Version and history for 9.7.4

Summary:
An earlier change (https://github.com/facebook/rocksdb/commit/b34cef57b798520791312f2f40681c4d12d5d33c) removed apparently unused functionality where an obsolete blob file number is passed for removal from TableCache, which manages SST files. This was actually relying on broken/fragile abstractions wherein TableCache and BlobFileCache share the same Cache and using the TableCache interface to manipulate blob file caching. No unit test was actually checking for removal of obsolete blob files from the cache (which is somewhat tricky to check and a second order correctness requirement).

Here we fix the leak and add a DEBUG+ASAN-only check in DB::Close() that no obsolete files are lingering in the table/blob file cache.

Fixes https://github.com/facebook/rocksdb/issues/13066

Important follow-up (FIXME): The added check discovered some apparent cases of leaked (into table_cache) SST file readers that would stick around until DB::Close(). Need to enable that check, diagnose, and fix.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/13106

Test Plan:
added a check that is called during DB::Close in ASAN builds (to minimize paying the cost in all unit tests). Without the fix, the check failed in at least these tests:

```
db_blob_basic_test DBBlobBasicTest.DynamicallyWarmCacheDuringFlush
db_blob_compaction_test DBBlobCompactionTest.CompactionReadaheadMerge
db_blob_compaction_test DBBlobCompactionTest.MergeBlobWithBase
db_blob_compaction_test DBBlobCompactionTest.CompactionDoNotFillCache
db_blob_compaction_test DBBlobCompactionTest.SkipUntilFilter
db_blob_compaction_test DBBlobCompactionTest.CompactionFilter
db_blob_compaction_test DBBlobCompactionTest.CompactionReadaheadFilter
db_blob_compaction_test DBBlobCompactionTest.CompactionReadaheadGarbageCollection
```

Reviewed By: ltamasi

Differential Revision: D65296123

Pulled By: pdillinger

fbshipit-source-id: 2276d76482beb2c75c9010bc1bec070bb23a24c0

HISTORY.md

@@ -1,6 +1,10 @@
 # Rocksdb Change Log
 > NOTE: Entries for next release do not go here. Follow instructions in `unreleased_history/README.txt`
 
+## 9.7.4 (10/31/2024)
+### Bug Fixes
+* Fix a leak of obsolete blob files left open until DB::Close(). This bug was introduced in version 9.4.0.
+
 ## 9.7.3 (10/16/2024)
 ### Behavior Changes
 * OPTIONS file to be loaded by remote worker is now preserved so that it does not get purged by the primary host. A similar technique as how we are preserving new SST files from getting purged is used for this. min_options_file_numbers_ is tracked like pending_outputs_ is tracked.

db/blob/blob_file_cache.cc

@@ -42,6 +42,7 @@ Status BlobFileCache::GetBlobFileReader(
   assert(blob_file_reader);
   assert(blob_file_reader->IsEmpty());
 
+  // NOTE: sharing same Cache with table_cache
   const Slice key = GetSliceForKey(&blob_file_number);
 
   assert(cache_);
@@ -98,4 +99,13 @@ Status BlobFileCache::GetBlobFileReader(
   return Status::OK();
 }
 
+void BlobFileCache::Evict(uint64_t blob_file_number) {
+  // NOTE: sharing same Cache with table_cache
+  const Slice key = GetSliceForKey(&blob_file_number);
+
+  assert(cache_);
+
+  cache_.get()->Erase(key);
+}
+
 }  // namespace ROCKSDB_NAMESPACE

db/blob/blob_file_cache.h

@@ -36,6 +36,15 @@ class BlobFileCache {
                            uint64_t blob_file_number,
                            CacheHandleGuard<BlobFileReader>* blob_file_reader);
 
+  // Called when a blob file is obsolete to ensure it is removed from the cache
+  // to avoid effectively leaking the open file and assicated memory
+  void Evict(uint64_t blob_file_number);
+
+  // Used to identify cache entries for blob files (not normally useful)
+  static const Cache::CacheItemHelper* GetHelper() {
+    return CacheInterface::GetBasicHelper();
+  }
+
  private:
   using CacheInterface =
       BasicTypedCacheInterface<BlobFileReader, CacheEntryRole::kMisc>;

db/column_family.h

@@ -401,6 +401,7 @@ class ColumnFamilyData {
                          SequenceNumber earliest_seq);
 
   TableCache* table_cache() const { return table_cache_.get(); }
+  BlobFileCache* blob_file_cache() const { return blob_file_cache_.get(); }
   BlobSource* blob_source() const { return blob_source_.get(); }
 
   // See documentation in compaction_picker.h

db/db_impl/db_impl.cc

@@ -659,8 +659,9 @@ Status DBImpl::CloseHelper() {
   // We need to release them before the block cache is destroyed. The block
   // cache may be destroyed inside versions_.reset(), when column family data
   // list is destroyed, so leaving handles in table cache after
-  // versions_.reset() may cause issues.
-  // Here we clean all unreferenced handles in table cache.
+  // versions_.reset() may cause issues. Here we clean all unreferenced handles
+  // in table cache, and (for certain builds/conditions) assert that no obsolete
+  // files are hanging around unreferenced (leak) in the table/blob file cache.
   // Now we assume all user queries have finished, so only version set itself
   // can possibly hold the blocks from block cache. After releasing unreferenced
   // handles here, only handles held by version set left and inside
@@ -668,6 +669,9 @@ Status DBImpl::CloseHelper() {
   // time a handle is released, we erase it from the cache too. By doing that,
   // we can guarantee that after versions_.reset(), table cache is empty
   // so the cache can be safely destroyed.
+#ifndef NDEBUG
+  TEST_VerifyNoObsoleteFilesCached(/*db_mutex_already_held=*/true);
+#endif  // !NDEBUG
   table_cache_->EraseUnRefEntries();
 
   for (auto& txn_entry : recovered_transactions_) {
@@ -3227,6 +3231,8 @@ Status DBImpl::MultiGetImpl(
       s = Status::Aborted();
       break;
     }
+    // This could be a long-running operation
+    ROCKSDB_THREAD_YIELD_HOOK();
   }
 
   // Post processing (decrement reference counts and record statistics)

db/db_impl/db_impl.h

@@ -1241,9 +1241,14 @@ class DBImpl : public DB {
   static Status TEST_ValidateOptions(const DBOptions& db_options) {
     return ValidateOptions(db_options);
   }
-
 #endif  // NDEBUG
 
+  // In certain configurations, verify that the table/blob file cache only
+  // contains entries for live files, to check for effective leaks of open
+  // files. This can only be called when purging of obsolete files has
+  // "settled," such as during parts of DB Close().
+  void TEST_VerifyNoObsoleteFilesCached(bool db_mutex_already_held) const;
+
   // persist stats to column family "_persistent_stats"
   void PersistStats();
 

db/db_impl/db_impl_debug.cc

@@ -9,6 +9,7 @@
 
 #ifndef NDEBUG
 
+#include "db/blob/blob_file_cache.h"
 #include "db/column_family.h"
 #include "db/db_impl/db_impl.h"
 #include "db/error_handler.h"
@@ -328,5 +329,49 @@ size_t DBImpl::TEST_EstimateInMemoryStatsHistorySize() const {
   InstrumentedMutexLock l(&const_cast<DBImpl*>(this)->stats_history_mutex_);
   return EstimateInMemoryStatsHistorySize();
 }
+
+void DBImpl::TEST_VerifyNoObsoleteFilesCached(
+    bool db_mutex_already_held) const {
+  // This check is somewhat expensive and obscure to make a part of every
+  // unit test in every build variety. Thus, we only enable it for ASAN builds.
+  if (!kMustFreeHeapAllocations) {
+    return;
+  }
+
+  std::optional<InstrumentedMutexLock> l;
+  if (db_mutex_already_held) {
+    mutex_.AssertHeld();
+  } else {
+    l.emplace(&mutex_);
+  }
+
+  std::vector<uint64_t> live_files;
+  for (auto cfd : *versions_->GetColumnFamilySet()) {
+    if (cfd->IsDropped()) {
+      continue;
+    }
+    // Sneakily add both SST and blob files to the same list
+    cfd->current()->AddLiveFiles(&live_files, &live_files);
+  }
+  std::sort(live_files.begin(), live_files.end());
+
+  auto fn = [&live_files](const Slice& key, Cache::ObjectPtr, size_t,
+                          const Cache::CacheItemHelper* helper) {
+    if (helper != BlobFileCache::GetHelper()) {
+      // Skip non-blob files for now
+      // FIXME: diagnose and fix the leaks of obsolete SST files revealed in
+      // unit tests.
+      return;
+    }
+    // See TableCache and BlobFileCache
+    assert(key.size() == sizeof(uint64_t));
+    uint64_t file_number;
+    GetUnaligned(reinterpret_cast<const uint64_t*>(key.data()), &file_number);
+    // Assert file is in sorted live_files
+    assert(
+        std::binary_search(live_files.begin(), live_files.end(), file_number));
+  };
+  table_cache_->ApplyToAllEntries(fn, {});
+}
 }  // namespace ROCKSDB_NAMESPACE
 #endif  // NDEBUG

db/db_iter.cc

@@ -540,6 +540,8 @@ bool DBIter::FindNextUserEntryInternal(bool skipping_saved_key,
     } else {
       iter_.Next();
     }
+    // This could be a long-running operation due to tombstones, etc.
+    ROCKSDB_THREAD_YIELD_HOOK();
   } while (iter_.Valid());
 
   valid_ = false;

db/table_cache.cc

@@ -164,6 +164,7 @@ Status TableCache::GetTableReader(
 }
 
 Cache::Handle* TableCache::Lookup(Cache* cache, uint64_t file_number) {
+  // NOTE: sharing same Cache with BlobFileCache
   Slice key = GetSliceForFileNumber(&file_number);
   return cache->Lookup(key);
 }
@@ -179,6 +180,7 @@ Status TableCache::FindTable(
     size_t max_file_size_for_l0_meta_pin, Temperature file_temperature) {
   PERF_TIMER_GUARD_WITH_CLOCK(find_table_nanos, ioptions_.clock);
   uint64_t number = file_meta.fd.GetNumber();
+  // NOTE: sharing same Cache with BlobFileCache
   Slice key = GetSliceForFileNumber(&number);
   *handle = cache_.Lookup(key);
   TEST_SYNC_POINT_CALLBACK("TableCache::FindTable:0",

db/version_builder.cc

@@ -24,6 +24,7 @@
 #include <vector>
 
 #include "cache/cache_reservation_manager.h"
+#include "db/blob/blob_file_cache.h"
 #include "db/blob/blob_file_meta.h"
 #include "db/dbformat.h"
 #include "db/internal_stats.h"
@@ -744,12 +745,9 @@ class VersionBuilder::Rep {
       return Status::Corruption("VersionBuilder", oss.str());
     }
 
-    // Note: we use C++11 for now but in C++14, this could be done in a more
-    // elegant way using generalized lambda capture.
-    VersionSet* const vs = version_set_;
-    const ImmutableCFOptions* const ioptions = ioptions_;
-
-    auto deleter = [vs, ioptions](SharedBlobFileMetaData* shared_meta) {
+    auto deleter = [vs = version_set_, ioptions = ioptions_,
+                    bc = cfd_ ? cfd_->blob_file_cache()
+                              : nullptr](SharedBlobFileMetaData* shared_meta) {
       if (vs) {
         assert(ioptions);
         assert(!ioptions->cf_paths.empty());
@@ -758,6 +756,9 @@ class VersionBuilder::Rep {
         vs->AddObsoleteBlobFile(shared_meta->GetBlobFileNumber(),
                                 ioptions->cf_paths.front().path);
       }
+      if (bc) {
+        bc->Evict(shared_meta->GetBlobFileNumber());
+      }
 
       delete shared_meta;
     };
@@ -766,7 +767,7 @@ class VersionBuilder::Rep {
         blob_file_number, blob_file_addition.GetTotalBlobCount(),
         blob_file_addition.GetTotalBlobBytes(),
         blob_file_addition.GetChecksumMethod(),
-        blob_file_addition.GetChecksumValue(), deleter);
+        blob_file_addition.GetChecksumValue(), std::move(deleter));
 
     mutable_blob_file_metas_.emplace(
         blob_file_number, MutableBlobFileMetaData(std::move(shared_meta)));

db/version_set.h

@@ -1514,7 +1514,6 @@ class VersionSet {
   void GetLiveFilesMetaData(std::vector<LiveFileMetaData>* metadata);
 
   void AddObsoleteBlobFile(uint64_t blob_file_number, std::string path) {
-    // TODO: Erase file from BlobFileCache?
     obsolete_blob_files_.emplace_back(blob_file_number, std::move(path));
   }
 

include/rocksdb/version.h

@@ -13,7 +13,7 @@
 // minor or major version number planned for release.
 #define ROCKSDB_MAJOR 9
 #define ROCKSDB_MINOR 7
-#define ROCKSDB_PATCH 3
+#define ROCKSDB_PATCH 4
 
 // Do not use these. We made the mistake of declaring macros starting with
 // double underscore. Now we have to live with our choice. We'll deprecate these

port/port.h

@@ -19,3 +19,19 @@
 #elif defined(OS_WIN)
 #include "port/win/port_win.h"
 #endif
+
+#ifdef OS_LINUX
+// A temporary hook into long-running RocksDB threads to support modifying their
+// priority etc. This should become a public API hook once the requirements
+// are better understood.
+extern "C" void RocksDbThreadYield() __attribute__((__weak__));
+#define ROCKSDB_THREAD_YIELD_HOOK() \
+  {                                 \
+    if (RocksDbThreadYield) {       \
+      RocksDbThreadYield();         \
+    }                               \
+  }
+#else
+#define ROCKSDB_THREAD_YIELD_HOOK() \
+  {}
+#endif