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rocksdb/util/blob_store.cc

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// 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 "util/blob_store.h"
namespace rocksdb {
using namespace std;
// BlobChunk
bool BlobChunk::ImmediatelyBefore(const BlobChunk& chunk) const {
// overlapping!?
assert(!Overlap(chunk));
// size == 0 is a marker, not a block
return size != 0 &&
bucket_id == chunk.bucket_id &&
offset + size == chunk.offset;
}
bool BlobChunk::Overlap(const BlobChunk &chunk) const {
return size != 0 && chunk.size != 0 && bucket_id == chunk.bucket_id &&
((offset >= chunk.offset && offset < chunk.offset + chunk.size) ||
(chunk.offset >= offset && chunk.offset < offset + size));
}
// Blob
string Blob::ToString() const {
string ret;
for (auto chunk : chunks) {
PutFixed32(&ret, chunk.bucket_id);
PutFixed32(&ret, chunk.offset);
PutFixed32(&ret, chunk.size);
}
return ret;
}
Blob::Blob(const std::string& blob) {
for (uint32_t i = 0; i < blob.size(); ) {
uint32_t t[3] = {0};
for (int j = 0; j < 3 && i + sizeof(uint32_t) - 1 < blob.size();
++j, i += sizeof(uint32_t)) {
t[j] = DecodeFixed32(blob.data() + i);
}
chunks.push_back(BlobChunk(t[0], t[1], t[2]));
}
}
// FreeList
FreeList::FreeList() {
// We add (0, 0, 0) blob because it makes our life easier and
// code cleaner. (0, 0, 0) is always in the list so we can
// guarantee that free_chunks_list_ != nullptr, which avoids
// lots of unnecessary ifs
free_chunks_list_ = (FreeChunk *)malloc(sizeof(FreeChunk));
free_chunks_list_->chunk = BlobChunk(0, 0, 0);
free_chunks_list_->next = nullptr;
}
FreeList::~FreeList() {
while (free_chunks_list_ != nullptr) {
FreeChunk* t = free_chunks_list_;
free_chunks_list_ = free_chunks_list_->next;
free(t);
}
}
Status FreeList::Free(const Blob& blob) {
MutexLock l(&mutex_);
// add it back to the free list
for (auto chunk : blob.chunks) {
FreeChunk* itr = free_chunks_list_;
// find a node AFTER which we'll add the block
for ( ; itr->next != nullptr && itr->next->chunk <= chunk;
itr = itr->next) {
}
// try to merge with previous block
if (itr->chunk.ImmediatelyBefore(chunk)) {
// merge
itr->chunk.size += chunk.size;
} else {
// Insert the block after itr
FreeChunk* t = (FreeChunk*)malloc(sizeof(FreeChunk));
if (t == nullptr) {
throw runtime_error("Malloc failed");
}
t->chunk = chunk;
t->next = itr->next;
itr->next = t;
itr = t;
}
// try to merge with the next block
if (itr->next != nullptr &&
itr->chunk.ImmediatelyBefore(itr->next->chunk)) {
FreeChunk *tobedeleted = itr->next;
itr->chunk.size += itr->next->chunk.size;
itr->next = itr->next->next;
free(tobedeleted);
}
}
return Status::OK();
}
Status FreeList::Allocate(uint32_t blocks, Blob* blob) {
MutexLock l(&mutex_);
FreeChunk** best_fit_node = nullptr;
// Find the smallest free chunk whose size is greater or equal to blocks
for (FreeChunk** itr = &free_chunks_list_; (*itr) != nullptr;
itr = &((*itr)->next)) {
if ((*itr)->chunk.size >= blocks &&
(best_fit_node == nullptr ||
(*best_fit_node)->chunk.size > (*itr)->chunk.size)) {
best_fit_node = itr;
}
}
if (best_fit_node == nullptr || *best_fit_node == nullptr) {
// Not enough memory
return Status::Incomplete("");
}
blob->SetOneChunk((*best_fit_node)->chunk.bucket_id,
(*best_fit_node)->chunk.offset,
blocks);
if ((*best_fit_node)->chunk.size > blocks) {
// just shorten best_fit_node
(*best_fit_node)->chunk.offset += blocks;
(*best_fit_node)->chunk.size -= blocks;
} else {
assert(blocks == (*best_fit_node)->chunk.size);
// delete best_fit_node
FreeChunk* t = *best_fit_node;
(*best_fit_node) = (*best_fit_node)->next;
free(t);
}
return Status::OK();
}
bool FreeList::Overlap(const Blob &blob) const {
MutexLock l(&mutex_);
for (auto chunk : blob.chunks) {
for (auto itr = free_chunks_list_; itr != nullptr; itr = itr->next) {
if (itr->chunk.Overlap(chunk)) {
return true;
}
}
}
return false;
}
// BlobStore
BlobStore::BlobStore(const string& directory,
uint64_t block_size,
uint32_t blocks_per_bucket,
Env* env) :
directory_(directory),
block_size_(block_size),
blocks_per_bucket_(blocks_per_bucket),
env_(env) {
env_->CreateDirIfMissing(directory_);
storage_options_.use_mmap_writes = false;
storage_options_.use_mmap_reads = false;
CreateNewBucket();
}
BlobStore::~BlobStore() {
// TODO we don't care about recovery for now
}
Status BlobStore::Put(const char* value, uint64_t size, Blob* blob) {
// convert size to number of blocks
Status s = Allocate((size + block_size_ - 1) / block_size_, blob);
if (!s.ok()) {
return s;
}
uint64_t offset = 0; // in bytes, not blocks
for (auto chunk : blob->chunks) {
uint64_t write_size = min(chunk.size * block_size_, size);
assert(chunk.bucket_id < buckets_.size());
s = buckets_[chunk.bucket_id].get()->Write(chunk.offset * block_size_,
Slice(value + offset,
write_size));
if (!s.ok()) {
Delete(*blob);
return s;
}
offset += write_size;
size -= write_size;
if (write_size < chunk.size * block_size_) {
// if we have any space left in the block, fill it up with zeros
string zero_string(chunk.size * block_size_ - write_size, 0);
s = buckets_[chunk.bucket_id].get()->Write(chunk.offset * block_size_ +
write_size,
Slice(zero_string));
}
}
if (size > 0) {
Delete(*blob);
return Status::IOError("Tried to write more data than fits in the blob");
}
return Status::OK();
}
Status BlobStore::Get(const Blob& blob,
string* value) const {
// assert that it doesn't overlap with free list
// it will get compiled out for release
assert(!free_list_.Overlap(blob));
uint32_t total_size = 0; // in blocks
for (auto chunk : blob.chunks) {
total_size += chunk.size;
}
assert(total_size > 0);
value->resize(total_size * block_size_);
uint64_t offset = 0; // in bytes, not blocks
for (auto chunk : blob.chunks) {
Slice result;
assert(chunk.bucket_id < buckets_.size());
Status s;
s = buckets_[chunk.bucket_id].get()->Read(chunk.offset * block_size_,
chunk.size * block_size_,
&result,
&value->at(offset));
if (!s.ok() || result.size() < chunk.size * block_size_) {
value->clear();
return Status::IOError("Could not read in from file");
}
offset += chunk.size * block_size_;
}
// remove the '\0's at the end of the string
value->erase(find(value->begin(), value->end(), '\0'), value->end());
return Status::OK();
}
Status BlobStore::Delete(const Blob& blob) {
return free_list_.Free(blob);
}
Status BlobStore::Allocate(uint32_t blocks, Blob* blob) {
// TODO we don't currently support fragmented blobs
MutexLock l(&allocate_mutex_);
assert(blocks <= blocks_per_bucket_);
Status s;
s = free_list_.Allocate(blocks, blob);
if (!s.ok()) {
s = CreateNewBucket();
if (!s.ok()) {
return s;
}
s = free_list_.Allocate(blocks, blob);
}
return s;
}
Status BlobStore::CreateNewBucket() {
int new_bucket_id;
new_bucket_id = buckets_.size();
buckets_.push_back(unique_ptr<RandomRWFile>());
char fname[200];
sprintf(fname, "%s/%d.bs", directory_.c_str(), new_bucket_id);
Status s = env_->NewRandomRWFile(string(fname),
&buckets_[new_bucket_id],
storage_options_);
if (!s.ok()) {
buckets_.erase(buckets_.begin() + new_bucket_id);
return s;
}
// whether Allocate succeeds or not, does not affect the overall correctness
// of this function - calling Allocate is really optional
// (also, tmpfs does not support allocate)
buckets_[new_bucket_id].get()->Allocate(0, block_size_ * blocks_per_bucket_);
return free_list_.Free(Blob(new_bucket_id, 0, blocks_per_bucket_));
}
} // namespace rocksdb