Add DB property for fast block cache stats collection (#10832)

Summary:
This new property allows users to trigger the background block cache stats collection mode through the `GetProperty()` and `GetMapProperty()` APIs. The background mode has much lower overhead at the expense of returning stale values in more cases.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10832

Test Plan: updated unit test

Reviewed By: pdillinger

Differential Revision: D40497883

Pulled By: ajkr

fbshipit-source-id: bdcc93402f426463abb2153756aad9e295447343

HISTORY.md

@@ -4,6 +4,7 @@
 * `DeleteRange()` now supports user-defined timestamp.
 * Provide support for async_io with tailing iterators when ReadOptions.tailing is enabled during scans.
 * Tiered Storage: allow data moving up from the last level to the penultimate level if the input level is penultimate level or above.
+* Added `DB::Properties::kFastBlockCacheEntryStats`, which is similar to `DB::Properties::kBlockCacheEntryStats`, except returns cached (stale) values in more cases to reduce overhead.
 * FIFO compaction now supports migrating from a multi-level DB via DB::Open(). During the migration phase, FIFO compaction picker will:
  * picks the sst file with the smallest starting key in the bottom-most non-empty level.
  * Note that during the migration phase, the file purge order will only be an approximation of "FIFO" as files in lower-level might sometime contain newer keys than files in upper-level.

db/db_block_cache_test.cc

@@ -170,13 +170,16 @@ class DBBlockCacheTest : public DBTestBase {
 #ifndef ROCKSDB_LITE
   const std::array<size_t, kNumCacheEntryRoles> GetCacheEntryRoleCountsBg() {
     // Verify in cache entry role stats
-    ColumnFamilyHandleImpl* cfh =
+    std::array<size_t, kNumCacheEntryRoles> cache_entry_role_counts;
-        static_cast<ColumnFamilyHandleImpl*>(dbfull()->DefaultColumnFamily());
+    std::map<std::string, std::string> values;
-    InternalStats* internal_stats_ptr = cfh->cfd()->internal_stats();
+    EXPECT_TRUE(db_->GetMapProperty(DB::Properties::kFastBlockCacheEntryStats,
-    InternalStats::CacheEntryRoleStats stats;
+                                    &values));
-    internal_stats_ptr->TEST_GetCacheEntryRoleStats(&stats,
+    for (size_t i = 0; i < kNumCacheEntryRoles; ++i) {
-                                                    /*foreground=*/false);
+      auto role = static_cast<CacheEntryRole>(i);
-    return stats.entry_counts;
+      cache_entry_role_counts[i] =
+          ParseSizeT(values[BlockCacheEntryStatsMapKeys::EntryCount(role)]);
+    }
+    return cache_entry_role_counts;
   }
 #endif  // ROCKSDB_LITE
 };
@@ -1500,23 +1503,38 @@ TEST_F(DBBlockCacheTest, CacheEntryRoleStats) {
       dbfull()->DumpStats();
       ASSERT_EQ(scan_count, 1);
 
-      env_->MockSleepForSeconds(10000);
+      env_->MockSleepForSeconds(60);
+      ASSERT_TRUE(db_->GetMapProperty(DB::Properties::kFastBlockCacheEntryStats,
+                                      &values));
+      ASSERT_EQ(scan_count, 1);
       ASSERT_TRUE(
           db_->GetMapProperty(DB::Properties::kBlockCacheEntryStats, &values));
       ASSERT_EQ(scan_count, 2);
 
       env_->MockSleepForSeconds(10000);
+      ASSERT_TRUE(db_->GetMapProperty(DB::Properties::kFastBlockCacheEntryStats,
+                                      &values));
+      ASSERT_EQ(scan_count, 3);
+
+      env_->MockSleepForSeconds(60);
       std::string value_str;
+      ASSERT_TRUE(db_->GetProperty(DB::Properties::kFastBlockCacheEntryStats,
+                                   &value_str));
+      ASSERT_EQ(scan_count, 3);
       ASSERT_TRUE(
           db_->GetProperty(DB::Properties::kBlockCacheEntryStats, &value_str));
-      ASSERT_EQ(scan_count, 3);
+      ASSERT_EQ(scan_count, 4);
 
       env_->MockSleepForSeconds(10000);
+      ASSERT_TRUE(db_->GetProperty(DB::Properties::kFastBlockCacheEntryStats,
+                                   &value_str));
+      ASSERT_EQ(scan_count, 5);
+
       ASSERT_TRUE(db_->GetProperty(DB::Properties::kCFStats, &value_str));
       // To match historical speed, querying this property no longer triggers
       // a scan, even if results are old. But periodic dump stats should keep
       // things reasonably updated.
-      ASSERT_EQ(scan_count, /*unchanged*/ 3);
+      ASSERT_EQ(scan_count, /*unchanged*/ 5);
 
       SyncPoint::GetInstance()->DisableProcessing();
       SyncPoint::GetInstance()->ClearAllCallBacks();

db/internal_stats.cc

@@ -247,6 +247,8 @@ static const std::string cf_file_histogram = "cf-file-histogram";
 static const std::string dbstats = "dbstats";
 static const std::string levelstats = "levelstats";
 static const std::string block_cache_entry_stats = "block-cache-entry-stats";
+static const std::string fast_block_cache_entry_stats =
+    "fast-block-cache-entry-stats";
 static const std::string num_immutable_mem_table = "num-immutable-mem-table";
 static const std::string num_immutable_mem_table_flushed =
     "num-immutable-mem-table-flushed";
@@ -326,6 +328,8 @@ const std::string DB::Properties::kDBStats = rocksdb_prefix + dbstats;
 const std::string DB::Properties::kLevelStats = rocksdb_prefix + levelstats;
 const std::string DB::Properties::kBlockCacheEntryStats =
     rocksdb_prefix + block_cache_entry_stats;
+const std::string DB::Properties::kFastBlockCacheEntryStats =
+    rocksdb_prefix + fast_block_cache_entry_stats;
 const std::string DB::Properties::kNumImmutableMemTable =
     rocksdb_prefix + num_immutable_mem_table;
 const std::string DB::Properties::kNumImmutableMemTableFlushed =
@@ -446,6 +450,9 @@ const UnorderedMap<std::string, DBPropertyInfo>
         {DB::Properties::kBlockCacheEntryStats,
          {true, &InternalStats::HandleBlockCacheEntryStats, nullptr,
           &InternalStats::HandleBlockCacheEntryStatsMap, nullptr}},
+        {DB::Properties::kFastBlockCacheEntryStats,
+         {true, &InternalStats::HandleFastBlockCacheEntryStats, nullptr,
+          &InternalStats::HandleFastBlockCacheEntryStatsMap, nullptr}},
         {DB::Properties::kSSTables,
          {false, &InternalStats::HandleSsTables, nullptr, nullptr, nullptr}},
         {DB::Properties::kAggregatedTableProperties,
@@ -739,30 +746,50 @@ void InternalStats::CacheEntryRoleStats::ToMap(
   }
 }
 
-bool InternalStats::HandleBlockCacheEntryStats(std::string* value,
+bool InternalStats::HandleBlockCacheEntryStatsInternal(std::string* value,
-                                               Slice /*suffix*/) {
+                                                       bool fast) {
   if (!cache_entry_stats_collector_) {
     return false;
   }
-  CollectCacheEntryStats(/*foreground*/ true);
+  CollectCacheEntryStats(!fast /* foreground */);
   CacheEntryRoleStats stats;
   cache_entry_stats_collector_->GetStats(&stats);
   *value = stats.ToString(clock_);
   return true;
 }
 
-bool InternalStats::HandleBlockCacheEntryStatsMap(
+bool InternalStats::HandleBlockCacheEntryStatsMapInternal(
-    std::map<std::string, std::string>* values, Slice /*suffix*/) {
+    std::map<std::string, std::string>* values, bool fast) {
   if (!cache_entry_stats_collector_) {
     return false;
   }
-  CollectCacheEntryStats(/*foreground*/ true);
+  CollectCacheEntryStats(!fast /* foreground */);
   CacheEntryRoleStats stats;
   cache_entry_stats_collector_->GetStats(&stats);
   stats.ToMap(values, clock_);
   return true;
 }
 
+bool InternalStats::HandleBlockCacheEntryStats(std::string* value,
+                                               Slice /*suffix*/) {
+  return HandleBlockCacheEntryStatsInternal(value, false /* fast */);
+}
+
+bool InternalStats::HandleBlockCacheEntryStatsMap(
+    std::map<std::string, std::string>* values, Slice /*suffix*/) {
+  return HandleBlockCacheEntryStatsMapInternal(values, false /* fast */);
+}
+
+bool InternalStats::HandleFastBlockCacheEntryStats(std::string* value,
+                                                   Slice /*suffix*/) {
+  return HandleBlockCacheEntryStatsInternal(value, true /* fast */);
+}
+
+bool InternalStats::HandleFastBlockCacheEntryStatsMap(
+    std::map<std::string, std::string>* values, Slice /*suffix*/) {
+  return HandleBlockCacheEntryStatsMapInternal(values, true /* fast */);
+}
+
 bool InternalStats::HandleLiveSstFilesSizeAtTemperature(std::string* value,
                                                         Slice suffix) {
   uint64_t temperature;

db/internal_stats.h

@@ -793,9 +793,15 @@ class InternalStats {
   bool HandleBlockCacheUsage(uint64_t* value, DBImpl* db, Version* version);
   bool HandleBlockCachePinnedUsage(uint64_t* value, DBImpl* db,
                                    Version* version);
+  bool HandleBlockCacheEntryStatsInternal(std::string* value, bool fast);
+  bool HandleBlockCacheEntryStatsMapInternal(
+      std::map<std::string, std::string>* values, bool fast);
   bool HandleBlockCacheEntryStats(std::string* value, Slice suffix);
   bool HandleBlockCacheEntryStatsMap(std::map<std::string, std::string>* values,
                                      Slice suffix);
+  bool HandleFastBlockCacheEntryStats(std::string* value, Slice suffix);
+  bool HandleFastBlockCacheEntryStatsMap(
+      std::map<std::string, std::string>* values, Slice suffix);
   bool HandleLiveSstFilesSizeAtTemperature(std::string* value, Slice suffix);
   bool HandleNumBlobFiles(uint64_t* value, DBImpl* db, Version* version);
   bool HandleBlobStats(std::string* value, Slice suffix);

include/rocksdb/db.h

@@ -911,6 +911,10 @@ class DB {
     //      available in the map form.
     static const std::string kBlockCacheEntryStats;
 
+    //  "rocksdb.fast-block-cache-entry-stats" - same as above, but returns
+    //      stale values more frequently to reduce overhead and latency.
+    static const std::string kFastBlockCacheEntryStats;
+
     //  "rocksdb.num-immutable-mem-table" - returns number of immutable
     //      memtables that have not yet been flushed.
     static const std::string kNumImmutableMemTable;