Transactions: Release Locks when rolling back to a savepoint

Summary: Transaction::RollbackToSavePoint() will now release any locks that were taken since the previous SavePoint.  To do this cleanly, I moved tracked_keys_ management into TransactionBase.

Test Plan: New Transaction test.

Reviewers: igor, rven, sdong

Reviewed By: sdong

Subscribers: dhruba, spetrunia, leveldb

Differential Revision: https://reviews.facebook.net/D46761

utilities/transactions/optimistic_transaction_impl.cc

@@ -38,7 +38,6 @@ OptimisticTransactionImpl::~OptimisticTransactionImpl() {
 
 void OptimisticTransactionImpl::Clear() {
   TransactionBaseImpl::Clear();
-  tracked_keys_.clear();
 }
 
 Status OptimisticTransactionImpl::Commit() {
@@ -83,18 +82,7 @@ Status OptimisticTransactionImpl::TryLock(ColumnFamilyHandle* column_family,
 
   std::string key_str = key.ToString();
 
-  auto iter = tracked_keys_[cfh_id].find(key_str);
-  if (iter == tracked_keys_[cfh_id].end()) {
-    // key not yet seen, store it.
-    tracked_keys_[cfh_id].insert({std::move(key_str), seq});
-  } else {
-    SequenceNumber old_seq = iter->second;
-    if (seq < old_seq) {
-      // Snapshot has changed since we last saw this key, need to
-      // store the earliest seen sequence number.
-      tracked_keys_[cfh_id][key_str] = seq;
-    }
-  }
+  TrackKey(cfh_id, key_str, seq);
 
   // Always return OK. Confilct checking will happen at commit time.
   return Status::OK();
@@ -113,19 +101,7 @@ Status OptimisticTransactionImpl::CheckTransactionForConflicts(DB* db) {
   assert(dynamic_cast<DBImpl*>(db) != nullptr);
   auto db_impl = reinterpret_cast<DBImpl*>(db);
 
-  return TransactionUtil::CheckKeysForConflicts(db_impl, &tracked_keys_);
-}
-
-uint64_t OptimisticTransactionImpl::GetNumKeys() const {
-  uint64_t count = 0;
-
-  // sum up locked keys in all column families
-  for (const auto& key_map_iter : tracked_keys_) {
-    const auto& keys = key_map_iter.second;
-    count += keys.size();
-  }
-
-  return count;
+  return TransactionUtil::CheckKeysForConflicts(db_impl, GetTrackedKeys());
 }
 
 }  // namespace rocksdb

utilities/transactions/optimistic_transaction_impl.h

@@ -38,23 +38,13 @@ class OptimisticTransactionImpl : public TransactionBaseImpl {
 
   void Rollback() override;
 
-  uint64_t GetNumKeys() const override;
-
-  const TransactionKeyMap* GetTrackedKeys() const { return &tracked_keys_; }
-
  protected:
   Status TryLock(ColumnFamilyHandle* column_family, const Slice& key,
                  bool untracked = false) override;
 
  private:
   OptimisticTransactionDB* const txn_db_;
 
-  // Map of Column Family IDs to keys and corresponding sequence numbers.
-  // The sequence number stored for a key will be used during commit to make
-  // sure this key has
-  // not changed since this sequence number.
-  TransactionKeyMap tracked_keys_;
-
   friend class OptimisticTransactionCallback;
 
   // Returns OK if it is safe to commit this transaction.  Returns Status::Busy

utilities/transactions/transaction_base.cc

@@ -28,6 +28,7 @@ TransactionBaseImpl::~TransactionBaseImpl() {}
 void TransactionBaseImpl::Clear() {
   save_points_.reset(nullptr);
   write_batch_->Clear();
+  tracked_keys_.clear();
   num_puts_ = 0;
   num_deletes_ = 0;
   num_merges_ = 0;
@@ -71,12 +72,25 @@ Status TransactionBaseImpl::RollbackToSavePoint() {
     num_deletes_ = save_point.num_deletes_;
     num_merges_ = save_point.num_merges_;
 
-    save_points_->pop();
-
     // Rollback batch
     Status s = write_batch_->RollbackToSavePoint();
     assert(s.ok());
 
+    // Rollback any keys that were tracked since the last savepoint
+    auto key_map = GetTrackedKeysSinceSavePoint();
+    assert(key_map);
+    for (auto& key_map_iter : *key_map) {
+      uint32_t column_family_id = key_map_iter.first;
+      auto& keys = key_map_iter.second;
+
+      for (auto& key_iter : keys) {
+        const std::string& key = key_iter.first;
+        tracked_keys_[column_family_id].erase(key);
+      }
+    }
+
+    save_points_->pop();
+
     return s;
   } else {
     assert(write_batch_->RollbackToSavePoint().IsNotFound());
@@ -306,6 +320,42 @@ uint64_t TransactionBaseImpl::GetNumDeletes() const { return num_deletes_; }
 
 uint64_t TransactionBaseImpl::GetNumMerges() const { return num_merges_; }
 
+uint64_t TransactionBaseImpl::GetNumKeys() const {
+  uint64_t count = 0;
+
+  // sum up locked keys in all column families
+  for (const auto& key_map_iter : tracked_keys_) {
+    const auto& keys = key_map_iter.second;
+    count += keys.size();
+  }
+
+  return count;
+}
+
+void TransactionBaseImpl::TrackKey(uint32_t cfh_id, const std::string& key,
+                                   SequenceNumber seq) {
+  auto iter = tracked_keys_[cfh_id].find(key);
+  if (iter == tracked_keys_[cfh_id].end()) {
+    tracked_keys_[cfh_id].insert({key, seq});
+
+    if (save_points_ != nullptr && !save_points_->empty()) {
+      // Aren't tracking this key, add it.
+      save_points_->top().new_keys_[cfh_id][key] = seq;
+    }
+  } else if (seq < iter->second) {
+    // Now tracking this key with an earlier sequence number
+    iter->second = seq;
+  }
+}
+
+const TransactionKeyMap* TransactionBaseImpl::GetTrackedKeysSinceSavePoint() {
+  if (save_points_ != nullptr && !save_points_->empty()) {
+    return &save_points_->top().new_keys_;
+  }
+
+  return nullptr;
+}
+
 }  // namespace rocksdb
 
 #endif  // ROCKSDB_LITE

utilities/transactions/transaction_base.h

@@ -19,6 +19,7 @@
 #include "rocksdb/utilities/transaction.h"
 #include "rocksdb/utilities/transaction_db.h"
 #include "rocksdb/utilities/write_batch_with_index.h"
+#include "utilities/transactions/transaction_util.h"
 
 namespace rocksdb {
 
@@ -166,7 +167,19 @@ class TransactionBaseImpl : public Transaction {
 
   uint64_t GetNumMerges() const override;
 
+  uint64_t GetNumKeys() const override;
+
+  // Get list of keys in this transaction that must not have any conflicts
+  // with writes in other transactions.
+  const TransactionKeyMap& GetTrackedKeys() const { return tracked_keys_; }
+
  protected:
+  // Add a key to the list of tracked keys.
+  // seqno is the earliest seqno this key was involved with this transaction.
+  void TrackKey(uint32_t cfh_id, const std::string& key, SequenceNumber seqno);
+
+  const TransactionKeyMap* GetTrackedKeysSinceSavePoint();
+
   DB* const db_;
 
   const WriteOptions write_options_;
@@ -194,6 +207,9 @@ class TransactionBaseImpl : public Transaction {
     uint64_t num_deletes_;
     uint64_t num_merges_;
 
+    // Record all keys tracked since the last savepoint
+    TransactionKeyMap new_keys_;
+
     SavePoint(std::shared_ptr<ManagedSnapshot> snapshot, uint64_t num_puts,
               uint64_t num_deletes, uint64_t num_merges)
         : snapshot_(snapshot),
@@ -202,11 +218,18 @@ class TransactionBaseImpl : public Transaction {
           num_merges_(num_merges) {}
   };
 
+ private:
   // Stack of the Snapshot saved at each save point.  Saved snapshots may be
   // nullptr if there was no snapshot at the time SetSavePoint() was called.
   std::unique_ptr<std::stack<TransactionBaseImpl::SavePoint>> save_points_;
 
- private:
+  // Map from column_family_id to map of keys that are involved in this
+  // transaction.
+  // Pessimistic Transactions will do conflict checking before adding a key
+  // by calling TrackKey().
+  // Optimistic Transactions will wait till commit time to do conflict checking.
+  TransactionKeyMap tracked_keys_;
+
   Status TryLock(ColumnFamilyHandle* column_family, const SliceParts& key,
                  bool untracked = false);
 };

utilities/transactions/transaction_db_impl.cc

@@ -141,7 +141,8 @@ Status TransactionDBImpl::TryLock(TransactionImpl* txn, uint32_t cfh_id,
   return lock_mgr_.TryLock(txn, cfh_id, key, GetEnv());
 }
 
-void TransactionDBImpl::UnLock(TransactionImpl* txn, TransactionKeyMap* keys) {
+void TransactionDBImpl::UnLock(TransactionImpl* txn,
+                               const TransactionKeyMap* keys) {
   lock_mgr_.UnLock(txn, keys, GetEnv());
 }
 

utilities/transactions/transaction_db_impl.h

@@ -54,7 +54,7 @@ class TransactionDBImpl : public TransactionDB {
 
   Status TryLock(TransactionImpl* txn, uint32_t cfh_id, const std::string& key);
 
-  void UnLock(TransactionImpl* txn, TransactionKeyMap* keys);
+  void UnLock(TransactionImpl* txn, const TransactionKeyMap* keys);
   void UnLock(TransactionImpl* txn, uint32_t cfh_id, const std::string& key);
 
   void AddColumnFamily(const ColumnFamilyHandle* handle);

utilities/transactions/transaction_impl.cc

@@ -58,14 +58,12 @@ TransactionImpl::TransactionImpl(TransactionDB* txn_db,
 }
 
 TransactionImpl::~TransactionImpl() {
-  txn_db_impl_->UnLock(this, &tracked_keys_);
+  txn_db_impl_->UnLock(this, &GetTrackedKeys());
 }
 
 void TransactionImpl::Clear() {
+  txn_db_impl_->UnLock(this, &GetTrackedKeys());
   TransactionBaseImpl::Clear();
-
-  txn_db_impl_->UnLock(this, &tracked_keys_);
-  tracked_keys_.clear();
 }
 
 bool TransactionImpl::IsExpired() const {
@@ -126,6 +124,16 @@ Status TransactionImpl::DoCommit(WriteBatch* batch) {
 
 void TransactionImpl::Rollback() { Clear(); }
 
+Status TransactionImpl::RollbackToSavePoint() {
+  // Unlock any keys locked since last transaction
+  auto keys = GetTrackedKeysSinceSavePoint();
+  if (keys) {
+    txn_db_impl_->UnLock(this, keys);
+  }
+
+  return TransactionBaseImpl::RollbackToSavePoint();
+}
+
 // Lock all keys in this batch.
 // On success, caller should unlock keys_to_unlock
 Status TransactionImpl::LockBatch(WriteBatch* batch,
@@ -221,19 +229,16 @@ Status TransactionImpl::TryLock(ColumnFamilyHandle* column_family,
   bool check_snapshot = !untracked;
 
   // lock this key if this transactions hasn't already locked it
-  auto iter = tracked_keys_[cfh_id].find(key_str);
-  if (iter == tracked_keys_[cfh_id].end()) {
+  SequenceNumber tracked_seqno = kMaxSequenceNumber;
+  auto tracked_keys = GetTrackedKeys();
+  auto iter = tracked_keys[cfh_id].find(key_str);
+  if (iter == tracked_keys[cfh_id].end()) {
     previously_locked = false;
 
     s = txn_db_impl_->TryLock(this, cfh_id, key_str);
-
-    if (s.ok()) {
-      // Record that we've locked this key
-      auto result = tracked_keys_[cfh_id].insert({key_str, kMaxSequenceNumber});
-      iter = result.first;
-    }
   } else {
     previously_locked = true;
+    tracked_seqno = iter->second;
   }
 
   if (s.ok()) {
@@ -244,37 +249,41 @@ Status TransactionImpl::TryLock(ColumnFamilyHandle* column_family,
       // key has not been modified after.  This is useful if this same
       // transaction
       // later tries to lock this key again.
-      if (iter->second == kMaxSequenceNumber) {
+      if (tracked_seqno == kMaxSequenceNumber) {
         // Since we haven't checked a snapshot, we only know this key has not
         // been modified since after we locked it.
-        iter->second = db_->GetLatestSequenceNumber();
+        tracked_seqno = db_->GetLatestSequenceNumber();
       }
     } else {
       // If the key has been previous validated at a sequence number earlier
       // than the curent snapshot's sequence number, we already know it has not
       // been modified.
       SequenceNumber seq = snapshot_->snapshot()->GetSequenceNumber();
-      bool already_validated = iter->second <= seq;
+      bool already_validated = tracked_seqno <= seq;
 
       if (!already_validated) {
         s = CheckKeySequence(column_family, key);
 
         if (s.ok()) {
           // Record that there have been no writes to this key after this
           // sequence.
-          iter->second = seq;
+          tracked_seqno = seq;
         } else {
           // Failed to validate key
           if (!previously_locked) {
             // Unlock key we just locked
             txn_db_impl_->UnLock(this, cfh_id, key.ToString());
-            tracked_keys_[cfh_id].erase(iter);
           }
         }
       }
     }
   }
 
+  if (s.ok()) {
+    // Let base class know we've conflict checked this key.
+    TrackKey(cfh_id, key_str, tracked_seqno);
+  }
+
   return s;
 }
 
@@ -298,18 +307,6 @@ Status TransactionImpl::CheckKeySequence(ColumnFamilyHandle* column_family,
   return result;
 }
 
-uint64_t TransactionImpl::GetNumKeys() const {
-  uint64_t count = 0;
-
-  // sum up locked keys in all column families
-  for (const auto& key_map_iter : tracked_keys_) {
-    const auto& keys = key_map_iter.second;
-    count += keys.size();
-  }
-
-  return count;
-}
-
 }  // namespace rocksdb
 
 #endif  // ROCKSDB_LITE

utilities/transactions/transaction_impl.h

@@ -44,7 +44,7 @@ class TransactionImpl : public TransactionBaseImpl {
 
   void Rollback() override;
 
-  uint64_t GetNumKeys() const override;
+  Status RollbackToSavePoint() override;
 
   // Generate a new unique transaction identifier
   static TransactionID GenTxnID();
@@ -86,12 +86,6 @@ class TransactionImpl : public TransactionBaseImpl {
   // Timeout in microseconds when locking a key or -1 if there is no timeout.
   int64_t lock_timeout_;
 
-  // Map from column_family_id to map of keys to Sequence Numbers.  Stores keys
-  // that have been locked.
-  // The key is known to not have been modified after the Sequence Number
-  // stored.
-  TransactionKeyMap tracked_keys_;
-
   void Clear() override;
 
   Status CheckKeySequence(ColumnFamilyHandle* column_family, const Slice& key);