->tuple;
+		return true;
+	}
+	return false;
+}
+
+/** Temporary allocated on region that stores a conflicting TX. */
+struct txn_conflict
+{
+	struct txn *other_txn;
+	struct txn_conflict *next;
+};
+
+static int
+txm_save_conflict(struct txn *other_txn, struct txn_conflict **coflicts_head,
+		  struct region *region)
+{
+	size_t err_size;
+	struct txn_conflict *next_conflict;
+	next_conflict = region_alloc_object(region, struct txn_conflict,
+					    &err_size);
+	if (next_conflict == NULL) {
+		diag_set(OutOfMemory, err_size,
+			 "txn_region", "txn conflict");
+		return -1;
+	}
+	next_conflict->other_txn = other_txn;
+	next_conflict->next = *coflicts_head;
+	*coflicts_head = next_conflict;
+	return 0;
+}
+
+int
+txm_story_find_visible(struct txn_stmt *stmt, struct txm_story *story,
+		       uint32_t ind, struct tuple **visible_replaced,
+		       struct txn_conflict **collected_conflicts,
+		       struct region *region)
+{
+	while (true) {
+		if (!story->link[ind].older.is_story) {
+			/*
+			 * the tuple is so old that we doesn't
+			 * know its story.
+			 */
+			*visible_replaced = story->link[ind].older.tuple;
+			assert(*visible_replaced == NULL ||
+			       !(*visible_replaced)->is_dirty);
+			break;
+		}
+		story = story->link[ind].older.story;
+		bool unused;
+		if (txm_story_is_visible(story, stmt->txn,
+					 visible_replaced, true, &unused))
+			break;
+
+		/*
+		 * We skip the story but once the story is committed
+		 * before out TX that may cause conflict.
+		 * The conflict will be inavoidable if this statement
+		 * relies on old_tuple. If not (it's a replace),
+		 * the conflict will take place only for secondary
+		 * index if the story will not be overwritten in primary
+		 * index.
+		 */
+		bool cross_conflict = false;
+		if (stmt->preserve_old_tuple) {
+			cross_conflict = true;
+		} else if (ind != 0) {
+			struct txm_story *look_up = story;
+			cross_conflict = true;
+			while (look_up->link[ind].newer_story != NULL) {
+				struct txm_story *over;
+				over = look_up->link[ind].newer_story;
+				if (over->add_stmt->txn == stmt->txn) {
+					cross_conflict = false;
+					break;
+				}
+				look_up = over;
+			}
+		}
+		if (cross_conflict) {
+			if (txm_save_conflict(story->add_stmt->txn,
+					      collected_conflicts,
+					      region) != 0)
+				return -1;
+
+		}
+	}
+	return 0;
+}
+
+int
+txm_history_link_stmt(struct txn_stmt *stmt,
+		      struct tuple *old_tuple, struct tuple *new_tuple,
+		      enum dup_replace_mode mode, struct tuple **result)
+{
+	struct txm_story *add_story = NULL;
+	uint32_t add_story_linked = 0;
+	struct txm_story *del_story = NULL;
+	bool del_story_created = false;
+	struct region *region = &stmt->txn->region;
+	size_t region_svp = region_used(region);
+
+	/**
+	 * List of transactions that will conflict us once one of them
+	 * become committed.
+	 */
+	struct txn_conflict *collected_conflicts = NULL;
+
+	if (new_tuple != NULL) {
+		add_story = txm_story_new_add_stmt(new_tuple, stmt);
+		if (add_story == NULL)
+			goto fail;
+
+		for (uint32_t i = 0; i < stmt->space->index_count; i++) {
+			struct tuple *replaced;
+			struct index *index = stmt->space->index[i];
+			if (index_replace(index, NULL, new_tuple,
+					  DUP_REPLACE_OR_INSERT,
+					  &replaced) != 0)
+				goto fail;
+			txm_story_link_tuple(add_story, replaced, i);
+			add_story_linked++;
+
+			struct tuple *visible_replaced = NULL;
+			if (txm_story_find_visible(stmt, add_story, i,
+						   &visible_replaced,
+						   &collected_conflicts,
+						   region) != 0)
+				goto fail;
+
+			uint32_t errcode;
+			errcode = replace_check_dup(old_tuple,
+						    visible_replaced,
+						    i == 0 ? mode : DUP_INSERT);
+			if (errcode != 0) {
+				struct space *sp = stmt->space;
+				if (sp != NULL)
+					diag_set(ClientError, errcode,
+						 sp->index[i]->def->name,
+						 space_name(sp));
+				goto fail;
+			}
+
+			if (i == 0) {
+				old_tuple = visible_replaced;
+				*result = visible_replaced;
+			}
+		}
+	} else {
+		assert(old_tuple != NULL);
+		*result = old_tuple;
+	}
+
+	struct tuple *del_tuple = NULL;
+	if (new_tuple != NULL) {
+		struct txm_story_link *link = &add_story->link[0];
+		if (link->older.is_story) {
+			del_story = link->older.story;
+			del_tuple = del_story->tuple;
+		} else {
+			del_tuple = link->older.tuple;
+		}
+	} else {
+		del_tuple = old_tuple;
+	}
+	if (del_tuple != NULL && del_story == NULL) {
+		if (del_tuple->is_dirty) {
+			del_story = txm_story_get(del_tuple);
+		} else {
+			del_story = txm_story_new_del_stmt(del_tuple, stmt);
+			if (del_story == NULL)
+				goto fail;
+			del_story_created = true;
+		}
+	}
+	if (new_tuple != NULL && del_story_created) {
+		for (uint32_t i = 0; i < add_story->index_count; i++) {
+			struct txm_story_link *link = &add_story->link[i];
+			if (link->older.is_story)
+				continue;
+			if (link->older.tuple == del_tuple) {
+				txm_story_unlink(add_story, i);
+				txm_story_link_story(add_story, del_story, i);
+			}
+		}
+	}
+	if (del_story != NULL) {
+		stmt->next_in_del_list = del_story->del_stmt;
+		del_story->del_stmt = stmt;
+		stmt->del_story = del_story;
+	}
+
+	while (collected_conflicts != NULL) {
+		if (txm_cause_conflict(collected_conflicts->other_txn,
+				       stmt->txn) != 0) {
+			goto fail;
+		}
+		collected_conflicts = collected_conflicts->next;
+	}
+	region_truncate(region, region_svp);
+	if (stmt->new_tuple != NULL)
+		tuple_ref(stmt->new_tuple);
+	if (*result != NULL)
+		tuple_ref(*result);
+	return 0;
+
+fail:
+	if (add_story != NULL) {
+		while (add_story_linked > 0) {
+			--add_story_linked;
+			uint32_t i = add_story_linked;
+
+			struct index *index = stmt->space->index[i];
+			struct txm_story_link *link = &add_story->link[i];
+			struct tuple *was = txm_story_older_tuple(link);
+			struct tuple *unused;
+			if (index_replace(index, new_tuple, was,
+					  DUP_INSERT,
+					  &unused) != 0) {
+				diag_log();
+				unreachable();
+				panic("failed to rollback change");
+			}
+
+			txm_story_unlink(stmt->add_story, i);
+
+		}
+		txm_story_delete_add_stmt(stmt->add_story);
+	}
+
+	if (del_story != NULL && del_story->del_stmt == stmt) {
+		del_story->del_stmt = stmt->next_in_del_list;
+		stmt->next_in_del_list = NULL;
+	}
+
+	if (del_story_created)
+		txm_story_delete_del_stmt(stmt->del_story);
+	else
+		stmt->del_story = NULL;
+
+	region_truncate(region, region_svp);
+	return -1;
+}
+
+void
+txm_history_unlink_stmt(struct txn_stmt *stmt)
+{
+	if (stmt->add_story != NULL) {
+		assert(stmt->add_story->tuple == stmt->new_tuple);
+		struct txm_story *story = stmt->add_story;
+
+		for (uint32_t i = 0; i < story->index_count; i++) {
+			struct txm_story_link *link = &story->link[i];
+			if (link->newer_story == NULL) {
+				struct tuple *unused;
+				struct index *index = stmt->space->index[i];
+				struct tuple *was = txm_story_older_tuple(link);
+				if (index_replace(index, story->tuple, was,
+						  DUP_INSERT, &unused) != 0) {
+					diag_log();
+					unreachable();
+					panic("failed to rollback change");
+				}
+			} else {
+				struct txm_story *newer = link->newer_story;
+				assert(newer->link[i].older.is_story);
+				assert(newer->link[i].older.story == story);
+				txm_story_unlink(newer, i);
+				if (link->older.is_story) {
+					struct txm_story *to = link->older.story;
+					txm_story_link_story(newer,to, i);
+				} else {
+					struct tuple *to = link->older.tuple;
+					txm_story_link_tuple(newer, to, i);
+				}
+			}
+			txm_story_unlink(story, i);
+		}
+		stmt->add_story->add_stmt = NULL;
+		stmt->add_story = NULL;
+		tuple_unref(stmt->new_tuple);
+	}
+
+	if (stmt->del_story != NULL) {
+		struct txm_story *story = stmt->del_story;
+
+		struct txn_stmt **prev = &story->del_stmt;
+		while (*prev != stmt) {
+			prev = &(*prev)->next_in_del_list;
+			assert(*prev != NULL);
+		}
+		*prev = stmt->next_in_del_list;
+		stmt->next_in_del_list = NULL;
+
+		stmt->del_story->del_stmt = NULL;
+		stmt->del_story = NULL;
+	}
+}
+
+void
+txm_history_prepare_stmt(struct txn_stmt *stmt)
+{
+	assert(stmt->txn->psn != 0);
+
+	/* Move story to the past to prepared stories. */
+
+	struct txm_story *story = stmt->add_story;
+	uint32_t index_count = story == NULL ? 0 : story->index_count;
+	for (uint32_t i = 0; i < index_count; ) {
+		if (!story->link[i].older.is_story) {
+			/* tuple is old. */
+			i++;
+			continue;
+		}
+		struct txm_story *old_story =
+			story->link[i].older.story;
+		if (old_story->del_psn != 0) {
+			/* is psn is set, the change is prepared. */
+			i++;
+			continue;
+		}
+		if (old_story->add_psn != 0) {
+			/* is psn is set, the change is prepared. */
+			i++;
+			continue;
+		}
+
+		if (old_story->add_stmt != NULL) {
+			/* ancient */
+			i++;
+			continue;
+		}
+		if (old_story->add_stmt->txn == stmt->txn) {
+			/* added by us. */
+			i++;
+			continue;
+		}
+
+		if (old_story->add_stmt->preserve_old_tuple || i != 0)
+			old_story->add_stmt->txn->status = TXN_CONFLICTED;
+
+		/* Swap story and old story. */
+		struct txm_story_link *link = &story->link[i];
+		if (link->newer_story == NULL) {
+			/* we have to replace the tuple in index. */
+			struct tuple *unused;
+			struct index *index = stmt->space->index[i];
+			if (index_replace(index, story->tuple,
+			                  old_story->tuple,
+			                  DUP_INSERT, &unused) != 0) {
+				diag_log();
+				unreachable();
+				panic("failed to rollback change");
+			}
+		} else {
+			struct txm_story *newer = link->newer_story;
+			assert(newer->link[i].older.is_story);
+			assert(newer->link[i].older.story == story);
+			txm_story_unlink(newer, i);
+			txm_story_link_story(newer, old_story, i);
+		}
+
+		txm_story_unlink(story, i);
+
+		txm_story_unlink(story, i);
+		if (old_story->link[i].older.is_story) {
+			struct txm_story *to =
+				old_story->link[i].older.story;
+			txm_story_unlink(old_story, i);
+			txm_story_link_story(story, to, i);
+		} else {
+			struct tuple *to =
+				old_story->link[i].older.tuple;
+			txm_story_unlink(old_story, i);
+			txm_story_link_tuple(story, to, i);
+		}
+
+		txm_story_link_story(old_story, story, i);
+
+		if (i == 0) {
+			assert(stmt->del_story == old_story);
+			assert(story->link[0].older.is_story ||
+			       story->link[0].older.tuple == NULL);
+
+			struct txn_stmt *dels = old_story->del_stmt;
+			assert(dels != NULL);
+			do {
+				if (dels->txn != stmt->txn)
+					dels->txn->status = TXN_CONFLICTED;
+				dels->del_story = NULL;
+				struct txn_stmt *next = dels->next_in_del_list;
+				dels->next_in_del_list = NULL;
+				dels = next;
+			} while (dels != NULL);
+			old_story->del_stmt = NULL;
+
+			if (story->link[0].older.is_story) {
+				struct txm_story *oldest_story =
+					story->link[0].older.story;
+				dels = oldest_story->del_stmt;
+				while (dels != NULL) {
+					assert(dels->txn != stmt->txn);
+					dels->del_story = NULL;
+					struct txn_stmt *next =
+						dels->next_in_del_list;
+					dels->next_in_del_list = NULL;
+					dels = next;
+				}
+				oldest_story->del_stmt = stmt;
+				stmt->del_story = oldest_story;
+			}
+		}
+	}
+	if (stmt->add_story != NULL)
+		stmt->add_story->add_psn = stmt->txn->psn;
+
+	if (stmt->del_story != NULL)
+		stmt->del_story->del_psn = stmt->txn->psn;
+}
+
+ssize_t
+txm_history_release_stmt(struct txn_stmt *stmt)
+{
+	size_t res = 0;
+	if (stmt->add_story != NULL) {
+		assert(stmt->add_story->add_stmt == stmt);
+		res += stmt->add_story->tuple->bsize;
+		stmt->add_story->add_stmt = NULL;
+		stmt->add_story = NULL;
+	}
+	if (stmt->del_story != NULL) {
+		assert(stmt->del_story->del_stmt == stmt);
+		assert(stmt->next_in_del_list == NULL);
+		res -= stmt->del_story->tuple->bsize;
+		tuple_unref(stmt->del_story->tuple);
+		stmt->del_story->del_stmt = NULL;
+		stmt->del_story = NULL;
+	}
+	return res;
+}
+
+struct tuple *
+txm_tuple_clarify_slow(struct txn* txn, struct tuple* tuple, uint32_t index,
+                       uint32_t mk_index, bool prepared_ok)
+{
+	assert(tuple->is_dirty);
+	struct txm_story *story = txm_story_get(tuple);
+	bool own_change = false;
+	struct tuple *result = NULL;
+
+	while (true) {
+		if (txm_story_is_visible(story, txn, &result,
+					 prepared_ok, &own_change)) {
+			break;
+		}
+		if (story->link[index].older.is_story) {
+			story = story->link[index].older.story;
+		} else {
+			result = story->link[index].older.tuple;
+			break;
+		}
+	}
+	(void)own_change; /* TODO: add conflict */
+	(void)mk_index; /* TODO: multiindex */
+	return result;
+}
+void
+txm_story_delete(struct txm_story *story)
+{
+	assert(story->add_stmt == NULL);
+	assert(story->del_stmt == NULL);
+
+	if (txm.traverse_all_stories == &story->in_all_stories)
+		txm.traverse_all_stories = rlist_next(txm.traverse_all_stories);
+	rlist_del(&story->in_all_stories);
+
+	mh_int_t pos = mh_history_find(txm.history, story->tuple, 0);
+	assert(pos != mh_end(txm.history));
+	mh_history_del(txm.history, pos, 0);
+
+	story->tuple->is_dirty = false;
+	tuple_unref(story->tuple);
+
+#ifndef NDEBUG
+	/* Expecting to delete fully unlinked story. */
+	for (uint32_t i = 0; i < story->index_count; i++) {
+		assert(story->link[i].newer_story == NULL);
+		assert(story->link[i].older.is_story == false);
+		assert(story->link[i].older.tuple == NULL);
+	}
+#endif
+
+	struct mempool *pool = &txm.txm_story_pool[story->index_count];
+	mempool_free(pool, story);
+}
diff --git a/src/box/txn.h b/src/box/txn.h
index 92c0116..bbe1c51 100644
--- a/src/box/txn.h
+++ b/src/box/txn.h
@@ -36,6 +36,7 @@
 #include "trigger.h"
 #include "fiber.h"
 #include "space.h"
+#include "tuple.h"
 
 #if defined(__cplusplus)
 extern "C" {
@@ -123,6 +124,18 @@ struct txn_stmt {
 	struct space *space;
 	struct tuple *old_tuple;
 	struct tuple *new_tuple;
+	/**
+	 * If new_tuple != NULL and this transaction was not prepared,
+	 * this member holds added story of the new_tuple.
+	 */
+	struct txm_story *add_story;
+	/**
+	 * If new_tuple == NULL and this transaction was not prepared,
+	 * this member holds added story of the old_tuple.
+	 */
+	struct txm_story *del_story;
+	/** Link in txm_story::del_stmt linked list. */
+	struct txn_stmt *next_in_del_list;
 	/** Engine savepoint for the start of this statement. */
 	void *engine_savepoint;
 	/** Redo info: the binary log row */
@@ -284,6 +297,87 @@ struct txn {
 	struct rlist conflicted_by_list;
 };
 
+/**
+ * Pointer to tuple or story.
+ */
+struct txm_story_or_tuple {
+	/** Flag whether it's a story. */
+	bool is_story;
+	union {
+		/** Pointer to story, it must be reverse liked. */
+		struct txm_story *story;
+		/** Smart pointer to tuple: the tuple is referenced if set. */
+		struct tuple *tuple;
+	};
+};
+
+/**
+ * Link that connects a txm_story with older and newer stories of the same
+ * key in index.
+ */
+struct txm_story_link {
+	/** Story that was happened after that story was ended. */
+	struct txm_story *newer_story;
+	/**
+	 * Older story or ancient tuple (so old that its story was lost).
+	 * In case of tuple is can also be NULL.
+	 */
+	struct txm_story_or_tuple older;
+};
+
+/**
+ * A part of a history of a value in space.
+ * It's a story about a tuple, from the point it was added to space to the
+ * point when it was deleted from a space.
+ * All stories are linked into a list of stories of the same key of each index.
+ */
+struct txm_story {
+	/** The story is about this tuple. The tuple is referenced. */
+
+	struct tuple *tuple;
+	/**
+	 * Statement that told this story. Is set to NULL when the statement's
+	 * transaction becomes committed. Can also be NULL if we don't know who
+	 * introduced that story.
+	 */
+	struct txn_stmt *add_stmt;
+	/**
+	 * Prepare sequence number of add_stmt's transaction. Is set when
+	 * the transactions is prepared. Can be 0 if the transaction is
+	 * in progress or we don't know who introduced that story.
+	 */
+	int64_t add_psn;
+	/**
+	 * Statement that ended this story. Is set to NULL when the statement's
+	 * transaction becomes committed. Can also be NULL if the tuple has not
+	 * been deleted yet.
+	 */
+	struct txn_stmt *del_stmt;
+	/**
+	 * Prepare sequence number of del_stmt's transaction. Is set when
+	 * the transactions is prepared. Can be 0 if the transaction is
+	 * in progress or if nobody has deleted the tuple.
+	 */
+	int64_t del_psn;
+	/**
+	 * List of trackers - transactions that has read this tuple.
+	 */
+	struct rlist reader_list;
+	/**
+	 * Link in tx_manager::all_stories
+	 */
+	struct rlist in_all_stories;
+	/**
+	 * Number of indexes in this space - and the count of link[].
+	 */
+	uint32_t index_count;
+	/**
+	 * Link with older and newer stories (and just tuples) for each
+	 * index respectively.
+	 */
+	struct txm_story_link link[];
+};
+
 static inline bool
 txn_has_flag(struct txn *txn, enum txn_flag flag)
 {
@@ -652,6 +746,39 @@ tx_manager_free();
 int
 txm_cause_conflict(struct txn *wreaker, struct txn *victim);
 
+struct txm_story *
+txm_story_new(struct tuple *tuple, uint32_t index_count);
+
+int
+txm_history_link_stmt(struct txn_stmt *stmt,
+		      struct tuple *old_tuple, struct tuple *new_tuple,
+		      enum dup_replace_mode mode, struct tuple **result);
+
+void
+txm_history_unlink_stmt(struct txn_stmt *stmt);
+
+void
+txm_history_prepare_stmt(struct txn_stmt *stmt);
+
+ssize_t
+txm_history_release_stmt(struct txn_stmt *stmt);
+
+struct tuple *
+txm_tuple_clarify_slow(struct txn *txn, struct tuple *tuple, uint32_t index,
+                       uint32_t mk_index, bool prepared_ok);
+
+static inline struct tuple*
+txm_tuple_clarify(struct txn *txn, struct tuple* tuple, uint32_t index,
+                  uint32_t mk_index, bool prepared_ok)
+{
+	if (!tuple->is_dirty)
+		return tuple;
+	return txm_tuple_clarify_slow(txn, tuple, index, mk_index, prepared_ok);
+}
+
+void
+txm_story_delete(struct txm_story *story);
+
 #if defined(__cplusplus)
 } /* extern "C" */
 #endif /* defined(__cplusplus) */
-- 
2.7.4