Provide mechanism to configure when to flush the block

Summary: Allow block based table to configure the way flushing the blocks. This feature will allow us to add support for prefix-aligned block.

Test Plan: make check

Reviewers: dhruba, haobo, sdong, igor

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D13875

db/db_impl.cc

@@ -214,6 +214,10 @@ Options SanitizeOptions(const std::string& dbname,
       std::make_shared<InternalKeyStatsCollector>()
   );
 
+  if (!result.flush_block_policy_factory) {
+    result.SetUpDefaultFlushBlockPolicyFactory();
+  }
+
   return result;
 }
 

db/table_stats_collector_test.cc

@@ -83,10 +83,13 @@ class DumbLogger : public Logger {
 
 // Utilities test functions
 void MakeBuilder(
-    const Options& options,
+    Options options,
     std::unique_ptr<FakeWritableFile>* writable,
     std::unique_ptr<TableBuilder>* builder) {
   writable->reset(new FakeWritableFile);
+  if (!options.flush_block_policy_factory) {
+    options.SetUpDefaultFlushBlockPolicyFactory();
+  }
   builder->reset(
       options.table_factory->GetTableBuilder(options, writable->get(),
                                              options.compression));