Fixed CompactionFilter::Decision::kRemoveAndSkipUntil

Summary:
Embarassingly enough, the first time I tried to use my new feature in logdevice it crashed with this assertion failure:

  db/pinned_iterators_manager.h:30: void rocksdb::PinnedIteratorsManager::StartPinning(): Assertion `pinning_enabled == false' failed

The issue was that `pinned_iters_mgr_.StartPinning()` was called but `pinned_iters_mgr_.ReleasePinnedData()` wasn't.
Closes https://github.com/facebook/rocksdb/pull/1611

Differential Revision: D4265622

Pulled By: al13n321

fbshipit-source-id: 747b10f

db/compaction_iterator.cc

@@ -437,9 +437,7 @@ void CompactionIterator::NextFromInput() {
                                 bottommost_level_);
       merge_out_iter_.SeekToFirst();
 
-      if (merge_helper_->FilteredUntil(&skip_until)) {
+      if (merge_out_iter_.Valid()) {
-        need_skip = true;
-      } else if (merge_out_iter_.Valid()) {
         // NOTE: key, value, and ikey_ refer to old entries.
         //       These will be correctly set below.
         key_ = merge_out_iter_.key();
@@ -460,6 +458,10 @@ void CompactionIterator::NextFromInput() {
         // coming after the merges
         has_current_user_key_ = false;
         pinned_iters_mgr_.ReleasePinnedData();
+
+        if (merge_helper_->FilteredUntil(&skip_until)) {
+          need_skip = true;
+        }
       }
     } else {
       // 1. new user key -OR-

db/compaction_iterator_test.cc

@@ -272,8 +272,8 @@ TEST_F(CompactionIteratorTest, CompactionFilterSkipUntil) {
         return Decision::kKeep;
       }
       if (k == "i") {
-        EXPECT_EQ(ValueType::kValue, t);
+        EXPECT_EQ(ValueType::kMergeOperand, t);
-        EXPECT_EQ("iv95", v);
+        EXPECT_EQ("im95", v);
         *skip_until = "z";
         return Decision::kRemoveAndSkipUntil;
       }
@@ -299,10 +299,10 @@ TEST_F(CompactionIteratorTest, CompactionFilterSkipUntil) {
        test::KeyStr("f", 30, kTypeMerge),  // skip to "g+"
        test::KeyStr("f", 25, kTypeValue), test::KeyStr("g", 90, kTypeValue),
        test::KeyStr("h", 91, kTypeValue),  // keep
-       test::KeyStr("i", 95, kTypeValue),  // skip to "z"
+       test::KeyStr("i", 95, kTypeMerge),  // skip to "z"
        test::KeyStr("j", 99, kTypeValue)},
       {"av50", "am45", "bv60", "bv40", "cv35", "dm70", "em71", "fm65", "fm30",
-       "fv25", "gv90", "hv91", "iv95", "jv99"},
+       "fv25", "gv90", "hv91", "im95", "jv99"},
       {}, {}, kMaxSequenceNumber, &merge_op, &filter);
 
   // Compaction should output just "a", "e" and "h" keys.