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Some refactorings on plain table

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Summary:
Plain table has been working well and this is just a nit-picking patch,
which is generated during my coding reading. No real functional changes.
only some changes regarding:

* Improve some comments from the perspective a "new" code reader.
* Change some magic number to constant, which can help us to parameterize them
  in the future.
* Did some style, naming, C++ convention changes.
* Fix warnings from new "arc lint"

Test Plan: make check

Reviewers: sdong, haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15429
This commit is contained in:
Kai Liu
2014-01-24 21:10:19 -08:00
parent 0ab766132b
commit 4b51dffcf8
3 changed files with 200 additions and 202 deletions
Download Patch File Download Diff File Expand all files Collapse all files

244
table/plain_table_reader.cc
View File

@@ -34,29 +34,66 @@
namespace rocksdb {
extern const uint64_t kPlainTableMagicNumber;
namespace {
static uint32_t GetSliceHash(Slice const& s) {
inline uint32_t GetSliceHash(Slice const& s) {
return Hash(s.data(), s.size(), 397) ;
}
static uint32_t getBucketIdFromHash(uint32_t hash, uint32_t num_buckets) {
inline uint32_t GetBucketIdFromHash(uint32_t hash, uint32_t num_buckets) {
return hash % num_buckets;
}
} // namespace
// Iterator to iterate IndexedTable
class PlainTableIterator : public Iterator {
public:
explicit PlainTableIterator(PlainTableReader* table);
~PlainTableIterator();
bool Valid() const;
void SeekToFirst();
void SeekToLast();
void Seek(const Slice& target);
void Next();
void Prev();
Slice key() const;
Slice value() const;
Status status() const;
private:
PlainTableReader* table_;
uint32_t offset_;
uint32_t next_offset_;
Slice key_;
Slice value_;
Status status_;
// No copying allowed
PlainTableIterator(const PlainTableIterator&) = delete;
void operator=(const Iterator&) = delete;
};
extern const uint64_t kPlainTableMagicNumber;
PlainTableReader::PlainTableReader(const EnvOptions& storage_options,
uint64_t file_size, int bloom_bits_per_key,
double hash_table_ratio,
const TableProperties& table_properties) :
hash_table_size_(0), soptions_(storage_options), file_size_(file_size),
hash_table_ratio_(hash_table_ratio),
bloom_bits_per_key_(bloom_bits_per_key),
table_properties_(table_properties), data_start_offset_(0),
data_end_offset_(table_properties_.data_size),
user_key_len_(table_properties.fixed_key_len) {
hash_table_ = nullptr;
bloom_ = nullptr;
sub_index_ = nullptr;
}
const TableProperties& table_properties)
: soptions_(storage_options),
file_size_(file_size),
kHashTableRatio(hash_table_ratio),
kBloomBitsPerKey(bloom_bits_per_key),
table_properties_(table_properties),
data_end_offset_(table_properties_.data_size),
user_key_len_(table_properties.fixed_key_len) {}
PlainTableReader::~PlainTableReader() {
delete[] hash_table_;
@@ -73,30 +110,20 @@ Status PlainTableReader::Open(const Options& options,
double hash_table_ratio) {
assert(options.allow_mmap_reads);
if (file_size > 2147483646) {
if (file_size > kMaxFileSize) {
return Status::NotSupported("File is too large for PlainTableReader!");
}
TableProperties table_properties;
auto s = ReadTableProperties(
file.get(),
file_size,
kPlainTableMagicNumber,
options.env,
options.info_log.get(),
&table_properties
);
auto s = ReadTableProperties(file.get(), file_size, kPlainTableMagicNumber,
options.env, options.info_log.get(),
&table_properties);
if (!s.ok()) {
return s;
}
std::unique_ptr<PlainTableReader> new_reader(new PlainTableReader(
soptions,
file_size,
bloom_num_bits,
hash_table_ratio,
table_properties
));
soptions, file_size, bloom_num_bits, hash_table_ratio, table_properties));
new_reader->file_ = std::move(file);
new_reader->options_ = options;
@@ -129,12 +156,11 @@ struct PlainTableReader::IndexRecord {
// Helper class to track all the index records
class PlainTableReader::IndexRecordList {
public:
explicit IndexRecordList(size_t num_records_per_group) :
num_records_per_group_(num_records_per_group),
current_group_(nullptr),
num_records_in_current_group_(num_records_per_group) {
}
public:
explicit IndexRecordList(size_t num_records_per_group)
: kNumRecordsPerGroup(num_records_per_group),
current_group_(nullptr),
num_records_in_current_group_(num_records_per_group) {}
~IndexRecordList() {
for (size_t i = 0; i < groups_.size(); i++) {
@@ -143,65 +169,59 @@ public:
}
void AddRecord(murmur_t hash, uint32_t offset) {
if (num_records_in_current_group_ == num_records_per_group_) {
if (num_records_in_current_group_ == kNumRecordsPerGroup) {
current_group_ = AllocateNewGroup();
num_records_in_current_group_ = 0;
}
auto& new_record = current_group_[num_records_in_current_group_];
auto& new_record = current_group_[num_records_in_current_group_++];
new_record.hash = hash;
new_record.offset = offset;
new_record.next = nullptr;
num_records_in_current_group_++;
}
size_t GetNumRecords() {
return (groups_.size() - 1) * num_records_per_group_
+ num_records_in_current_group_;
size_t GetNumRecords() const {
return (groups_.size() - 1) * kNumRecordsPerGroup +
num_records_in_current_group_;
}
IndexRecord* At(size_t index) {
return &(groups_[index / num_records_per_group_]
[index % num_records_per_group_]);
return &(groups_[index / kNumRecordsPerGroup][index % kNumRecordsPerGroup]);
}
private:
IndexRecord* AllocateNewGroup() {
IndexRecord* result = new IndexRecord[num_records_per_group_];
IndexRecord* result = new IndexRecord[kNumRecordsPerGroup];
groups_.push_back(result);
return result;
}
private:
const size_t num_records_per_group_;
const size_t kNumRecordsPerGroup;
IndexRecord* current_group_;
// List of arrays allocated
std::vector<IndexRecord*> groups_;
size_t num_records_in_current_group_;
};
int PlainTableReader::PopulateIndexRecordList(
IndexRecordList& record_list) {
Slice key_slice;
Slice key_prefix_slice;
Slice key_suffix_slice;
Slice value_slice;
int PlainTableReader::PopulateIndexRecordList(IndexRecordList* record_list) {
Slice prev_key_prefix_slice;
uint32_t prev_key_prefix_hash = 0;
uint32_t pos = data_start_offset_;
int key_index_within_prefix = 0;
bool first = true;
std::string prefix_sub_index;
bool is_first_record = true;
HistogramImpl keys_per_prefix_hist;
// Need map to be ordered to make sure sub indexes generated
// are in order.
int num_prefixes = 0;
while (pos < data_end_offset_) {
uint32_t key_offset = pos;
Slice key_slice;
Slice value_slice;
status_ = Next(pos, &key_slice, &value_slice, pos);
key_prefix_slice = GetPrefix(key_slice);
Slice key_prefix_slice = GetPrefix(key_slice);
if (first || prev_key_prefix_slice != key_prefix_slice) {
num_prefixes++;
if (!first) {
if (is_first_record || prev_key_prefix_slice != key_prefix_slice) {
++num_prefixes;
if (!is_first_record) {
keys_per_prefix_hist.Add(key_index_within_prefix);
}
key_index_within_prefix = 0;
@@ -209,12 +229,13 @@ int PlainTableReader::PopulateIndexRecordList(
prev_key_prefix_hash = GetSliceHash(key_prefix_slice);
}
if (key_index_within_prefix++ % 16 == 0) {
// Add an index key for every 16 keys
record_list.AddRecord(prev_key_prefix_hash, key_offset);
if (key_index_within_prefix++ % kIndexIntervalForSamePrefixKeys == 0) {
// Add an index key for every kIndexIntervalForSamePrefixKeys keys
record_list->AddRecord(prev_key_prefix_hash, key_offset);
}
first = false;
is_first_record = false;
}
keys_per_prefix_hist.Add(key_index_within_prefix);
Log(options_.info_log, "Number of Keys per prefix Histogram: %s",
keys_per_prefix_hist.ToString().c_str());
@@ -222,23 +243,22 @@ int PlainTableReader::PopulateIndexRecordList(
return num_prefixes;
}
void PlainTableReader::Allocate(int num_prefixes) {
if (hash_table_ != nullptr) {
delete[] hash_table_;
}
if (bloom_bits_per_key_ > 0) {
bloom_ = new DynamicBloom(num_prefixes * bloom_bits_per_key_);
void PlainTableReader::AllocateIndexAndBloom(int num_prefixes) {
delete[] hash_table_;
if (kBloomBitsPerKey > 0) {
bloom_ = new DynamicBloom(num_prefixes * kBloomBitsPerKey);
}
double hash_table_size_multipier =
(hash_table_ratio_ > 1.0) ? 1.0 : 1.0 / hash_table_ratio_;
(kHashTableRatio > 1.0) ? 1.0 : 1.0 / kHashTableRatio;
hash_table_size_ = num_prefixes * hash_table_size_multipier + 1;
hash_table_ = new uint32_t[hash_table_size_];
}
size_t PlainTableReader::BucketizeIndexesAndFillBloom(
IndexRecordList& record_list, int num_prefixes,
std::vector<IndexRecord*>& hash2offsets,
std::vector<uint32_t>& bucket_count) {
std::vector<IndexRecord*>* hash_to_offsets,
std::vector<uint32_t>* bucket_count) {
size_t sub_index_size_needed = 0;
bool first = true;
uint32_t prev_hash = 0;
@@ -253,32 +273,34 @@ size_t PlainTableReader::BucketizeIndexesAndFillBloom(
bloom_->AddHash(cur_hash);
}
}
uint32_t bucket = getBucketIdFromHash(cur_hash, hash_table_size_);
IndexRecord* prev_bucket_head = hash2offsets[bucket];
uint32_t bucket = GetBucketIdFromHash(cur_hash, hash_table_size_);
IndexRecord* prev_bucket_head = (*hash_to_offsets)[bucket];
index_record->next = prev_bucket_head;
hash2offsets[bucket] = index_record;
if (bucket_count[bucket] > 0) {
if (bucket_count[bucket] == 1) {
(*hash_to_offsets)[bucket] = index_record;
auto& item_count = (*bucket_count)[bucket];
if (item_count > 0) {
if (item_count == 1) {
sub_index_size_needed += kOffsetLen + 1;
}
if (bucket_count[bucket] == 127) {
if (item_count == 127) {
// Need more than one byte for length
sub_index_size_needed++;
}
sub_index_size_needed += kOffsetLen;
}
bucket_count[bucket]++;
item_count++;
}
return sub_index_size_needed;
}
void PlainTableReader::FillIndexes(size_t sub_index_size_needed,
std::vector<IndexRecord*>& hash2offsets,
std::vector<uint32_t>& bucket_count) {
void PlainTableReader::FillIndexes(
size_t sub_index_size_needed,
const std::vector<IndexRecord*>& hash_to_offsets,
const std::vector<uint32_t>& bucket_count) {
Log(options_.info_log, "Reserving %zu bytes for sub index",
sub_index_size_needed);
// 4 bytes buffer for variable length size
size_t buffer_size = 64;
// 8 bytes buffer for variable length size
size_t buffer_size = 8 * 8;
size_t buffer_used = 0;
sub_index_size_needed += buffer_size;
sub_index_ = new char[sub_index_size_needed];
@@ -286,7 +308,6 @@ void PlainTableReader::FillIndexes(size_t sub_index_size_needed,
char* prev_ptr;
char* cur_ptr;
uint32_t* sub_index_ptr;
IndexRecord* record;
for (int i = 0; i < hash_table_size_; i++) {
uint32_t num_keys_for_bucket = bucket_count[i];
switch (num_keys_for_bucket) {
@@ -296,14 +317,14 @@ void PlainTableReader::FillIndexes(size_t sub_index_size_needed,
break;
case 1:
// point directly to the file offset
hash_table_[i] = hash2offsets[i]->offset;
hash_table_[i] = hash_to_offsets[i]->offset;
break;
default:
// point to second level indexes.
hash_table_[i] = sub_index_offset | kSubIndexMask;
prev_ptr = sub_index_ + sub_index_offset;
cur_ptr = EncodeVarint32(prev_ptr, num_keys_for_bucket);
sub_index_offset += cur_ptr - prev_ptr;
sub_index_offset += (cur_ptr - prev_ptr);
if (cur_ptr - prev_ptr > 2
|| (cur_ptr - prev_ptr == 2 && num_keys_for_bucket <= 127)) {
// Need to resize sub_index. Exponentially grow buffer.
@@ -321,10 +342,10 @@ void PlainTableReader::FillIndexes(size_t sub_index_size_needed,
}
}
sub_index_ptr = (uint32_t*) (sub_index_ + sub_index_offset);
record = hash2offsets[i];
IndexRecord* record = hash_to_offsets[i];
int j;
for (j = num_keys_for_bucket - 1;
j >= 0 && record; j--, record = record->next) {
for (j = num_keys_for_bucket - 1; j >= 0 && record;
j--, record = record->next) {
sub_index_ptr[j] = record->offset;
}
assert(j == -1 && record == nullptr);
@@ -337,24 +358,6 @@ void PlainTableReader::FillIndexes(size_t sub_index_size_needed,
hash_table_size_, sub_index_size_needed);
}
// PopulateIndex() builds index of keys.
// hash_table_ contains buckets size of hash_table_size_, each is a 32-bit
// integer. The lower 31 bits contain an offset value (explained below) and
// the first bit of the integer indicates type of the offset:
//
// 0 indicates that the bucket contains only one prefix (no conflict when
// hashing this prefix), whose first row starts from this offset of the file.
// 1 indicates that the bucket contains more than one prefixes, or there
// are too many rows for one prefix so we need a binary search for it. In
// this case, the offset indicates the offset of sub_index_ holding the
// binary search indexes of keys for those rows. Those binary search indexes
// are organized in this way:
//
// The first 4 bytes, indicates how many indexes (N) are stored after it. After
// it, there are N 32-bit integers, each points of an offset of the file, which
// points to starting of a row. Those offsets need to be guaranteed to be in
// ascending order so the keys they are pointing to are also in ascending order
// to make sure we can use them to do binary searches.
Status PlainTableReader::PopulateIndex() {
// Get mmapped memory to file_data_.
Status s = file_->Read(0, file_size_, &file_data_, nullptr);
@@ -362,25 +365,24 @@ Status PlainTableReader::PopulateIndex() {
return s;
}
IndexRecordList record_list(256);
// First, read the whole file, for every 16 rows for a prefix (starting from
// the first one), generate a record of (hash, offset) and append it to
// IndexRecordList, which is a data structure created to store them.
int num_prefixes = PopulateIndexRecordList(record_list);
IndexRecordList record_list(kRecordsPerGroup);
// First, read the whole file, for every kIndexIntervalForSamePrefixKeys rows
// for a prefix (starting from the first one), generate a record of (hash,
// offset) and append it to IndexRecordList, which is a data structure created
// to store them.
int num_prefixes = PopulateIndexRecordList(&record_list);
// Calculated hash table and bloom filter size and allocate memory for indexes
// and bloom filter based on the number of prefixes.
Allocate(num_prefixes);
AllocateIndexAndBloom(num_prefixes);
// Bucketize all the index records to a temp data structure, in which for
// each bucket, we generate a linked list of IndexRecord, in reversed order.
std::vector<IndexRecord*> hash2offsets(hash_table_size_, nullptr);
std::vector<IndexRecord*> hash_to_offsets(hash_table_size_, nullptr);
std::vector<uint32_t> bucket_count(hash_table_size_, 0);
size_t sub_index_size_needed = BucketizeIndexesAndFillBloom(record_list,
num_prefixes,
hash2offsets,
bucket_count);
size_t sub_index_size_needed = BucketizeIndexesAndFillBloom(
record_list, num_prefixes, &hash_to_offsets, &bucket_count);
// From the temp data structure, populate indexes.
FillIndexes(sub_index_size_needed, hash2offsets, bucket_count);
FillIndexes(sub_index_size_needed, hash_to_offsets, bucket_count);
return Status::OK();
}
@@ -389,7 +391,7 @@ Status PlainTableReader::GetOffset(const Slice& target, const Slice& prefix,
uint32_t prefix_hash, bool& prefix_matched,
uint32_t& ret_offset) {
prefix_matched = false;
int bucket = getBucketIdFromHash(prefix_hash, hash_table_size_);
int bucket = GetBucketIdFromHash(prefix_hash, hash_table_size_);
uint32_t bucket_value = hash_table_[bucket];
if (bucket_value == data_end_offset_) {
ret_offset = data_end_offset_;