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

content/browser/indexed_db/leveldb/leveldb_database.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/indexed_db/leveldb/leveldb_database.h"
 
 #include <inttypes.h>
 #include <stdint.h>
 
 #include <cerrno>
@@ skipping 23 matching lines @@
 #include "third_party/leveldatabase/env_chromium.h"
 #include "third_party/leveldatabase/src/helpers/memenv/memenv.h"
 #include "third_party/leveldatabase/src/include/leveldb/db.h"
 #include "third_party/leveldatabase/src/include/leveldb/env.h"
 #include "third_party/leveldatabase/src/include/leveldb/filter_policy.h"
 #include "third_party/leveldatabase/src/include/leveldb/slice.h"
 
 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
 // busy with background compactions. Not syncing trades off reliability for
 // performance. Note that background compactions which move data from the
 // log to SSTs are always done with reliable writes.
 //
 // Sync writes are necessary on Windows for quota calculations; POSIX
 // calculates file sizes correctly even when not synced to disk.
 #if defined(OS_WIN)
@@ skipping 31 matching lines @@
     const leveldb::Slice& limit) const {}
 
 void LevelDBDatabase::ComparatorAdapter::FindShortSuccessor(
     std::string* key) const {}
 
 LevelDBSnapshot::LevelDBSnapshot(LevelDBDatabase* db)
     : db_(db->db_.get()), snapshot_(db_->GetSnapshot()) {}
 
 LevelDBSnapshot::~LevelDBSnapshot() { db_->ReleaseSnapshot(snapshot_); }
 
-LevelDBDatabase::LevelDBDatabase() {}
+LevelDBDatabase::LevelDBDatabase()
+    : iterator_lru_(kMaxOpenIteratorsPerDatabase) {}
 
 LevelDBDatabase::~LevelDBDatabase() {
   base::trace_event::MemoryDumpManager::GetInstance()->UnregisterDumpProvider(
       this);
   // db_'s destructor uses comparator_adapter_; order of deletion is important.
   CloseDatabase();
   comparator_adapter_.reset();
   env_.reset();
 }
 
@@ skipping 366 matching lines @@
                   base::trace_event::MemoryAllocatorDump::kUnitsBytes, size);
   dump->AddString("file_name", "", file_name_for_tracing);
 
   // Memory is allocated from system allocator (malloc).
   pmd->AddSuballocation(dump->guid(),
                         base::trace_event::MemoryDumpManager::GetInstance()
                             ->system_allocator_pool_name());
   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