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rocksdb/table/block_based_table_reader.cc

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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 "table/block.h"
#include "table/filter_block.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 uint64_t kBlockBasedTableMagicNumber;
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.
// Set *didIO to true if didIO is not null.
// On failure return non-OK.
// On success fill *result and return OK - caller owns *result
Status ReadBlockFromFile(RandomAccessFile* file, const ReadOptions& options,
const BlockHandle& handle, Block** result, Env* env,
bool* didIO = nullptr, bool do_uncompress = true) {
BlockContents contents;
Status s =
ReadBlockContents(file, options, handle, &contents, env, do_uncompress);
if (s.ok()) {
*result = new Block(contents);
}
if (didIO != nullptr) {
*didIO = true;
}
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 BlockHandle& index_handle,
Env* env, const Comparator* comparator,
IndexReader** index_reader) {
Block* index_block = nullptr;
auto s = ReadBlockFromFile(file, 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_;
};
// TODO(kailiu) This class is only a stub for now. And the comment below is also
// not completed.
// Index that leverages an internal hash table to quicken the lookup for a given
// key.
class HashIndexReader : public IndexReader {
public:
static Status Create(RandomAccessFile* file, const BlockHandle& index_handle,
Env* env, const Comparator* comparator,
BlockBasedTable* table,
const SliceTransform* prefix_extractor,
IndexReader** index_reader) {
return Status::NotSupported("not implemented yet!");
}
};
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;
// Handle to metaindex_block: saved from footer
BlockHandle metaindex_handle;
// Handle to index: saved from footer
BlockHandle index_handle;
// 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;
};
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->metaindex_handle = footer.metaindex_handle();
rep->index_handle = footer.index_handle();
rep->index_type = table_options.index_type;
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
meta_iter->Seek(kPropertiesBlock);
if (meta_iter->Valid() && meta_iter->key() == kPropertiesBlock) {
s = meta_iter->status();
TableProperties* table_properties = nullptr;
if (s.ok()) {
s = ReadProperties(meta_iter->value(), rep->file.get(), 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);
}
}
// 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);
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());
meta_iter->Seek(key);
if (meta_iter->Valid() && meta_iter->key() == Slice(key)) {
rep->filter.reset(ReadFilter(meta_iter->value(), 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(),
ReadOptions(),
rep->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 Slice& filter_handle_value,
BlockBasedTable::Rep* rep,
size_t* filter_size) {
Slice v = filter_handle_value;
BlockHandle filter_handle;
if (!filter_handle.DecodeFrom(&v).ok()) {
return nullptr;
}
// 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(), 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);
}
// Convert an index iterator value (i.e., an encoded BlockHandle)
// into an iterator over the contents of the corresponding block.
Iterator* BlockBasedTable::DataBlockReader(void* arg,
const ReadOptions& options,
const Slice& index_value,
bool* didIO, bool for_compaction) {
const bool no_io = (options.read_tier == kBlockCacheTier);
BlockBasedTable* table = reinterpret_cast<BlockBasedTable*>(arg);
Cache* block_cache = table->rep_->options.block_cache.get();
Cache* block_cache_compressed = table->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 = table->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(table->rep_->cache_key_prefix,
table->rep_->cache_key_prefix_size, handle, cache_key);
}
if (block_cache_compressed != nullptr) {
ckey = GetCacheKey(table->rep_->compressed_cache_key_prefix,
table->rep_->compressed_cache_key_prefix_size, handle,
compressed_cache_key);
}
s = GetDataBlockFromCache(key, ckey, block_cache, block_cache_compressed,
statistics, options, &block);
if (block.value == nullptr && !no_io && options.fill_cache) {
Histograms histogram = for_compaction ?
READ_BLOCK_COMPACTION_MICROS : READ_BLOCK_GET_MICROS;
Block* raw_block = nullptr;
{
StopWatch sw(table->rep_->options.env, statistics, histogram);
s = ReadBlockFromFile(table->rep_->file.get(), options, handle,
&raw_block, table->rep_->options.env, didIO,
block_cache_compressed == nullptr);
}
if (s.ok()) {
s = PutDataBlockToCache(key, ckey, block_cache, block_cache_compressed,
options, 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(table->rep_->file.get(), options, handle,
&block.value, table->rep_->options.env, didIO);
}
Iterator* iter;
if (block.value != nullptr) {
iter = block.value->NewIterator(&table->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;
}
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_->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());
iter->Seek(filter_block_key);
if (iter->Valid() && iter->key() == Slice(filter_block_key)) {
filter = ReadFilter(iter->value(), 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)
const {
// 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_->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;
}
Iterator* BlockBasedTable::DataBlockReader(
void* arg, const ReadOptions& options, const EnvOptions& soptions,
const InternalKeyComparator& icomparator, const Slice& index_value,
bool for_compaction) {
return DataBlockReader(arg, options, index_value, nullptr, for_compaction);
}
// 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_prefix) {
bool may_match = true;
Status s;
if (!rep_->options.filter_policy) {
return true;
}
// 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& options) {
if (options.prefix) {
InternalKey internal_prefix(*options.prefix, 0, kTypeValue);
if (!PrefixMayMatch(internal_prefix.Encode())) {
// nothing in this file can match the prefix, so we should not
// bother doing I/O to this file when iterating.
return NewEmptyIterator();
}
}
return NewTwoLevelIterator(NewIndexIterator(options),
&BlockBasedTable::DataBlockReader,
const_cast<BlockBasedTable*>(this), options,
rep_->soptions, rep_->internal_comparator);
}
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, bool didIO),
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 {
bool didIO = false;
unique_ptr<Iterator> block_iter(
DataBlockReader(this, read_options, iiter->value(), &didIO));
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(),
didIO)) {
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;
}
namespace {
bool SaveDidIO(void* arg, const ParsedInternalKey& key, const Slice& value,
bool didIO) {
*reinterpret_cast<bool*>(arg) = didIO;
return false;
}
} // namespace
bool BlockBasedTable::TEST_KeyInCache(const ReadOptions& options,
const Slice& key) {
// We use Get() as it has logic that checks whether we read the
// block from the disk or not.
bool didIO = false;
Status s = Get(options, key, &didIO, SaveDidIO);
assert(s.ok());
return !didIO;
}
// 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) const {
// 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 = BlockBasedTableOptions::kBinarySearch;
auto& props = rep_->table_properties->user_collected_properties;
auto pos = props.find(BlockBasedTablePropertyNames::kIndexType);
if (pos != props.end()) {
index_type = static_cast<BlockBasedTableOptions::IndexType>(
DecodeFixed32(pos->second.c_str()));
}
switch (index_type) {
case BlockBasedTableOptions::kBinarySearch: {
return BinarySearchIndexReader::Create(
rep_->file.get(), rep_->index_handle, rep_->options.env,
&rep_->internal_comparator, index_reader);
}
default: {
std::string error_message =
"Unrecognized index type: " + std::to_string(rep_->index_type);
// equivalent to assert(false), but more informative.
assert(!error_message.c_str());
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_->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 = rep_->table_properties->data_size;
// table_properties is not present in the table.
if (result == 0) {
result = rep_->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