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Add support to specify the number of shards for the Block cache. By default, the block cache is sharded into 16 parts.

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Summary:
Task ID: #

Blame Rev:

Test Plan: Revert Plan:

Differential Revision: https://reviews.facebook.net/D3273
This commit is contained in:
Dhruba Borthakur 2012-05-16 17:22:33 -07:00
parent 95af128225
commit a2a0e358cb
3 changed files with 33 additions and 7 deletions
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12
db/db_bench.cc
View File

@ -102,6 +102,11 @@ static bool FLAGS_use_existing_db = false;
// Use the db with the following name.
static const char* FLAGS_db = "/tmp/dbbench";
// Number of shards for the block cache is 2 ** FLAGS_cache_numshardbits.
// Negative means use default settings. This is applied only
// if FLAGS_cache_size is non-negative.
static int FLAGS_cache_numshardbits = -1;
namespace leveldb {
namespace {
@ -390,7 +395,10 @@ class Benchmark {
public:
Benchmark()
: cache_(FLAGS_cache_size >= 0 ? NewLRUCache(FLAGS_cache_size) : NULL),
: cache_(FLAGS_cache_size >= 0 ?
(FLAGS_cache_numshardbits >= 1 ?
NewLRUCache(FLAGS_cache_size, FLAGS_cache_numshardbits) :
NewLRUCache(FLAGS_cache_size)) : NULL),
filter_policy_(FLAGS_bloom_bits >= 0
? NewBloomFilterPolicy(FLAGS_bloom_bits)
: NULL),
@ -955,6 +963,8 @@ int main(int argc, char** argv) {
FLAGS_write_buffer_size = n;
} else if (sscanf(argv[i], "--cache_size=%ld%c", &n, &junk) == 1) {
FLAGS_cache_size = n;
} else if (sscanf(argv[i], "--cache_numshardbits=%d%c", &n, &junk) == 1) {
FLAGS_cache_numshardbits = n;
} else if (sscanf(argv[i], "--bloom_bits=%d%c", &n, &junk) == 1) {
FLAGS_bloom_bits = n;
} else if (sscanf(argv[i], "--open_files=%d%c", &n, &junk) == 1) {

1
include/leveldb/cache.h
View File

@ -28,6 +28,7 @@ class Cache;
// Create a new cache with a fixed size capacity. This implementation
// of Cache uses a least-recently-used eviction policy.
extern Cache* NewLRUCache(size_t capacity);
extern Cache* NewLRUCache(size_t capacity, int numShardBits);
class Cache {
public:

27
util/cache.cc
View File

@ -267,12 +267,12 @@ void LRUCache::Erase(const Slice& key, uint32_t hash) {
}
}
static const int kNumShardBits = 4;
static const int kNumShards = 1 << kNumShardBits;
static int kNumShardBits = 4; // default values, can be overridden
static int kNumShards = 1 << kNumShardBits;
class ShardedLRUCache : public Cache {
private:
LRUCache shard_[kNumShards];
LRUCache* shard_;
port::Mutex id_mutex_;
uint64_t last_id_;
@ -284,14 +284,25 @@ class ShardedLRUCache : public Cache {
return hash >> (32 - kNumShardBits);
}
public:
explicit ShardedLRUCache(size_t capacity)
: last_id_(0) {
void init(size_t capacity, int numShardBits) {
kNumShardBits = numShardBits;
kNumShards = 1 << kNumShardBits;
shard_ = new LRUCache[kNumShards];
const size_t per_shard = (capacity + (kNumShards - 1)) / kNumShards;
for (int s = 0; s < kNumShards; s++) {
shard_[s].SetCapacity(per_shard);
}
}
public:
explicit ShardedLRUCache(size_t capacity)
: last_id_(0) {
init(capacity, kNumShardBits);
}
ShardedLRUCache(size_t capacity, int numShardBits)
: last_id_(0) {
init(capacity, numShardBits);
}
virtual ~ShardedLRUCache() { }
virtual Handle* Insert(const Slice& key, void* value, size_t charge,
void (*deleter)(const Slice& key, void* value)) {
@ -325,4 +336,8 @@ Cache* NewLRUCache(size_t capacity) {
return new ShardedLRUCache(capacity);
}
Cache* NewLRUCache(size_t capacity, int numShardBits) {
return new ShardedLRUCache(capacity, numShardBits);
}
} // namespace leveldb