rocksdb/table/table.cc
Tyler Harter f5f1842282 Prefix filters for scans (v4)
Summary: Similar to v2 (db and table code understands prefixes), but use ReadOptions as in v3.  Also, make the CreateFilter code faster and cleaner.

Test Plan: make db_test; export LEVELDB_TESTS=PrefixScan; ./db_test

Reviewers: dhruba

Reviewed By: dhruba

CC: haobo, emayanke

Differential Revision: https://reviews.facebook.net/D12027
2013-08-13 14:04:56 -07:00

480 lines
16 KiB
C++

// 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/table.h"
#include "db/dbformat.h"
#include "leveldb/cache.h"
#include "leveldb/comparator.h"
#include "leveldb/env.h"
#include "leveldb/filter_policy.h"
#include "leveldb/options.h"
#include "leveldb/statistics.h"
#include "table/block.h"
#include "table/filter_block.h"
#include "table/format.h"
#include "table/two_level_iterator.h"
#include "util/coding.h"
#include "util/stop_watch.h"
namespace leveldb {
// 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.
const size_t kMaxCacheKeyPrefixSize = kMaxVarint64Length*3+1;
struct Table::Rep {
~Rep() {
delete filter;
delete [] filter_data;
delete index_block;
}
Rep(const EnvOptions& storage_options) :
soptions(storage_options) {
}
Options options;
const EnvOptions& soptions;
Status status;
unique_ptr<RandomAccessFile> file;
char cache_key_prefix[kMaxCacheKeyPrefixSize];
size_t cache_key_prefix_size;
FilterBlockReader* filter;
const char* filter_data;
BlockHandle metaindex_handle; // Handle to metaindex_block: saved from footer
Block* index_block;
};
// Helper function to setup the cache key's prefix for the Table.
void Table::SetupCacheKeyPrefix(Rep* rep) {
assert(kMaxCacheKeyPrefixSize >= 10);
rep->cache_key_prefix_size = 0;
if (rep->options.block_cache) {
rep->cache_key_prefix_size = rep->file->GetUniqueId(rep->cache_key_prefix,
kMaxCacheKeyPrefixSize);
if (rep->cache_key_prefix_size == 0) {
// If the prefix wasn't generated or was too long, we create one from the
// cache.
char* end = EncodeVarint64(rep->cache_key_prefix,
rep->options.block_cache->NewId());
rep->cache_key_prefix_size =
static_cast<size_t>(end - rep->cache_key_prefix);
}
}
}
namespace { // anonymous namespace, not visible externally
// 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 ReadBlock(RandomAccessFile* file,
const ReadOptions& options,
const BlockHandle& handle,
Block** result,
bool* didIO = nullptr) {
BlockContents contents;
Status s = ReadBlockContents(file, options, handle, &contents);
if (s.ok()) {
*result = new Block(contents);
}
if (didIO) {
*didIO = true;
}
return s;
}
} // end of anonymous namespace
Status Table::Open(const Options& options,
const EnvOptions& soptions,
unique_ptr<RandomAccessFile>&& file,
uint64_t size,
unique_ptr<Table>* table) {
table->reset();
if (size < Footer::kEncodedLength) {
return Status::InvalidArgument("file is too short to be an sstable");
}
char footer_space[Footer::kEncodedLength];
Slice footer_input;
Status s = file->Read(size - Footer::kEncodedLength, Footer::kEncodedLength,
&footer_input, footer_space);
if (!s.ok()) return s;
// Check that we actually read the whole footer from the file. It may be
// that size isn't correct.
if (footer_input.size() != Footer::kEncodedLength) {
return Status::InvalidArgument("file is too short to be an sstable");
}
Footer footer;
s = footer.DecodeFrom(&footer_input);
if (!s.ok()) return s;
Block* index_block = nullptr;
// TODO: we never really verify check sum for index block
s = ReadBlock(file.get(), ReadOptions(), footer.index_handle(), &index_block);
if (s.ok()) {
// We've successfully read the footer and the index block: we're
// ready to serve requests.
Rep* rep = new Table::Rep(soptions);
rep->options = options;
rep->file = std::move(file);
rep->metaindex_handle = footer.metaindex_handle();
rep->index_block = index_block;
SetupCacheKeyPrefix(rep);
rep->filter_data = nullptr;
rep->filter = nullptr;
table->reset(new Table(rep));
(*table)->ReadMeta(footer);
} else {
if (index_block) delete index_block;
}
return s;
}
void Table::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;
}
void Table::ReadMeta(const Footer& footer) {
if (rep_->options.filter_policy == nullptr) {
return; // Do not need any metadata
}
// 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;
if (!ReadBlock(rep_->file.get(), ReadOptions(), footer.metaindex_handle(),
&meta).ok()) {
// Do not propagate errors since meta info is not needed for operation
return;
}
Iterator* iter = meta->NewIterator(BytewiseComparator());
std::string key = "filter.";
key.append(rep_->options.filter_policy->Name());
iter->Seek(key);
if (iter->Valid() && iter->key() == Slice(key)) {
ReadFilter(iter->value());
}
delete iter;
delete meta;
}
void Table::ReadFilter(const Slice& filter_handle_value) {
Slice v = filter_handle_value;
BlockHandle filter_handle;
if (!filter_handle.DecodeFrom(&v).ok()) {
return;
}
// TODO: We might want to unify with ReadBlock() if we start
// requiring checksum verification in Table::Open.
ReadOptions opt;
BlockContents block;
if (!ReadBlockContents(rep_->file.get(), opt, filter_handle, &block).ok()) {
return;
}
if (block.heap_allocated) {
rep_->filter_data = block.data.data(); // Will need to delete later
}
rep_->filter = new FilterBlockReader(rep_->options, block.data);
}
Table::~Table() {
delete rep_;
}
static void DeleteBlock(void* arg, void* ignored) {
delete reinterpret_cast<Block*>(arg);
}
static void DeleteCachedBlock(const Slice& key, void* value) {
Block* block = reinterpret_cast<Block*>(value);
delete block;
}
static void ReleaseBlock(void* arg, void* h) {
Cache* cache = reinterpret_cast<Cache*>(arg);
Cache::Handle* handle = reinterpret_cast<Cache::Handle*>(h);
cache->Release(handle);
}
// Convert an index iterator value (i.e., an encoded BlockHandle)
// into an iterator over the contents of the corresponding block.
Iterator* Table::BlockReader(void* arg,
const ReadOptions& options,
const Slice& index_value,
bool* didIO,
bool for_compaction,
const bool no_io) {
Table* table = reinterpret_cast<Table*>(arg);
Cache* block_cache = table->rep_->options.block_cache.get();
std::shared_ptr<Statistics> statistics = table->rep_->options.statistics;
Block* block = nullptr;
Cache::Handle* cache_handle = nullptr;
BlockHandle handle;
Slice input = index_value;
Status s = handle.DecodeFrom(&input);
// We intentionally allow extra stuff in index_value so that we
// can add more features in the future.
if (s.ok()) {
if (block_cache != nullptr) {
char cache_key[kMaxCacheKeyPrefixSize + kMaxVarint64Length];
const size_t cache_key_prefix_size = table->rep_->cache_key_prefix_size;
assert(cache_key_prefix_size != 0);
assert(cache_key_prefix_size <= kMaxCacheKeyPrefixSize);
memcpy(cache_key, table->rep_->cache_key_prefix,
cache_key_prefix_size);
char* end = EncodeVarint64(cache_key + cache_key_prefix_size,
handle.offset());
Slice key(cache_key, static_cast<size_t>(end-cache_key));
cache_handle = block_cache->Lookup(key);
if (cache_handle != nullptr) {
block = reinterpret_cast<Block*>(block_cache->Value(cache_handle));
RecordTick(statistics, BLOCK_CACHE_HIT);
} else if (no_io) {
return nullptr; // Did not find in block_cache and can't do IO
} else {
Histograms histogram = for_compaction ?
READ_BLOCK_COMPACTION_MICROS : READ_BLOCK_GET_MICROS;
{ // block for stop watch
StopWatch sw(table->rep_->options.env, statistics, histogram);
s = ReadBlock(
table->rep_->file.get(),
options,
handle,
&block,
didIO
);
}
if (s.ok()) {
if (block->isCachable() && options.fill_cache) {
cache_handle = block_cache->Insert(
key, block, block->size(), &DeleteCachedBlock);
}
}
RecordTick(statistics, BLOCK_CACHE_MISS);
}
} else if (no_io) {
return nullptr; // Could not read from block_cache and can't do IO
}else {
s = ReadBlock(table->rep_->file.get(), options, handle, &block, didIO);
}
}
Iterator* iter;
if (block != nullptr) {
iter = block->NewIterator(table->rep_->options.comparator);
if (cache_handle == nullptr) {
iter->RegisterCleanup(&DeleteBlock, block, nullptr);
} else {
iter->RegisterCleanup(&ReleaseBlock, block_cache, cache_handle);
}
} else {
iter = NewErrorIterator(s);
}
return iter;
}
Iterator* Table::BlockReader(void* arg,
const ReadOptions& options,
const EnvOptions& soptions,
const Slice& index_value,
bool for_compaction) {
return BlockReader(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
bool Table::PrefixMayMatch(const Slice& internal_prefix) const {
FilterBlockReader* filter = rep_->filter;
bool may_match = true;
Status s;
if (filter == nullptr) {
return true;
}
Iterator* iiter = rep_->index_block->NewIterator(rep_->options.comparator);
iiter->Seek(internal_prefix);
if (! iiter->Valid()) {
// we're past end of file
may_match = false;
} else if (iiter->key().starts_with(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());
may_match = filter->PrefixMayMatch(handle.offset(), internal_prefix);
}
delete iiter;
return may_match;
}
Iterator* Table::NewIterator(const ReadOptions& options) const {
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(
rep_->index_block->NewIterator(rep_->options.comparator),
&Table::BlockReader, const_cast<Table*>(this), options, rep_->soptions);
}
Status Table::InternalGet(const ReadOptions& options, const Slice& k,
void* arg,
bool (*saver)(void*, const Slice&, const Slice&,
bool),
void (*mark_key_may_exist)(void*),
const bool no_io) {
Status s;
Iterator* iiter = rep_->index_block->NewIterator(rep_->options.comparator);
bool done = false;
for (iiter->Seek(k); iiter->Valid() && !done; iiter->Next()) {
Slice handle_value = iiter->value();
FilterBlockReader* filter = rep_->filter;
BlockHandle handle;
if (filter != nullptr &&
handle.DecodeFrom(&handle_value).ok() &&
!filter->KeyMayMatch(handle.offset(), k)) {
// 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, BLOOM_FILTER_USEFUL);
break;
} else {
bool didIO = false;
Iterator* block_iter = BlockReader(this, options, iiter->value(),
&didIO, no_io);
if (no_io && !block_iter) { // 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)(arg);
break;
}
// Call the *saver function on each entry/block until it returns false
for (block_iter->Seek(k); block_iter->Valid(); block_iter->Next()) {
if (!(*saver)(arg, block_iter->key(), block_iter->value(), didIO)) {
done = true;
break;
}
}
s = block_iter->status();
delete block_iter;
}
}
if (s.ok()) {
s = iiter->status();
}
delete iiter;
return s;
}
bool SaveDidIO(void* arg, const Slice& key, const Slice& value, bool didIO) {
*reinterpret_cast<bool*>(arg) = didIO;
return false;
}
bool Table::TEST_KeyInCache(const ReadOptions& options, const Slice& key) {
// We use InternalGet() as it has logic that checks whether we read the
// block from the disk or not.
bool didIO = false;
Status s = InternalGet(options, key, &didIO, SaveDidIO);
assert(s.ok());
return !didIO;
}
uint64_t Table::ApproximateOffsetOf(const Slice& key) const {
Iterator* index_iter =
rep_->index_block->NewIterator(rep_->options.comparator);
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. Approximate the offset
// by returning the offset of the metaindex block (which is
// right near the end of the file).
result = rep_->metaindex_handle.offset();
}
delete index_iter;
return result;
}
} // namespace leveldb