Implement secondary cache admission policy to allow all evicted blocks (#12599)

Summary:
Add a secondary cache admission policy to admit all blocks evicted from the block cache.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/12599

Reviewed By: pdillinger

Differential Revision: D56891760

Pulled By: anand1976

fbshipit-source-id: 193c98c055aa3477f4e3a78e5d3daef27a5eacf4

cache/secondary_cache_adapter.cc

@@ -134,12 +134,14 @@ bool CacheWithSecondaryAdapter::EvictionHandler(const Slice& key,
     auto obj = target_->Value(handle);
     // Ignore dummy entry
     if (obj != kDummyObj) {
-      bool hit = false;
+      bool force = false;
       if (adm_policy_ == TieredAdmissionPolicy::kAdmPolicyAllowCacheHits) {
-        hit = was_hit;
+        force = was_hit;
+      } else if (adm_policy_ == TieredAdmissionPolicy::kAdmPolicyAllowAll) {
+        force = true;
       }
       // Spill into secondary cache.
-      secondary_cache_->Insert(key, obj, helper, hit).PermitUncheckedError();
+      secondary_cache_->Insert(key, obj, helper, force).PermitUncheckedError();
     }
   }
   // Never takes ownership of obj
@@ -661,6 +663,7 @@ std::shared_ptr<Cache> NewTieredCache(const TieredCacheOptions& _opts) {
         break;
       case TieredAdmissionPolicy::kAdmPolicyPlaceholder:
       case TieredAdmissionPolicy::kAdmPolicyAllowCacheHits:
+      case TieredAdmissionPolicy::kAdmPolicyAllowAll:
         if (opts.nvm_sec_cache) {
           valid_adm_policy = false;
         }

cache/tiered_secondary_cache_test.cc

@@ -816,11 +816,69 @@ TEST_P(DBTieredAdmPolicyTest, CompressedOnlyTest) {
   Destroy(options);
 }
 
+TEST_P(DBTieredAdmPolicyTest, CompressedCacheAdmission) {
+  if (!LZ4_Supported()) {
+    ROCKSDB_GTEST_SKIP("This test requires LZ4 support.");
+    return;
+  }
+
+  BlockBasedTableOptions table_options;
+  // We want a block cache of size 5KB, and a compressed secondary cache of
+  // size 5KB. However, we specify a block cache size of 256KB here in order
+  // to take into account the cache reservation in the block cache on
+  // behalf of the compressed cache. The unit of cache reservation is 256KB.
+  // The effective block cache capacity will be calculated as 256 + 5 = 261KB,
+  // and 256KB will be reserved for the compressed cache, leaving 10KB for
+  // the primary block cache. We only have to worry about this here because
+  // the cache size is so small.
+  table_options.block_cache = NewCache(256 * 1024, 5 * 1024, 0, GetParam());
+  table_options.block_size = 4 * 1024;
+  table_options.cache_index_and_filter_blocks = false;
+  Options options = GetDefaultOptions();
+  options.create_if_missing = true;
+  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
+
+  size_t comp_cache_usage = compressed_secondary_cache()->TEST_GetUsage();
+  // Disable paranoid_file_checks so that flush will not read back the newly
+  // written file
+  options.paranoid_file_checks = false;
+  DestroyAndReopen(options);
+  Random rnd(301);
+  const int N = 256;
+  for (int i = 0; i < N; i++) {
+    std::string p_v;
+    test::CompressibleString(&rnd, 0.5, 1007, &p_v);
+    ASSERT_OK(Put(Key(i), p_v));
+  }
+
+  ASSERT_OK(Flush());
+
+  // The second Get (for 5) will evict the data block loaded by the first
+  // Get, which will be admitted into the compressed secondary cache only
+  // for the kAdmPolicyAllowAll policy
+  std::string v = Get(Key(0));
+  ASSERT_EQ(1007, v.size());
+
+  v = Get(Key(5));
+  ASSERT_EQ(1007, v.size());
+
+  if (GetParam() == TieredAdmissionPolicy::kAdmPolicyAllowAll) {
+    ASSERT_GT(compressed_secondary_cache()->TEST_GetUsage(),
+              comp_cache_usage + 128);
+  } else {
+    ASSERT_LT(compressed_secondary_cache()->TEST_GetUsage(),
+              comp_cache_usage + 128);
+  }
+
+  Destroy(options);
+}
+
 INSTANTIATE_TEST_CASE_P(
     DBTieredAdmPolicyTest, DBTieredAdmPolicyTest,
     ::testing::Values(TieredAdmissionPolicy::kAdmPolicyAuto,
                       TieredAdmissionPolicy::kAdmPolicyPlaceholder,
-                      TieredAdmissionPolicy::kAdmPolicyAllowCacheHits));
+                      TieredAdmissionPolicy::kAdmPolicyAllowCacheHits,
+                      TieredAdmissionPolicy::kAdmPolicyAllowAll));
 
 }  // namespace ROCKSDB_NAMESPACE
 

include/rocksdb/cache.h

@@ -523,6 +523,11 @@ enum TieredAdmissionPolicy {
   // compressed secondary, and a compressed local flash (non-volatile) cache.
   // Each tier is managed as an independent queue.
   kAdmPolicyThreeQueue,
+  // Allow all blocks evicted from the primary block cache into the secondary
+  // cache. This may increase CPU overhead due to more blocks being admitted
+  // and compressed, but may increase the compressed secondary cache hit rate
+  // for some workloads
+  kAdmPolicyAllowAll,
   kAdmPolicyMax,
 };
 

tools/db_bench_tool.cc

@@ -1299,6 +1299,8 @@ static enum ROCKSDB_NAMESPACE::TieredAdmissionPolicy StringToAdmissionPolicy(
     return ROCKSDB_NAMESPACE::kAdmPolicyAllowCacheHits;
   } else if (!strcasecmp(policy, "three_queue")) {
     return ROCKSDB_NAMESPACE::kAdmPolicyThreeQueue;
+  } else if (!strcasecmp(policy, "allow_all")) {
+    return ROCKSDB_NAMESPACE::kAdmPolicyAllowAll;
   } else {
     fprintf(stderr, "Cannot parse admission policy %s\n", policy);
     exit(1);

unreleased_history/public_api_changes/sec_cache_allow_all.md

@@ -0,0 +1 @@
+Add a kAdmPolicyAllowAll option to TieredAdmissionPolicy that admits all blocks evicted from the primary block cache into the compressed secondary cache.