Allow per-platform log buffer size

Author: dango-msft

db/log_format.h

@@ -24,8 +24,6 @@ enum RecordType {
 };
 static const int kMaxRecordType = kLastType;
 
-static const int kBlockSize = 32768;
-
 // Header is checksum (4 bytes), length (2 bytes), type (1 byte).
 static const int kHeaderSize = 4 + 2 + 1;
 

db/log_reader.cc

@@ -20,7 +20,7 @@ Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
     : file_(file),
       reporter_(reporter),
       checksum_(checksum),
-      backing_store_(new char[kBlockSize]),
+      backing_store_(new char[port::kLogBlockSize]),
       buffer_(),
       eof_(false),
       last_record_offset_(0),
@@ -31,12 +31,12 @@ Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
 Reader::~Reader() { delete[] backing_store_; }
 
 bool Reader::SkipToInitialBlock() {
-  const size_t offset_in_block = initial_offset_ % kBlockSize;
+  const size_t offset_in_block = initial_offset_ % port::kLogBlockSize;
   uint64_t block_start_location = initial_offset_ - offset_in_block;
 
   // Don't search a block if we'd be in the trailer
-  if (offset_in_block > kBlockSize - 6) {
-    block_start_location += kBlockSize;
+  if (offset_in_block > port::kLogBlockSize - 6) {
+    block_start_location += port::kLogBlockSize;
   }
 
   end_of_buffer_offset_ = block_start_location;
@@ -192,14 +192,14 @@ unsigned int Reader::ReadPhysicalRecord(Slice* result) {
       if (!eof_) {
         // Last read was a full read, so this is a trailer to skip
         buffer_.clear();
-        Status status = file_->Read(kBlockSize, &buffer_, backing_store_);
+        Status status = file_->Read(port::kLogBlockSize, &buffer_, backing_store_);
         end_of_buffer_offset_ += buffer_.size();
         if (!status.ok()) {
           buffer_.clear();
-          ReportDrop(kBlockSize, status);
+          ReportDrop(port::kLogBlockSize, status);
           eof_ = true;
           return kEof;
-        } else if (buffer_.size() < kBlockSize) {
+        } else if (buffer_.size() < port::kLogBlockSize) {
           eof_ = true;
         }
         continue;

db/log_reader.h

@@ -90,7 +90,7 @@ class Reader {
   bool const checksum_;
   char* const backing_store_;
   Slice buffer_;
-  bool eof_;  // Last Read() indicated EOF by returning < kBlockSize
+  bool eof_;  // Last Read() indicated EOF by returning < port::kLogBlockSize
 
   // Offset of the last record returned by ReadRecord.
   uint64_t last_record_offset_;

db/log_writer.cc

@@ -25,7 +25,7 @@ Writer::Writer(WritableFile* dest) : dest_(dest), block_offset_(0) {
 }
 
 Writer::Writer(WritableFile* dest, uint64_t dest_length)
-    : dest_(dest), block_offset_(dest_length % kBlockSize) {
+    : dest_(dest), block_offset_(dest_length % port::kLogBlockSize) {
   InitTypeCrc(type_crc_);
 }
 
@@ -41,7 +41,7 @@ Status Writer::AddRecord(const Slice& slice) {
   Status s;
   bool begin = true;
   do {
-    const int leftover = kBlockSize - block_offset_;
+    const int leftover = port::kLogBlockSize - block_offset_;
     assert(leftover >= 0);
     if (leftover < kHeaderSize) {
       // Switch to a new block
@@ -54,9 +54,9 @@ Status Writer::AddRecord(const Slice& slice) {
     }
 
     // Invariant: we never leave < kHeaderSize bytes in a block.
-    assert(kBlockSize - block_offset_ - kHeaderSize >= 0);
+    assert(port::kLogBlockSize - block_offset_ - kHeaderSize >= 0);
 
-    const size_t avail = kBlockSize - block_offset_ - kHeaderSize;
+    const size_t avail = port::kLogBlockSize - block_offset_ - kHeaderSize;
     const size_t fragment_length = (left < avail) ? left : avail;
 
     RecordType type;
@@ -82,7 +82,7 @@ Status Writer::AddRecord(const Slice& slice) {
 Status Writer::EmitPhysicalRecord(RecordType t, const char* ptr,
                                   size_t length) {
   assert(length <= 0xffff);  // Must fit in two bytes
-  assert(block_offset_ + kHeaderSize + length <= kBlockSize);
+  assert(block_offset_ + kHeaderSize + length <= port::kLogBlockSize);
 
   // Format the header
   char buf[kHeaderSize];

port/port_example.h

@@ -18,6 +18,9 @@ namespace port {
 // TODO(jorlow): Many of these belong more in the environment class rather than
 //               here. We should try moving them and see if it affects perf.
 
+// Buffer size for log
+static const int kLogBlockSize = 32768;
+
 // ------------------ Threading -------------------
 
 // A Mutex represents an exclusive lock.

port/port_stdcxx.h

@@ -47,6 +47,8 @@ namespace port {
 
 class CondVar;
 
+static const int kLogBlockSize = 32768;
+
 // Thinly wraps std::mutex.
 class LOCKABLE Mutex {
  public: