1 files changed, 128 insertions, 0 deletions
diff --git a/src/rocksdb/db/log_writer.h b/src/rocksdb/db/log_writer.h
new file mode 100644
index 000000000..5d266e434
--- /dev/null
+++ b/src/rocksdb/db/log_writer.h
@@ -0,0 +1,128 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+#pragma once
+
+#include <cstdint>
+#include <memory>
+
+#include "db/log_format.h"
+#include "rocksdb/compression_type.h"
+#include "rocksdb/env.h"
+#include "rocksdb/io_status.h"
+#include "rocksdb/slice.h"
+#include "rocksdb/status.h"
+#include "util/compression.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class WritableFileWriter;
+
+namespace log {
+
+/**
+ * Writer is a general purpose log stream writer. It provides an append-only
+ * abstraction for writing data. The details of the how the data is written is
+ * handled by the WritableFile sub-class implementation.
+ *
+ * File format:
+ *
+ * File is broken down into variable sized records. The format of each record
+ * is described below.
+ *       +-----+-------------+--+----+----------+------+-- ... ----+
+ * File  | r0  |        r1   |P | r2 |    r3    |  r4  |           |
+ *       +-----+-------------+--+----+----------+------+-- ... ----+
+ *       <--- kBlockSize ------>|<-- kBlockSize ------>|
+ *  rn = variable size records
+ *  P = Padding
+ *
+ * Data is written out in kBlockSize chunks. If next record does not fit
+ * into the space left, the leftover space will be padded with \0.
+ *
+ * Legacy record format:
+ *
+ * +---------+-----------+-----------+--- ... ---+
+ * |CRC (4B) | Size (2B) | Type (1B) | Payload   |
+ * +---------+-----------+-----------+--- ... ---+
+ *
+ * CRC = 32bit hash computed over the record type and payload using CRC
+ * Size = Length of the payload data
+ * Type = Type of record
+ *        (kZeroType, kFullType, kFirstType, kLastType, kMiddleType )
+ *        The type is used to group a bunch of records together to represent
+ *        blocks that are larger than kBlockSize
+ * Payload = Byte stream as long as specified by the payload size
+ *
+ * Recyclable record format:
+ *
+ * +---------+-----------+-----------+----------------+--- ... ---+
+ * |CRC (4B) | Size (2B) | Type (1B) | Log number (4B)| Payload   |
+ * +---------+-----------+-----------+----------------+--- ... ---+
+ *
+ * Same as above, with the addition of
+ * Log number = 32bit log file number, so that we can distinguish between
+ * records written by the most recent log writer vs a previous one.
+ */
+class Writer {
+ public:
+  // Create a writer that will append data to "*dest".
+  // "*dest" must be initially empty.
+  // "*dest" must remain live while this Writer is in use.
+  explicit Writer(std::unique_ptr<WritableFileWriter>&& dest,
+                  uint64_t log_number, bool recycle_log_files,
+                  bool manual_flush = false,
+                  CompressionType compressionType = kNoCompression);
+  // No copying allowed
+  Writer(const Writer&) = delete;
+  void operator=(const Writer&) = delete;
+
+  ~Writer();
+
+  IOStatus AddRecord(const Slice& slice,
+                     Env::IOPriority rate_limiter_priority = Env::IO_TOTAL);
+  IOStatus AddCompressionTypeRecord();
+
+  WritableFileWriter* file() { return dest_.get(); }
+  const WritableFileWriter* file() const { return dest_.get(); }
+
+  uint64_t get_log_number() const { return log_number_; }
+
+  IOStatus WriteBuffer();
+
+  IOStatus Close();
+
+  bool BufferIsEmpty();
+
+ private:
+  std::unique_ptr<WritableFileWriter> dest_;
+  size_t block_offset_;  // Current offset in block
+  uint64_t log_number_;
+  bool recycle_log_files_;
+
+  // crc32c values for all supported record types.  These are
+  // pre-computed to reduce the overhead of computing the crc of the
+  // record type stored in the header.
+  uint32_t type_crc_[kMaxRecordType + 1];
+
+  IOStatus EmitPhysicalRecord(
+      RecordType type, const char* ptr, size_t length,
+      Env::IOPriority rate_limiter_priority = Env::IO_TOTAL);
+
+  // If true, it does not flush after each write. Instead it relies on the upper
+  // layer to manually does the flush by calling ::WriteBuffer()
+  bool manual_flush_;
+
+  // Compression Type
+  CompressionType compression_type_;
+  StreamingCompress* compress_;
+  // Reusable compressed output buffer
+  std::unique_ptr<char[]> compressed_buffer_;
+};
+
+}  // namespace log
+}  // namespace ROCKSDB_NAMESPACE