Fix kBlockCacheTier read when merge-chain base value is in a blob file (#12462)

Summary:
The original goal is to propagate failures from `GetContext::SaveValue()` -> `GetContext::GetBlobValue()` -> `BlobFetcher::FetchBlob()` up to the user. This call sequence happens when a merge chain ends with a base value in a blob file.

There's also fixes for bugs encountered along the way where non-ok statuses were ignored/overwritten, and a bit of plumbing work for functions that had no capability to return a status.

Pull Request resolved: #12462

Test Plan:
A repro command

```
db=/dev/shm/dbstress_db ; exp=/dev/shm/dbstress_exp ; rm -rf $db $exp ; mkdir -p $db $exp
./db_stress \
        --clear_column_family_one_in=0 \
        --test_batches_snapshots=0 \
        --write_fault_one_in=0 \
        --use_put_entity_one_in=0 \
        --prefixpercent=0 \
        --read_fault_one_in=0 \
        --readpercent=0 \
        --reopen=0 \
        --set_options_one_in=10000 \
        --delpercent=0 \
        --delrangepercent=0 \
        --open_metadata_write_fault_one_in=0 \
        --open_read_fault_one_in=0 \
        --open_write_fault_one_in=0 \
        --destroy_db_initially=0 \
        --ingest_external_file_one_in=0 \
        --iterpercent=0 \
        --nooverwritepercent=0 \
        --db=$db \
        --enable_blob_files=1 \
        --expected_values_dir=$exp \
        --max_background_compactions=20 \
        --max_bytes_for_level_base=2097152 \
        --max_key=100000 \
        --min_blob_size=0 \
        --open_files=-1 \
        --ops_per_thread=100000000 \
        --prefix_size=-1 \
        --target_file_size_base=524288 \
        --use_merge=1 \
        --value_size_mult=32 \
        --write_buffer_size=524288 \
        --writepercent=100
```

It used to fail like:

```
...
frame #9: 0x00007fc63903bc93 libc.so.6`__GI___assert_fail(assertion="HasDefaultColumn(columns)", file="fbcode/internal_repo_rocksdb/repo/db/wide/wide_columns_helper.h", line=33, function="static const rocksdb::Slice &rocksdb::WideColumnsHelper::GetDefaultColumn(const rocksdb::WideColumns &)") at assert.c:101:3
frame #10: 0x00000000006f7e92 db_stress`rocksdb::Version::Get(rocksdb::ReadOptions const&, rocksdb::LookupKey const&, rocksdb::PinnableSlice*, rocksdb::PinnableWideColumns*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, rocksdb::Status*, rocksdb::MergeContext*, unsigned long*, rocksdb::PinnedIteratorsManager*, bool*, bool*, unsigned long*, rocksdb::ReadCallback*, bool*, bool) [inlined] rocksdb::WideColumnsHelper::GetDefaultColumn(columns=size=0) at wide_columns_helper.h:33
frame #11: 0x00000000006f7e76 db_stress`rocksdb::Version::Get(this=0x00007fc5ec763000, read_options=<unavailable>, k=<unavailable>, value=0x0000000000000000, columns=0x00007fc6035fd1d8, timestamp=<unavailable>, status=0x00007fc6035fd250, merge_context=0x00007fc6035fce40, max_covering_tombstone_seq=0x00007fc6035fce90, pinned_iters_mgr=0x00007fc6035fcdf0, value_found=0x0000000000000000, key_exists=0x0000000000000000, seq=0x0000000000000000, callback=0x0000000000000000, is_blob=0x0000000000000000, do_merge=<unavailable>) at version_set.cc:2492
frame #12: 0x000000000051e245 db_stress`rocksdb::DBImpl::GetImpl(this=0x00007fc637a86000, read_options=0x00007fc6035fcf60, key=<unavailable>, get_impl_options=0x00007fc6035fd000) at db_impl.cc:2408
frame #13: 0x000000000050cec2 db_stress`rocksdb::DBImpl::GetEntity(this=0x00007fc637a86000, _read_options=<unavailable>, column_family=<unavailable>, key=0x00007fc6035fd3c8, columns=0x00007fc6035fd1d8) at db_impl.cc:2109
frame #14: 0x000000000074f688 db_stress`rocksdb::(anonymous namespace)::MemTableInserter::MergeCF(this=0x00007fc6035fd450, column_family_id=2, key=0x00007fc6035fd3c8, value=0x00007fc6035fd3a0) at write_batch.cc:2656
frame #15: 0x00000000007476fc db_stress`rocksdb::WriteBatchInternal::Iterate(wb=0x00007fc6035fe698, handler=0x00007fc6035fd450, begin=12, end=<unavailable>) at write_batch.cc:607
frame #16: 0x000000000074d7dd db_stress`rocksdb::WriteBatchInternal::InsertInto(rocksdb::WriteThread::WriteGroup&, unsigned long, rocksdb::ColumnFamilyMemTables*, rocksdb::FlushScheduler*, rocksdb::TrimHistoryScheduler*, bool, unsigned long, rocksdb::DB*, bool, bool, bool) [inlined] rocksdb::WriteBatch::Iterate(this=<unavailable>, handler=0x00007fc6035fd450) const at write_batch.cc:505
frame #17: 0x000000000074d77b db_stress`rocksdb::WriteBatchInternal::InsertInto(write_group=<unavailable>, sequence=<unavailable>, memtables=<unavailable>, flush_scheduler=<unavailable>, trim_history_scheduler=<unavailable>, ignore_missing_column_families=<unavailable>, recovery_log_number=0, db=0x00007fc637a86000, concurrent_memtable_writes=<unavailable>, seq_per_batch=false, batch_per_txn=<unavailable>) at write_batch.cc:3084
frame #18: 0x0000000000631d77 db_stress`rocksdb::DBImpl::PipelinedWriteImpl(this=0x00007fc637a86000, write_options=<unavailable>, my_batch=0x00007fc6035fe698, callback=0x0000000000000000, log_used=<unavailable>, log_ref=0, disable_memtable=<unavailable>, seq_used=0x0000000000000000) at db_impl_write.cc:807
frame #19: 0x000000000062ceeb db_stress`rocksdb::DBImpl::WriteImpl(this=<unavailable>, write_options=<unavailable>, my_batch=0x00007fc6035fe698, callback=0x0000000000000000, log_used=<unavailable>, log_ref=0, disable_memtable=<unavailable>, seq_used=0x0000000000000000, batch_cnt=0, pre_release_callback=0x0000000000000000, post_memtable_callback=0x0000000000000000) at db_impl_write.cc:312
frame #20: 0x000000000062c8ec db_stress`rocksdb::DBImpl::Write(this=0x00007fc637a86000, write_options=0x00007fc6035feca8, my_batch=0x00007fc6035fe698) at db_impl_write.cc:157
frame #21: 0x000000000062b847 db_stress`rocksdb::DB::Merge(this=0x00007fc637a86000, opt=0x00007fc6035feca8, column_family=0x00007fc6370bf140, key=0x00007fc6035fe8d8, value=0x00007fc6035fe830) at db_impl_write.cc:2544
frame #22: 0x000000000062b6ef db_stress`rocksdb::DBImpl::Merge(this=0x00007fc637a86000, o=<unavailable>, column_family=0x00007fc6370bf140, key=0x00007fc6035fe8d8, val=0x00007fc6035fe830) at db_impl_write.cc:72
frame #23: 0x00000000004d6397 db_stress`rocksdb::NonBatchedOpsStressTest::TestPut(this=0x00007fc637041000, thread=0x00007fc6370dbc00, write_opts=0x00007fc6035feca8, read_opts=0x00007fc6035fe9c8, rand_column_families=<unavailable>, rand_keys=size=1, value={P\xe9_\x03\xc6\x7f\0\0}) at no_batched_ops_stress.cc:1317
frame #24: 0x000000000049361d db_stress`rocksdb::StressTest::OperateDb(this=0x00007fc637041000, thread=0x00007fc6370dbc00) at db_stress_test_base.cc:1148
...
```

Reviewed By: ltamasi

Differential Revision: D55157795

Pulled By: ajkr

fbshipit-source-id: 5f7c1380ead5794c29d41680028e34b839744764

Author: ajkr

db/blob/db_blob_basic_test.cc

@@ -1182,6 +1182,30 @@ TEST_F(DBBlobBasicTest, GetMergeBlobWithPut) {
   ASSERT_EQ(Get("Key1"), "v1,v2,v3");
 }
 
+TEST_F(DBBlobBasicTest, GetMergeBlobFromMemoryTier) {
+  Options options = GetDefaultOptions();
+  options.merge_operator = MergeOperators::CreateStringAppendOperator();
+  options.enable_blob_files = true;
+  options.min_blob_size = 0;
+
+  Reopen(options);
+
+  ASSERT_OK(Put(Key(0), "v1"));
+  ASSERT_OK(Flush());
+  ASSERT_OK(Merge(Key(0), "v2"));
+  ASSERT_OK(Flush());
+
+  // Regular `Get()` loads data block to cache.
+  std::string value;
+  ASSERT_OK(db_->Get(ReadOptions(), Key(0), &value));
+  ASSERT_EQ("v1,v2", value);
+
+  // Base value blob is still uncached, so an in-memory read will fail.
+  ReadOptions read_options;
+  read_options.read_tier = kBlockCacheTier;
+  ASSERT_TRUE(db_->Get(read_options, Key(0), &value).IsIncomplete());
+}
+
 TEST_F(DBBlobBasicTest, MultiGetMergeBlobWithPut) {
   constexpr size_t num_keys = 3;
 

db/table_cache.cc

@@ -395,7 +395,7 @@ uint64_t TableCache::CreateRowCacheKeyPrefix(const ReadOptions& options,
 
 bool TableCache::GetFromRowCache(const Slice& user_key, IterKey& row_cache_key,
                                  size_t prefix_size, GetContext* get_context,
-                                 SequenceNumber seq_no) {
+                                 Status* read_status, SequenceNumber seq_no) {
   bool found = false;
 
   row_cache_key.TrimAppend(prefix_size, user_key.data(), user_key.size());
@@ -414,8 +414,8 @@ bool TableCache::GetFromRowCache(const Slice& user_key, IterKey& row_cache_key,
     row_cache.RegisterReleaseAsCleanup(row_handle, value_pinner);
     // If row cache hit, knowing cache key is the same to row_cache_key,
     // can use row_cache_key's seq no to construct InternalKey.
-    replayGetContextLog(*row_cache.Value(row_handle), user_key, get_context,
-                        &value_pinner, seq_no);
+    *read_status = replayGetContextLog(*row_cache.Value(row_handle), user_key,
+                                       get_context, &value_pinner, seq_no);
     RecordTick(ioptions_.stats, ROW_CACHE_HIT);
     found = true;
   } else {
@@ -440,21 +440,20 @@ Status TableCache::Get(
 
   // Check row cache if enabled.
   // Reuse row_cache_key sequence number when row cache hits.
+  Status s;
   if (ioptions_.row_cache && !get_context->NeedToReadSequence()) {
     auto user_key = ExtractUserKey(k);
     uint64_t cache_entry_seq_no =
         CreateRowCacheKeyPrefix(options, fd, k, get_context, row_cache_key);
     done = GetFromRowCache(user_key, row_cache_key, row_cache_key.Size(),
-                           get_context, cache_entry_seq_no);
+                           get_context, &s, cache_entry_seq_no);
     if (!done) {
       row_cache_entry = &row_cache_entry_buffer;
     }
   }
-  Status s;
   TableReader* t = fd.table_reader;
   TypedHandle* handle = nullptr;
-  if (!done) {
-    assert(s.ok());
+  if (s.ok() && !done) {
     if (t == nullptr) {
       s = FindTable(options, file_options_, internal_comparator, file_meta,
                     &handle, block_protection_bytes_per_key, prefix_extractor,

db/table_cache.h

@@ -273,6 +273,7 @@ class TableCache {
   // user key to row_cache_key at offset prefix_size
   bool GetFromRowCache(const Slice& user_key, IterKey& row_cache_key,
                        size_t prefix_size, GetContext* get_context,
+                       Status* read_status,
                        SequenceNumber seq_no = kMaxSequenceNumber);
 
   const ImmutableOptions& ioptions_;
@@ -286,4 +287,4 @@ class TableCache {
   std::string db_session_id_;
 };
 
-}  // namespace ROCKSDB_NAMESPACE
+}  // namespace ROCKSDB_NAMESPACE

db/table_cache_sync_and_async.h

@@ -50,8 +50,14 @@ DEFINE_SYNC_AND_ASYNC(Status, TableCache::MultiGet)
 
       GetContext* get_context = miter->get_context;
 
-      if (GetFromRowCache(user_key, row_cache_key, row_cache_key_prefix_size,
-                          get_context)) {
+      Status read_status;
+      bool ret =
+          GetFromRowCache(user_key, row_cache_key, row_cache_key_prefix_size,
+                          get_context, &read_status);
+      if (!read_status.ok()) {
+        CO_RETURN read_status;
+      }
+      if (ret) {
         table_range.SkipKey(miter);
       } else {
         row_cache_entries.emplace_back();

table/block_based/block_based_table_reader.cc

@@ -2339,11 +2339,18 @@ Status BlockBasedTable::Get(const ReadOptions& read_options, const Slice& key,
               biter.key(), &parsed_key, false /* log_err_key */);  // TODO
           if (!pik_status.ok()) {
             s = pik_status;
+            break;
           }
 
-          if (!get_context->SaveValue(
-                  parsed_key, biter.value(), &matched,
-                  biter.IsValuePinned() ? &biter : nullptr)) {
+          Status read_status;
+          bool ret = get_context->SaveValue(
+              parsed_key, biter.value(), &matched, &read_status,
+              biter.IsValuePinned() ? &biter : nullptr);
+          if (!read_status.ok()) {
+            s = read_status;
+            break;
+          }
+          if (!ret) {
             if (get_context->State() == GetContext::GetState::kFound) {
               does_referenced_key_exist = true;
               referenced_data_size = biter.key().size() + biter.value().size();
@@ -2352,7 +2359,9 @@ Status BlockBasedTable::Get(const ReadOptions& read_options, const Slice& key,
             break;
           }
         }
-        s = biter.status();
+        if (s.ok()) {
+          s = biter.status();
+        }
         if (!s.ok()) {
           break;
         }

table/block_based/block_based_table_reader_sync_and_async.h

@@ -735,9 +735,17 @@ DEFINE_SYNC_AND_ASYNC(void, BlockBasedTable::MultiGet)
               biter->key(), &parsed_key, false /* log_err_key */);  // TODO
           if (!pik_status.ok()) {
             s = pik_status;
+            break;
+          }
+          Status read_status;
+          bool ret = get_context->SaveValue(
+              parsed_key, biter->value(), &matched, &read_status,
+              value_pinner ? value_pinner : nullptr);
+          if (!read_status.ok()) {
+            s = read_status;
+            break;
           }
-          if (!get_context->SaveValue(parsed_key, biter->value(), &matched,
-                                      value_pinner)) {
+          if (!ret) {
             if (get_context->State() == GetContext::GetState::kFound) {
               does_referenced_key_exist = true;
               referenced_data_size =
@@ -746,7 +754,9 @@ DEFINE_SYNC_AND_ASYNC(void, BlockBasedTable::MultiGet)
             done = true;
             break;
           }
-          s = biter->status();
+          if (s.ok()) {
+            s = biter->status();
+          }
         }
         // Write the block cache access.
         // XXX: There appear to be 'break' statements above that bypass this

table/cuckoo/cuckoo_table_reader.cc

@@ -186,7 +186,10 @@ Status CuckooTableReader::Get(const ReadOptions& /*readOptions*/,
             return s;
           }
           bool dont_care __attribute__((__unused__));
-          get_context->SaveValue(found_ikey, value, &dont_care);
+          get_context->SaveValue(found_ikey, value, &dont_care, &s);
+          if (!s.ok()) {
+            return s;
+          }
         }
         // We don't support merge operations. So, we return here.
         return Status::OK();

table/get_context.cc

@@ -221,7 +221,7 @@ void GetContext::ReportCounters() {
 
 bool GetContext::SaveValue(const ParsedInternalKey& parsed_key,
                            const Slice& value, bool* matched,
-                           Cleanable* value_pinner) {
+                           Status* read_status, Cleanable* value_pinner) {
   assert(matched);
   assert((state_ != kMerge && parsed_key.type != kTypeMerge) ||
          merge_context_ != nullptr);
@@ -356,8 +356,8 @@ bool GetContext::SaveValue(const ParsedInternalKey& parsed_key,
             // merge_context_->operand_list
             if (type == kTypeBlobIndex) {
               PinnableSlice pin_val;
-              if (GetBlobValue(parsed_key.user_key, unpacked_value, &pin_val) ==
-                  false) {
+              if (GetBlobValue(parsed_key.user_key, unpacked_value, &pin_val,
+                               read_status) == false) {
                 return false;
               }
               Slice blob_value(pin_val);
@@ -383,8 +383,8 @@ bool GetContext::SaveValue(const ParsedInternalKey& parsed_key,
           assert(merge_operator_ != nullptr);
           if (type == kTypeBlobIndex) {
             PinnableSlice pin_val;
-            if (GetBlobValue(parsed_key.user_key, unpacked_value, &pin_val) ==
-                false) {
+            if (GetBlobValue(parsed_key.user_key, unpacked_value, &pin_val,
+                             read_status) == false) {
               return false;
             }
             Slice blob_value(pin_val);
@@ -547,14 +547,14 @@ void GetContext::MergeWithWideColumnBaseValue(const Slice& entity) {
 }
 
 bool GetContext::GetBlobValue(const Slice& user_key, const Slice& blob_index,
-                              PinnableSlice* blob_value) {
+                              PinnableSlice* blob_value, Status* read_status) {
   constexpr FilePrefetchBuffer* prefetch_buffer = nullptr;
   constexpr uint64_t* bytes_read = nullptr;
 
-  Status status = blob_fetcher_->FetchBlob(
-      user_key, blob_index, prefetch_buffer, blob_value, bytes_read);
-  if (!status.ok()) {
-    if (status.IsIncomplete()) {
+  *read_status = blob_fetcher_->FetchBlob(user_key, blob_index, prefetch_buffer,
+                                          blob_value, bytes_read);
+  if (!read_status->ok()) {
+    if (read_status->IsIncomplete()) {
       // FIXME: this code is not covered by unit tests
       MarkKeyMayExist();
       return false;
@@ -577,9 +577,9 @@ void GetContext::push_operand(const Slice& value, Cleanable* value_pinner) {
   }
 }
 
-void replayGetContextLog(const Slice& replay_log, const Slice& user_key,
-                         GetContext* get_context, Cleanable* value_pinner,
-                         SequenceNumber seq_no) {
+Status replayGetContextLog(const Slice& replay_log, const Slice& user_key,
+                           GetContext* get_context, Cleanable* value_pinner,
+                           SequenceNumber seq_no) {
   Slice s = replay_log;
   Slice ts;
   size_t ts_sz = get_context->TimestampSize();
@@ -610,8 +610,13 @@ void replayGetContextLog(const Slice& replay_log, const Slice& user_key,
 
     (void)ret;
 
-    get_context->SaveValue(ikey, value, &dont_care, value_pinner);
+    Status read_status;
+    get_context->SaveValue(ikey, value, &dont_care, &read_status, value_pinner);
+    if (!read_status.ok()) {
+      return read_status;
+    }
   }
+  return Status::OK();
 }
 
 }  // namespace ROCKSDB_NAMESPACE

table/get_context.h

@@ -135,7 +135,8 @@ class GetContext {
   // Returns True if more keys need to be read (due to merges) or
   //         False if the complete value has been found.
   bool SaveValue(const ParsedInternalKey& parsed_key, const Slice& value,
-                 bool* matched, Cleanable* value_pinner = nullptr);
+                 bool* matched, Status* read_status,
+                 Cleanable* value_pinner = nullptr);
 
   // Simplified version of the previous function. Should only be used when we
   // know that the operation is a Put.
@@ -204,7 +205,7 @@ class GetContext {
   void MergeWithWideColumnBaseValue(const Slice& entity);
 
   bool GetBlobValue(const Slice& user_key, const Slice& blob_index,
-                    PinnableSlice* blob_value);
+                    PinnableSlice* blob_value, Status* read_status);
 
   void appendToReplayLog(ValueType type, Slice value, Slice ts);
 
@@ -250,9 +251,9 @@ class GetContext {
 // Call this to replay a log and bring the get_context up to date. The replay
 // log must have been created by another GetContext object, whose replay log
 // must have been set by calling GetContext::SetReplayLog().
-void replayGetContextLog(const Slice& replay_log, const Slice& user_key,
-                         GetContext* get_context,
-                         Cleanable* value_pinner = nullptr,
-                         SequenceNumber seq_no = kMaxSequenceNumber);
+Status replayGetContextLog(const Slice& replay_log, const Slice& user_key,
+                           GetContext* get_context,
+                           Cleanable* value_pinner = nullptr,
+                           SequenceNumber seq_no = kMaxSequenceNumber);
 
 }  // namespace ROCKSDB_NAMESPACE

table/mock_table.cc

@@ -220,7 +220,13 @@ Status MockTableReader::Get(const ReadOptions&, const Slice& key,
     }
 
     bool dont_care __attribute__((__unused__));
-    if (!get_context->SaveValue(parsed_key, iter->value(), &dont_care)) {
+    Status read_status;
+    bool ret = get_context->SaveValue(parsed_key, iter->value(), &dont_care,
+                                      &read_status);
+    if (!read_status.ok()) {
+      return read_status;
+    }
+    if (!ret) {
       break;
     }
   }

table/plain/plain_table_reader.cc

@@ -614,8 +614,12 @@ Status PlainTableReader::Get(const ReadOptions& /*ro*/, const Slice& target,
     // can we enable the fast path?
     if (internal_comparator_.Compare(found_key, parsed_target) >= 0) {
       bool dont_care __attribute__((__unused__));
-      if (!get_context->SaveValue(found_key, found_value, &dont_care,
-                                  dummy_cleanable_.get())) {
+      bool ret = get_context->SaveValue(found_key, found_value, &dont_care, &s,
+                                        dummy_cleanable_.get());
+      if (!s.ok()) {
+        return s;
+      }
+      if (!ret) {
         break;
       }
     }

unreleased_history/bug_fixes/blockcachetier_blob_as_mergebase.md

@@ -0,0 +1 @@
+* Fixed `kBlockCacheTier` reads to return `Status::Incomplete` when I/O is needed to fetch a merge chain's base value from a blob file.