fixes #5961 pass a callback to the ydb layer when escalation occurs for a...

fixes #5961 pass a callback to the ydb layer when escalation occurs for a txnid, providing the locktree and range_buffer describing how to update the txn's internal data structures so they don't grow out of control for very long lived write transactions


git-svn-id: file:///svn/toku/tokudb@52941 c7de825b-a66e-492c-adef-691d508d4ae1

locktree/locktree.cc

@@ -507,6 +507,25 @@ static int extract_first_n_row_locks(concurrent_tree::locked_keyrange *lkr,
     return num_extracted;
 }
 
+// Store each newly escalated lock in a range buffer for appropriate txnid.
+// We'll rebuild the locktree by iterating over these ranges, and then we
+// can pass back each txnid/buffer pair individually through a callback
+// to notify higher layers that locks have changed.
+struct txnid_range_buffer {
+    TXNID txnid;
+    range_buffer buffer;
+
+    static int find_by_txnid(const struct txnid_range_buffer &other_buffer, const TXNID &txnid) {
+        if (txnid < other_buffer.txnid) {
+            return -1;
+        } else if (other_buffer.txnid == txnid) {
+            return 0;
+        } else {
+            return 1;
+        }
+    }
+};
+
 // escalate the locks in the locktree by merging adjacent
 // locks that have the same txnid into one larger lock.
 //
@@ -514,9 +533,9 @@ static int extract_first_n_row_locks(concurrent_tree::locked_keyrange *lkr,
 // approach works well. if there are many txnids and each
 // has locks in a random/alternating order, then this does
 // not work so well.
-void locktree::escalate(void) {
-    GrowableArray<row_lock> escalated_locks;
-    escalated_locks.init();
+void locktree::escalate(manager::lt_escalate_cb after_escalate_callback, void *after_escalate_callback_extra) {
+    omt<struct txnid_range_buffer, struct txnid_range_buffer *> range_buffers;
+    range_buffers.create();
 
     // prepare and acquire a locked keyrange on the entire locktree
     concurrent_tree::locked_keyrange lkr;
@@ -533,7 +552,7 @@ void locktree::escalate(void) {
 
     // extract and remove batches of row locks from the locktree
     int num_extracted;
-    static const int num_row_locks_per_batch = 128;
+    const int num_row_locks_per_batch = 128;
     row_lock *XCALLOC_N(num_row_locks_per_batch, extracted_buf);
 
     // we always remove the "first" n because we are removing n
@@ -553,18 +572,33 @@ void locktree::escalate(void) {
                 next_txnid_index++;
             }
 
-            // create a range which dominates the ranges between 
-            // the current index and the next txnid's index (excle).
-            keyrange merged_range;
-            merged_range.create(
-                    extracted_buf[current_index].range.get_left_key(), 
-                    extracted_buf[next_txnid_index - 1].range.get_right_key());
-
-            // save the new lock, continue from the next txnid's index
-            row_lock merged_row_lock;
-            merged_row_lock.range.create_copy(merged_range);
-            merged_row_lock.txnid = extracted_buf[current_index].txnid;
-            escalated_locks.push(merged_row_lock);
+            // Create an escalated range for the current txnid that dominates
+            // each range between the current indext and the next txnid's index.
+            const TXNID current_txnid = extracted_buf[current_index].txnid;
+            const DBT *escalated_left_key = extracted_buf[current_index].range.get_left_key(); 
+            const DBT *escalated_right_key = extracted_buf[next_txnid_index - 1].range.get_right_key();
+
+            // Try to find a range buffer for the current txnid. Create one if it doesn't exist.
+            // Then, append the new escalated range to the buffer.
+            uint32_t idx;
+            struct txnid_range_buffer new_range_buffer;
+            struct txnid_range_buffer *existing_range_buffer;
+            int r = range_buffers.find_zero<TXNID, txnid_range_buffer::find_by_txnid>(
+                    current_txnid,
+                    &existing_range_buffer,
+                    &idx
+                    );
+            if (r == DB_NOTFOUND) {
+                new_range_buffer.txnid = current_txnid;
+                new_range_buffer.buffer.create();
+                new_range_buffer.buffer.append(escalated_left_key, escalated_right_key);
+                range_buffers.insert_at(new_range_buffer, idx);
+            } else {
+                invariant_zero(r);
+                invariant(existing_range_buffer->txnid == current_txnid);
+                existing_range_buffer->buffer.append(escalated_left_key, escalated_right_key);
+            }
+
             current_index = next_txnid_index;
         }
 
@@ -575,17 +609,35 @@ void locktree::escalate(void) {
     }
     toku_free(extracted_buf);
 
-    // we should have extracted every lock from the old rangetree.
-    // now it is time to repopulate it with the escalated locks.
+    // Rebuild the locktree from each range in each range buffer,
+    // then notify higher layers that the txnid's locks have changed.
     invariant(m_rangetree->is_empty());
-    size_t new_num_locks = escalated_locks.get_size();
-    for (size_t i = 0; i < new_num_locks; i++) {
-        row_lock lock = escalated_locks.fetch_unchecked(i);
-        insert_row_lock_into_tree(&lkr, lock, m_mem_tracker);
-        lock.range.destroy();
+    const size_t num_range_buffers = range_buffers.size();
+    for (size_t i = 0; i < num_range_buffers; i++) {
+        struct txnid_range_buffer *current_range_buffer;
+        int r = range_buffers.fetch(i, &current_range_buffer);
+        invariant_zero(r);
+
+        const TXNID current_txnid = current_range_buffer->txnid;
+        range_buffer::iterator iter;
+        range_buffer::iterator::record rec;
+        iter.create(&current_range_buffer->buffer);
+        while (iter.current(&rec)) {
+            keyrange range;
+            range.create(rec.get_left_key(), rec.get_right_key());
+            row_lock lock = { .range = range, .txnid = current_txnid };
+            insert_row_lock_into_tree(&lkr, lock, m_mem_tracker);
+            iter.next();
+        }
+
+        // Notify higher layers that locks have changed for the current txnid
+        if (after_escalate_callback) {
+            after_escalate_callback(current_txnid, this, current_range_buffer->buffer, after_escalate_callback_extra);
+        }
+        current_range_buffer->buffer.destroy();
     }
+    range_buffers.destroy();
 
-    escalated_locks.deinit();
     lkr.release();
 }
 
@@ -605,7 +657,7 @@ void locktree::set_descriptor(DESCRIPTOR desc) {
     m_cmp->set_descriptor(desc);
 }
 
-int locktree::compare(locktree *lt) {
+int locktree::compare(const locktree *lt) {
     if (m_dict_id.dictid < lt->m_dict_id.dictid) {
         return -1;
     } else if (m_dict_id.dictid == lt->m_dict_id.dictid) {

locktree/locktree.h

@@ -75,7 +75,7 @@ public:
 
     void set_descriptor(DESCRIPTOR desc);
 
-    int compare(locktree *lt);
+    int compare(const locktree *lt);
 
     // The locktree stores some data for lock requests. It doesn't have to know
     // how they work or even what a lock request object looks like.
@@ -101,10 +101,11 @@ public:
     public:
         typedef void (*lt_create_cb)(locktree *lt, void *extra);
         typedef void (*lt_destroy_cb)(locktree *lt);
+        typedef void (*lt_escalate_cb)(TXNID txnid, const locktree *lt, const range_buffer &buffer, void *extra);
 
         // note: create_cb is called just after a locktree is first created.
         //       destroy_cb is called just before a locktree is destroyed.
-        void create(lt_create_cb create_cb, lt_destroy_cb destroy_cb);
+        void create(lt_create_cb create_cb, lt_destroy_cb destroy_cb, lt_escalate_cb, void *extra);
 
         void destroy(void);
 
@@ -189,6 +190,8 @@ public:
         // the create and destroy callbacks for the locktrees
         lt_create_cb m_lt_create_callback;
         lt_destroy_cb m_lt_destroy_callback;
+        lt_escalate_cb m_lt_escalate_callback;
+        void *m_lt_escalate_callback_extra;
 
         omt<locktree *> m_locktree_map;
 
@@ -408,7 +411,7 @@ private:
     int try_acquire_lock(bool is_write_request, TXNID txnid,
             const DBT *left_key, const DBT *right_key, txnid_set *conflicts);
 
-    void escalate();
+    void escalate(manager::lt_escalate_cb after_escalate_callback, void *extra);
 
     friend class locktree_unit_test;
     friend class manager_unit_test;

locktree/manager.cc

@@ -12,7 +12,7 @@
 
 namespace toku {
 
-void locktree::manager::create(lt_create_cb create_cb, lt_destroy_cb destroy_cb) {
+void locktree::manager::create(lt_create_cb create_cb, lt_destroy_cb destroy_cb, lt_escalate_cb escalate_cb, void *escalate_extra) {
     m_max_lock_memory = DEFAULT_MAX_LOCK_MEMORY;
     m_current_lock_memory = 0;
     m_lock_wait_time_ms = DEFAULT_LOCK_WAIT_TIME;
@@ -21,6 +21,9 @@ void locktree::manager::create(lt_create_cb create_cb, lt_destroy_cb destroy_cb)
     m_locktree_map.create();
     m_lt_create_callback = create_cb;
     m_lt_destroy_callback = destroy_cb;
+    m_lt_escalate_callback = escalate_cb;
+    m_lt_escalate_callback_extra = escalate_extra;
+
     ZERO_STRUCT(m_mutex);
     toku_mutex_init(&m_mutex, nullptr);
 }
@@ -218,7 +221,7 @@ void locktree::manager::run_escalation(void) {
         locktree *lt;
         int r = m_locktree_map.fetch(i, &lt);
         invariant_zero(r);
-        lt->escalate();
+        lt->escalate(m_lt_escalate_callback, m_lt_escalate_callback_extra);
     }
 }
 

locktree/range_buffer.h

@@ -17,7 +17,10 @@ namespace toku {
 // be stored, iterated over, and then destroyed all at once.
 
 class range_buffer {
-private:
+// Private in spirit: We fail POD asserts when we try to store range_buffers in an omt.
+// So make it all public, but don't touch.
+public:
+//private:
 
     // the key range buffer is a bunch of records in a row.
     // each record has the following header, followed by the
@@ -109,7 +112,7 @@ public:
 
     void destroy(void);
 
-private:
+//private:
     char *m_buf;
     size_t m_buf_size;
     size_t m_buf_current;

locktree/tests/lock_request_start_deadlock.cc

@@ -16,7 +16,7 @@ void lock_request_unit_test::test_start_deadlock(void) {
     // something short
     const uint64_t lock_wait_time = 10;
 
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DICTIONARY_ID dict_id = { 1 };
     lt = mgr.get_lt(dict_id, nullptr, compare_dbts, nullptr);
 

locktree/tests/lock_request_start_pending.cc

@@ -18,7 +18,7 @@ void lock_request_unit_test::test_start_pending(void) {
     // bogus, just has to be something.
     const uint64_t lock_wait_time = 0;
 
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DICTIONARY_ID dict_id = { 1 };
     lt = mgr.get_lt(dict_id, nullptr, compare_dbts, nullptr);
 

locktree/tests/locktree_conflicts.cc

@@ -21,7 +21,7 @@ namespace toku {
 // test read lock conflicts when write locks exist
 void locktree_unit_test::test_conflicts(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, compare_dbts, nullptr);

locktree/tests/locktree_create_destroy.cc

@@ -11,7 +11,7 @@ namespace toku {
 // test simple create and destroy of the locktree
 void locktree_unit_test::test_create_destroy(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, compare_dbts, nullptr);

locktree/tests/locktree_infinity.cc

@@ -11,7 +11,7 @@ namespace toku {
 // test that ranges with infinite endpoints work
 void locktree_unit_test::test_infinity(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, compare_dbts, nullptr);

locktree/tests/locktree_misc.cc

@@ -23,7 +23,7 @@ static int my_compare_dbts(DB *db, const DBT *a, const DBT *b) {
 // test that get/set userdata works, and that get_manager() works
 void locktree_unit_test::test_misc(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, my_compare_dbts, nullptr);

locktree/tests/locktree_overlapping_relock.cc

@@ -14,7 +14,7 @@ namespace toku {
 // or write locks are consolidated by overlapping relocks.
 void locktree_unit_test::test_overlapping_relock(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, compare_dbts, nullptr);

locktree/tests/locktree_simple_lock.cc

@@ -11,7 +11,7 @@ namespace toku {
 // test simple, non-overlapping read locks and then write locks
 void locktree_unit_test::test_simple_lock(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, compare_dbts, nullptr);

locktree/tests/locktree_single_txnid_optimization.cc

@@ -14,7 +14,7 @@ namespace toku {
 // or write locks are consolidated by overlapping relocks.
 void locktree_unit_test::test_single_txnid_optimization(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
     DESCRIPTOR desc = nullptr;
     DICTIONARY_ID dict_id = { 1 };
     locktree *lt = mgr.get_lt(dict_id, desc, compare_dbts, nullptr);

locktree/tests/manager_create_destroy.cc

@@ -14,7 +14,10 @@ void manager_unit_test::test_create_destroy(void) {
         (locktree::manager::lt_create_cb) (long) 1;
     locktree::manager::lt_destroy_cb destroy_callback =
         (locktree::manager::lt_destroy_cb) (long) 2;
-    mgr.create(create_callback, destroy_callback);
+    locktree::manager::lt_escalate_cb escalate_callback =
+        (locktree::manager::lt_escalate_cb) (long) 3;
+    void *extra = (void *) (long) 4;
+    mgr.create(create_callback, destroy_callback, escalate_callback, extra);
 
     invariant(mgr.m_max_lock_memory == locktree::manager::DEFAULT_MAX_LOCK_MEMORY);
     invariant(mgr.m_current_lock_memory == 0);
@@ -23,6 +26,8 @@ void manager_unit_test::test_create_destroy(void) {
     invariant(mgr.m_locktree_map.size() == 0);
     invariant(mgr.m_lt_create_callback == create_callback);
     invariant(mgr.m_lt_destroy_callback == destroy_callback);
+    invariant(mgr.m_lt_escalate_callback == escalate_callback);
+    invariant(mgr.m_lt_escalate_callback_extra == extra);
 
     mgr.mutex_lock();
     mgr.mutex_unlock();

locktree/tests/manager_locktree_map.cc

@@ -10,7 +10,7 @@ namespace toku {
 
 void manager_unit_test::test_lt_map(void) {
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
 
     locktree aa;
     locktree bb;

locktree/tests/manager_params.cc

@@ -11,7 +11,7 @@ namespace toku {
 void manager_unit_test::test_params(void) {
     int r;
     locktree::manager mgr;
-    mgr.create(nullptr, nullptr);
+    mgr.create(nullptr, nullptr, nullptr, nullptr);
 
     uint64_t new_max_lock_memory = 15307752356;
     r = mgr.set_max_lock_memory(new_max_lock_memory);

locktree/tests/manager_reference_release_lt.cc

@@ -23,7 +23,7 @@ static void destroy_cb(locktree *lt) {
 
 void manager_unit_test::test_reference_release_lt(void) {
     locktree::manager mgr;
-    mgr.create(create_cb, destroy_cb);
+    mgr.create(create_cb, destroy_cb, nullptr, nullptr);
 
     DICTIONARY_ID a = { 0 };
     DICTIONARY_ID b = { 1 };

src/ydb.cc

@@ -2199,7 +2199,10 @@ toku_env_create(DB_ENV ** envp, uint32_t flags) {
     assert_zero(r);
     assert(result->i->logger);
 
-    result->i->ltm.create(toku_db_lt_on_create_callback, toku_db_lt_on_destroy_callback);
+    // Create the locktree manager, passing in the create/destroy/escalate callbacks.
+    // The extra parameter for escalation is simply a pointer to this environment.
+    // The escalate callback will need it to translate txnids to DB_TXNs
+    result->i->ltm.create(toku_db_lt_on_create_callback, toku_db_lt_on_destroy_callback, toku_db_txn_escalate_callback, result);
 
     r = toku_omt_create(&result->i->open_dbs);
     toku_mutex_init(&result->i->open_dbs_lock, NULL);

src/ydb_row_lock.cc

@@ -27,14 +27,14 @@ static DB_TXN *txn_oldest_ancester(DB_TXN* txn) {
 }
 
 int find_key_ranges_by_lt(const txn_lt_key_ranges &ranges,
-        toku::locktree *const &find_lt);
+        const toku::locktree *const &find_lt);
 int find_key_ranges_by_lt(const txn_lt_key_ranges &ranges,
-        toku::locktree *const &find_lt) {
+        const toku::locktree *const &find_lt) {
     return ranges.lt->compare(find_lt);
 }
 
 static void db_txn_note_row_lock(DB *db, DB_TXN *txn, const DBT *left_key, const DBT *right_key) {
-    toku::locktree *lt = db->i->lt;
+    const toku::locktree *lt = db->i->lt;
 
     toku_mutex_lock(&db_txn_struct_i(txn)->txn_mutex);
 
@@ -44,16 +44,16 @@ static void db_txn_note_row_lock(DB *db, DB_TXN *txn, const DBT *left_key, const
 
     // if this txn has not yet already referenced this
     // locktree, then add it to this txn's locktree map
-    int r = map->find_zero<toku::locktree *, find_key_ranges_by_lt>(lt, &ranges, &idx);
+    int r = map->find_zero<const toku::locktree *, find_key_ranges_by_lt>(lt, &ranges, &idx);
     if (r == DB_NOTFOUND) {
-        ranges.lt = lt;
+        ranges.lt = db->i->lt;
         XMALLOC(ranges.buffer);
         ranges.buffer->create();
         map->insert_at(ranges, idx);
 
         // let the manager know we're referencing this lt
         toku::locktree::manager *ltm = &txn->mgrp->i->ltm;
-        ltm->reference_lt(lt);
+        ltm->reference_lt(ranges.lt);
     } else {
         invariant_zero(r);
     }
@@ -64,6 +64,71 @@ static void db_txn_note_row_lock(DB *db, DB_TXN *txn, const DBT *left_key, const
     toku_mutex_unlock(&db_txn_struct_i(txn)->txn_mutex);
 }
 
+void toku_db_txn_escalate_callback(TXNID txnid, const toku::locktree *lt, const toku::range_buffer &buffer, void *extra) {
+    DB_ENV *CAST_FROM_VOIDP(env, extra);
+
+    // Get the TOKUTXN and DB_TXN for this txnid from the environment's txn manager.
+    // Only the parent id is used in the search.
+    TOKUTXN ttxn;
+    TXNID_PAIR txnid_pair = { .parent_id64 = txnid, .child_id64 = 0 };
+    TXN_MANAGER txn_manager = toku_logger_get_txn_manager(env->i->logger);
+
+    toku_txn_manager_suspend(txn_manager);
+    toku_txn_manager_id2txn_unlocked(txn_manager, txnid_pair, &ttxn);
+
+    // We are still holding the txn manager lock. If we couldn't find the txn,
+    // then we lost a race with a committing transaction that got removed
+    // from the txn manager before it released its locktree locks. In this
+    // case we do nothing - that transaction has or is just about to release
+    // its locks and be gone, so there's not point in updating its lt_map
+    // with the new escalated ranges. It will go about releasing the old
+    // locks it thinks it had, and will succeed as if nothing happened.
+    //
+    // If we did find the transaction, then it has not yet been removed
+    // from the manager and therefore has not yet released its locks.
+    // We must be able to find and replace the range buffer associated
+    // with this locktree. This is impotant, otherwise it can grow out of
+    // control (ticket 5961).
+
+    if (ttxn != nullptr) {
+        DB_TXN *txn = toku_txn_get_container_db_txn(ttxn);
+
+        // One subtle point is that if the transaction is still live, it is impossible
+        // to deadlock on the txn mutex, even though we are holding the locktree's root
+        // mutex and release locks takes them in the opposite order.
+        //
+        // Proof: releasing locks takes the txn mutex and then acquires the locktree's
+        // root mutex, escalation takes the root mutex and possibly takes the txn mutex.
+        // releasing locks implies the txn is not live, and a non-live txn implies we
+        // will not need to take the txn mutex, so the deadlock is avoided.
+        toku_mutex_lock(&db_txn_struct_i(txn)->txn_mutex);
+
+        // We should be able to find this locktree. It was just escalated, and we had locks.
+        uint32_t idx;
+        txn_lt_key_ranges ranges;
+        toku::omt<txn_lt_key_ranges> *map = &db_txn_struct_i(txn)->lt_map;
+        int r = map->find_zero<const toku::locktree *, find_key_ranges_by_lt>(lt, &ranges, &idx);
+        invariant_zero(r);
+
+        // Destroy the old range buffer, create a new one, and insert the new ranges.
+        //
+        // We could theoretically steal the memory from the caller instead of copying
+        // it, but it's simpler to have a callback API that doesn't transfer memory ownership.
+        ranges.buffer->destroy();
+        ranges.buffer->create();
+        toku::range_buffer::iterator iter;
+        toku::range_buffer::iterator::record rec;
+        iter.create(&buffer);
+        while (iter.current(&rec)) {
+            ranges.buffer->append(rec.get_left_key(), rec.get_right_key());
+            iter.next();
+        }
+
+        toku_mutex_unlock(&db_txn_struct_i(txn)->txn_mutex);
+    }
+
+    toku_txn_manager_resume(txn_manager);
+}
 
 // Get a range lock.
 // Return when the range lock is acquired or the default lock tree timeout has expired.  

src/ydb_row_lock.h

@@ -11,6 +11,10 @@
 
 #include <locktree/lock_request.h>
 
+// Expose the escalate callback to ydb.cc,
+// so it can pass the function pointer to the locktree
+void toku_db_txn_escalate_callback(TXNID txnid, const toku::locktree *lt, const toku::range_buffer &buffer, void *extra);
+
 int toku_db_get_range_lock(DB *db, DB_TXN *txn, const DBT *left_key, const DBT *right_key,
         toku::lock_request::type lock_type);
 

src/ydb_txn.cc

@@ -25,6 +25,11 @@ toku_txn_id64(DB_TXN * txn) {
 
 static void 
 toku_txn_release_locks(DB_TXN *txn) {
+    // Prevent access to the locktree map while releasing.
+    // It is possible for lock escalation to attempt to
+    // modify this data structure while the txn commits.
+    toku_mutex_lock(&db_txn_struct_i(txn)->txn_mutex);
+
     size_t num_ranges = db_txn_struct_i(txn)->lt_map.size();
     for (size_t i = 0; i < num_ranges; i++) {
         txn_lt_key_ranges ranges;
@@ -32,6 +37,8 @@ toku_txn_release_locks(DB_TXN *txn) {
         invariant_zero(r);
         toku_db_release_lt_key_ranges(txn, &ranges);
     }
+
+    toku_mutex_unlock(&db_txn_struct_i(txn)->txn_mutex);
 }
 
 static void