[PATCH 3/4] txn: use savepoints to roll back statements on yield or error
Vladimir Davydov
vdavydov.dev at gmail.com
Fri Jul 19 21:08:41 MSK 2019
Currently, txn_savepoint objects are only used for savepoints created by
the user while internally we use stailq_entry instead. This is okay now,
because txn_savepoint is equivalent to a stailq_entry in most cases, but
in order to properly deal with commit/rollback triggers, we will need to
maintain extra information in each savepoint. So this patch makes txn
use txn_savepoint for internal needs.
Note that this patch increases txn::sub_stmt_begin array size by 1,
because we could actually write beyond the array bounds - it didn't
lead to any problems before, because it only overwrote txn::signature.
With the increased array entry size, it can overwrite more vital parts
of the txn struct.
---
src/box/txn.c | 44 ++++++++++++++++++++++++++++++++------------
src/box/txn.h | 7 ++++---
2 files changed, 36 insertions(+), 15 deletions(-)
diff --git a/src/box/txn.c b/src/box/txn.c
index 0a42d440..3f0017f8 100644
--- a/src/box/txn.c
+++ b/src/box/txn.c
@@ -52,6 +52,29 @@ fiber_set_txn(struct fiber *fiber, struct txn *txn)
fiber->storage.txn = txn;
}
+/**
+ * A savepoint that points to the beginning of a transaction.
+ * Use it to rollback all statements of any transaction.
+ */
+static struct txn_savepoint zero_svp = {
+ /* .in_sub_stmt = */ 0,
+ /* .stmt = */ NULL,
+ /* .fk_deferred_count = */ 0,
+};
+
+/**
+ * Create a savepoint that can be used to rollback to
+ * the current transaction state.
+ */
+static void
+txn_create_svp(struct txn *txn, struct txn_savepoint *svp)
+{
+ svp->in_sub_stmt = txn->in_sub_stmt;
+ svp->stmt = stailq_last(&txn->stmts);
+ if (txn->psql_txn != NULL)
+ svp->fk_deferred_count = txn->psql_txn->fk_deferred_count;
+}
+
static int
txn_add_redo(struct txn *txn, struct txn_stmt *stmt, struct request *request)
{
@@ -102,7 +125,7 @@ txn_stmt_new(struct txn *txn)
stmt->row = NULL;
/* Set the savepoint for statement rollback. */
- txn->sub_stmt_begin[txn->in_sub_stmt] = stailq_last(&txn->stmts);
+ txn_create_svp(txn, &txn->sub_stmt_begin[txn->in_sub_stmt]);
txn->in_sub_stmt++;
stailq_add_tail_entry(&txn->stmts, stmt, next);
@@ -119,11 +142,11 @@ txn_stmt_unref_tuples(struct txn_stmt *stmt)
}
static void
-txn_rollback_to_svp(struct txn *txn, struct stailq_entry *svp)
+txn_rollback_to_svp(struct txn *txn, struct txn_savepoint *svp)
{
struct txn_stmt *stmt;
struct stailq rollback;
- stailq_cut_tail(&txn->stmts, svp, &rollback);
+ stailq_cut_tail(&txn->stmts, svp->stmt, &rollback);
stailq_reverse(&rollback);
stailq_foreach_entry(stmt, &rollback, next) {
if (txn->engine != NULL && stmt->space != NULL)
@@ -142,6 +165,8 @@ txn_rollback_to_svp(struct txn *txn, struct stailq_entry *svp)
stmt->space = NULL;
stmt->row = NULL;
}
+ if (txn->psql_txn != NULL)
+ txn->psql_txn->fk_deferred_count = svp->fk_deferred_count;
}
/*
@@ -565,7 +590,7 @@ txn_rollback_stmt(struct txn *txn)
if (txn == NULL || txn->in_sub_stmt == 0)
return;
txn->in_sub_stmt--;
- txn_rollback_to_svp(txn, txn->sub_stmt_begin[txn->in_sub_stmt]);
+ txn_rollback_to_svp(txn, &txn->sub_stmt_begin[txn->in_sub_stmt]);
}
void
@@ -702,10 +727,7 @@ box_txn_savepoint()
"region", "struct txn_savepoint");
return NULL;
}
- svp->stmt = stailq_last(&txn->stmts);
- svp->in_sub_stmt = txn->in_sub_stmt;
- if (txn->psql_txn != NULL)
- svp->fk_deferred_count = txn->psql_txn->fk_deferred_count;
+ txn_create_svp(txn, svp);
return svp;
}
@@ -731,9 +753,7 @@ box_txn_rollback_to_savepoint(box_txn_savepoint_t *svp)
diag_set(ClientError, ER_NO_SUCH_SAVEPOINT);
return -1;
}
- txn_rollback_to_svp(txn, svp->stmt);
- if (txn->psql_txn != NULL)
- txn->psql_txn->fk_deferred_count = svp->fk_deferred_count;
+ txn_rollback_to_svp(txn, svp);
return 0;
}
@@ -769,7 +789,7 @@ txn_on_yield(struct trigger *trigger, void *event)
(void) event;
struct txn *txn = in_txn();
assert(txn != NULL && !txn->can_yield);
- txn_rollback_to_svp(txn, NULL);
+ txn_rollback_to_svp(txn, &zero_svp);
if (txn->has_triggers) {
txn_run_triggers(txn, &txn->on_rollback);
txn->has_triggers = false;
diff --git a/src/box/txn.h b/src/box/txn.h
index df173924..a1685b5f 100644
--- a/src/box/txn.h
+++ b/src/box/txn.h
@@ -182,7 +182,7 @@ struct txn {
* First statement at each statement-level.
* Needed to rollback sub statements.
*/
- struct stailq_entry *sub_stmt_begin[TXN_SUB_STMT_MAX];
+ struct txn_savepoint sub_stmt_begin[TXN_SUB_STMT_MAX + 1];
/** LSN of this transaction when written to WAL. */
int64_t signature;
/** Engine involved in multi-statement transaction. */
@@ -390,8 +390,9 @@ txn_current_stmt(struct txn *txn)
{
if (txn->in_sub_stmt == 0)
return NULL;
- struct stailq_entry *stmt = txn->sub_stmt_begin[txn->in_sub_stmt - 1];
- stmt = stmt != NULL ? stailq_next(stmt) : stailq_first(&txn->stmts);
+ struct txn_savepoint *svp = &txn->sub_stmt_begin[txn->in_sub_stmt - 1];
+ struct stailq_entry *stmt = svp->stmt != NULL ?
+ stailq_next(svp->stmt) : stailq_first(&txn->stmts);
return stailq_entry(stmt, struct txn_stmt, next);
}
--
2.11.0
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