[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..c521d33bb374ce2a317ebccc08b88a16d678ae0f 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 kMaxOpenIteratorsPerDatabase = 50;

[jsbell, 2017/03/21 00:15:48]

We should get UMA stats on this. It may be that we can make the number much
lower without impacting most sites today, and give ourselves more headroom in
the future.

[dmurph, 2017/03/21 20:13:25]

Hm... so I'll keep track of the max, and then report it when we're destructing
maybe?

 
 // Forcing flushes to disk at the end of a transaction guarantees that the
 // data hit disk, but drastically impacts throughput when the filesystem is
@@ -92,7 +93,8 @@ LevelDBSnapshot::LevelDBSnapshot(LevelDBDatabase* db)
 
 LevelDBSnapshot::~LevelDBSnapshot() { db_->ReleaseSnapshot(snapshot_); }
 
-LevelDBDatabase::LevelDBDatabase() {}
+LevelDBDatabase::LevelDBDatabase()
+    : iterator_lru_(kMaxOpenIteratorsPerDatabase) {}
 
 LevelDBDatabase::~LevelDBDatabase() {
   base::trace_event::MemoryDumpManager::GetInstance()->UnregisterDumpProvider(
@@ -479,4 +481,22 @@ bool LevelDBDatabase::OnMemoryDump(
   return true;
 }
 
+void LevelDBDatabase::NotifyIteratorUsed(LevelDBIterator* iter) {
+  if (iterator_lru_.size() == iterator_lru_.max_size()) {
+    auto to_evict_iter = iterator_lru_.rbegin();
+    LevelDBIterator* to_evict = to_evict_iter->first;
+    to_evict->EvictWorkingMemory();
+    iterator_lru_.Erase(to_evict_iter);
+  }
+  iterator_lru_.Put(iter, iter);
+}
+
+void LevelDBDatabase::NotifyIteratorDestroyed(LevelDBIterator* iter) {
+  auto it = iterator_lru_.Get(iter);
+  if (it == iterator_lru_.end()) {

[jsbell, 2017/03/21 00:15:48]

nit: no need for {}

[dmurph, 2017/03/21 20:13:25]

Done.

+    return;
+  }
+  iterator_lru_.Erase(it);
+  LOG(ERROR) << "iterator erased";

[jsbell, 2017/03/21 00:15:48]

nit: obviously remove before landing. :)

[dmurph, 2017/03/21 20:13:25]

Done.

+}
 }  // namespace content