Persistent Cache: Expose stats to user via public API

Summary:
Exposing persistent cache stats (counters) to the user via public API.
Closes https://github.com/facebook/rocksdb/pull/1485

Differential Revision: D4155274

Pulled By: siying

fbshipit-source-id: 30a9f50

db/db_test2.cc

@@ -1470,6 +1470,10 @@ class MockPersistentCache : public PersistentCache {
 
   virtual ~MockPersistentCache() {}
 
+  PersistentCache::StatsType Stats() override {
+    return PersistentCache::StatsType();
+  }
+
   Status Insert(const Slice& page_key, const char* data,
                 const size_t size) override {
     MutexLock _(&lock_);

include/rocksdb/persistent_cache.h

@@ -24,6 +24,8 @@ namespace rocksdb {
 // cache interface is specifically designed for persistent read cache.
 class PersistentCache {
  public:
+  typedef std::vector<std::map<std::string, double>> StatsType;
+
   virtual ~PersistentCache() {}
 
   // Insert to page cache
@@ -46,6 +48,12 @@ class PersistentCache {
   //
   // True if the cache is configured to store uncompressed data else false
   virtual bool IsCompressed() = 0;
+
+  // Return stats as map of {string, double} per-tier
+  //
+  // Persistent cache can be initialized as a tier of caches. The stats are per
+  // tire top-down
+  virtual StatsType Stats() = 0;
 };
 
 // Factor method to create a new persistent cache

utilities/persistent_cache/block_cache_tier.cc

@@ -123,34 +123,42 @@ Status BlockCacheTier::Close() {
   return Status::OK();
 }
 
-std::string BlockCacheTier::PrintStats() {
+template<class T>
-  std::ostringstream os;
+void Add(std::map<std::string, double>* stats, const std::string& key,
-  os << "persistentcache.blockcachetier.bytes_piplined: "
+         const T& t) {
-     << stats_.bytes_pipelined_.ToString() << std::endl
+  stats->insert({key, static_cast<const double>(t)});
-     << "persistentcache.blockcachetier.bytes_written: "
+}
-     << stats_.bytes_written_.ToString() << std::endl
+
-     << "persistentcache.blockcachetier.bytes_read: "
+PersistentCache::StatsType BlockCacheTier::Stats() {
-     << stats_.bytes_read_.ToString() << std::endl
+  std::map<std::string, double> stats;
-     << "persistentcache.blockcachetier.insert_dropped"
+  Add(&stats, "persistentcache.blockcachetier.bytes_piplined",
-     << stats_.insert_dropped_ << std::endl
+      stats_.bytes_pipelined_.Average());
-     << "persistentcache.blockcachetier.cache_hits: " << stats_.cache_hits_
+  Add(&stats, "persistentcache.blockcachetier.bytes_written",
-     << std::endl
+      stats_.bytes_written_.Average());
-     << "persistentcache.blockcachetier.cache_misses: " << stats_.cache_misses_
+  Add(&stats, "persistentcache.blockcachetier.bytes_read",
-     << std::endl
+      stats_.bytes_read_.Average());
-     << "persistentcache.blockcachetier.cache_errors: " << stats_.cache_errors_
+  Add(&stats, "persistentcache.blockcachetier.insert_dropped",
-     << std::endl
+      stats_.insert_dropped_);
-     << "persistentcache.blockcachetier.cache_hits_pct: "
+  Add(&stats, "persistentcache.blockcachetier.cache_hits",
-     << stats_.CacheHitPct() << std::endl
+      stats_.cache_hits_);
-     << "persistentcache.blockcachetier.cache_misses_pct: "
+  Add(&stats, "persistentcache.blockcachetier.cache_misses",
-     << stats_.CacheMissPct() << std::endl
+      stats_.cache_misses_);
-     << "persistentcache.blockcachetier.read_hit_latency: "
+  Add(&stats, "persistentcache.blockcachetier.cache_errors",
-     << stats_.read_hit_latency_.ToString() << std::endl
+      stats_.cache_errors_);
-     << "persistentcache.blockcachetier.read_miss_latency: "
+  Add(&stats, "persistentcache.blockcachetier.cache_hits_pct",
-     << stats_.read_miss_latency_.ToString() << std::endl
+      stats_.CacheHitPct());
-     << "persistenetcache.blockcachetier.write_latency: "
+  Add(&stats, "persistentcache.blockcachetier.cache_misses_pct",
-     << stats_.write_latency_.ToString() << std::endl
+      stats_.CacheMissPct());
-     << PersistentCacheTier::PrintStats();
+  Add(&stats, "persistentcache.blockcachetier.read_hit_latency",
-  return os.str();
+      stats_.read_hit_latency_.Average());
+  Add(&stats, "persistentcache.blockcachetier.read_miss_latency",
+      stats_.read_miss_latency_.Average());
+  Add(&stats, "persistenetcache.blockcachetier.write_latency",
+      stats_.write_latency_.Average());
+
+  auto out = PersistentCacheTier::Stats();
+  out.push_back(stats);
+  return out;
 }
 
 Status BlockCacheTier::Insert(const Slice& key, const char* data,

utilities/persistent_cache/block_cache_tier.h

@@ -64,7 +64,7 @@ class BlockCacheTier : public PersistentCacheTier {
 
   bool IsCompressed() override { return opt_.is_compressed; }
 
-  std::string PrintStats() override;
+  PersistentCache::StatsType Stats() override;
 
   void TEST_Flush() override {
     while (insert_ops_.Size()) {
@@ -110,7 +110,7 @@ class BlockCacheTier : public PersistentCacheTier {
   Status CleanupCacheFolder(const std::string& folder);
 
   // Statistics
-  struct Stats {
+  struct Statistics {
     HistogramImpl bytes_pipelined_;
     HistogramImpl bytes_written_;
     HistogramImpl bytes_read_;
@@ -143,7 +143,7 @@ class BlockCacheTier : public PersistentCacheTier {
   ThreadedWriter writer_;                       // Writer threads
   BlockCacheTierMetadata metadata_;             // Cache meta data manager
   std::atomic<uint64_t> size_{0};               // Size of the cache
-  Stats stats_;                                 // Statistics
+  Statistics stats_;                                 // Statistics
 };
 
 }  // namespace rocksdb

utilities/persistent_cache/persistent_cache_test.cc

@@ -244,6 +244,8 @@ TEST_F(PersistentCacheTierTest, FactoryTest) {
                                  /*size=*/1 * 1024 * 1024 * 1024, log, nvm_opt,
                                  &cache));
     ASSERT_TRUE(cache);
+    ASSERT_EQ(cache->Stats().size(), 1);
+    ASSERT_TRUE(cache->Stats()[0].size());
     cache.reset();
   }
 }

utilities/persistent_cache/persistent_cache_tier.cc

@@ -8,6 +8,7 @@
 #include "utilities/persistent_cache/persistent_cache_tier.h"
 
 #include <string>
+#include <sstream>
 
 namespace rocksdb {
 
@@ -40,17 +41,21 @@ bool PersistentCacheTier::Erase(const Slice& key) {
 }
 
 std::string PersistentCacheTier::PrintStats() {
-  if (next_tier_) {
+  std::ostringstream os;
-    return next_tier_->PrintStats();
+  for (auto tier_stats : Stats()) {
+    os << "---- next tier -----" << std::endl;
+    for (auto stat : tier_stats) {
+      os << stat.first << ": " << stat.second << std::endl;
     }
-  return std::string();
+  }
+  return os.str();
 }
 
-std::vector<PersistentCacheTier::TierStats> PersistentCacheTier::Stats() {
+PersistentCache::StatsType PersistentCacheTier::Stats() {
   if (next_tier_) {
     return next_tier_->Stats();
   }
-  return std::vector<TierStats>{};
+  return PersistentCache::StatsType{};
 }
 
 //
@@ -77,7 +82,7 @@ bool PersistentTieredCache::Erase(const Slice& key) {
   return tiers_.front()->Erase(key);
 }
 
-std::vector<PersistentCacheTier::TierStats> PersistentTieredCache::Stats() {
+PersistentCache::StatsType PersistentTieredCache::Stats() {
   assert(!tiers_.empty());
   return tiers_.front()->Stats();
 }

utilities/persistent_cache/persistent_cache_tier.h

@@ -231,7 +231,6 @@ struct PersistentCacheConfig {
 class PersistentCacheTier : public PersistentCache {
  public:
   typedef std::shared_ptr<PersistentCacheTier> Tier;
-  typedef std::map<std::string, double> TierStats;
 
   virtual ~PersistentCacheTier() {}
 
@@ -250,8 +249,7 @@ class PersistentCacheTier : public PersistentCache {
   // Print stats to string recursively
   virtual std::string PrintStats();
 
-  // Expose stats
+  virtual PersistentCache::StatsType Stats();
-  virtual std::vector<TierStats> Stats();
 
   // Insert to page cache
   virtual Status Insert(const Slice& page_key, const char* data,
@@ -296,7 +294,7 @@ class PersistentTieredCache : public PersistentCacheTier {
   Status Close() override;
   bool Erase(const Slice& key) override;
   std::string PrintStats() override;
-  std::vector<TierStats> Stats() override;
+  PersistentCache::StatsType Stats() override;
   Status Insert(const Slice& page_key, const char* data,
                 const size_t size) override;
   Status Lookup(const Slice& page_key, std::unique_ptr<char[]>* data,

utilities/persistent_cache/volatile_tier_impl.cc

@@ -18,8 +18,8 @@ void VolatileCacheTier::DeleteCacheData(VolatileCacheTier::CacheData* data) {
 
 VolatileCacheTier::~VolatileCacheTier() { index_.Clear(&DeleteCacheData); }
 
-std::vector<PersistentCacheTier::TierStats> VolatileCacheTier::Stats() {
+PersistentCache::StatsType VolatileCacheTier::Stats() {
-  PersistentCacheTier::TierStats stat;
+  std::map<std::string, double> stat;
   stat.insert({"persistent_cache.volatile_cache.hits",
                static_cast<double>(stats_.cache_hits_)});
   stat.insert({"persistent_cache.volatile_cache.misses",
@@ -33,26 +33,9 @@ std::vector<PersistentCacheTier::TierStats> VolatileCacheTier::Stats() {
   stat.insert({"persistent_cache.volatile_cache.miss_pct",
                static_cast<double>(stats_.CacheMissPct())});
 
-  std::vector<PersistentCacheTier::TierStats> tier_stats;
+  auto out = PersistentCacheTier::Stats();
-  if (next_tier()) {
+  out.push_back(stat);
-    tier_stats = next_tier()->Stats();
+  return out;
-  }
-  tier_stats.push_back(stat);
-  return tier_stats;
-}
-
-std::string VolatileCacheTier::PrintStats() {
-  std::ostringstream ss;
-  ss << "pagecache.volatilecache.hits: " << stats_.cache_hits_ << std::endl
-     << "pagecache.volatilecache.misses: " << stats_.cache_misses_ << std::endl
-     << "pagecache.volatilecache.inserts: " << stats_.cache_inserts_
-     << std::endl
-     << "pagecache.volatilecache.evicts: " << stats_.cache_evicts_ << std::endl
-     << "pagecache.volatilecache.hit_pct: " << stats_.CacheHitPct() << std::endl
-     << "pagecache.volatilecache.miss_pct: " << stats_.CacheMissPct()
-     << std::endl
-     << PersistentCacheTier::PrintStats();
-  return ss.str();
 }
 
 Status VolatileCacheTier::Insert(const Slice& page_key, const char* data,

utilities/persistent_cache/volatile_tier_impl.h

@@ -63,10 +63,7 @@ class VolatileCacheTier : public PersistentCacheTier {
   bool Erase(const Slice& key) override;
 
   // Expose stats as map
-  std::vector<TierStats> Stats() override;
+  PersistentCache::StatsType Stats() override;
-
-  // Print stats to string
-  std::string PrintStats() override;
 
  private:
   //