[RocksDB][Bug] Look at all the files, not just the first file in TransactionLogIter as BatchWrites can leave it in Limbo

Summary:
Transaction Log Iterator did not move to the next file in the series if there was a write batch at the end of the currentFile.
The solution is if the last seq no. of the current file is < RequestedSeqNo. Assume the first seqNo. of the next file has to satisfy the request.

Also major refactoring around the code. Moved opening the logreader to a seperate function, got rid of goto.

Test Plan: added a unit test for it.

Reviewers: dhruba, heyongqiang

Reviewed By: heyongqiang

CC: leveldb, emayanke

Differential Revision: https://reviews.facebook.net/D10029

db/db_impl.cc

@@ -907,7 +907,7 @@ Status DBImpl::GetUpdatesSince(SequenceNumber seq,
                                    probableWALFiles,
                                    &last_flushed_sequence_));
   iter->get()->Next();
-  return Status::OK();
+  return iter->get()->status();
 }
 
 Status DBImpl::FindProbableWALFiles(std::vector<LogFile>* const allLogs,

db/db_test.cc

@@ -2700,6 +2700,22 @@ TEST(DBTest, TransactionLogIteratorCheckAfterRestart) {
   ExpectRecords(2, iter);
 }
 
+TEST(DBTest, TransactionLogIteratorBatchOperations) {
+  Options options = OptionsForLogIterTest();
+  DestroyAndReopen(&options);
+  WriteBatch batch;
+  batch.Put("key1", DummyString(1024));
+  batch.Put("key2", DummyString(1024));
+  batch.Put("key3", DummyString(1024));
+  batch.Delete("key2");
+  dbfull()->Write(WriteOptions(), &batch);
+  dbfull()->Flush(FlushOptions());
+  Reopen(&options);
+  Put("key4", DummyString(1024));
+  auto iter = OpenTransactionLogIter(3);
+  ExpectRecords(1, iter);
+}
+
 TEST(DBTest, ReadCompaction) {
   std::string value(4096, '4'); // a string of size 4K
   {

db/transaction_log_iterator_impl.cc

@@ -14,10 +14,10 @@ TransactionLogIteratorImpl::TransactionLogIteratorImpl(
   dbname_(dbname),
   options_(options),
   soptions_(soptions),
-  sequenceNumber_(seq),
+  startingSequenceNumber_(seq),
   files_(files),
   started_(false),
-  isValid_(true),
+  isValid_(false),
   currentFileIndex_(0),
   lastFlushedSequence_(lastFlushedSequence) {
   assert(files_ != nullptr);
@@ -73,54 +73,49 @@ bool TransactionLogIteratorImpl::Valid() {
 }
 
 void TransactionLogIteratorImpl::Next() {
-//  First seek to the given seqNo. in the current file.
   LogFile currentLogFile = files_->at(currentFileIndex_);
   LogReporter reporter = NewLogReporter(currentLogFile.logNumber);
+
+//  First seek to the given seqNo. in the current file.
   std::string scratch;
   Slice record;
-
   if (!started_) {
+    started_ = true;  // this piece only runs onced.
     isValid_ = false;
-    if (sequenceNumber_ > *lastFlushedSequence_) {
+    if (startingSequenceNumber_ > *lastFlushedSequence_) {
       currentStatus_ = Status::IOError("Looking for a sequence, "
                                         "which is not flushed yet.");
       return;
     }
-    unique_ptr<SequentialFile> file;
+    Status s = OpenLogReader(currentLogFile);
-    Status status = OpenLogFile(currentLogFile, &file);
+    if (!s.ok()) {
-    if (!status.ok()) {
+      currentStatus_ = s;
-      currentStatus_ = status;
+      isValid_ = false;
       return;
     }
-    assert(file);
+    while (currentLogReader_->ReadRecord(&record, &scratch)) {
-    unique_ptr<log::Reader> reader(
-      new log::Reader(std::move(file), &reporter, true, 0));
-    assert(reader);
-    while (reader->ReadRecord(&record, &scratch)) {
       if (record.size() < 12) {
         reporter.Corruption(
           record.size(), Status::Corruption("log record too small"));
         continue;
       }
       UpdateCurrentWriteBatch(record);
-      if (currentSequence_ >= sequenceNumber_) {
+      if (currentSequence_ >= startingSequenceNumber_) {
         assert(currentSequence_ <= *lastFlushedSequence_);
         isValid_ = true;
-        currentLogReader_ = std::move(reader);
         break;
+      } else {
+        isValid_ = false;
       }
     }
-    if (!isValid_) {
+    if (isValid_) {
-      //  TODO read the entire first file. and did not find the seq number.
+      // Done for this iteration
-      //  Error out.
+      return;
-      currentStatus_ =
-        Status::NotFound("Did not find the Seq no. in first file");
     }
-    started_ = true;
+  }
-  } else {
+  bool openNextFile = true;
-LOOK_NEXT_FILE:
+  while(openNextFile) {
     assert(currentLogReader_);
-    bool openNextFile = true;
     if (currentSequence_ < *lastFlushedSequence_) {
       if (currentLogReader_->IsEOF()) {
         currentLogReader_->UnmarkEOF();
@@ -141,28 +136,22 @@ LOOK_NEXT_FILE:
     if (openNextFile) {
       if (currentFileIndex_ < files_->size() - 1) {
         ++currentFileIndex_;
-        currentLogReader_.reset();
+        Status status = OpenLogReader(files_->at(currentFileIndex_));
-        unique_ptr<SequentialFile> file;
-        Status status = OpenLogFile(files_->at(currentFileIndex_), &file);
         if (!status.ok()) {
           isValid_ = false;
           currentStatus_ = status;
           return;
         }
-        currentLogReader_.reset(
-          new log::Reader(std::move(file), &reporter, true, 0));
-        goto LOOK_NEXT_FILE;
-      } else if (currentSequence_ == *lastFlushedSequence_) {
-        // The last update has been read. and next is being called.
-        isValid_ = false;
-        currentStatus_ = Status::OK();
       } else {
-        //  LOOKED AT FILES. WE ARE DONE HERE.
         isValid_ = false;
-        currentStatus_ = Status::IOError(" NO MORE DATA LEFT");
+        openNextFile = false;
+        if (currentSequence_ == *lastFlushedSequence_) {
+          currentStatus_ = Status::OK();
+        } else {
+          currentStatus_ = Status::IOError(" NO MORE DATA LEFT");
+        }
       }
     }
-
   }
 }
 
@@ -175,4 +164,17 @@ void TransactionLogIteratorImpl::UpdateCurrentWriteBatch(const Slice& record) {
   currentStatus_ = Status::OK();
 }
 
+Status TransactionLogIteratorImpl::OpenLogReader(const LogFile& logFile) {
+  LogReporter reporter = NewLogReporter(logFile.logNumber);
+  unique_ptr<SequentialFile> file;
+  Status status = OpenLogFile(logFile, &file);
+  if (!status.ok()) {
+    return status;
+  }
+  assert(file);
+  currentLogReader_.reset(
+    new log::Reader(std::move(file), &reporter, true, 0)
+  );
+  return Status::OK();
+}
 }  //  namespace leveldb

db/transaction_log_iterator_impl.h

@@ -50,7 +50,7 @@ class TransactionLogIteratorImpl : public TransactionLogIterator {
   const std::string& dbname_;
   const Options* options_;
   const StorageOptions& soptions_;
-  const uint64_t sequenceNumber_;
+  const uint64_t startingSequenceNumber_;
   const std::vector<LogFile>* files_;
   bool started_;
   bool isValid_;  // not valid when it starts of.
@@ -65,6 +65,7 @@ class TransactionLogIteratorImpl : public TransactionLogIterator {
   SequenceNumber currentSequence_;
 
   void UpdateCurrentWriteBatch(const Slice& record);
+  Status OpenLogReader(const LogFile& file);
 };