From c4ce8e637faf5a6b909f2c725bf5ed49984d4bda Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=A5=8F=E4=B9=8B=E7=AB=A0?= <mm304321141@gmail.com>
Date: Thu, 12 Dec 2019 15:16:13 -0800
Subject: [PATCH] Fix RangeDeletion bug (#6062)

Summary:
Read keys from a snapshot that a range deletion were added after the snapshot  was created and this range deletion was inside an immutable memtable, we will get wrong key set.
More detail rest in codes.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6062

Differential Revision: D18966785

Pulled By: pdillinger

fbshipit-source-id: 38a60bb1e2d0a1dbfc8ec641617200b6a02b86c3
---
 HISTORY.md              |  4 +++-
 db/db_range_del_test.cc | 41 +++++++++++++++++++++++++++++++++++++++++
 db/memtable_list.cc     |  9 ++++++---
 3 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/HISTORY.md b/HISTORY.md
index e791cfab28..87fa2f84ae 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,7 +1,9 @@
 # Rocksdb Change Log
 ## Unreleased
-### Buf Fixes
+### Bug Fixes
 * Fix a bug that can cause unnecessary bg thread to be scheduled(#6104).
+* Fix a bug in which a snapshot read could be affected by a DeleteRange after the snapshot (#6062).
+
 ## 6.6.0 (11/25/2019)
 ### Bug Fixes
 * Fix data corruption caused by output of intra-L0 compaction on ingested file not being placed in correct order in L0.
diff --git a/db/db_range_del_test.cc b/db/db_range_del_test.cc
index ec448b731e..f2953a746c 100644
--- a/db/db_range_del_test.cc
+++ b/db/db_range_del_test.cc
@@ -1427,6 +1427,47 @@ TEST_F(DBRangeDelTest, SnapshotPreventsDroppedKeys) {
   db_->ReleaseSnapshot(snapshot);
 }
 
+TEST_F(DBRangeDelTest, SnapshotPreventsDroppedKeysInImmMemTables) {
+  const int kFileBytes = 1 << 20;
+
+  Options options = CurrentOptions();
+  options.compression = kNoCompression;
+  options.disable_auto_compactions = true;
+  options.target_file_size_base = kFileBytes;
+  Reopen(options);
+
+  // block flush thread -> pin immtables in memory
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"SnapshotPreventsDroppedKeysInImmMemTables:AfterNewIterator",
+       "DBImpl::BGWorkFlush"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+
+  ASSERT_OK(Put(Key(0), "a"));
+  std::unique_ptr<const Snapshot, std::function<void(const Snapshot*)>>
+      snapshot(db_->GetSnapshot(),
+               [this](const Snapshot* s) { db_->ReleaseSnapshot(s); });
+
+  ASSERT_OK(db_->DeleteRange(WriteOptions(), db_->DefaultColumnFamily(), Key(0),
+                             Key(10)));
+
+  ASSERT_OK(dbfull()->TEST_SwitchMemtable());
+
+  ReadOptions read_opts;
+  read_opts.snapshot = snapshot.get();
+  std::unique_ptr<Iterator> iter(db_->NewIterator(read_opts));
+
+  TEST_SYNC_POINT("SnapshotPreventsDroppedKeysInImmMemTables:AfterNewIterator");
+
+  iter->SeekToFirst();
+  ASSERT_TRUE(iter->Valid());
+  ASSERT_EQ(Key(0), iter->key());
+
+  iter->Next();
+  ASSERT_FALSE(iter->Valid());
+}
+
 TEST_F(DBRangeDelTest, RangeTombstoneWrittenToMinimalSsts) {
   // Adapted from
   // https://github.com/cockroachdb/cockroach/blob/de8b3ea603dd1592d9dc26443c2cc92c356fbc2f/pkg/storage/engine/rocksdb_test.go#L1267-L1398.
diff --git a/db/memtable_list.cc b/db/memtable_list.cc
index d9159b7937..93ab2e77c4 100644
--- a/db/memtable_list.cc
+++ b/db/memtable_list.cc
@@ -186,11 +186,14 @@ Status MemTableListVersion::AddRangeTombstoneIterators(
     const ReadOptions& read_opts, Arena* /*arena*/,
     RangeDelAggregator* range_del_agg) {
   assert(range_del_agg != nullptr);
+  // Except for snapshot read, using kMaxSequenceNumber is OK because these
+  // are immutable memtables.
+  SequenceNumber read_seq = read_opts.snapshot != nullptr
+                                ? read_opts.snapshot->GetSequenceNumber()
+                                : kMaxSequenceNumber;
   for (auto& m : memlist_) {
-    // Using kMaxSequenceNumber is OK because these are immutable memtables.
     std::unique_ptr<FragmentedRangeTombstoneIterator> range_del_iter(
-        m->NewRangeTombstoneIterator(read_opts,
-                                     kMaxSequenceNumber /* read_seq */));
+        m->NewRangeTombstoneIterator(read_opts, read_seq));
     range_del_agg->AddTombstones(std::move(range_del_iter));
   }
   return Status::OK();