[IndexedDB] Transaction limitting

content/browser/indexed_db/indexed_db_transaction_coordinator.cc

Index: content/browser/indexed_db/indexed_db_transaction_coordinator.cc
diff --git a/content/browser/indexed_db/indexed_db_transaction_coordinator.cc b/content/browser/indexed_db/indexed_db_transaction_coordinator.cc
index 80345303ab195efadd7a765b33fb8d8b154033b1..3f7fd4677880796d18693e206e4541b0585f17d9 100644
--- a/content/browser/indexed_db/indexed_db_transaction_coordinator.cc
+++ b/content/browser/indexed_db/indexed_db_transaction_coordinator.cc
@@ -9,6 +9,15 @@
 #include "third_party/WebKit/public/platform/modules/indexeddb/WebIDBTypes.h"
 
 namespace content {
+namespace {
+
+// Only this many transactions can be active at any time before they are queued.
+// Limited prevent transaction trashing. Ten is chosen to reduce performance

[cmumford, 2017/02/16 23:36:14]

"Limited to prevent"

[pwnall, 2017/02/16 23:38:28]

Is this accurate? I thought we're limiting txns to prevent the browser process
from consuming unbounded amounts of RAM.

[dmurph, 2017/02/16 23:50:27]

That's a side effect of the transaction trashing.

+// regressions.
+// TODO(dmurph): Choose this number better, or implement a scheduler.

[pwnall, 2017/02/16 23:38:28]

crbug in the todo?

[dmurph, 2017/02/16 23:50:27]

Done.

+static const size_t kMaxStartedTransactions = 10;
+
+}  // namespace
 
 IndexedDBTransactionCoordinator::IndexedDBTransactionCoordinator() {}
 
@@ -146,6 +155,9 @@ static bool DoSetsIntersect(const std::set<T>& set1,
 bool IndexedDBTransactionCoordinator::CanStartTransaction(
     IndexedDBTransaction* const transaction,
     const std::set<int64_t>& locked_scope) const {
+  if (started_transactions_.size() >= kMaxStartedTransactions) {
+    return false;
+  }
   DCHECK(queued_transactions_.count(transaction));
   switch (transaction->mode()) {
     case blink::WebIDBTransactionModeVersionChange: