[tarantool-patches] [PATCH 01/10] 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            |  2 +-
 src/box/sql/vdbe.c           |  2 +-
 src/box/txn.c                | 71 +++++++++++++++++++++++++++++-------
 src/box/txn.h                |  2 +
 test/box/misc.result         |  2 +-
 test/engine/savepoint.result |  2 +-
 test/sql/savepoints.result   |  6 +--
 7 files changed, 66 insertions(+), 21 deletions(-)

diff --git a/src/box/errcode.h b/src/box/errcode.h
index 3f8cb8e0e..a273826b3 100644
--- a/src/box/errcode.h
+++ b/src/box/errcode.h
@@ -166,7 +166,7 @@ struct errcode_record {
 	/*111 */_(ER_WRONG_SPACE_OPTIONS,	"Wrong space options (field %u): %s") \
 	/*112 */_(ER_UNSUPPORTED_INDEX_FEATURE,	"Index '%s' (%s) of space '%s' (%s) does not support %s") \
 	/*113 */_(ER_VIEW_IS_RO,		"View '%s' is read-only") \
-	/*114 */_(ER_SAVEPOINT_NO_TRANSACTION,	"Can not set a savepoint in absence of active transaction") \
+	/*114 */_(ER_NO_TRANSACTION,		"No active transaction") \
 	/*115 */_(ER_SYSTEM,			"%s") \
 	/*116 */_(ER_LOADING,			"Instance bootstrap hasn't finished yet") \
 	/*117 */_(ER_CONNECTION_TO_SELF,	"Connection to self") \
diff --git a/src/box/sql/vdbe.c b/src/box/sql/vdbe.c
index ed7bf8870..9fc70980c 100644
--- a/src/box/sql/vdbe.c
+++ b/src/box/sql/vdbe.c
@@ -3017,7 +3017,7 @@ case OP_Savepoint: {
 
 	if (psql_txn == NULL) {
 		assert(!box_txn());
-		diag_set(ClientError, ER_SAVEPOINT_NO_TRANSACTION);
+		diag_set(ClientError, ER_NO_TRANSACTION);
 		rc = SQL_TARANTOOL_ERROR;
 		goto abort_due_to_error;
 	}
diff --git a/src/box/txn.c b/src/box/txn.c
index d51bfc67a..815199645 100644
--- a/src/box/txn.c
+++ b/src/box/txn.c
@@ -37,6 +37,9 @@
 
 double too_long_threshold;
 
+/* Txn cache. */
+static struct stailq txn_cache = {NULL, &txn_cache.first};
+
 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 +137,50 @@ 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.
+ */
+inline static struct txn *
+txn_new()
+{
+	if (!stailq_empty(&txn_cache))
+		return stailq_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;
+	}
+	assert(region_used(&region) == sizeof(*txn));
+	txn->region = region;
+	return txn;
+}
+
+/*
+ * Free txn memory and return it to a cache.
+ */
+inline static void
+txn_free(struct txn *txn)
+{
+	/* Truncate region up to struct txn size. */
+	region_truncate(&txn->region, sizeof(struct txn));
+	stailq_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 +288,7 @@ 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 +430,8 @@ 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 +470,10 @@ 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 +558,18 @@ 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));
 }
 
@@ -535,11 +578,11 @@ box_txn_savepoint()
 {
 	struct txn *txn = in_txn();
 	if (txn == NULL) {
-		diag_set(ClientError, ER_SAVEPOINT_NO_TRANSACTION);
+		diag_set(ClientError, ER_NO_TRANSACTION);
 		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),
@@ -558,7 +601,7 @@ box_txn_rollback_to_savepoint(box_txn_savepoint_t *svp)
 {
 	struct txn *txn = in_txn();
 	if (txn == NULL) {
-		diag_set(ClientError, ER_SAVEPOINT_NO_TRANSACTION);
+		diag_set(ClientError, ER_NO_TRANSACTION);
 		return -1;
 	}
 	struct txn_stmt *stmt = svp->stmt == NULL ? NULL :
diff --git a/src/box/txn.h b/src/box/txn.h
index 747b38db3..fe8a299f2 100644
--- a/src/box/txn.h
+++ b/src/box/txn.h
@@ -132,6 +132,8 @@ struct autoinc_id_entry {
 };
 
 struct txn {
+	struct stailq_entry 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 a1f7a0990..d7d76d87e 100644
--- a/test/box/misc.result
+++ b/test/box/misc.result
@@ -443,7 +443,7 @@ t;
   111: box.error.WRONG_SPACE_OPTIONS
   112: box.error.UNSUPPORTED_INDEX_FEATURE
   113: box.error.VIEW_IS_RO
-  114: box.error.SAVEPOINT_NO_TRANSACTION
+  114: box.error.NO_TRANSACTION
   115: box.error.SYSTEM
   116: box.error.LOADING
   117: box.error.CONNECTION_TO_SELF
diff --git a/test/engine/savepoint.result b/test/engine/savepoint.result
index b3a918de0..86a2d0be2 100644
--- a/test/engine/savepoint.result
+++ b/test/engine/savepoint.result
@@ -14,7 +14,7 @@ s1 = nil
 ...
 s1 = box.savepoint()
 ---
-- error: Can not set a savepoint in absence of active transaction
+- error: No active transaction
 ...
 box.rollback_to_savepoint(s1)
 ---
diff --git a/test/sql/savepoints.result b/test/sql/savepoints.result
index 2f943bd9b..bb4a296fa 100644
--- a/test/sql/savepoints.result
+++ b/test/sql/savepoints.result
@@ -14,15 +14,15 @@ box.execute('pragma sql_default_engine=\''..engine..'\'')
 --
 box.execute('SAVEPOINT t1;');
 ---
-- error: Can not set a savepoint in absence of active transaction
+- error: No active transaction
 ...
 box.execute('RELEASE SAVEPOINT t1;');
 ---
-- error: Can not set a savepoint in absence of active transaction
+- error: No active transaction
 ...
 box.execute('ROLLBACK TO SAVEPOINT t1;');
 ---
-- error: Can not set a savepoint in absence of active transaction
+- error: No active transaction
 ...
 box.begin() box.execute('SAVEPOINT t1;') box.execute('RELEASE SAVEPOINT t1;') box.commit();
 ---
-- 
2.21.0