WriteUnPrepared: use WriteUnpreparedTxnReadCallback for ValidateSnapshot (#5657)

Summary:
In DeferSnapshotSavePointTest, writes were failing with snapshot validation error because the key with the latest sequence number was an unprepared key from the current transaction.

Fix this by passing down the correct read callback.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5657

Differential Revision: D16582466

Pulled By: lth

fbshipit-source-id: 11645dac0e7c1374d917ef5fdf757d13c1d1108d

utilities/transactions/write_unprepared_txn.cc

@@ -574,6 +574,39 @@ Iterator* WriteUnpreparedTxn::GetIterator(const ReadOptions& options,
   return write_batch_.NewIteratorWithBase(column_family, db_iter);
 }
 
+Status WriteUnpreparedTxn::ValidateSnapshot(ColumnFamilyHandle* column_family,
+                                            const Slice& key,
+                                            SequenceNumber* tracked_at_seq) {
+  // TODO(lth): Reduce duplicate code with WritePrepared ValidateSnapshot logic.
+  assert(snapshot_);
+
+  SequenceNumber min_uncommitted =
+      static_cast_with_check<const SnapshotImpl, const Snapshot>(
+          snapshot_.get())
+          ->min_uncommitted_;
+  SequenceNumber snap_seq = snapshot_->GetSequenceNumber();
+  // tracked_at_seq is either max or the last snapshot with which this key was
+  // trackeed so there is no need to apply the IsInSnapshot to this comparison
+  // here as tracked_at_seq is not a prepare seq.
+  if (*tracked_at_seq <= snap_seq) {
+    // 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.
+    return Status::OK();
+  }
+
+  *tracked_at_seq = snap_seq;
+
+  ColumnFamilyHandle* cfh =
+      column_family ? column_family : db_impl_->DefaultColumnFamily();
+
+  WriteUnpreparedTxnReadCallback snap_checker(wupt_db_, snap_seq,
+                                              min_uncommitted, unprep_seqs_);
+  return TransactionUtil::CheckKeyForConflicts(db_impl_, cfh, key.ToString(),
+                                               snap_seq, false /* cache_only */,
+                                               &snap_checker, min_uncommitted);
+}
+
 const std::map<SequenceNumber, size_t>&
 WriteUnpreparedTxn::GetUnpreparedSequenceNumbers() {
   return unprep_seqs_;

utilities/transactions/write_unprepared_txn.h

@@ -158,6 +158,10 @@ class WriteUnpreparedTxn : public WritePreparedTxn {
   virtual Iterator* GetIterator(const ReadOptions& options,
                                 ColumnFamilyHandle* column_family) override;
 
+  virtual Status ValidateSnapshot(ColumnFamilyHandle* column_family,
+                                  const Slice& key,
+                                  SequenceNumber* tracked_at_seq) override;
+
  private:
   friend class WriteUnpreparedTransactionTest_ReadYourOwnWrite_Test;
   friend class WriteUnpreparedTransactionTest_RecoveryTest_Test;