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log_{reader,write}: recyclable record format

Browse Source 
Introduce new tags for records that have a log_number.  This changes the
header size from 7 to 11 for these records, making this a
backward-incompatible change.

If we read a record that belongs to a different log_number (i.e., a
previous instantiation of this log file, before it was most recently
recycled), we return kOldRecord from ReadPhysicalRecord.  ReadRecord
will translate this into a kEof or kBadRecord depending on what the
WAL recovery mode is.

We make several adjustments to the log_test.cc tests to compensate for the
fact that the header size varies between the two modes.

Signed-off-by: Sage Weil <sage@redhat.com>
main
Sage Weil 9 years ago
parent 4104e9bb67
commit a7b2bedfb0
6 changed files with 215 additions and 93 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 14
      db/log_format.h
  2. 73
      db/log_reader.cc
  3. 5
      db/log_reader.h
  4. 105
      db/log_test.cc
  5. 58
      db/log_writer.cc
  6. 11
      db/log_writer.h

14
db/log_format.h
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@ -22,14 +22,24 @@ enum RecordType {
// For fragments
kFirstType = 2,
kMiddleType = 3,
kLastType = 4
kLastType = 4,
// For recycled log files
kRecyclableFullType = 5,
kRecyclableFirstType = 6,
kRecyclableMiddleType = 7,
kRecyclableLastType = 8,
};
static const int kMaxRecordType = kLastType;
static const int kMaxRecordType = kRecyclableLastType;
static const unsigned int kBlockSize = 32768;
// Header is checksum (4 bytes), type (1 byte), length (2 bytes).
static const int kHeaderSize = 4 + 1 + 2;
// Recyclable header is checksum (4 bytes), type (1 byte), log number
// (4 bytes), length (2 bytes).
static const int kRecyclableHeaderSize = 4 + 1 + 4 + 2;
} // namespace log
} // namespace rocksdb

73
db/log_reader.cc
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@ -95,6 +95,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
const unsigned int record_type = ReadPhysicalRecord(&fragment, &drop_size);
switch (record_type) {
case kFullType:
case kRecyclableFullType:
if (in_fragmented_record && !scratch->empty()) {
// Handle bug in earlier versions of log::Writer where
// it could emit an empty kFirstType record at the tail end
@ -109,6 +110,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
return true;
case kFirstType:
case kRecyclableFirstType:
if (in_fragmented_record && !scratch->empty()) {
// Handle bug in earlier versions of log::Writer where
// it could emit an empty kFirstType record at the tail end
@ -122,6 +124,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
break;
case kMiddleType:
case kRecyclableMiddleType:
if (!in_fragmented_record) {
ReportCorruption(fragment.size(),
"missing start of fragmented record(1)");
@ -131,6 +134,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
break;
case kLastType:
case kRecyclableLastType:
if (!in_fragmented_record) {
ReportCorruption(fragment.size(),
"missing start of fragmented record(2)");
@ -162,6 +166,23 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch,
}
return false;
case kOldRecord:
if (wal_recovery_mode != WALRecoveryMode::kSkipAnyCorruptedRecords) {
// Treat a record from a previous instance of the log as EOF.
if (in_fragmented_record) {
if (wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
// in clean shutdown we don't expect any error in the log files
ReportCorruption(scratch->size(), "error reading trailing data");
}
// This can be caused by the writer dying immediately after
// writing a physical record but before completing the next; don't
// treat it as a corruption, just ignore the entire logical record.
scratch->clear();
}
return false;
}
// fall-thru
case kBadRecord:
if (in_fragmented_record) {
ReportCorruption(scratch->size(), "error in middle of record");
@ -263,9 +284,7 @@ void Reader::ReportDrop(size_t bytes, const Status& reason) {
}
}
unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
while (true) {
if (buffer_.size() < (size_t)kHeaderSize) {
bool Reader::ReadMore(size_t* drop_size, int *error) {
if (!eof_ && !read_error_) {
// Last read was a full read, so this is a trailer to skip
buffer_.clear();
@ -275,12 +294,13 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
buffer_.clear();
ReportDrop(kBlockSize, status);
read_error_ = true;
return kEof;
*error = kEof;
return false;
} else if (buffer_.size() < (size_t)kBlockSize) {
eof_ = true;
eof_offset_ = buffer_.size();
}
continue;
return true;
} else {
// Note that if buffer_ is non-empty, we have a truncated header at the
// end of the file, which can be caused by the writer crashing in the
@ -289,11 +309,24 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
if (buffer_.size()) {
*drop_size = buffer_.size();
buffer_.clear();
return kBadHeader;
*error = kBadHeader;
return false;
}
buffer_.clear();
return kEof;
*error = kEof;
return false;
}
}
unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
while (true) {
// We need at least the minimum header size
if (buffer_.size() < (size_t)kHeaderSize) {
int r;
if (!ReadMore(drop_size, &r)) {
return r;
}
continue;
}
// Parse the header
@ -302,7 +335,23 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
const uint32_t b = static_cast<uint32_t>(header[5]) & 0xff;
const unsigned int type = header[6];
const uint32_t length = a | (b << 8);
if (kHeaderSize + length > buffer_.size()) {
int header_size = kHeaderSize;
if (type >= kRecyclableFullType && type <= kRecyclableLastType) {
header_size = kRecyclableHeaderSize;
// We need enough for the larger header
if (buffer_.size() < (size_t)kRecyclableHeaderSize) {
int r;
if (!ReadMore(drop_size, &r)) {
return r;
}
continue;
}
const uint32_t log_num = DecodeFixed32(header + 7);
if (log_num != log_number_) {
return kOldRecord;
}
}
if (header_size + length > buffer_.size()) {
*drop_size = buffer_.size();
buffer_.clear();
if (!eof_) {
@ -331,7 +380,7 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
// Check crc
if (checksum_) {
uint32_t expected_crc = crc32c::Unmask(DecodeFixed32(header));
uint32_t actual_crc = crc32c::Value(header + 6, 1 + length);
uint32_t actual_crc = crc32c::Value(header + 6, length + header_size - 6);
if (actual_crc != expected_crc) {
// Drop the rest of the buffer since "length" itself may have
// been corrupted and if we trust it, we could find some
@ -344,16 +393,16 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
}
}
buffer_.remove_prefix(kHeaderSize + length);
buffer_.remove_prefix(header_size + length);
// Skip physical record that started before initial_offset_
if (end_of_buffer_offset_ - buffer_.size() - kHeaderSize - length <
if (end_of_buffer_offset_ - buffer_.size() - header_size - length <
initial_offset_) {
result->clear();
return kBadRecord;
}
*result = Slice(header + kHeaderSize, length);
*result = Slice(header + header_size, length);
return type;
}
}

5
db/log_reader.h
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@ -124,6 +124,8 @@ class Reader {
kBadRecord = kMaxRecordType + 2,
// Returned when we fail to read a valid header.
kBadHeader = kMaxRecordType + 3,
// Returned when we read an old record from a previous user of the log.
kOldRecord = kMaxRecordType + 4,
};
// Skips all blocks that are completely before "initial_offset_".
@ -134,6 +136,9 @@ class Reader {
// Return type, or one of the preceding special values
unsigned int ReadPhysicalRecord(Slice* result, size_t* drop_size);
// Read some more
bool ReadMore(size_t* drop_size, int *error);
// Reports dropped bytes to the reporter.
// buffer_ must be updated to remove the dropped bytes prior to invocation.
void ReportCorruption(size_t bytes, const char* reason);

105
db/log_test.cc
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@ -153,7 +153,7 @@ class LogTest : public ::testing::TestWithParam<int> {
// Record metadata for testing initial offset functionality
static size_t initial_offset_record_sizes_[];
static uint64_t initial_offset_last_record_offsets_[];
uint64_t initial_offset_last_record_offsets_[4];
public:
LogTest()
@ -163,8 +163,16 @@ class LogTest : public ::testing::TestWithParam<int> {
source_holder_(
test::GetSequentialFileReader(new StringSource(reader_contents_))),
writer_(std::move(dest_holder_), 123, GetParam()),
reader_(NULL, std::move(source_holder_), &report_,
true /*checksum*/, 0 /*initial_offset*/, 123) {}
reader_(NULL, std::move(source_holder_), &report_, true /*checksum*/,
0 /*initial_offset*/, 123) {
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
initial_offset_last_record_offsets_[0] = 0;
initial_offset_last_record_offsets_[1] = header_size + 10000;
initial_offset_last_record_offsets_[2] = 2 * (header_size + 10000);
initial_offset_last_record_offsets_[3] = 2 * (header_size + 10000) +
(2 * log::kBlockSize - 1000) +
3 * header_size;
}
void Write(const std::string& msg) {
writer_.AddRecord(Slice(msg));
@ -200,9 +208,11 @@ class LogTest : public ::testing::TestWithParam<int> {
dest->Drop(bytes);
}
void FixChecksum(int header_offset, int len) {
void FixChecksum(int header_offset, int len, bool recyclable) {
// Compute crc of type/len/data
uint32_t crc = crc32c::Value(&dest_contents()[header_offset+6], 1 + len);
int header_size = recyclable ? kRecyclableHeaderSize : kHeaderSize;
uint32_t crc = crc32c::Value(&dest_contents()[header_offset + 6],
header_size - 6 + len);
crc = crc32c::Mask(crc);
EncodeFixed32(&dest_contents()[header_offset], crc);
}
@ -292,13 +302,6 @@ size_t LogTest::initial_offset_record_sizes_[] =
2 * log::kBlockSize - 1000, // Span three blocks
1};
uint64_t LogTest::initial_offset_last_record_offsets_[] =
{0,
kHeaderSize + 10000,
2 * (kHeaderSize + 10000),
2 * (kHeaderSize + 10000) +
(2 * log::kBlockSize - 1000) + 3 * kHeaderSize};
TEST_P(LogTest, Empty) { ASSERT_EQ("EOF", Read()); }
TEST_P(LogTest, ReadWrite) {
@ -336,9 +339,10 @@ TEST_P(LogTest, Fragmentation) {
TEST_P(LogTest, MarginalTrailer) {
// Make a trailer that is exactly the same length as an empty record.
const int n = kBlockSize - 2*kHeaderSize;
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
const int n = kBlockSize - 2 * header_size;
Write(BigString("foo", n));
ASSERT_EQ((unsigned int)(kBlockSize - kHeaderSize), WrittenBytes());
ASSERT_EQ((unsigned int)(kBlockSize - header_size), WrittenBytes());
Write("");
Write("bar");
ASSERT_EQ(BigString("foo", n), Read());
@ -349,9 +353,10 @@ TEST_P(LogTest, MarginalTrailer) {
TEST_P(LogTest, MarginalTrailer2) {
// Make a trailer that is exactly the same length as an empty record.
const int n = kBlockSize - 2*kHeaderSize;
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
const int n = kBlockSize - 2 * header_size;
Write(BigString("foo", n));
ASSERT_EQ((unsigned int)(kBlockSize - kHeaderSize), WrittenBytes());
ASSERT_EQ((unsigned int)(kBlockSize - header_size), WrittenBytes());
Write("bar");
ASSERT_EQ(BigString("foo", n), Read());
ASSERT_EQ("bar", Read());
@ -361,9 +366,10 @@ TEST_P(LogTest, MarginalTrailer2) {
}
TEST_P(LogTest, ShortTrailer) {
const int n = kBlockSize - 2*kHeaderSize + 4;
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
const int n = kBlockSize - 2 * header_size + 4;
Write(BigString("foo", n));
ASSERT_EQ((unsigned int)(kBlockSize - kHeaderSize + 4), WrittenBytes());
ASSERT_EQ((unsigned int)(kBlockSize - header_size + 4), WrittenBytes());
Write("");
Write("bar");
ASSERT_EQ(BigString("foo", n), Read());
@ -373,9 +379,10 @@ TEST_P(LogTest, ShortTrailer) {
}
TEST_P(LogTest, AlignedEof) {
const int n = kBlockSize - 2*kHeaderSize + 4;
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
const int n = kBlockSize - 2 * header_size + 4;
Write(BigString("foo", n));
ASSERT_EQ((unsigned int)(kBlockSize - kHeaderSize + 4), WrittenBytes());
ASSERT_EQ((unsigned int)(kBlockSize - header_size + 4), WrittenBytes());
ASSERT_EQ(BigString("foo", n), Read());
ASSERT_EQ("EOF", Read());
}
@ -407,7 +414,7 @@ TEST_P(LogTest, BadRecordType) {
Write("foo");
// Type is stored in header[6]
IncrementByte(6, 100);
FixChecksum(0, 3);
FixChecksum(0, 3, false);
ASSERT_EQ("EOF", Read());
ASSERT_EQ(3U, DroppedBytes());
ASSERT_EQ("OK", MatchError("unknown record type"));
@ -432,7 +439,8 @@ TEST_P(LogTest, TruncatedTrailingRecordIsNotIgnored) {
}
TEST_P(LogTest, BadLength) {
const int kPayloadSize = kBlockSize - kHeaderSize;
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
const int kPayloadSize = kBlockSize - header_size;
Write(BigString("bar", kPayloadSize));
Write("foo");
// Least significant size byte is stored in header[4].
@ -459,17 +467,17 @@ TEST_P(LogTest, BadLengthAtEndIsNotIgnored) {
}
TEST_P(LogTest, ChecksumMismatch) {
Write("foo");
IncrementByte(0, 10);
Write("foooooo");
IncrementByte(0, 14);
ASSERT_EQ("EOF", Read());
ASSERT_EQ(10U, DroppedBytes());
ASSERT_EQ(14U + 4 * !!GetParam(), DroppedBytes());
ASSERT_EQ("OK", MatchError("checksum mismatch"));
}
TEST_P(LogTest, UnexpectedMiddleType) {
Write("foo");
SetByte(6, kMiddleType);
FixChecksum(0, 3);
SetByte(6, GetParam() ? kRecyclableMiddleType : kMiddleType);
FixChecksum(0, 3, !!GetParam());
ASSERT_EQ("EOF", Read());
ASSERT_EQ(3U, DroppedBytes());
ASSERT_EQ("OK", MatchError("missing start"));
@ -477,8 +485,8 @@ TEST_P(LogTest, UnexpectedMiddleType) {
TEST_P(LogTest, UnexpectedLastType) {
Write("foo");
SetByte(6, kLastType);
FixChecksum(0, 3);
SetByte(6, GetParam() ? kRecyclableLastType : kLastType);
FixChecksum(0, 3, !!GetParam());
ASSERT_EQ("EOF", Read());
ASSERT_EQ(3U, DroppedBytes());
ASSERT_EQ("OK", MatchError("missing start"));
@ -487,8 +495,8 @@ TEST_P(LogTest, UnexpectedLastType) {
TEST_P(LogTest, UnexpectedFullType) {
Write("foo");
Write("bar");
SetByte(6, kFirstType);
FixChecksum(0, 3);
SetByte(6, GetParam() ? kRecyclableFirstType : kFirstType);
FixChecksum(0, 3, !!GetParam());
ASSERT_EQ("bar", Read());
ASSERT_EQ("EOF", Read());
ASSERT_EQ(3U, DroppedBytes());
@ -498,8 +506,8 @@ TEST_P(LogTest, UnexpectedFullType) {
TEST_P(LogTest, UnexpectedFirstType) {
Write("foo");
Write(BigString("bar", 100000));
SetByte(6, kFirstType);
FixChecksum(0, 3);
SetByte(6, GetParam() ? kRecyclableFirstType : kFirstType);
FixChecksum(0, 3, !!GetParam());
ASSERT_EQ(BigString("bar", 100000), Read());
ASSERT_EQ("EOF", Read());
ASSERT_EQ(3U, DroppedBytes());
@ -573,13 +581,25 @@ TEST_P(LogTest, ReadSecondOneOff) { CheckInitialOffsetRecord(1, 1); }
TEST_P(LogTest, ReadSecondTenThousand) { CheckInitialOffsetRecord(10000, 1); }
TEST_P(LogTest, ReadSecondStart) { CheckInitialOffsetRecord(10007, 1); }
TEST_P(LogTest, ReadSecondStart) {
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
CheckInitialOffsetRecord(10000 + header_size, 1);
}
TEST_P(LogTest, ReadThirdOneOff) { CheckInitialOffsetRecord(10008, 2); }
TEST_P(LogTest, ReadThirdOneOff) {
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
CheckInitialOffsetRecord(10000 + header_size + 1, 2);
}
TEST_P(LogTest, ReadThirdStart) { CheckInitialOffsetRecord(20014, 2); }
TEST_P(LogTest, ReadThirdStart) {
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
CheckInitialOffsetRecord(20000 + 2 * header_size, 2);
}
TEST_P(LogTest, ReadFourthOneOff) { CheckInitialOffsetRecord(20015, 3); }
TEST_P(LogTest, ReadFourthOneOff) {
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
CheckInitialOffsetRecord(20000 + 2 * header_size + 1, 3);
}
TEST_P(LogTest, ReadFourthFirstBlockTrailer) {
CheckInitialOffsetRecord(log::kBlockSize - 4, 3);
@ -594,8 +614,9 @@ TEST_P(LogTest, ReadFourthLastBlock) {
}
TEST_P(LogTest, ReadFourthStart) {
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
CheckInitialOffsetRecord(
2 * (kHeaderSize + 1000) + (2 * log::kBlockSize - 1000) + 3 * kHeaderSize,
2 * (header_size + 1000) + (2 * log::kBlockSize - 1000) + 3 * header_size,
3);
}
@ -606,7 +627,8 @@ TEST_P(LogTest, ReadPastEnd) { CheckOffsetPastEndReturnsNoRecords(5); }
TEST_P(LogTest, ClearEofSingleBlock) {
Write("foo");
Write("bar");
ForceEOF(3 + kHeaderSize + 2);
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
ForceEOF(3 + header_size + 2);
ASSERT_EQ("foo", Read());
UnmarkEOF();
ASSERT_EQ("bar", Read());
@ -620,10 +642,11 @@ TEST_P(LogTest, ClearEofSingleBlock) {
TEST_P(LogTest, ClearEofMultiBlock) {
size_t num_full_blocks = 5;
size_t n = (kBlockSize - kHeaderSize) * num_full_blocks + 25;
int header_size = GetParam() ? kRecyclableHeaderSize : kHeaderSize;
size_t n = (kBlockSize - header_size) * num_full_blocks + 25;
Write(BigString("foo", n));
Write(BigString("bar", n));
ForceEOF(n + num_full_blocks * kHeaderSize + 10);
ForceEOF(n + num_full_blocks * header_size + header_size + 3);
ASSERT_EQ(BigString("foo", n), Read());
ASSERT_TRUE(IsEOF());
UnmarkEOF();

58
db/log_writer.cc
Unescape View File

@ -37,6 +37,10 @@ Status Writer::AddRecord(const Slice& slice) {
const char* ptr = slice.data();
size_t left = slice.size();
// Header size varies depending on whether we are recycling or not.
const int header_size =
recycle_log_files_ ? kRecyclableHeaderSize : kHeaderSize;
// 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
@ -45,32 +49,34 @@ Status Writer::AddRecord(const Slice& slice) {
do {
const int leftover = kBlockSize - block_offset_;
assert(leftover >= 0);
if (leftover < kHeaderSize) {
if (leftover < header_size) {
// 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));
// Fill the trailer (literal below relies on kHeaderSize and
// kRecyclableHeaderSize being <= 11)
assert(header_size <= 11);
dest_->Append(
Slice("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", leftover));
}
block_offset_ = 0;
}
// Invariant: we never leave < kHeaderSize bytes in a block.
assert(static_cast<int>(kBlockSize) - block_offset_ >= kHeaderSize);
// Invariant: we never leave < header_size bytes in a block.
assert(static_cast<int>(kBlockSize) - block_offset_ >= header_size);
const size_t avail = kBlockSize - block_offset_ - kHeaderSize;
const size_t avail = kBlockSize - block_offset_ - header_size;
const size_t fragment_length = (left < avail) ? left : avail;
RecordType type;
const bool end = (left == fragment_length);
if (begin && end) {
type = kFullType;
type = recycle_log_files_ ? kRecyclableFullType : kFullType;
} else if (begin) {
type = kFirstType;
type = recycle_log_files_ ? kRecyclableFirstType : kFirstType;
} else if (end) {
type = kLastType;
type = recycle_log_files_ ? kRecyclableLastType : kLastType;
} else {
type = kMiddleType;
type = recycle_log_files_ ? kRecyclableMiddleType : kMiddleType;
}
s = EmitPhysicalRecord(type, ptr, fragment_length);
@ -83,28 +89,48 @@ Status Writer::AddRecord(const Slice& slice) {
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);
size_t header_size;
char buf[kRecyclableHeaderSize];
// 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);
uint32_t crc = type_crc_[t];
if (t < kRecyclableFullType) {
// Legacy record format
assert(block_offset_ + kHeaderSize + n <= kBlockSize);
header_size = kHeaderSize;
} else {
// Recyclable record format
assert(block_offset_ + kRecyclableHeaderSize + n <= kBlockSize);
header_size = kRecyclableHeaderSize;
// Only encode low 32-bits of the 64-bit log number. This means
// we will fail to detect an old record if we recycled a log from
// ~4 billion logs ago, but that is effectively impossible, and
// even if it were we'dbe far more likely to see a false positive
// on the 32-bit CRC.
EncodeFixed32(buf + 7, static_cast<uint32_t>(log_number_));
crc = crc32c::Extend(crc, buf + 7, 4);
}
// Compute the crc of the record type and the payload.
uint32_t crc = crc32c::Extend(type_crc_[t], ptr, n);
crc = crc32c::Extend(crc, 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));
Status s = dest_->Append(Slice(buf, header_size));
if (s.ok()) {
s = dest_->Append(Slice(ptr, n));
if (s.ok()) {
s = dest_->Flush();
}
}
block_offset_ += kHeaderSize + n;
block_offset_ += header_size + n;
return s;
}

11
db/log_writer.h
Unescape View File

@ -43,7 +43,7 @@ namespace log {
* 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.
*
* Record format:
* Legacy record format:
*
* +---------+-----------+-----------+--- ... ---+
* |CRC (4B) | Size (2B) | Type (1B) | Payload |
@ -57,6 +57,15 @@ namespace log {
* 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:

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