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rocksdb/table/block_based_table_reader.cc
Lei Jin 40fa8a4cd5 make statistics forward-able 
Summary:
Make StatisticsImpl being able to forward stats to provided statistics
implementation. The main purpose is to allow us to collect internal
stats in the future even when user supplies custom statistics
implementation. It avoids intrumenting 2 sets of stats collection code.
One immediate use case is tuning advisor, which needs to collect some
internal stats, users may not be interested.

Test Plan:
ran db_bench and see stats show up at the end of run
Will run make all check since some tests rely on statistics

Reviewers: yhchiang, sdong, igor

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D20145
2014-07-28 12:05:36 -07:00

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same 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.
#include "table/block_based_table_reader.h"
#include <string>
#include <utility>
#include "db/dbformat.h"
#include "rocksdb/cache.h"
#include "rocksdb/comparator.h"
#include "rocksdb/env.h"
#include "rocksdb/filter_policy.h"
#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
#include "rocksdb/statistics.h"
#include "rocksdb/table.h"
#include "rocksdb/table_properties.h"
#include "table/block.h"
#include "table/filter_block.h"
#include "table/block_hash_index.h"
#include "table/block_prefix_index.h"
#include "table/format.h"
#include "table/meta_blocks.h"
#include "table/two_level_iterator.h"
#include "util/coding.h"
#include "util/perf_context_imp.h"
#include "util/stop_watch.h"
namespace rocksdb {
extern const uint64_t kBlockBasedTableMagicNumber;
extern const std::string kHashIndexPrefixesBlock;
extern const std::string kHashIndexPrefixesMetadataBlock;
using std::unique_ptr;
typedef BlockBasedTable::IndexReader IndexReader;
namespace {
// The longest the prefix of the cache key used to identify blocks can be.
// We are using the fact that we know for Posix files the unique ID is three
// varints.
// For some reason, compiling for iOS complains that this variable is unused
const size_t kMaxCacheKeyPrefixSize __attribute__((unused)) =
kMaxVarint64Length * 3 + 1;
// Read the block identified by "handle" from "file".
// The only relevant option is options.verify_checksums for now.
// On failure return non-OK.
// On success fill *result and return OK - caller owns *result
Status ReadBlockFromFile(RandomAccessFile* file, const Footer& footer,
const ReadOptions& options, const BlockHandle& handle,
Block** result, Env* env, bool do_uncompress = true) {
BlockContents contents;
Status s = ReadBlockContents(file, footer, options, handle, &contents, env,
do_uncompress);
if (s.ok()) {
*result = new Block(contents);
}
return s;
}
// Delete the resource that is held by the iterator.
template <class ResourceType>
void DeleteHeldResource(void* arg, void* ignored) {
delete reinterpret_cast<ResourceType*>(arg);
}
// Delete the entry resided in the cache.
template <class Entry>
void DeleteCachedEntry(const Slice& key, void* value) {
auto entry = reinterpret_cast<Entry*>(value);
delete entry;
}
// Release the cached entry and decrement its ref count.
void ReleaseCachedEntry(void* arg, void* h) {
Cache* cache = reinterpret_cast<Cache*>(arg);
Cache::Handle* handle = reinterpret_cast<Cache::Handle*>(h);
cache->Release(handle);
}
Slice GetCacheKey(const char* cache_key_prefix, size_t cache_key_prefix_size,
const BlockHandle& handle, char* cache_key) {
assert(cache_key != nullptr);
assert(cache_key_prefix_size != 0);
assert(cache_key_prefix_size <= kMaxCacheKeyPrefixSize);
memcpy(cache_key, cache_key_prefix, cache_key_prefix_size);
char* end =
EncodeVarint64(cache_key + cache_key_prefix_size, handle.offset());
return Slice(cache_key, static_cast<size_t>(end - cache_key));
}
Cache::Handle* GetEntryFromCache(Cache* block_cache, const Slice& key,
Tickers block_cache_miss_ticker,
Tickers block_cache_hit_ticker,
Statistics* statistics) {
auto cache_handle = block_cache->Lookup(key);
if (cache_handle != nullptr) {
PERF_COUNTER_ADD(block_cache_hit_count, 1);
// overall cache hit
RecordTick(statistics, BLOCK_CACHE_HIT);
// block-type specific cache hit
RecordTick(statistics, block_cache_hit_ticker);
} else {
// overall cache miss
RecordTick(statistics, BLOCK_CACHE_MISS);
// block-type specific cache miss
RecordTick(statistics, block_cache_miss_ticker);
}
return cache_handle;
}
} // namespace
// -- IndexReader and its subclasses
// IndexReader is the interface that provide the functionality for index access.
class BlockBasedTable::IndexReader {
public:
explicit IndexReader(const Comparator* comparator)
: comparator_(comparator) {}
virtual ~IndexReader() {}
// Create an iterator for index access.
virtual Iterator* NewIterator() = 0;
// The size of the index.
virtual size_t size() const = 0;
protected:
const Comparator* comparator_;
};
// Index that allows binary search lookup for the first key of each block.
// This class can be viewed as a thin wrapper for `Block` class which already
// supports binary search.
class BinarySearchIndexReader : public IndexReader {
public:
// Read index from the file and create an intance for
// `BinarySearchIndexReader`.
// On success, index_reader will be populated; otherwise it will remain
// unmodified.
static Status Create(RandomAccessFile* file, const Footer& footer,
const BlockHandle& index_handle, Env* env,
const Comparator* comparator,
IndexReader** index_reader) {
Block* index_block = nullptr;
auto s = ReadBlockFromFile(file, footer, ReadOptions(), index_handle,
&index_block, env);
if (s.ok()) {
*index_reader = new BinarySearchIndexReader(comparator, index_block);
}
return s;
}
virtual Iterator* NewIterator() override {
return index_block_->NewIterator(comparator_);
}
virtual size_t size() const override { return index_block_->size(); }
private:
BinarySearchIndexReader(const Comparator* comparator, Block* index_block)
: IndexReader(comparator), index_block_(index_block) {
assert(index_block_ != nullptr);
}
std::unique_ptr<Block> index_block_;
};
// Index that leverages an internal hash table to quicken the lookup for a given
// key.
class HashIndexReader : public IndexReader {
public:
static Status Create(const SliceTransform* hash_key_extractor,
const Footer& footer, RandomAccessFile* file, Env* env,
const Comparator* comparator,
const BlockHandle& index_handle,
Iterator* meta_index_iter, IndexReader** index_reader,
bool hash_index_allow_collision) {
Block* index_block = nullptr;
auto s = ReadBlockFromFile(file, footer, ReadOptions(), index_handle,
&index_block, env);
if (!s.ok()) {
return s;
}
// Note, failure to create prefix hash index does not need to be a
// hard error. We can still fall back to the original binary search index.
// So, Create will succeed regardless, from this point on.
auto new_index_reader =
new HashIndexReader(comparator, index_block);
*index_reader = new_index_reader;
// Get prefixes block
BlockHandle prefixes_handle;
s = FindMetaBlock(meta_index_iter, kHashIndexPrefixesBlock,
&prefixes_handle);
if (!s.ok()) {
// TODO: log error
return Status::OK();
}
// Get index metadata block
BlockHandle prefixes_meta_handle;
s = FindMetaBlock(meta_index_iter, kHashIndexPrefixesMetadataBlock,
&prefixes_meta_handle);
if (!s.ok()) {
// TODO: log error
return Status::OK();
}
// Read contents for the blocks
BlockContents prefixes_contents;
s = ReadBlockContents(file, footer, ReadOptions(), prefixes_handle,
&prefixes_contents, env, true /* do decompression */);
if (!s.ok()) {
return s;
}
BlockContents prefixes_meta_contents;
s = ReadBlockContents(file, footer, ReadOptions(), prefixes_meta_handle,
&prefixes_meta_contents, env,
true /* do decompression */);
if (!s.ok()) {
if (prefixes_contents.heap_allocated) {
delete[] prefixes_contents.data.data();
}
// TODO: log error
return Status::OK();
}
if (!hash_index_allow_collision) {
// TODO: deprecate once hash_index_allow_collision proves to be stable.
BlockHashIndex* hash_index = nullptr;
s = CreateBlockHashIndex(hash_key_extractor,
prefixes_contents.data,
prefixes_meta_contents.data,
&hash_index);
// TODO: log error
if (s.ok()) {
new_index_reader->index_block_->SetBlockHashIndex(hash_index);
new_index_reader->OwnPrefixesContents(prefixes_contents);
}
} else {
BlockPrefixIndex* prefix_index = nullptr;
s = BlockPrefixIndex::Create(hash_key_extractor,
prefixes_contents.data,
prefixes_meta_contents.data,
&prefix_index);
// TODO: log error
if (s.ok()) {
new_index_reader->index_block_->SetBlockPrefixIndex(prefix_index);
}
}
// Always release prefix meta block
if (prefixes_meta_contents.heap_allocated) {
delete[] prefixes_meta_contents.data.data();
}
// Release prefix content block if we don't own it.
if (!new_index_reader->own_prefixes_contents_) {
if (prefixes_contents.heap_allocated) {
delete[] prefixes_contents.data.data();
}
}
return Status::OK();
}
virtual Iterator* NewIterator() override {
return index_block_->NewIterator(comparator_);
}
virtual size_t size() const override { return index_block_->size(); }
private:
HashIndexReader(const Comparator* comparator, Block* index_block)
: IndexReader(comparator),
index_block_(index_block),
own_prefixes_contents_(false) {
assert(index_block_ != nullptr);
}
~HashIndexReader() {
if (own_prefixes_contents_ && prefixes_contents_.heap_allocated) {
delete[] prefixes_contents_.data.data();
}
}
void OwnPrefixesContents(const BlockContents& prefixes_contents) {
prefixes_contents_ = prefixes_contents;
own_prefixes_contents_ = true;
}
std::unique_ptr<Block> index_block_;
bool own_prefixes_contents_;
BlockContents prefixes_contents_;
};
struct BlockBasedTable::Rep {
Rep(const EnvOptions& storage_options,
const InternalKeyComparator& internal_comparator)
: soptions(storage_options), internal_comparator(internal_comparator) {}
Options options;
const EnvOptions& soptions;
const InternalKeyComparator& internal_comparator;
Status status;
unique_ptr<RandomAccessFile> file;
char cache_key_prefix[kMaxCacheKeyPrefixSize];
size_t cache_key_prefix_size = 0;
char compressed_cache_key_prefix[kMaxCacheKeyPrefixSize];
size_t compressed_cache_key_prefix_size = 0;
// Footer contains the fixed table information
Footer footer;
// index_reader and filter will be populated and used only when
// options.block_cache is nullptr; otherwise we will get the index block via
// the block cache.
unique_ptr<IndexReader> index_reader;
unique_ptr<FilterBlockReader> filter;
std::shared_ptr<const TableProperties> table_properties;
BlockBasedTableOptions::IndexType index_type;
bool hash_index_allow_collision;
// TODO(kailiu) It is very ugly to use internal key in table, since table
// module should not be relying on db module. However to make things easier
// and compatible with existing code, we introduce a wrapper that allows
// block to extract prefix without knowing if a key is internal or not.
unique_ptr<SliceTransform> internal_prefix_transform;
};
BlockBasedTable::~BlockBasedTable() {
delete rep_;
}
// CachableEntry represents the entries that *may* be fetched from block cache.
// field `value` is the item we want to get.
// field `cache_handle` is the cache handle to the block cache. If the value
// was not read from cache, `cache_handle` will be nullptr.
template <class TValue>
struct BlockBasedTable::CachableEntry {
CachableEntry(TValue* value, Cache::Handle* cache_handle)
: value(value)
, cache_handle(cache_handle) {
}
CachableEntry(): CachableEntry(nullptr, nullptr) { }
void Release(Cache* cache) {
if (cache_handle) {
cache->Release(cache_handle);
value = nullptr;
cache_handle = nullptr;
}
}
TValue* value = nullptr;
// if the entry is from the cache, cache_handle will be populated.
Cache::Handle* cache_handle = nullptr;
};
// Helper function to setup the cache key's prefix for the Table.
void BlockBasedTable::SetupCacheKeyPrefix(Rep* rep) {
assert(kMaxCacheKeyPrefixSize >= 10);
rep->cache_key_prefix_size = 0;
rep->compressed_cache_key_prefix_size = 0;
if (rep->options.block_cache != nullptr) {
GenerateCachePrefix(rep->options.block_cache.get(), rep->file.get(),
&rep->cache_key_prefix[0],
&rep->cache_key_prefix_size);
}
if (rep->options.block_cache_compressed != nullptr) {
GenerateCachePrefix(rep->options.block_cache_compressed.get(),
rep->file.get(), &rep->compressed_cache_key_prefix[0],
&rep->compressed_cache_key_prefix_size);
}
}
void BlockBasedTable::GenerateCachePrefix(Cache* cc,
RandomAccessFile* file, char* buffer, size_t* size) {
// generate an id from the file
*size = file->GetUniqueId(buffer, kMaxCacheKeyPrefixSize);
// If the prefix wasn't generated or was too long,
// create one from the cache.
if (*size == 0) {
char* end = EncodeVarint64(buffer, cc->NewId());
*size = static_cast<size_t>(end - buffer);
}
}
void BlockBasedTable::GenerateCachePrefix(Cache* cc,
WritableFile* file, char* buffer, size_t* size) {
// generate an id from the file
*size = file->GetUniqueId(buffer, kMaxCacheKeyPrefixSize);
// If the prefix wasn't generated or was too long,
// create one from the cache.
if (*size == 0) {
char* end = EncodeVarint64(buffer, cc->NewId());
*size = static_cast<size_t>(end - buffer);
}
}
Status BlockBasedTable::Open(const Options& options, const EnvOptions& soptions,
const BlockBasedTableOptions& table_options,
const InternalKeyComparator& internal_comparator,
unique_ptr<RandomAccessFile>&& file,
uint64_t file_size,
unique_ptr<TableReader>* table_reader) {
table_reader->reset();
Footer footer(kBlockBasedTableMagicNumber);
auto s = ReadFooterFromFile(file.get(), file_size, &footer);
if (!s.ok()) return s;
// We've successfully read the footer and the index block: we're
// ready to serve requests.
Rep* rep = new BlockBasedTable::Rep(soptions, internal_comparator);
rep->options = options;
rep->file = std::move(file);
rep->footer = footer;
rep->index_type = table_options.index_type;
rep->hash_index_allow_collision = table_options.hash_index_allow_collision;
SetupCacheKeyPrefix(rep);
unique_ptr<BlockBasedTable> new_table(new BlockBasedTable(rep));
// Read meta index
std::unique_ptr<Block> meta;
std::unique_ptr<Iterator> meta_iter;
s = ReadMetaBlock(rep, &meta, &meta_iter);
// Read the properties
bool found_properties_block = true;
s = SeekToPropertiesBlock(meta_iter.get(), &found_properties_block);
if (found_properties_block) {
s = meta_iter->status();
TableProperties* table_properties = nullptr;
if (s.ok()) {
s = ReadProperties(meta_iter->value(), rep->file.get(), rep->footer,
rep->options.env, rep->options.info_log.get(),
&table_properties);
}
if (!s.ok()) {
auto err_msg =
"[Warning] Encountered error while reading data from properties "
"block " + s.ToString();
Log(rep->options.info_log, "%s", err_msg.c_str());
} else {
rep->table_properties.reset(table_properties);
}
} else {
Log(WARN_LEVEL, rep->options.info_log,
"Cannot find Properties block from file.");
}
// Will use block cache for index/filter blocks access?
if (options.block_cache && table_options.cache_index_and_filter_blocks) {
// Hack: Call NewIndexIterator() to implicitly add index to the block_cache
unique_ptr<Iterator> iter(new_table->NewIndexIterator(ReadOptions()));
s = iter->status();
if (s.ok()) {
// Hack: Call GetFilter() to implicitly add filter to the block_cache
auto filter_entry = new_table->GetFilter();
filter_entry.Release(options.block_cache.get());
}
} else {
// If we don't use block cache for index/filter blocks access, we'll
// pre-load these blocks, which will kept in member variables in Rep
// and with a same life-time as this table object.
IndexReader* index_reader = nullptr;
// TODO: we never really verify check sum for index block
s = new_table->CreateIndexReader(&index_reader, meta_iter.get());
if (s.ok()) {
rep->index_reader.reset(index_reader);
// Set filter block
if (rep->options.filter_policy) {
std::string key = kFilterBlockPrefix;
key.append(rep->options.filter_policy->Name());
BlockHandle handle;
if (FindMetaBlock(meta_iter.get(), key, &handle).ok()) {
rep->filter.reset(ReadFilter(handle, rep));
}
}
} else {
delete index_reader;
}
}
if (s.ok()) {
*table_reader = std::move(new_table);
}
return s;
}
void BlockBasedTable::SetupForCompaction() {
switch (rep_->options.access_hint_on_compaction_start) {
case Options::NONE:
break;
case Options::NORMAL:
rep_->file->Hint(RandomAccessFile::NORMAL);
break;
case Options::SEQUENTIAL:
rep_->file->Hint(RandomAccessFile::SEQUENTIAL);
break;
case Options::WILLNEED:
rep_->file->Hint(RandomAccessFile::WILLNEED);
break;
default:
assert(false);
}
compaction_optimized_ = true;
}
std::shared_ptr<const TableProperties> BlockBasedTable::GetTableProperties()
const {
return rep_->table_properties;
}
// Load the meta-block from the file. On success, return the loaded meta block
// and its iterator.
Status BlockBasedTable::ReadMetaBlock(
Rep* rep,
std::unique_ptr<Block>* meta_block,
std::unique_ptr<Iterator>* iter) {
// TODO(sanjay): Skip this if footer.metaindex_handle() size indicates
// it is an empty block.
// TODO: we never really verify check sum for meta index block
Block* meta = nullptr;
Status s = ReadBlockFromFile(
rep->file.get(),
rep->footer,
ReadOptions(),
rep->footer.metaindex_handle(),
&meta,
rep->options.env);
if (!s.ok()) {
auto err_msg =
"[Warning] Encountered error while reading data from properties"
"block " + s.ToString();
Log(rep->options.info_log, "%s", err_msg.c_str());
}
if (!s.ok()) {
delete meta;
return s;
}
meta_block->reset(meta);
// meta block uses bytewise comparator.
iter->reset(meta->NewIterator(BytewiseComparator()));
return Status::OK();
}
Status BlockBasedTable::GetDataBlockFromCache(
const Slice& block_cache_key, const Slice& compressed_block_cache_key,
Cache* block_cache, Cache* block_cache_compressed, Statistics* statistics,
const ReadOptions& read_options,
BlockBasedTable::CachableEntry<Block>* block) {
Status s;
Block* compressed_block = nullptr;
Cache::Handle* block_cache_compressed_handle = nullptr;
// Lookup uncompressed cache first
if (block_cache != nullptr) {
block->cache_handle =
GetEntryFromCache(block_cache, block_cache_key, BLOCK_CACHE_DATA_MISS,
BLOCK_CACHE_DATA_HIT, statistics);
if (block->cache_handle != nullptr) {
block->value =
reinterpret_cast<Block*>(block_cache->Value(block->cache_handle));
return s;
}
}
// If not found, search from the compressed block cache.
assert(block->cache_handle == nullptr && block->value == nullptr);
if (block_cache_compressed == nullptr) {
return s;
}
assert(!compressed_block_cache_key.empty());
block_cache_compressed_handle =
block_cache_compressed->Lookup(compressed_block_cache_key);
// if we found in the compressed cache, then uncompress and insert into
// uncompressed cache
if (block_cache_compressed_handle == nullptr) {
RecordTick(statistics, BLOCK_CACHE_COMPRESSED_MISS);
return s;
}
// found compressed block
RecordTick(statistics, BLOCK_CACHE_COMPRESSED_HIT);
compressed_block = reinterpret_cast<Block*>(
block_cache_compressed->Value(block_cache_compressed_handle));
assert(compressed_block->compression_type() != kNoCompression);
// Retrieve the uncompressed contents into a new buffer
BlockContents contents;
s = UncompressBlockContents(compressed_block->data(),
compressed_block->size(), &contents);
// Insert uncompressed block into block cache
if (s.ok()) {
block->value = new Block(contents); // uncompressed block
assert(block->value->compression_type() == kNoCompression);
if (block_cache != nullptr && block->value->cachable() &&
read_options.fill_cache) {
block->cache_handle =
block_cache->Insert(block_cache_key, block->value,
block->value->size(), &DeleteCachedEntry<Block>);
assert(reinterpret_cast<Block*>(
block_cache->Value(block->cache_handle)) == block->value);
}
}
// Release hold on compressed cache entry
block_cache_compressed->Release(block_cache_compressed_handle);
return s;
}
Status BlockBasedTable::PutDataBlockToCache(
const Slice& block_cache_key, const Slice& compressed_block_cache_key,
Cache* block_cache, Cache* block_cache_compressed,
const ReadOptions& read_options, Statistics* statistics,
CachableEntry<Block>* block, Block* raw_block) {
assert(raw_block->compression_type() == kNoCompression ||
block_cache_compressed != nullptr);
Status s;
// Retrieve the uncompressed contents into a new buffer
BlockContents contents;
if (raw_block->compression_type() != kNoCompression) {
s = UncompressBlockContents(raw_block->data(), raw_block->size(),
&contents);
}
if (!s.ok()) {
delete raw_block;
return s;
}
if (raw_block->compression_type() != kNoCompression) {
block->value = new Block(contents); // uncompressed block
} else {
block->value = raw_block;
raw_block = nullptr;
}
// Insert compressed block into compressed block cache.
// Release the hold on the compressed cache entry immediately.
if (block_cache_compressed != nullptr && raw_block != nullptr &&
raw_block->cachable()) {
auto cache_handle = block_cache_compressed->Insert(
compressed_block_cache_key, raw_block, raw_block->size(),
&DeleteCachedEntry<Block>);
block_cache_compressed->Release(cache_handle);
RecordTick(statistics, BLOCK_CACHE_COMPRESSED_MISS);
// Avoid the following code to delete this cached block.
raw_block = nullptr;
}
delete raw_block;
// insert into uncompressed block cache
assert((block->value->compression_type() == kNoCompression));
if (block_cache != nullptr && block->value->cachable()) {
block->cache_handle =
block_cache->Insert(block_cache_key, block->value, block->value->size(),
&DeleteCachedEntry<Block>);
RecordTick(statistics, BLOCK_CACHE_ADD);
assert(reinterpret_cast<Block*>(block_cache->Value(block->cache_handle)) ==
block->value);
}
return s;
}
FilterBlockReader* BlockBasedTable::ReadFilter(const BlockHandle& filter_handle,
BlockBasedTable::Rep* rep,
size_t* filter_size) {
// TODO: We might want to unify with ReadBlockFromFile() if we start
// requiring checksum verification in Table::Open.
ReadOptions opt;
BlockContents block;
if (!ReadBlockContents(rep->file.get(), rep->footer, opt, filter_handle,
&block, rep->options.env, false).ok()) {
return nullptr;
}
if (filter_size) {
*filter_size = block.data.size();
}
return new FilterBlockReader(
rep->options, block.data, block.heap_allocated);
}
BlockBasedTable::CachableEntry<FilterBlockReader> BlockBasedTable::GetFilter(
bool no_io) const {
// filter pre-populated
if (rep_->filter != nullptr) {
return {rep_->filter.get(), nullptr /* cache handle */};
}
if (rep_->options.filter_policy == nullptr /* do not use filter at all */ ||
rep_->options.block_cache == nullptr /* no block cache at all */) {
return {nullptr /* filter */, nullptr /* cache handle */};
}
// Fetching from the cache
Cache* block_cache = rep_->options.block_cache.get();
char cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
auto key = GetCacheKey(
rep_->cache_key_prefix,
rep_->cache_key_prefix_size,
rep_->footer.metaindex_handle(),
cache_key
);
Statistics* statistics = rep_->options.statistics.get();
auto cache_handle =
GetEntryFromCache(block_cache, key, BLOCK_CACHE_FILTER_MISS,
BLOCK_CACHE_FILTER_HIT, statistics);
FilterBlockReader* filter = nullptr;
if (cache_handle != nullptr) {
filter = reinterpret_cast<FilterBlockReader*>(
block_cache->Value(cache_handle));
} else if (no_io) {
// Do not invoke any io.
return CachableEntry<FilterBlockReader>();
} else {
size_t filter_size = 0;
std::unique_ptr<Block> meta;
std::unique_ptr<Iterator> iter;
auto s = ReadMetaBlock(rep_, &meta, &iter);
if (s.ok()) {
std::string filter_block_key = kFilterBlockPrefix;
filter_block_key.append(rep_->options.filter_policy->Name());
BlockHandle handle;
if (FindMetaBlock(iter.get(), filter_block_key, &handle).ok()) {
filter = ReadFilter(handle, rep_, &filter_size);
assert(filter);
assert(filter_size > 0);
cache_handle = block_cache->Insert(
key, filter, filter_size, &DeleteCachedEntry<FilterBlockReader>);
RecordTick(statistics, BLOCK_CACHE_ADD);
}
}
}
return { filter, cache_handle };
}
Iterator* BlockBasedTable::NewIndexIterator(const ReadOptions& read_options) {
// index reader has already been pre-populated.
if (rep_->index_reader) {
return rep_->index_reader->NewIterator();
}
bool no_io = read_options.read_tier == kBlockCacheTier;
Cache* block_cache = rep_->options.block_cache.get();
char cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
auto key = GetCacheKey(rep_->cache_key_prefix, rep_->cache_key_prefix_size,
rep_->footer.index_handle(), cache_key);
Statistics* statistics = rep_->options.statistics.get();
auto cache_handle =
GetEntryFromCache(block_cache, key, BLOCK_CACHE_INDEX_MISS,
BLOCK_CACHE_INDEX_HIT, statistics);
if (cache_handle == nullptr && no_io) {
return NewErrorIterator(Status::Incomplete("no blocking io"));
}
IndexReader* index_reader = nullptr;
if (cache_handle != nullptr) {
index_reader =
reinterpret_cast<IndexReader*>(block_cache->Value(cache_handle));
} else {
// Create index reader and put it in the cache.
Status s;
s = CreateIndexReader(&index_reader);
if (!s.ok()) {
// make sure if something goes wrong, index_reader shall remain intact.
assert(index_reader == nullptr);
return NewErrorIterator(s);
}
cache_handle = block_cache->Insert(key, index_reader, index_reader->size(),
&DeleteCachedEntry<IndexReader>);
RecordTick(statistics, BLOCK_CACHE_ADD);
}
assert(cache_handle);
auto iter = index_reader->NewIterator();
iter->RegisterCleanup(&ReleaseCachedEntry, block_cache, cache_handle);
return iter;
}
// Convert an index iterator value (i.e., an encoded BlockHandle)
// into an iterator over the contents of the corresponding block.
Iterator* BlockBasedTable::NewDataBlockIterator(Rep* rep,
const ReadOptions& ro, const Slice& index_value) {
const bool no_io = (ro.read_tier == kBlockCacheTier);
Cache* block_cache = rep->options.block_cache.get();
Cache* block_cache_compressed = rep->options.
block_cache_compressed.get();
CachableEntry<Block> block;
BlockHandle handle;
Slice input = index_value;
// We intentionally allow extra stuff in index_value so that we
// can add more features in the future.
Status s = handle.DecodeFrom(&input);
if (!s.ok()) {
return NewErrorIterator(s);
}
// If either block cache is enabled, we'll try to read from it.
if (block_cache != nullptr || block_cache_compressed != nullptr) {
Statistics* statistics = rep->options.statistics.get();
char cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
char compressed_cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
Slice key, /* key to the block cache */
ckey /* key to the compressed block cache */;
// create key for block cache
if (block_cache != nullptr) {
key = GetCacheKey(rep->cache_key_prefix,
rep->cache_key_prefix_size, handle, cache_key);
}
if (block_cache_compressed != nullptr) {
ckey = GetCacheKey(rep->compressed_cache_key_prefix,
rep->compressed_cache_key_prefix_size, handle,
compressed_cache_key);
}
s = GetDataBlockFromCache(key, ckey, block_cache, block_cache_compressed,
statistics, ro, &block);
if (block.value == nullptr && !no_io && ro.fill_cache) {
Block* raw_block = nullptr;
{
StopWatch sw(rep->options.env, statistics, READ_BLOCK_GET_MICROS);
s = ReadBlockFromFile(rep->file.get(), rep->footer, ro, handle,
&raw_block, rep->options.env,
block_cache_compressed == nullptr);
}
if (s.ok()) {
s = PutDataBlockToCache(key, ckey, block_cache, block_cache_compressed,
ro, statistics, &block, raw_block);
}
}
}
// Didn't get any data from block caches.
if (block.value == nullptr) {
if (no_io) {
// Could not read from block_cache and can't do IO
return NewErrorIterator(Status::Incomplete("no blocking io"));
}
s = ReadBlockFromFile(rep->file.get(), rep->footer, ro, handle,
&block.value, rep->options.env);
}
Iterator* iter;
if (block.value != nullptr) {
iter = block.value->NewIterator(&rep->internal_comparator);
if (block.cache_handle != nullptr) {
iter->RegisterCleanup(&ReleaseCachedEntry, block_cache,
block.cache_handle);
} else {
iter->RegisterCleanup(&DeleteHeldResource<Block>, block.value, nullptr);
}
} else {
iter = NewErrorIterator(s);
}
return iter;
}
class BlockBasedTable::BlockEntryIteratorState : public TwoLevelIteratorState {
public:
BlockEntryIteratorState(BlockBasedTable* table,
const ReadOptions& read_options)
: TwoLevelIteratorState(table->rep_->options.prefix_extractor != nullptr),
table_(table),
read_options_(read_options) {}
Iterator* NewSecondaryIterator(const Slice& index_value) override {
return NewDataBlockIterator(table_->rep_, read_options_, index_value);
}
bool PrefixMayMatch(const Slice& internal_key) override {
return table_->PrefixMayMatch(internal_key);
}
private:
// Don't own table_
BlockBasedTable* table_;
const ReadOptions read_options_;
};
// This will be broken if the user specifies an unusual implementation
// of Options.comparator, or if the user specifies an unusual
// definition of prefixes in Options.filter_policy. In particular, we
// require the following three properties:
//
// 1) key.starts_with(prefix(key))
// 2) Compare(prefix(key), key) <= 0.
// 3) If Compare(key1, key2) <= 0, then Compare(prefix(key1), prefix(key2)) <= 0
//
// Otherwise, this method guarantees no I/O will be incurred.
//
// REQUIRES: this method shouldn't be called while the DB lock is held.
bool BlockBasedTable::PrefixMayMatch(const Slice& internal_key) {
if (!rep_->options.filter_policy) {
return true;
}
assert(rep_->options.prefix_extractor != nullptr);
auto prefix = rep_->options.prefix_extractor->Transform(
ExtractUserKey(internal_key));
InternalKey internal_key_prefix(prefix, 0, kTypeValue);
auto internal_prefix = internal_key_prefix.Encode();
bool may_match = true;
Status s;
// To prevent any io operation in this method, we set `read_tier` to make
// sure we always read index or filter only when they have already been
// loaded to memory.
ReadOptions no_io_read_options;
no_io_read_options.read_tier = kBlockCacheTier;
unique_ptr<Iterator> iiter(NewIndexIterator(no_io_read_options));
iiter->Seek(internal_prefix);
if (!iiter->Valid()) {
// we're past end of file
// if it's incomplete, it means that we avoided I/O
// and we're not really sure that we're past the end
// of the file
may_match = iiter->status().IsIncomplete();
} else if (ExtractUserKey(iiter->key()).starts_with(
ExtractUserKey(internal_prefix))) {
// we need to check for this subtle case because our only
// guarantee is that "the key is a string >= last key in that data
// block" according to the doc/table_format.txt spec.
//
// Suppose iiter->key() starts with the desired prefix; it is not
// necessarily the case that the corresponding data block will
// contain the prefix, since iiter->key() need not be in the
// block. However, the next data block may contain the prefix, so
// we return true to play it safe.
may_match = true;
} else {
// iiter->key() does NOT start with the desired prefix. Because
// Seek() finds the first key that is >= the seek target, this
// means that iiter->key() > prefix. Thus, any data blocks coming
// after the data block corresponding to iiter->key() cannot
// possibly contain the key. Thus, the corresponding data block
// is the only one which could potentially contain the prefix.
Slice handle_value = iiter->value();
BlockHandle handle;
s = handle.DecodeFrom(&handle_value);
assert(s.ok());
auto filter_entry = GetFilter(true /* no io */);
may_match =
filter_entry.value == nullptr ||
filter_entry.value->PrefixMayMatch(handle.offset(), internal_prefix);
filter_entry.Release(rep_->options.block_cache.get());
}
Statistics* statistics = rep_->options.statistics.get();
RecordTick(statistics, BLOOM_FILTER_PREFIX_CHECKED);
if (!may_match) {
RecordTick(statistics, BLOOM_FILTER_PREFIX_USEFUL);
}
return may_match;
}
Iterator* BlockBasedTable::NewIterator(const ReadOptions& read_options,
Arena* arena) {
return NewTwoLevelIterator(new BlockEntryIteratorState(this, read_options),
NewIndexIterator(read_options), arena);
}
Status BlockBasedTable::Get(
const ReadOptions& read_options, const Slice& key, void* handle_context,
bool (*result_handler)(void* handle_context, const ParsedInternalKey& k,
const Slice& v),
void (*mark_key_may_exist_handler)(void* handle_context)) {
Status s;
Iterator* iiter = NewIndexIterator(read_options);
auto filter_entry = GetFilter(read_options.read_tier == kBlockCacheTier);
FilterBlockReader* filter = filter_entry.value;
bool done = false;
for (iiter->Seek(key); iiter->Valid() && !done; iiter->Next()) {
Slice handle_value = iiter->value();
BlockHandle handle;
bool may_not_exist_in_filter =
filter != nullptr &&
handle.DecodeFrom(&handle_value).ok() &&
!filter->KeyMayMatch(handle.offset(), key);
if (may_not_exist_in_filter) {
// Not found
// TODO: think about interaction with Merge. If a user key cannot
// cross one data block, we should be fine.
RecordTick(rep_->options.statistics.get(), BLOOM_FILTER_USEFUL);
break;
} else {
unique_ptr<Iterator> block_iter(
NewDataBlockIterator(rep_, read_options, iiter->value()));
if (read_options.read_tier && block_iter->status().IsIncomplete()) {
// couldn't get block from block_cache
// Update Saver.state to Found because we are only looking for whether
// we can guarantee the key is not there when "no_io" is set
(*mark_key_may_exist_handler)(handle_context);
break;
}
// Call the *saver function on each entry/block until it returns false
for (block_iter->Seek(key); block_iter->Valid(); block_iter->Next()) {
ParsedInternalKey parsed_key;
if (!ParseInternalKey(block_iter->key(), &parsed_key)) {
s = Status::Corruption(Slice());
}
if (!(*result_handler)(handle_context, parsed_key,
block_iter->value())) {
done = true;
break;
}
}
s = block_iter->status();
}
}
filter_entry.Release(rep_->options.block_cache.get());
if (s.ok()) {
s = iiter->status();
}
delete iiter;
return s;
}
bool BlockBasedTable::TEST_KeyInCache(const ReadOptions& options,
const Slice& key) {
std::unique_ptr<Iterator> iiter(NewIndexIterator(options));
iiter->Seek(key);
assert(iiter->Valid());
CachableEntry<Block> block;
BlockHandle handle;
Slice input = iiter->value();
Status s = handle.DecodeFrom(&input);
assert(s.ok());
Cache* block_cache = rep_->options.block_cache.get();
assert(block_cache != nullptr);
char cache_key_storage[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
Slice cache_key =
GetCacheKey(rep_->cache_key_prefix, rep_->cache_key_prefix_size, handle,
cache_key_storage);
Slice ckey;
s = GetDataBlockFromCache(cache_key, ckey, block_cache, nullptr, nullptr,
options, &block);
assert(s.ok());
bool in_cache = block.value != nullptr;
if (in_cache) {
ReleaseCachedEntry(block_cache, block.cache_handle);
}
return in_cache;
}
// REQUIRES: The following fields of rep_ should have already been populated:
// 1. file
// 2. index_handle,
// 3. options
// 4. internal_comparator
// 5. index_type
Status BlockBasedTable::CreateIndexReader(IndexReader** index_reader,
Iterator* preloaded_meta_index_iter) {
// Some old version of block-based tables don't have index type present in
// table properties. If that's the case we can safely use the kBinarySearch.
auto index_type_on_file = BlockBasedTableOptions::kBinarySearch;
if (rep_->table_properties) {
auto& props = rep_->table_properties->user_collected_properties;
auto pos = props.find(BlockBasedTablePropertyNames::kIndexType);
if (pos != props.end()) {
index_type_on_file = static_cast<BlockBasedTableOptions::IndexType>(
DecodeFixed32(pos->second.c_str()));
}
}
auto file = rep_->file.get();
auto env = rep_->options.env;
auto comparator = &rep_->internal_comparator;
const Footer& footer = rep_->footer;
if (index_type_on_file == BlockBasedTableOptions::kHashSearch &&
rep_->options.prefix_extractor == nullptr) {
Log(rep_->options.info_log,
"BlockBasedTableOptions::kHashSearch requires "
"options.prefix_extractor to be set."
" Fall back to binary seach index.");
index_type_on_file = BlockBasedTableOptions::kBinarySearch;
}
switch (index_type_on_file) {
case BlockBasedTableOptions::kBinarySearch: {
return BinarySearchIndexReader::Create(
file, footer, footer.index_handle(), env, comparator, index_reader);
}
case BlockBasedTableOptions::kHashSearch: {
std::unique_ptr<Block> meta_guard;
std::unique_ptr<Iterator> meta_iter_guard;
auto meta_index_iter = preloaded_meta_index_iter;
if (meta_index_iter == nullptr) {
auto s = ReadMetaBlock(rep_, &meta_guard, &meta_iter_guard);
if (!s.ok()) {
// we simply fall back to binary search in case there is any
// problem with prefix hash index loading.
Log(rep_->options.info_log,
"Unable to read the metaindex block."
" Fall back to binary seach index.");
return BinarySearchIndexReader::Create(
file, footer, footer.index_handle(), env, comparator, index_reader);
}
meta_index_iter = meta_iter_guard.get();
}
// We need to wrap data with internal_prefix_transform to make sure it can
// handle prefix correctly.
rep_->internal_prefix_transform.reset(
new InternalKeySliceTransform(rep_->options.prefix_extractor.get()));
return HashIndexReader::Create(
rep_->internal_prefix_transform.get(), footer, file, env, comparator,
footer.index_handle(), meta_index_iter, index_reader,
rep_->hash_index_allow_collision);
}
default: {
std::string error_message =
"Unrecognized index type: " + std::to_string(rep_->index_type);
return Status::InvalidArgument(error_message.c_str());
}
}
}
uint64_t BlockBasedTable::ApproximateOffsetOf(const Slice& key) {
unique_ptr<Iterator> index_iter(NewIndexIterator(ReadOptions()));
index_iter->Seek(key);
uint64_t result;
if (index_iter->Valid()) {
BlockHandle handle;
Slice input = index_iter->value();
Status s = handle.DecodeFrom(&input);
if (s.ok()) {
result = handle.offset();
} else {
// Strange: we can't decode the block handle in the index block.
// We'll just return the offset of the metaindex block, which is
// close to the whole file size for this case.
result = rep_->footer.metaindex_handle().offset();
}
} else {
// key is past the last key in the file. If table_properties is not
// available, approximate the offset by returning the offset of the
// metaindex block (which is right near the end of the file).
result = 0;
if (rep_->table_properties) {
result = rep_->table_properties->data_size;
}
// table_properties is not present in the table.
if (result == 0) {
result = rep_->footer.metaindex_handle().offset();
}
}
return result;
}
bool BlockBasedTable::TEST_filter_block_preloaded() const {
return rep_->filter != nullptr;
}
bool BlockBasedTable::TEST_index_reader_preloaded() const {
return rep_->index_reader != nullptr;
}
} // namespace rocksdb
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