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Bugfix for issue 33; reduce lock contention in Get(), parallel benchmarks.

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- Fix for issue 33 (non-null-terminated result from
  leveldb_property_value())

- Support for running multiple instances of a benchmark in parallel.

- Reduce lock contention on Get():
  (1) Do not hold the lock while searching memtables.
  (2) Shard block and table caches 16-ways.

  Benchmark for evaluating this change:
  $ db_bench --benchmarks=fillseq1,readrandom --threads=$n
  (fillseq1 is a small hack to make sure fillseq runs once regardless
  of number of threads specified on the command line).



git-svn-id: https://leveldb.googlecode.com/svn/trunk@49 62dab493-f737-651d-591e-8d6aee1b9529
This commit is contained in:
gabor@google.com
2011-08-22 21:08:51 +00:00
parent ab323f7e1e
commit e3584f9c28
7 changed files with 510 additions and 259 deletions
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149
util/cache.cc
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@@ -30,7 +30,8 @@ struct LRUHandle {
LRUHandle* prev;
size_t charge; // TODO(opt): Only allow uint32_t?
size_t key_length;
size_t refs; // TODO(opt): Pack with "key_length"?
uint32_t refs;
uint32_t hash; // Hash of key(); used for fast sharding and comparisons
char key_data[1]; // Beginning of key
Slice key() const {
@@ -54,12 +55,12 @@ class HandleTable {
HandleTable() : length_(0), elems_(0), list_(NULL) { Resize(); }
~HandleTable() { delete[] list_; }
LRUHandle* Lookup(LRUHandle* h) {
return *FindPointer(h);
LRUHandle* Lookup(const Slice& key, uint32_t hash) {
return *FindPointer(key, hash);
}
LRUHandle* Insert(LRUHandle* h) {
LRUHandle** ptr = FindPointer(h);
LRUHandle** ptr = FindPointer(h->key(), h->hash);
LRUHandle* old = *ptr;
h->next_hash = (old == NULL ? NULL : old->next_hash);
*ptr = h;
@@ -74,8 +75,8 @@ class HandleTable {
return old;
}
LRUHandle* Remove(LRUHandle* h) {
LRUHandle** ptr = FindPointer(h);
LRUHandle* Remove(const Slice& key, uint32_t hash) {
LRUHandle** ptr = FindPointer(key, hash);
LRUHandle* result = *ptr;
if (result != NULL) {
*ptr = result->next_hash;
@@ -92,13 +93,12 @@ class HandleTable {
LRUHandle** list_;
// Return a pointer to slot that points to a cache entry that
// matches *h. If there is no such cache entry, return a pointer to
// the trailing slot in the corresponding linked list.
LRUHandle** FindPointer(LRUHandle* h) {
Slice key = h->key();
uint32_t hash = Hash(key.data(), key.size(), 0);
// matches key/hash. If there is no such cache entry, return a
// pointer to the trailing slot in the corresponding linked list.
LRUHandle** FindPointer(const Slice& key, uint32_t hash) {
LRUHandle** ptr = &list_[hash & (length_ - 1)];
while (*ptr != NULL && key != (*ptr)->key()) {
while (*ptr != NULL &&
((*ptr)->hash != hash || key != (*ptr)->key())) {
ptr = &(*ptr)->next_hash;
}
return ptr;
@@ -117,7 +117,7 @@ class HandleTable {
while (h != NULL) {
LRUHandle* next = h->next_hash;
Slice key = h->key();
uint32_t hash = Hash(key.data(), key.size(), 0);
uint32_t hash = h->hash;
LRUHandle** ptr = &new_list[hash & (new_length - 1)];
h->next_hash = *ptr;
*ptr = h;
@@ -132,26 +132,30 @@ class HandleTable {
}
};
class LRUCache : public Cache {
// A single shard of sharded cache.
class LRUCache {
public:
explicit LRUCache(size_t capacity);
virtual ~LRUCache();
LRUCache();
~LRUCache();
virtual Handle* Insert(const Slice& key, void* value, size_t charge,
void (*deleter)(const Slice& key, void* value));
virtual Handle* Lookup(const Slice& key);
virtual void Release(Handle* handle);
virtual void* Value(Handle* handle);
virtual void Erase(const Slice& key);
virtual uint64_t NewId();
// Separate from constructor so caller can easily make an array of LRUCache
void SetCapacity(size_t capacity) { capacity_ = capacity; }
// Like Cache methods, but with an extra "hash" parameter.
Cache::Handle* Insert(const Slice& key, uint32_t hash,
void* value, size_t charge,
void (*deleter)(const Slice& key, void* value));
Cache::Handle* Lookup(const Slice& key, uint32_t hash);
void Release(Cache::Handle* handle);
void Erase(const Slice& key, uint32_t hash);
private:
void LRU_Remove(LRUHandle* e);
void LRU_Append(LRUHandle* e);
void Unref(LRUHandle* e);
// Constructor parameters
const size_t capacity_;
// Initialized before use.
size_t capacity_;
// mutex_ protects the following state.
port::Mutex mutex_;
@@ -165,9 +169,8 @@ class LRUCache : public Cache {
HandleTable table_;
};
LRUCache::LRUCache(size_t capacity)
: capacity_(capacity),
usage_(0),
LRUCache::LRUCache()
: usage_(0),
last_id_(0) {
// Make empty circular linked list
lru_.next = &lru_;
@@ -206,32 +209,25 @@ void LRUCache::LRU_Append(LRUHandle* e) {
e->next->prev = e;
}
Cache::Handle* LRUCache::Lookup(const Slice& key) {
Cache::Handle* LRUCache::Lookup(const Slice& key, uint32_t hash) {
MutexLock l(&mutex_);
LRUHandle dummy;
dummy.next = &dummy;
dummy.value = const_cast<Slice*>(&key);
LRUHandle* e = table_.Lookup(&dummy);
LRUHandle* e = table_.Lookup(key, hash);
if (e != NULL) {
e->refs++;
LRU_Remove(e);
LRU_Append(e);
}
return reinterpret_cast<Handle*>(e);
return reinterpret_cast<Cache::Handle*>(e);
}
void* LRUCache::Value(Handle* handle) {
return reinterpret_cast<LRUHandle*>(handle)->value;
}
void LRUCache::Release(Handle* handle) {
void LRUCache::Release(Cache::Handle* handle) {
MutexLock l(&mutex_);
Unref(reinterpret_cast<LRUHandle*>(handle));
}
Cache::Handle* LRUCache::Insert(const Slice& key, void* value, size_t charge,
void (*deleter)(const Slice& key, void* value)) {
Cache::Handle* LRUCache::Insert(
const Slice& key, uint32_t hash, void* value, size_t charge,
void (*deleter)(const Slice& key, void* value)) {
MutexLock l(&mutex_);
LRUHandle* e = reinterpret_cast<LRUHandle*>(
@@ -240,6 +236,7 @@ Cache::Handle* LRUCache::Insert(const Slice& key, void* value, size_t charge,
e->deleter = deleter;
e->charge = charge;
e->key_length = key.size();
e->hash = hash;
e->refs = 2; // One from LRUCache, one for the returned handle
memcpy(e->key_data, key.data(), key.size());
LRU_Append(e);
@@ -254,35 +251,77 @@ Cache::Handle* LRUCache::Insert(const Slice& key, void* value, size_t charge,
while (usage_ > capacity_ && lru_.next != &lru_) {
LRUHandle* old = lru_.next;
LRU_Remove(old);
table_.Remove(old);
table_.Remove(old->key(), old->hash);
Unref(old);
}
return reinterpret_cast<Handle*>(e);
return reinterpret_cast<Cache::Handle*>(e);
}
void LRUCache::Erase(const Slice& key) {
void LRUCache::Erase(const Slice& key, uint32_t hash) {
MutexLock l(&mutex_);
LRUHandle dummy;
dummy.next = &dummy;
dummy.value = const_cast<Slice*>(&key);
LRUHandle* e = table_.Remove(&dummy);
LRUHandle* e = table_.Remove(key, hash);
if (e != NULL) {
LRU_Remove(e);
Unref(e);
}
}
uint64_t LRUCache::NewId() {
MutexLock l(&mutex_);
return ++(last_id_);
}
static const int kNumShardBits = 4;
static const int kNumShards = 1 << kNumShardBits;
class ShardedLRUCache : public Cache {
private:
LRUCache shard_[kNumShards];
port::Mutex id_mutex_;
uint64_t last_id_;
static inline uint32_t HashSlice(const Slice& s) {
return Hash(s.data(), s.size(), 0);
}
static uint32_t Shard(uint32_t hash) {
return hash >> (32 - kNumShardBits);
}
public:
explicit ShardedLRUCache(size_t capacity) {
const size_t per_shard = (capacity + (kNumShards - 1)) / kNumShards;
for (int s = 0; s < kNumShards; s++) {
shard_[s].SetCapacity(per_shard);
}
}
virtual ~ShardedLRUCache() { }
virtual Handle* Insert(const Slice& key, void* value, size_t charge,
void (*deleter)(const Slice& key, void* value)) {
const uint32_t hash = HashSlice(key);
return shard_[Shard(hash)].Insert(key, hash, value, charge, deleter);
}
virtual Handle* Lookup(const Slice& key) {
const uint32_t hash = HashSlice(key);
return shard_[Shard(hash)].Lookup(key, hash);
}
virtual void Release(Handle* handle) {
LRUHandle* h = reinterpret_cast<LRUHandle*>(handle);
shard_[Shard(h->hash)].Release(handle);
}
virtual void Erase(const Slice& key) {
const uint32_t hash = HashSlice(key);
shard_[Shard(hash)].Erase(key, hash);
}
virtual void* Value(Handle* handle) {
return reinterpret_cast<LRUHandle*>(handle)->value;
}
virtual uint64_t NewId() {
MutexLock l(&id_mutex_);
return ++(last_id_);
}
};
} // end anonymous namespace
Cache* NewLRUCache(size_t capacity) {
return new LRUCache(capacity);
return new ShardedLRUCache(capacity);
}
}