rocksdb/table/table.cc
Kosie van der Merwe 4dcc0c89f4 Fixed cache key for block cache
Summary:
Added function to `RandomAccessFile` to generate an unique ID for that file. Currently only `PosixRandomAccessFile` has this behaviour implemented and only on Linux.

Changed how key is generated in `Table::BlockReader`.

Added tests to check whether the unique ID is stable, unique and not a prefix of another unique ID. Added tests to see that `Table` uses the cache more efficiently.

Test Plan: make check

Reviewers: chip, vamsi, dhruba

Reviewed By: chip

CC: leveldb

Differential Revision: https://reviews.facebook.net/D8145
2013-01-31 15:20:24 -08:00

347 lines
11 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 "leveldb/table.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"
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;
}
Options options;
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);
}
}
}
Status Table::Open(const Options& options,
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;
// Read the index block
BlockContents contents;
Block* index_block = NULL;
if (s.ok()) {
s = ReadBlock(file.get(), ReadOptions(), footer.index_handle(), &contents);
if (s.ok()) {
index_block = new Block(contents);
}
}
if (s.ok()) {
// We've successfully read the footer and the index block: we're
// ready to serve requests.
Rep* rep = new Table::Rep;
rep->options = options;
rep->file = std::move(file);
rep->metaindex_handle = footer.metaindex_handle();
rep->index_block = index_block;
SetupCacheKeyPrefix(rep);
rep->filter_data = NULL;
rep->filter = NULL;
table->reset(new Table(rep));
(*table)->ReadMeta(footer);
} else {
if (index_block) delete index_block;
}
return s;
}
void Table::ReadMeta(const Footer& footer) {
if (rep_->options.filter_policy == NULL) {
return; // Do not need any metadata
}
// TODO(sanjay): Skip this if footer.metaindex_handle() size indicates
// it is an empty block.
ReadOptions opt;
BlockContents contents;
if (!ReadBlock(rep_->file.get(), opt, footer.metaindex_handle(),
&contents).ok()) {
// Do not propagate errors since meta info is not needed for operation
return;
}
Block* meta = new Block(contents);
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;
}
// We might want to unify with ReadBlock() if we start
// requiring checksum verification in Table::Open.
ReadOptions opt;
BlockContents block;
if (!ReadBlock(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.filter_policy, 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) {
Table* table = reinterpret_cast<Table*>(arg);
Cache* block_cache = table->rep_->options.block_cache.get();
Statistics* const statistics = table->rep_->options.statistics;
Block* block = NULL;
Cache::Handle* cache_handle = NULL;
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()) {
BlockContents contents;
if (block_cache != NULL) {
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 != NULL) {
block = reinterpret_cast<Block*>(block_cache->Value(cache_handle));
RecordTick(statistics, BLOCK_CACHE_HIT);
} else {
s = ReadBlock(table->rep_->file.get(), options, handle, &contents);
if (s.ok()) {
block = new Block(contents);
if (contents.cachable && options.fill_cache) {
cache_handle = block_cache->Insert(
key, block, block->size(), &DeleteCachedBlock);
}
}
if (didIO != NULL) {
*didIO = true; // we did some io from storage
}
RecordTick(statistics, BLOCK_CACHE_MISS);
}
} else {
s = ReadBlock(table->rep_->file.get(), options, handle, &contents);
if (s.ok()) {
block = new Block(contents);
}
if (didIO != NULL) {
*didIO = true; // we did some io from storage
}
}
}
Iterator* iter;
if (block != NULL) {
iter = block->NewIterator(table->rep_->options.comparator);
if (cache_handle == NULL) {
iter->RegisterCleanup(&DeleteBlock, block, NULL);
} else {
iter->RegisterCleanup(&ReleaseBlock, block_cache, cache_handle);
}
} else {
iter = NewErrorIterator(s);
}
return iter;
}
Iterator* Table::BlockReader(void* arg,
const ReadOptions& options,
const Slice& index_value) {
return BlockReader(arg, options, index_value, NULL);
}
Iterator* Table::NewIterator(const ReadOptions& options) const {
return NewTwoLevelIterator(
rep_->index_block->NewIterator(rep_->options.comparator),
&Table::BlockReader, const_cast<Table*>(this), options);
}
Status Table::InternalGet(const ReadOptions& options, const Slice& k,
void* arg,
void (*saver)(void*, const Slice&, const Slice&, bool)) {
Status s;
Iterator* iiter = rep_->index_block->NewIterator(rep_->options.comparator);
iiter->Seek(k);
if (iiter->Valid()) {
Slice handle_value = iiter->value();
FilterBlockReader* filter = rep_->filter;
BlockHandle handle;
if (filter != NULL &&
handle.DecodeFrom(&handle_value).ok() &&
!filter->KeyMayMatch(handle.offset(), k)) {
// Not found
RecordTick(rep_->options.statistics, BLOOM_FILTER_USEFUL);
} else {
bool didIO = false;
Iterator* block_iter = BlockReader(this, options, iiter->value(),
&didIO);
block_iter->Seek(k);
if (block_iter->Valid()) {
(*saver)(arg, block_iter->key(), block_iter->value(), didIO);
}
s = block_iter->status();
delete block_iter;
}
}
if (s.ok()) {
s = iiter->status();
}
delete iiter;
return s;
}
void SaveDidIO(void* arg, const Slice& key, const Slice& value, bool didIO) {
*reinterpret_cast<bool*>(arg) = didIO;
}
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