Add option verify_checksums_in_compaction

Summary:
If verify_checksums_in_compaction is true, compaction will verify checksums. This is default.
If it's false, compaction doesn't verify checksums. This is useful for in-memory workloads.

Test Plan: corruption_test

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16695

HISTORY.md

@@ -9,6 +9,7 @@
 * Added is_manual_compaction to CompactionFilter::Context
 * Added "virtual void WaitForJoin() = 0" in class Env
 * Removed BackupEngine::DeleteBackupsNewerThan() function
+* Added new option -- verify_checksums_in_compaction
 
 ### New Features
 * If we find one truncated record at the end of the MANIFEST or WAL files,

db/version_set.cc

@@ -2179,6 +2179,7 @@ Compaction* VersionSet::CompactRange(int input_level, int output_level,
 
 Iterator* VersionSet::MakeInputIterator(Compaction* c) {
   ReadOptions options;
+  options.verify_checksums = options_->verify_checksums_in_compaction;
   options.fill_cache = false;
 
   // Level-0 files have to be merged together.  For other levels,

include/rocksdb/options.h

@@ -612,6 +612,11 @@ struct Options {
   // The options needed to support Universal Style compactions
   CompactionOptionsUniversal compaction_options_universal;
 
+  // If true, compaction will verify checksum on every read that happens
+  // as part of compaction
+  // Default: true
+  bool verify_checksums_in_compaction;
+
   // Use KeyMayExist API to filter deletes when this is true.
   // If KeyMayExist returns false, i.e. the key definitely does not exist, then
   // the delete is a noop. KeyMayExist only incurs in-memory look up.

util/options.cc

@@ -101,6 +101,7 @@ Options::Options()
       use_adaptive_mutex(false),
       bytes_per_sync(0),
       compaction_style(kCompactionStyleLevel),
+      verify_checksums_in_compaction(true),
       filter_deletes(false),
       max_sequential_skip_in_iterations(8),
       memtable_factory(std::shared_ptr<SkipListFactory>(new SkipListFactory)),
@@ -278,6 +279,8 @@ Options::Dump(Logger* log) const
         (unsigned long)bytes_per_sync);
     Log(log,"                          Options.filter_deletes: %d",
         filter_deletes);
+    Log(log, "          Options.verify_checksums_in_compaction: %d",
+        verify_checksums_in_compaction);
     Log(log,"                        Options.compaction_style: %d",
         compaction_style);
     Log(log," Options.compaction_options_universal.size_ratio: %u",