chore: minor refactorings around dense_set deletions (#4390)

chore: refactorings around deletions

Done as a preparation to introduce asynchronous deletions for sets/zsets/hmaps.
1. Restrict the interface around DbSlice::Del. Now it requires for the iterator to be valid and the checks should
be explicit before the call. Most callers already provides a valid iterator.

2. Some minor refactoring in compact_object_test.
3. Expose DenseSet::ClearStep to allow iterative deletions of elements.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/core/compact_object.cc

@@ -791,8 +791,8 @@ uint64_t CompactObj::HashCode() const {
   }
 
   if (encoded) {
-    GetString(&tl.tmp_str);
+    string_view sv = GetSlice(&tl.tmp_str);
-    return XXH3_64bits_withSeed(tl.tmp_str.data(), tl.tmp_str.size(), kHashSeed);
+    return XXH3_64bits_withSeed(sv.data(), sv.size(), kHashSeed);
   }
 
   switch (taglen_) {

src/core/compact_object_test.cc

@@ -76,18 +76,15 @@ void DeallocateAtRandom(size_t steps, std::vector<void*>* ptrs) {
   }
 }
 
-class CompactObjectTest : public ::testing::Test {
+static void InitThreadStructs() {
- protected:
-  static void SetUpTestSuite() {
-    InitRedisTables();  // to initialize server struct.
-
   auto* tlh = mi_heap_get_backing();
   init_zmalloc_threadlocal(tlh);
   SmallString::InitThreadLocal(tlh);
-    CompactObj::InitThreadLocal(PMR_NS::get_default_resource());
+  thread_local MiMemoryResource mi_resource(tlh);
-  }
+  CompactObj::InitThreadLocal(&mi_resource);
+};
 
-  static void TearDownTestSuite() {
+static void CheckEverythingDeallocated() {
   mi_heap_collect(mi_heap_get_backing(), true);
 
   auto cb_visit = [](const mi_heap_t* heap, const mi_heap_area_t* area, void* block,
@@ -99,6 +96,18 @@ class CompactObjectTest : public ::testing::Test {
 
   mi_heap_visit_blocks(mi_heap_get_backing(), false /* do not visit all blocks*/, cb_visit,
                        nullptr);
+}
+
+class CompactObjectTest : public ::testing::Test {
+ protected:
+  static void SetUpTestSuite() {
+    InitRedisTables();  // to initialize server struct.
+
+    InitThreadStructs();
+  }
+
+  static void TearDownTestSuite() {
+    CheckEverythingDeallocated();
   }
 
   CompactObj cobj_;

src/core/dense_set.cc

@@ -168,14 +168,14 @@ auto DenseSet::PopPtrFront(DenseSet::ChainVectorIterator it) -> DensePtr {
   return front;
 }
 
-uint32_t DenseSet::ClearInternal(uint32_t start, uint32_t count) {
+uint32_t DenseSet::ClearStep(uint32_t start, uint32_t count) {
   constexpr unsigned kArrLen = 32;
   ClearItem arr[kArrLen];
   unsigned len = 0;
 
   size_t end = min<size_t>(entries_.size(), start + count);
   for (size_t i = start; i < end; ++i) {
-    DensePtr ptr = entries_[i];
+    DensePtr& ptr = entries_[i];
     if (ptr.IsEmpty())
       continue;
 
@@ -190,6 +190,7 @@ uint32_t DenseSet::ClearInternal(uint32_t start, uint32_t count) {
       dest.ptr = ptr;
       dest.obj = nullptr;
     }
+    ptr.Reset();
     if (len == kArrLen) {
       ClearBatch(kArrLen, arr);
       len = 0;

src/core/dense_set.h

@@ -215,9 +215,13 @@ class DenseSet {
   virtual ~DenseSet();
 
   void Clear() {
-    ClearInternal(0, entries_.size());
+    ClearStep(0, entries_.size());
   }
 
+  // Returns the next bucket index that should be cleared.
+  // Returns BucketCount when all objects are erased.
+  uint32_t ClearStep(uint32_t start, uint32_t count);
+
   // Returns the number of elements in the map. Note that it might be that some of these elements
   // have expired and can't be accessed.
   size_t UpperBoundSize() const {
@@ -303,11 +307,6 @@ class DenseSet {
 
   void* PopInternal();
 
-  // Note this does not free any dynamic allocations done by derived classes, that a DensePtr
-  // in the set may point to. This function only frees the allocated DenseLinkKeys created by
-  // DenseSet. All data allocated by a derived class should be freed before calling this
-  uint32_t ClearInternal(uint32_t start, uint32_t count);
-
   void IncreaseMallocUsed(size_t delta) {
     obj_malloc_used_ += delta;
   }

src/server/db_slice.cc

@@ -669,10 +669,8 @@ void DbSlice::ActivateDb(DbIndex db_ind) {
   CreateDb(db_ind);
 }
 
-bool DbSlice::Del(Context cntx, Iterator it) {
+void DbSlice::Del(Context cntx, Iterator it) {
-  if (!IsValid(it)) {
+  CHECK(IsValid(it));
-    return false;
-  }
 
   auto& db = db_arr_[cntx.db_index];
   auto obj_type = it->second.ObjType();
@@ -683,8 +681,6 @@ bool DbSlice::Del(Context cntx, Iterator it) {
     doc_del_cb_(key, cntx, it->second);
   }
   PerformDeletion(it, db.get());
-
-  return true;
 }
 
 void DbSlice::FlushSlotsFb(const cluster::SlotSet& slot_ids) {
@@ -917,7 +913,7 @@ OpResult<int64_t> DbSlice::UpdateExpire(const Context& cntx, Iterator prime_it,
   }
 
   if (rel_msec <= 0) {  // implicit - don't persist
-    CHECK(Del(cntx, prime_it));
+    Del(cntx, prime_it);
     return -1;
   } else if (IsValid(expire_it) && !params.persist) {
     auto current = ExpireTime(expire_it);

src/server/db_slice.h

@@ -346,7 +346,8 @@ class DbSlice {
   // Delete a key referred by its iterator.
   void PerformDeletion(Iterator del_it, DbTable* table);
 
-  bool Del(Context cntx, Iterator it);
+  // Deletes the iterator. The iterator must be valid.
+  void Del(Context cntx, Iterator it);
 
   constexpr static DbIndex kDbAll = 0xFFFF;
 

src/server/engine_shard.cc

@@ -426,11 +426,10 @@ bool EngineShard::DoDefrag() {
 //     priority.
 //     otherwise lower the task priority so that it would not use the CPU when not required
 uint32_t EngineShard::DefragTask() {
-  if (!namespaces) {
-    return util::ProactorBase::kOnIdleMaxLevel;
-  }
-
   constexpr uint32_t kRunAtLowPriority = 0u;
+  if (!namespaces) {
+    return kRunAtLowPriority;
+  }
 
   if (defrag_state_.CheckRequired()) {
     VLOG(2) << shard_id_ << ": need to run defrag memory cursor state: " << defrag_state_.cursor;

src/server/generic_family.cc

@@ -440,7 +440,7 @@ OpStatus Renamer::DelSrc(Transaction* t, EngineShard* shard) {
   DVLOG(1) << "Rename: removing the key '" << src_key_;
 
   res.post_updater.Run();
-  CHECK(db_slice.Del(t->GetDbContext(), it));
+  db_slice.Del(t->GetDbContext(), it);
   if (shard->journal()) {
     RecordJournal(t->GetOpArgs(shard), "DEL"sv, ArgSlice{src_key_}, 2);
   }
@@ -462,7 +462,7 @@ OpStatus Renamer::DeserializeDest(Transaction* t, EngineShard* shard) {
   if (dest_found_) {
     DVLOG(1) << "Rename: deleting the destiny key '" << dest_key_;
     dest_res.post_updater.Run();
-    CHECK(db_slice.Del(op_args.db_cntx, dest_res.it));
+    db_slice.Del(op_args.db_cntx, dest_res.it);
   }
 
   if (restore_args.Expired()) {
@@ -554,7 +554,7 @@ OpResult<bool> OpRestore(const OpArgs& op_args, std::string_view key, std::strin
         VLOG(1) << "restore command is running with replace, found old key '" << key
                 << "' and removing it";
         res.post_updater.Run();
-        CHECK(db_slice.Del(op_args.db_cntx, res.it));
+        db_slice.Del(op_args.db_cntx, res.it);
       } else {
         // we are not allowed to replace it.
         return OpStatus::KEY_EXISTS;
@@ -812,7 +812,7 @@ OpStatus OpMove(const OpArgs& op_args, string_view key, DbIndex target_db) {
   // Restore expire flag after std::move.
   from_res.it->second.SetExpire(IsValid(from_res.exp_it));
 
-  CHECK(db_slice.Del(op_args.db_cntx, from_res.it));
+  db_slice.Del(op_args.db_cntx, from_res.it);
   auto op_result = db_slice.AddNew(target_cntx, key, std::move(from_obj), exp_ts);
   RETURN_ON_BAD_STATUS(op_result);
   auto& add_res = *op_result;
@@ -868,13 +868,13 @@ OpResult<void> OpRen(const OpArgs& op_args, string_view from_key, string_view to
     to_res.post_updater.Run();
 
     from_res.post_updater.Run();
-    CHECK(db_slice.Del(op_args.db_cntx, from_res.it));
+    db_slice.Del(op_args.db_cntx, from_res.it);
   } else {
     // Here we first delete from_it because AddNew below could invalidate from_it.
     // On the other hand, AddNew does not rely on the iterators - this is why we keep
     // the value in `from_obj`.
     from_res.post_updater.Run();
-    CHECK(db_slice.Del(op_args.db_cntx, from_res.it));
+    db_slice.Del(op_args.db_cntx, from_res.it);
     auto op_result = db_slice.AddNew(op_args.db_cntx, to_key, std::move(from_obj), exp_ts);
     RETURN_ON_BAD_STATUS(op_result);
     to_res = std::move(*op_result);
@@ -995,35 +995,14 @@ std::optional<int32_t> ParseExpireOptionsOrReply(const CmdArgList args, SinkRepl
   return flags;
 }
 
-}  // namespace
+void DeleteGeneric(CmdArgList args, const CommandContext& cmd_cntx) {
-
-OpResult<uint32_t> GenericFamily::OpDel(const OpArgs& op_args, const ShardArgs& keys) {
-  DVLOG(1) << "Del: " << keys.Front();
-  auto& db_slice = op_args.GetDbSlice();
-
-  uint32_t res = 0;
-
-  for (string_view key : keys) {
-    auto fres = db_slice.FindMutable(op_args.db_cntx, key);
-    if (!IsValid(fres.it))
-      continue;
-    fres.post_updater.Run();
-    res += int(db_slice.Del(op_args.db_cntx, fres.it));
-  }
-
-  return res;
-}
-
-void GenericFamily::Del(CmdArgList args, const CommandContext& cmd_cntx) {
-  VLOG(1) << "Del " << ArgS(args, 0);
-
   atomic_uint32_t result{0};
   auto* builder = cmd_cntx.rb;
   bool is_mc = (builder->GetProtocol() == Protocol::MEMCACHE);
 
   auto cb = [&result](const Transaction* t, EngineShard* shard) {
     ShardArgs args = t->GetShardArgs(shard->shard_id());
-    auto res = OpDel(t->GetOpArgs(shard), args);
+    auto res = GenericFamily::OpDel(t->GetOpArgs(shard), args);
     result.fetch_add(res.value_or(0), memory_order_relaxed);
 
     return OpStatus::OK;
@@ -1049,6 +1028,36 @@ void GenericFamily::Del(CmdArgList args, const CommandContext& cmd_cntx) {
   }
 }
 
+}  // namespace
+
+OpResult<uint32_t> GenericFamily::OpDel(const OpArgs& op_args, const ShardArgs& keys) {
+  DVLOG(1) << "Del: " << keys.Front();
+  auto& db_slice = op_args.GetDbSlice();
+
+  uint32_t res = 0;
+
+  for (string_view key : keys) {
+    auto it = db_slice.FindMutable(op_args.db_cntx, key).it;  // post_updater will run immediately
+    if (!IsValid(it))
+      continue;
+
+    db_slice.Del(op_args.db_cntx, it);
+    ++res;
+  }
+
+  return res;
+}
+
+void GenericFamily::Del(CmdArgList args, const CommandContext& cmd_cntx) {
+  VLOG(1) << "Del " << ArgS(args, 0);
+
+  DeleteGeneric(args, cmd_cntx);
+}
+
+void GenericFamily::Unlink(CmdArgList args, const CommandContext& cmd_cntx) {
+  DeleteGeneric(args, cmd_cntx);
+}
+
 void GenericFamily::Ping(CmdArgList args, const CommandContext& cmd_cntx) {
   auto* rb = static_cast<RedisReplyBuilder*>(cmd_cntx.rb);
   if (args.size() > 1) {
@@ -1886,7 +1895,7 @@ void GenericFamily::Register(CommandRegistry* registry) {
       << CI{"TIME", CO::LOADING | CO::FAST, 1, 0, 0, acl::kTime}.HFUNC(Time)
       << CI{"TYPE", CO::READONLY | CO::FAST | CO::LOADING, 2, 1, 1, acl::kType}.HFUNC(Type)
       << CI{"DUMP", CO::READONLY, 2, 1, 1, acl::kDump}.HFUNC(Dump)
-      << CI{"UNLINK", CO::WRITE, -2, 1, -1, acl::kUnlink}.HFUNC(Del)
+      << CI{"UNLINK", CO::WRITE, -2, 1, -1, acl::kUnlink}.HFUNC(Unlink)
       << CI{"STICK", CO::WRITE, -2, 1, -1, acl::kStick}.HFUNC(Stick)
       << CI{"SORT", CO::READONLY, -2, 1, 1, acl::kSort}.HFUNC(Sort)
       << CI{"MOVE", CO::WRITE | CO::GLOBAL_TRANS | CO::NO_AUTOJOURNAL, 3, 1, 1, acl::kMove}.HFUNC(

src/server/generic_family.h

@@ -35,6 +35,7 @@ class GenericFamily {
   using SinkReplyBuilder = facade::SinkReplyBuilder;
 
   static void Del(CmdArgList args, const CommandContext& cmd_cntx);
+  static void Unlink(CmdArgList args, const CommandContext& cmd_cntx);
   static void Ping(CmdArgList args, const CommandContext& cmd_cntx);
   static void Exists(CmdArgList args, const CommandContext& cmd_cntx);
   static void Expire(CmdArgList args, const CommandContext& cmd_cntx);

src/server/hset_family.cc

@@ -585,10 +585,10 @@ OpResult<vector<string>> OpGetAll(const OpArgs& op_args, string_view key, uint8_
   // and the enconding is guaranteed to be a DenseSet since we only support expiring
   // value with that enconding.
   if (res.empty()) {
-    auto mutable_res = db_slice.FindMutable(op_args.db_cntx, key, OBJ_HASH);
+    // post_updater will run immediately
-    // Run postupdater, it means that we deleted the keys
+    auto it = db_slice.FindMutable(op_args.db_cntx, key).it;
-    mutable_res->post_updater.Run();
+
-    db_slice.Del(op_args.db_cntx, mutable_res->it);
+    db_slice.Del(op_args.db_cntx, it);
   }
 
   return res;
@@ -1169,10 +1169,10 @@ void HSetFamily::HRandField(CmdArgList args, const CommandContext& cmd_cntx) {
         }
       }
 
-      if (string_map->Empty()) {
+      if (string_map->Empty()) {  // Can happen if we use a TTL on hash members.
-        auto it_mutable = db_slice.FindMutable(db_context, key, OBJ_HASH);
+        // post_updater will run immediately
-        it_mutable->post_updater.Run();
+        auto it = db_slice.FindMutable(db_context, key).it;
-        db_slice.Del(db_context, it_mutable->it);
+        db_slice.Del(db_context, it);
         return facade::OpStatus::KEY_NOTFOUND;
       }
     } else if (pv.Encoding() == kEncodingListPack) {
@@ -1207,8 +1207,7 @@ void HSetFamily::HRandField(CmdArgList args, const CommandContext& cmd_cntx) {
         }
       }
     } else {
-      LOG(ERROR) << "Invalid encoding " << pv.Encoding();
+      LOG(FATAL) << "Invalid encoding " << pv.Encoding();
-      return OpStatus::INVALID_VALUE;
     }
     return str_vec;
   };

src/server/json_family.cc

@@ -913,8 +913,13 @@ OpResult<long> OpDel(const OpArgs& op_args, string_view key, string_view path,
   if (json_path.RefersToRootElement()) {
     auto& db_slice = op_args.GetDbSlice();
     auto it = db_slice.FindMutable(op_args.db_cntx, key).it;  // post_updater will run immediately
-    return static_cast<long>(db_slice.Del(op_args.db_cntx, it));
+    if (IsValid(it)) {
+      db_slice.Del(op_args.db_cntx, it);
+      return 1;
     }
+    return 0;
+  }
+
   JsonMemTracker tracker;
   // FindMutable because we need to run the AutoUpdater at the end which will account
   // the deltas calculated from the MemoryTracker

src/server/list_family.cc

@@ -180,7 +180,7 @@ std::string OpBPop(Transaction* t, EngineShard* shard, std::string_view key, Lis
   OpArgs op_args = t->GetOpArgs(shard);
   if (len == 0) {
     DVLOG(1) << "deleting key " << key << " " << t->DebugId();
-    CHECK(op_args.GetDbSlice().Del(op_args.db_cntx, it));
+    op_args.GetDbSlice().Del(op_args.db_cntx, it);
   }
 
   if (op_args.shard->journal()) {
@@ -276,7 +276,7 @@ OpResult<string> OpMoveSingleShard(const OpArgs& op_args, string_view src, strin
   dest_res.post_updater.Run();
 
   if (prev_len == 1) {
-    CHECK(db_slice.Del(op_args.db_cntx, src_it));
+    db_slice.Del(op_args.db_cntx, src_it);
   }
 
   return val;
@@ -452,7 +452,7 @@ OpResult<StringVec> OpPop(const OpArgs& op_args, string_view key, ListDir dir, u
   it_res->post_updater.Run();
 
   if (count == prev_len) {
-    CHECK(db_slice.Del(op_args.db_cntx, it));
+    db_slice.Del(op_args.db_cntx, it);
   }
 
   if (op_args.shard->journal() && journal_rewrite) {
@@ -765,7 +765,7 @@ OpResult<uint32_t> OpRem(const OpArgs& op_args, string_view key, string_view ele
   it_res->post_updater.Run();
 
   if (len == 0) {
-    CHECK(db_slice.Del(op_args.db_cntx, it));
+    db_slice.Del(op_args.db_cntx, it);
   }
 
   return removed;
@@ -840,7 +840,7 @@ OpStatus OpTrim(const OpArgs& op_args, string_view key, long start, long end) {
   it_res->post_updater.Run();
 
   if (it->second.Size() == 0) {
-    CHECK(db_slice.Del(op_args.db_cntx, it));
+    db_slice.Del(op_args.db_cntx, it);
   }
   return OpStatus::OK;
 }

src/server/set_family.cc

@@ -443,10 +443,12 @@ OpResult<uint32_t> OpAdd(const OpArgs& op_args, std::string_view key, const NewE
   // key if it exists.
   if (overwrite && (vals_it.begin() == vals_it.end())) {
     auto it = db_slice.FindMutable(op_args.db_cntx, key).it;  // post_updater will run immediately
+    if (IsValid(it)) {
       db_slice.Del(op_args.db_cntx, it);
       if (journal_update && op_args.shard->journal()) {
         RecordJournal(op_args, "DEL"sv, ArgSlice{key});
       }
+    }
     return 0;
   }
 
@@ -561,7 +563,7 @@ OpResult<uint32_t> OpRem(const OpArgs& op_args, string_view key, facade::ArgRang
   find_res->post_updater.Run();
 
   if (isempty) {
-    CHECK(db_slice.Del(op_args.db_cntx, find_res->it));
+    db_slice.Del(op_args.db_cntx, find_res->it);
   }
   if (journal_rewrite && op_args.shard->journal()) {
     vector<string_view> mapped(vals.Size() + 1);
@@ -886,7 +888,7 @@ OpResult<StringVec> OpPop(const OpArgs& op_args, string_view key, unsigned count
 
     // Delete the set as it is now empty
     find_res->post_updater.Run();
-    CHECK(db_slice.Del(op_args.db_cntx, find_res->it));
+    db_slice.Del(op_args.db_cntx, find_res->it);
 
     // Replicate as DEL.
     if (op_args.shard->journal()) {

src/server/zset_family.cc

@@ -964,7 +964,9 @@ OpResult<AddResult> OpAdd(const OpArgs& op_args, const ZParams& zparams, string_
 
   if (zparams.override && members.empty()) {
     auto it = db_slice.FindMutable(op_args.db_cntx, key).it;  // post_updater will run immediately
+    if (IsValid(it)) {
       db_slice.Del(op_args.db_cntx, it);
+    }
     return OpStatus::OK;
   }
 
@@ -1219,7 +1221,7 @@ ScoredArray OpBZPop(Transaction* t, EngineShard* shard, std::string_view key, bo
   auto zlen = pv.Size();
   if (zlen == 0) {
     DVLOG(1) << "deleting key " << key << " " << t->DebugId();
-    CHECK(db_slice.Del(t->GetDbContext(), it_res->it));
+    db_slice.Del(t->GetDbContext(), it_res->it);
   }
 
   OpArgs op_args = t->GetOpArgs(shard);
@@ -1330,7 +1332,7 @@ auto OpPopCount(const ZSetFamily::ZRangeSpec& range_spec, const OpArgs& op_args,
 
   auto zlen = pv.Size();
   if (zlen == 0) {
-    CHECK(op_args.GetDbSlice().Del(op_args.db_cntx, res_it->it));
+    op_args.GetDbSlice().Del(op_args.db_cntx, res_it->it);
   }
 
   return iv.PopResult();
@@ -1384,7 +1386,7 @@ OpResult<unsigned> OpRemRange(const OpArgs& op_args, string_view key,
 
   auto zlen = pv.Size();
   if (zlen == 0) {
-    CHECK(op_args.GetDbSlice().Del(op_args.db_cntx, res_it->it));
+    op_args.GetDbSlice().Del(op_args.db_cntx, res_it->it);
   }
 
   return iv.removed();
@@ -1563,7 +1565,7 @@ OpResult<unsigned> OpRem(const OpArgs& op_args, string_view key, facade::ArgRang
   res_it->post_updater.Run();
 
   if (zlen == 0) {
-    CHECK(op_args.GetDbSlice().Del(op_args.db_cntx, res_it->it));
+    op_args.GetDbSlice().Del(op_args.db_cntx, res_it->it);
   }
 
   return deleted;