aboutsummaryrefslogtreecommitdiff
path: root/src/leveldb/db/log_writer.cc
diff options
context:
space:
mode:
Diffstat (limited to 'src/leveldb/db/log_writer.cc')
-rw-r--r--src/leveldb/db/log_writer.cc103
1 files changed, 103 insertions, 0 deletions
diff --git a/src/leveldb/db/log_writer.cc b/src/leveldb/db/log_writer.cc
new file mode 100644
index 0000000000..2da99ac088
--- /dev/null
+++ b/src/leveldb/db/log_writer.cc
@@ -0,0 +1,103 @@
+// 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.
+
+#include "db/log_writer.h"
+
+#include <stdint.h>
+#include "leveldb/env.h"
+#include "util/coding.h"
+#include "util/crc32c.h"
+
+namespace leveldb {
+namespace log {
+
+Writer::Writer(WritableFile* dest)
+ : dest_(dest),
+ block_offset_(0) {
+ for (int i = 0; i <= kMaxRecordType; i++) {
+ char t = static_cast<char>(i);
+ type_crc_[i] = crc32c::Value(&t, 1);
+ }
+}
+
+Writer::~Writer() {
+}
+
+Status Writer::AddRecord(const Slice& slice) {
+ const char* ptr = slice.data();
+ size_t left = slice.size();
+
+ // Fragment the record if necessary and emit it. Note that if slice
+ // is empty, we still want to iterate once to emit a single
+ // zero-length record
+ Status s;
+ bool begin = true;
+ do {
+ const int leftover = kBlockSize - block_offset_;
+ assert(leftover >= 0);
+ if (leftover < kHeaderSize) {
+ // Switch to a new block
+ if (leftover > 0) {
+ // Fill the trailer (literal below relies on kHeaderSize being 7)
+ assert(kHeaderSize == 7);
+ dest_->Append(Slice("\x00\x00\x00\x00\x00\x00", leftover));
+ }
+ block_offset_ = 0;
+ }
+
+ // Invariant: we never leave < kHeaderSize bytes in a block.
+ assert(kBlockSize - block_offset_ - kHeaderSize >= 0);
+
+ const size_t avail = kBlockSize - block_offset_ - kHeaderSize;
+ const size_t fragment_length = (left < avail) ? left : avail;
+
+ RecordType type;
+ const bool end = (left == fragment_length);
+ if (begin && end) {
+ type = kFullType;
+ } else if (begin) {
+ type = kFirstType;
+ } else if (end) {
+ type = kLastType;
+ } else {
+ type = kMiddleType;
+ }
+
+ s = EmitPhysicalRecord(type, ptr, fragment_length);
+ ptr += fragment_length;
+ left -= fragment_length;
+ begin = false;
+ } while (s.ok() && left > 0);
+ return s;
+}
+
+Status Writer::EmitPhysicalRecord(RecordType t, const char* ptr, size_t n) {
+ assert(n <= 0xffff); // Must fit in two bytes
+ assert(block_offset_ + kHeaderSize + n <= kBlockSize);
+
+ // Format the header
+ char buf[kHeaderSize];
+ buf[4] = static_cast<char>(n & 0xff);
+ buf[5] = static_cast<char>(n >> 8);
+ buf[6] = static_cast<char>(t);
+
+ // Compute the crc of the record type and the payload.
+ uint32_t crc = crc32c::Extend(type_crc_[t], ptr, n);
+ crc = crc32c::Mask(crc); // Adjust for storage
+ EncodeFixed32(buf, crc);
+
+ // Write the header and the payload
+ Status s = dest_->Append(Slice(buf, kHeaderSize));
+ if (s.ok()) {
+ s = dest_->Append(Slice(ptr, n));
+ if (s.ok()) {
+ s = dest_->Flush();
+ }
+ }
+ block_offset_ += kHeaderSize + n;
+ return s;
+}
+
+} // namespace log
+} // namespace leveldb