[tarantool-patches] [PATCH 1/2] Introduce a txn memory region

[Georgy Kirichenko <georgy@tarantool.org>]

Attach a separate memory region for each txn structure in order to store
all txn internal data until the transaction finished. This patch is a
preparation to detach a txn from a fiber and a fiber gc storage.

Prerequisites: #1254
---
 src/box/errcode.h    |  1 +
 src/box/txn.c        | 66 ++++++++++++++++++++++++++++++++++++--------
 src/box/txn.h        |  2 ++
 test/box/misc.result |  1 +
 4 files changed, 58 insertions(+), 12 deletions(-)

diff --git a/src/box/errcode.h b/src/box/errcode.h
index 3f8cb8e0e..bd1a684ab 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_NO_TRANSACTION,		"No active transaction") \
 
 /*
  * !IMPORTANT! Please follow instructions at start of the file
diff --git a/src/box/txn.c b/src/box/txn.c
index d51bfc67a..be5e209b6 100644
--- a/src/box/txn.c
+++ b/src/box/txn.c
@@ -37,6 +37,9 @@
 
 double too_long_threshold;
 
+/* Txn cache. */
+static struct rlist txn_cache = RLIST_HEAD_INITIALIZER(txn_cache);
+
 static inline void
 fiber_set_txn(struct fiber *fiber, struct txn *txn)
 {
@@ -44,7 +47,7 @@ fiber_set_txn(struct fiber *fiber, struct txn *txn)
 }
 
 static int
-txn_add_redo(struct txn_stmt *stmt, struct request *request)
+txn_add_redo(struct txn *txn, struct txn_stmt *stmt, struct request *request)
 {
 	stmt->row = request->header;
 	if (request->header != NULL)
@@ -52,7 +55,7 @@ txn_add_redo(struct txn_stmt *stmt, struct request *request)
 
 	/* Create a redo log row for Lua requests */
 	struct xrow_header *row;
-	row = region_alloc_object(&fiber()->gc, struct xrow_header);
+	row = region_alloc_object(&txn->region, struct xrow_header);
 	if (row == NULL) {
 		diag_set(OutOfMemory, sizeof(*row),
 			 "region", "struct xrow_header");
@@ -77,7 +80,7 @@ static struct txn_stmt *
 txn_stmt_new(struct txn *txn)
 {
 	struct txn_stmt *stmt;
-	stmt = region_alloc_object(&fiber()->gc, struct txn_stmt);
+	stmt = region_alloc_object(&txn->region, struct txn_stmt);
 	if (stmt == NULL) {
 		diag_set(OutOfMemory, sizeof(*stmt),
 			 "region", "struct txn_stmt");
@@ -134,16 +137,49 @@ txn_rollback_to_svp(struct txn *txn, struct stailq_entry *svp)
 	}
 }
 
+/*
+ * Return a txn from cache or create a new one if cache is empty.
+ */
+static struct txn *
+txn_new()
+{
+	if (!rlist_empty(&txn_cache))
+		return rlist_shift_entry(&txn_cache, struct txn, list);
+
+	/* Create a region. */
+	struct region region;
+	region_create(&region, &cord()->slabc);
+
+	/* Place txn structure on the region. */
+	struct txn *txn = region_alloc_object(&region, struct txn);
+	if (txn == NULL) {
+		diag_set(OutOfMemory, sizeof(*txn), "region", "struct txn");
+		return NULL;
+	}
+	txn->region = region;
+	return txn;
+}
+
+/*
+ * Free txn memory and return it to a cache.
+ */
+static void
+txn_free(struct txn *txn)
+{
+	/* Truncate region up to struct txn size. */
+	region_truncate(&txn->region, sizeof(struct txn));
+	rlist_add(&txn_cache, &txn->list);
+}
+
 struct txn *
 txn_begin(bool is_autocommit)
 {
 	static int64_t tsn = 0;
 	assert(! in_txn());
-	struct txn *txn = region_alloc_object(&fiber()->gc, struct txn);
-	if (txn == NULL) {
-		diag_set(OutOfMemory, sizeof(*txn), "region", "struct txn");
+	struct txn *txn = txn_new();
+	if (txn == NULL)
 		return NULL;
-	}
+
 	/* Initialize members explicitly to save time on memset() */
 	stailq_create(&txn->stmts);
 	txn->n_new_rows = 0;
@@ -251,7 +287,7 @@ txn_commit_stmt(struct txn *txn, struct request *request)
 	 * stmt->space can be NULL for IRPOTO_NOP.
 	 */
 	if (stmt->space == NULL || !space_is_temporary(stmt->space)) {
-		if (txn_add_redo(stmt, request) != 0)
+		if (txn_add_redo(txn, stmt, request) != 0)
 			goto fail;
 		assert(stmt->row != NULL);
 		if (stmt->row->replica_id == 0) {
@@ -393,8 +429,8 @@ txn_commit(struct txn *txn)
 	stailq_foreach_entry(stmt, &txn->stmts, next)
 		txn_stmt_unref_tuples(stmt);
 
-	TRASH(txn);
 	fiber_set_txn(fiber(), NULL);
+	txn_free(txn);
 	return 0;
 fail:
 	txn_rollback();
@@ -433,10 +469,10 @@ txn_rollback()
 	stailq_foreach_entry(stmt, &txn->stmts, next)
 		txn_stmt_unref_tuples(stmt);
 
-	TRASH(txn);
 	/** Free volatile txn memory. */
 	fiber_gc();
 	fiber_set_txn(fiber(), NULL);
+	txn_free(txn);
 }
 
 void
@@ -521,12 +557,18 @@ box_txn_rollback()
 void *
 box_txn_alloc(size_t size)
 {
+	struct txn *txn = in_txn();
+	if (txn == NULL) {
+		/* There are no transaction yet - return an error. */
+		diag_set(ClientError, ER_NO_TRANSACTION);
+		return NULL;
+	}
 	union natural_align {
 		void *p;
 		double lf;
 		long l;
 	};
-	return region_aligned_alloc(&fiber()->gc, size,
+	return region_aligned_alloc(&txn->region, size,
 	                            alignof(union natural_align));
 }
 
@@ -539,7 +581,7 @@ box_txn_savepoint()
 		return NULL;
 	}
 	struct txn_savepoint *svp =
-		(struct txn_savepoint *) region_alloc_object(&fiber()->gc,
+		(struct txn_savepoint *) region_alloc_object(&txn->region,
 							struct txn_savepoint);
 	if (svp == NULL) {
 		diag_set(OutOfMemory, sizeof(*svp),
diff --git a/src/box/txn.h b/src/box/txn.h
index 747b38db3..84c82af92 100644
--- a/src/box/txn.h
+++ b/src/box/txn.h
@@ -132,6 +132,8 @@ struct autoinc_id_entry {
 };
 
 struct txn {
+	struct rlist list;
+	struct region region;
 	/**
 	 * A sequentially growing transaction id, assigned when
 	 * a transaction is initiated. Used to identify
diff --git a/test/box/misc.result b/test/box/misc.result
index e2b618c9c..be3cbde37 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.NO_TRANSACTION
 ...
 test_run:cmd("setopt delimiter ''");
 ---
-- 
2.21.0