[IndexedDB] Pool and evict leveldb iterators, to save memory

content/browser/indexed_db/leveldb/leveldb_database.cc

Index: content/browser/indexed_db/leveldb/leveldb_database.cc
diff --git a/content/browser/indexed_db/leveldb/leveldb_database.cc b/content/browser/indexed_db/leveldb/leveldb_database.cc
index 7eaa89405cb23782b5c070ca97947a64edb9f3ef..8804a680b1ee856d5ae45194c4feadefce188495 100644
--- a/content/browser/indexed_db/leveldb/leveldb_database.cc
+++ b/content/browser/indexed_db/leveldb/leveldb_database.cc
@@ -41,6 +41,7 @@
 using base::StringPiece;
 
 namespace content {
+static const size_t kDefaultMaxOpenIteratorsPerDatabase = 50;

[jsbell, 2017/03/22 23:55:32]

We should note that this applies only to iterators managed by
LevelDBTransaction.

Iterators opened directly against the database are not counted, but there should
be a bounded number of those, not under the control of script. (Although
enumerating those seems wise - I haven't checked myself.)

(That said... maybe that's a todo for the future.)

[dmurph, 2017/03/23 20:56:48]

Done.

 
 // Forcing flushes to disk at the end of a transaction guarantees that the
 // data hit disk, but drastically impacts throughput when the filesystem is
@@ -92,9 +93,15 @@ LevelDBSnapshot::LevelDBSnapshot(LevelDBDatabase* db)
 
 LevelDBSnapshot::~LevelDBSnapshot() { db_->ReleaseSnapshot(snapshot_); }
 
-LevelDBDatabase::LevelDBDatabase() {}
+LevelDBDatabase::LevelDBDatabase()
+    : iterator_lru_(kDefaultMaxOpenIteratorsPerDatabase) {}
+
+LevelDBDatabase::LevelDBDatabase(size_t max_open_iterators)
+    : iterator_lru_(max_open_iterators) {}
 
 LevelDBDatabase::~LevelDBDatabase() {
+  LOCAL_HISTOGRAM_COUNTS_10000("Storage.IndexedDB.LevelDB.MaxIterators",
+                               max_iterators_);
   base::trace_event::MemoryDumpManager::GetInstance()->UnregisterDumpProvider(
       this);
   // db_'s destructor uses comparator_adapter_; order of deletion is important.
@@ -285,6 +292,43 @@ static void HistogramLevelDBError(const std::string& histogram_name,
     ParseAndHistogramCorruptionDetails(histogram_name, s);
 }
 
+leveldb::Status LevelDBDatabase::OpenForTesting(

[jsbell, 2017/03/22 23:55:32]

Too much duplicated code. :( Can we refactor?

I don't object to changing the signature of LevelDBDatabase::Open() - we could
pass in an options object and/or move the default # of cursors into
IndexedDBBackingStore.

Or just pull out the guts of Open() into OpenInternal()

[dmurph, 2017/03/23 20:56:48]

Done.

+    const base::FilePath& file_name,
+    const LevelDBComparator* comparator,
+    std::unique_ptr<LevelDBDatabase>* result,
+    size_t max_open_cursors) {
+  IDB_TRACE("LevelDBDatabase::Open");
+  base::TimeTicks begin_time = base::TimeTicks::Now();
+
+  std::unique_ptr<ComparatorAdapter> comparator_adapter(
+      base::MakeUnique<ComparatorAdapter>(comparator));
+
+  std::unique_ptr<leveldb::DB> db;
+  std::unique_ptr<const leveldb::FilterPolicy> filter_policy;
+  const leveldb::Status s = OpenDB(comparator_adapter.get(), LevelDBEnv::Get(),
+                                   file_name, &db, &filter_policy);
+
+  if (!s.ok()) {
+    HistogramLevelDBError("WebCore.IndexedDB.LevelDBOpenErrors", s);
+    LOG(ERROR) << "Failed to open LevelDB database from "
+               << file_name.AsUTF8Unsafe() << "," << s.ToString();
+    return s;
+  }
+
+  UMA_HISTOGRAM_MEDIUM_TIMES("WebCore.IndexedDB.LevelDB.OpenTime",
+                             base::TimeTicks::Now() - begin_time);
+
+  CheckFreeSpace("Success", file_name);
+
+  (*result) = base::WrapUnique(new LevelDBDatabase(max_open_cursors));
+  (*result)->db_ = std::move(db);
+  (*result)->comparator_adapter_ = std::move(comparator_adapter);
+  (*result)->comparator_ = comparator;
+  (*result)->filter_policy_ = std::move(filter_policy);
+  (*result)->file_name_for_tracing = file_name.BaseName().AsUTF8Unsafe();
+  return s;
+}
+
 leveldb::Status LevelDBDatabase::Open(const base::FilePath& file_name,
                                       const LevelDBComparator* comparator,
                                       std::unique_ptr<LevelDBDatabase>* result,
@@ -479,4 +523,30 @@ bool LevelDBDatabase::OnMemoryDump(
   return true;
 }
 
+void LevelDBDatabase::NotifyIteratorCreated(LevelDBIterator* iter) {
+  num_iterators_++;
+  max_iterators_ = std::max(max_iterators_, num_iterators_);
+}
+
+void LevelDBDatabase::NotifyIteratorUsed(LevelDBIterator* iter) {
+  // This line updates the LRU if the item exists.
+  if (iterator_lru_.Get(iter) != iterator_lru_.end())
+    return;
+  if (iterator_lru_.size() == iterator_lru_.max_size()) {
+    auto to_evict_iter = iterator_lru_.rbegin();
+    LevelDBIterator* to_evict = to_evict_iter->first;
+    to_evict->PurgeMemory();
+    iterator_lru_.Erase(to_evict_iter);
+  }
+  iterator_lru_.Put(iter, iter);
+}
+
+void LevelDBDatabase::NotifyIteratorDestroyed(LevelDBIterator* iter) {
+  DCHECK_GT(num_iterators_, 0u);
+  --num_iterators_;
+  auto it = iterator_lru_.Get(iter);

[jsbell, 2017/03/22 23:55:32]

Peek() instead of Get(), since we don't need to mess with the ordering?

[dmurph, 2017/03/23 20:56:47]

Done.

+  if (it == iterator_lru_.end())
+    return;
+  iterator_lru_.Erase(it);
+}
 }  // namespace content