feat(server): expiry notifications (#3154)

Adds basic support for keyspace notifications, only Ex

Signed-off-by: Vladislav Oleshko <vlad@dragonflydb.io>

src/core/bloom.cc

@@ -8,6 +8,7 @@
 #include <absl/numeric/bits.h>
 #include <xxhash.h>
 
+#include <algorithm>
 #include <cmath>
 
 #include "base/logging.h"

src/facade/dragonfly_connection.cc

@@ -275,22 +275,6 @@ struct Connection::Shutdown {
   }
 };
 
-Connection::PubMessage::PubMessage(string pattern, shared_ptr<char[]> buf, size_t channel_len,
-                                   size_t message_len)
-    : pattern{std::move(pattern)},
-      buf{std::move(buf)},
-      channel_len{channel_len},
-      message_len{message_len} {
-}
-
-string_view Connection::PubMessage::Channel() const {
-  return {buf.get(), channel_len};
-}
-
-string_view Connection::PubMessage::Message() const {
-  return {buf.get() + channel_len, message_len};
-}
-
 void Connection::PipelineMessage::SetArgs(const RespVec& args) {
   auto* next = storage.data();
   for (size_t i = 0; i < args.size(); ++i) {
@@ -361,7 +345,7 @@ size_t Connection::PipelineMessage::StorageCapacity() const {
 size_t Connection::MessageHandle::UsedMemory() const {
   struct MessageSize {
     size_t operator()(const PubMessagePtr& msg) {
-      return sizeof(PubMessage) + (msg->channel_len + msg->message_len);
+      return sizeof(PubMessage) + (msg->channel.size() + msg->message.size());
     }
     size_t operator()(const PipelineMessagePtr& msg) {
       return sizeof(PipelineMessage) + msg->args.capacity() * sizeof(MutableSlice) +
@@ -449,8 +433,8 @@ void Connection::DispatchOperations::operator()(const PubMessage& pub_msg) {
     arr[i++] = "pmessage";
     arr[i++] = pub_msg.pattern;
   }
-  arr[i++] = pub_msg.Channel();
+  arr[i++] = pub_msg.channel;
-  arr[i++] = pub_msg.Message();
+  arr[i++] = pub_msg.message;
   rbuilder->SendStringArr(absl::Span<string_view>{arr.data(), i},
                           RedisReplyBuilder::CollectionType::PUSH);
 }

src/facade/dragonfly_connection.h

@@ -71,15 +71,9 @@ class Connection : public util::Connection {
 
   // PubSub message, either incoming message for active subscription or reply for new subscription.
   struct PubMessage {
-    std::string pattern{};            // non-empty for pattern subscriber
+    std::string pattern{};              // non-empty for pattern subscriber
-    std::shared_ptr<char[]> buf;      // stores channel name and message
+    std::shared_ptr<char[]> buf;        // stores channel name and message
-    size_t channel_len, message_len;  // lengths in buf
+    std::string_view channel, message;  // channel and message parts from buf
-
-    std::string_view Channel() const;
-    std::string_view Message() const;
-
-    PubMessage(std::string pattern, std::shared_ptr<char[]> buf, size_t channel_len,
-               size_t message_len);
   };
 
   // Pipeline message, accumulated Redis command to be executed.

src/facade/reply_builder.cc

@@ -496,7 +496,7 @@ void RedisReplyBuilder::SendMGetResponse(MGetResponse resp) {
 
 void RedisReplyBuilder::SendSimpleStrArr(StrSpan arr) {
   string res = absl::StrCat("*", arr.Size(), kCRLF);
-  for (std::string_view str : arr)
+  for (string_view str : arr)
     StrAppend(&res, "+", str, kCRLF);
 
   SendRaw(res);

src/server/CMakeLists.txt

@@ -32,7 +32,7 @@ add_library(dfly_transaction db_slice.cc malloc_stats.cc blocking_controller.cc
             common.cc journal/journal.cc journal/types.cc journal/journal_slice.cc
             server_state.cc table.cc  top_keys.cc transaction.cc tx_base.cc
             serializer_commons.cc journal/serializer.cc journal/executor.cc journal/streamer.cc
-            ${TX_LINUX_SRCS} acl/acl_log.cc slowlog.cc)
+            ${TX_LINUX_SRCS} acl/acl_log.cc slowlog.cc channel_store.cc)
 
 SET(DF_SEARCH_SRCS search/search_family.cc search/doc_index.cc search/doc_accessors.cc
     search/aggregator.cc)
@@ -43,7 +43,7 @@ if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
   cxx_test(tiered_storage_test dfly_test_lib LABELS DFLY)
 endif()
 
-add_library(dragonfly_lib bloom_family.cc engine_shard_set.cc channel_store.cc
+add_library(dragonfly_lib bloom_family.cc engine_shard_set.cc
             config_registry.cc conn_context.cc debugcmd.cc dflycmd.cc
             generic_family.cc hset_family.cc http_api.cc json_family.cc
             list_family.cc main_service.cc memory_cmd.cc rdb_load.cc rdb_save.cc replica.cc

src/server/channel_store.cc

@@ -10,6 +10,8 @@ extern "C" {
 #include "redis/util.h"
 }
 
+#include <absl/container/fixed_array.h>
+
 #include "base/logging.h"
 #include "server/engine_shard_set.h"
 #include "server/server_state.h"
@@ -23,6 +25,32 @@ bool Matches(string_view pattern, string_view channel) {
   return stringmatchlen(pattern.data(), pattern.size(), channel.data(), channel.size(), 0) == 1;
 }
 
+// Build functor for sending messages to connection
+auto BuildSender(string_view channel, facade::ArgRange messages) {
+  absl::FixedArray<string_view, 1> views(messages.Size());
+  size_t messages_size = accumulate(messages.begin(), messages.end(), 0,
+                                    [](int sum, string_view str) { return sum + str.size(); });
+  auto buf = shared_ptr<char[]>{new char[channel.size() + messages_size]};
+  {
+    memcpy(buf.get(), channel.data(), channel.size());
+    char* ptr = buf.get() + channel.size();
+
+    size_t i = 0;
+    for (string_view message : messages) {
+      memcpy(ptr, message.data(), message.size());
+      views[i++] = {ptr, message.size()};
+      ptr += message.size();
+    }
+  }
+
+  return [channel, buf = std::move(buf), views = std::move(views)](facade::Connection* conn,
+                                                                   string pattern) {
+    string_view channel_view{buf.get(), channel.size()};
+    for (std::string_view message_view : views)
+      conn->SendPubMessageAsync({std::move(pattern), buf, channel_view, message_view});
+  };
+}
+
 }  // namespace
 
 bool ChannelStore::Subscriber::ByThread(const Subscriber& lhs, const Subscriber& rhs) {
@@ -95,6 +123,39 @@ void ChannelStore::Destroy() {
 
 ChannelStore::ControlBlock ChannelStore::control_block;
 
+unsigned ChannelStore::SendMessages(std::string_view channel, facade::ArgRange messages) const {
+  vector<Subscriber> subscribers = FetchSubscribers(channel);
+  if (subscribers.empty())
+    return 0;
+
+  // Make sure none of the threads publish buffer limits is reached. We don't reserve memory ahead
+  // and don't prevent the buffer from possibly filling, but the approach is good enough for
+  // limiting fast producers. Most importantly, we can use DispatchBrief below as we block here
+  optional<uint32_t> last_thread;
+  for (auto& sub : subscribers) {
+    DCHECK_LE(last_thread.value_or(0), sub.Thread());
+    if (last_thread && *last_thread == sub.Thread())  // skip same thread
+      continue;
+
+    if (sub.EnsureMemoryBudget())  // Invalid pointers are skipped
+      last_thread = sub.Thread();
+  }
+
+  auto subscribers_ptr = make_shared<decltype(subscribers)>(std::move(subscribers));
+  auto cb = [subscribers_ptr, send = BuildSender(channel, messages)](unsigned idx, auto*) {
+    auto it = lower_bound(subscribers_ptr->begin(), subscribers_ptr->end(), idx,
+                          ChannelStore::Subscriber::ByThreadId);
+    while (it != subscribers_ptr->end() && it->Thread() == idx) {
+      if (auto* ptr = it->Get(); ptr)
+        send(ptr, it->pattern);
+      it++;
+    }
+  };
+  shard_set->pool()->DispatchBrief(std::move(cb));
+
+  return subscribers_ptr->size();
+}
+
 vector<ChannelStore::Subscriber> ChannelStore::FetchSubscribers(string_view channel) const {
   vector<Subscriber> res;
 

src/server/channel_store.h

@@ -54,6 +54,9 @@ class ChannelStore {
 
   ChannelStore();
 
+  // Send messages to channel, block on connection backpressure
+  unsigned SendMessages(std::string_view channel, facade::ArgRange messages) const;
+
   // Fetch all subscribers for channel, including matching patterns.
   std::vector<Subscriber> FetchSubscribers(std::string_view channel) const;
 

src/server/db_slice.cc

@@ -9,6 +9,7 @@
 #include "base/flags.h"
 #include "base/logging.h"
 #include "generic_family.h"
+#include "server/channel_store.h"
 #include "server/cluster/cluster_defs.h"
 #include "server/engine_shard_set.h"
 #include "server/error.h"
@@ -33,6 +34,9 @@ ABSL_FLAG(double, table_growth_margin, 0.4,
           "Prevents table from growing if number of free slots x average object size x this ratio "
           "is larger than memory budget.");
 
+ABSL_FLAG(std::string, notify_keyspace_events, "",
+          "notify-keyspace-events. Only Ex is supported for now");
+
 namespace dfly {
 
 using namespace std;
@@ -204,9 +208,7 @@ unsigned PrimeEvictionPolicy::Evict(const PrimeTable::HotspotBuckets& eb, PrimeT
 
     // log the evicted keys to journal.
     if (auto journal = db_slice_->shard_owner()->journal(); journal) {
-      ArgSlice delete_args(&key, 1);
+      RecordExpiry(cntx_.db_index, key);
-      journal->RecordEntry(0, journal::Op::EXPIRED, cntx_.db_index, 1, cluster::KeySlot(key),
-                           Payload("DEL", delete_args), false);
     }
 
     db_slice_->PerformDeletion(DbSlice::Iterator(last_slot_it, StringOrView::FromView(key)), table);
@@ -268,6 +270,13 @@ DbSlice::DbSlice(uint32_t index, bool caching_mode, EngineShard* owner)
   CreateDb(0);
   expire_base_[0] = expire_base_[1] = 0;
   soft_budget_limit_ = (0.3 * max_memory_limit / shard_set->size());
+
+  std::string keyspace_events = GetFlag(FLAGS_notify_keyspace_events);
+  if (!keyspace_events.empty() && keyspace_events != "Ex") {
+    LOG(ERROR) << "Only Ex is currently supported";
+    exit(0);
+  }
+  expired_keys_events_recording_ = !keyspace_events.empty();
 }
 
 DbSlice::~DbSlice() {
@@ -1041,11 +1050,15 @@ DbSlice::PrimeItAndExp DbSlice::ExpireIfNeeded(const Context& cntx, PrimeIterato
                << ", expire table size: " << db->expire.size()
                << ", prime table size: " << db->prime.size() << util::fb2::GetStacktrace();
   }
+
   // Replicate expiry
   if (auto journal = owner_->journal(); journal) {
     RecordExpiry(cntx.db_index, key);
   }
 
+  if (expired_keys_events_recording_)
+    db->expired_keys_events_.emplace_back(key);
+
   auto obj_type = it->second.ObjType();
   if (doc_del_cb_ && (obj_type == OBJ_JSON || obj_type == OBJ_HASH)) {
     doc_del_cb_(key, cntx, it->second);
@@ -1160,6 +1173,13 @@ auto DbSlice::DeleteExpiredStep(const Context& cntx, unsigned count) -> DeleteEx
     }
   }
 
+  // Send and clear accumulated expired key events
+  if (auto& events = db_arr_[cntx.db_index]->expired_keys_events_; !events.empty()) {
+    ChannelStore* store = ServerState::tlocal()->channel_store();
+    store->SendMessages(absl::StrCat("__keyevent@", cntx.db_index, "__:expired"), events);
+    events.clear();
+  }
+
   return result;
 }
 
@@ -1188,6 +1208,8 @@ void DbSlice::FreeMemWithEvictionStep(DbIndex db_ind, size_t increase_goal_bytes
   string tmp;
   int32_t starting_segment_id = rand() % num_segments;
   size_t used_memory_before = owner_->UsedMemory();
+
+  bool record_keys = owner_->journal() != nullptr || expired_keys_events_recording_;
   vector<string> keys_to_journal;
 
   {
@@ -1216,9 +1238,8 @@ void DbSlice::FreeMemWithEvictionStep(DbIndex db_ind, size_t increase_goal_bytes
           if (lt.Find(LockTag(key)).has_value())
             continue;
 
-          if (auto journal = owner_->journal(); journal) {
+          if (record_keys)
-            keys_to_journal.push_back(string(key));
+            keys_to_journal.emplace_back(key);
-          }
 
           PerformDeletion(Iterator(evict_it, StringOrView::FromView(key)), db_table.get());
           ++evicted;
@@ -1236,12 +1257,12 @@ void DbSlice::FreeMemWithEvictionStep(DbIndex db_ind, size_t increase_goal_bytes
 finish:
   // send the deletion to the replicas.
   // fiber preemption could happen in this phase.
-  if (auto journal = owner_->journal(); journal) {
+  for (string_view key : keys_to_journal) {
-    for (string_view key : keys_to_journal) {
+    if (auto journal = owner_->journal(); journal)
-      ArgSlice delete_args(&key, 1);
+      RecordExpiry(db_ind, key);
-      journal->RecordEntry(0, journal::Op::EXPIRED, db_ind, 1, cluster::KeySlot(key),
+
-                           Payload("DEL", delete_args), false);
+    if (expired_keys_events_recording_)
-    }
+      db_table->expired_keys_events_.emplace_back(key);
   }
 
   auto time_finish = absl::GetCurrentTimeNanos();

src/server/db_slice.h

@@ -569,6 +569,9 @@ class DbSlice {
   // Registered by shard indices on when first document index is created.
   DocDeletionCallback doc_del_cb_;
 
+  // Record whenever a key expired to DbTable::expired_keys_events_ for keyspace notifications
+  bool expired_keys_events_recording_ = true;
+
   struct Hash {
     size_t operator()(const facade::Connection::WeakRef& c) const {
       return std::hash<uint32_t>()(c.GetClientId());

src/server/dragonfly_test.cc

@@ -514,8 +514,8 @@ TEST_F(DflyEngineTest, PSubscribe) {
   ASSERT_EQ(1, SubscriberMessagesLen("IO1"));
 
   const auto& msg = GetPublishedMessage("IO1", 0);
-  EXPECT_EQ("foo", msg.Message());
+  EXPECT_EQ("foo", msg.message);
-  EXPECT_EQ("ab", msg.Channel());
+  EXPECT_EQ("ab", msg.channel);
   EXPECT_EQ("a*", msg.pattern);
 }
 

src/server/main_service.cc

@@ -2243,49 +2243,10 @@ void Service::Exec(CmdArgList args, ConnectionContext* cntx) {
 
 void Service::Publish(CmdArgList args, ConnectionContext* cntx) {
   string_view channel = ArgS(args, 0);
-  string_view msg = ArgS(args, 1);
+  string_view messages[] = {ArgS(args, 1)};
 
   auto* cs = ServerState::tlocal()->channel_store();
-  vector<ChannelStore::Subscriber> subscribers = cs->FetchSubscribers(channel);
+  cntx->SendLong(cs->SendMessages(channel, messages));
-  int num_published = subscribers.size();
-  if (!subscribers.empty()) {
-    // Make sure neither of the threads limits is reached.
-    // This check actually doesn't reserve any memory ahead and doesn't prevent the buffer
-    // from eventually filling up, especially if multiple clients are unblocked simultaneously,
-    // but is generally good enough to limit too fast producers.
-    // Most importantly, this approach allows not blocking and not awaiting in the dispatch below,
-    // thus not adding any overhead to backpressure checks.
-    optional<uint32_t> last_thread;
-    for (auto& sub : subscribers) {
-      DCHECK_LE(last_thread.value_or(0), sub.Thread());
-      if (last_thread && *last_thread == sub.Thread())  // skip same thread
-        continue;
-
-      if (sub.EnsureMemoryBudget())  // Invalid pointers are skipped
-        last_thread = sub.Thread();
-    }
-
-    auto subscribers_ptr = make_shared<decltype(subscribers)>(std::move(subscribers));
-    auto buf = shared_ptr<char[]>{new char[channel.size() + msg.size()]};
-    memcpy(buf.get(), channel.data(), channel.size());
-    memcpy(buf.get() + channel.size(), msg.data(), msg.size());
-
-    auto cb = [subscribers_ptr, buf, channel, msg](unsigned idx, util::ProactorBase*) {
-      auto it = lower_bound(subscribers_ptr->begin(), subscribers_ptr->end(), idx,
-                            ChannelStore::Subscriber::ByThreadId);
-
-      while (it != subscribers_ptr->end() && it->Thread() == idx) {
-        if (auto* ptr = it->Get(); ptr) {
-          ptr->SendPubMessageAsync(
-              {std::move(it->pattern), std::move(buf), channel.size(), msg.size()});
-        }
-        it++;
-      }
-    };
-    shard_set->pool()->DispatchBrief(std::move(cb));
-  }
-
-  cntx->SendLong(num_published);
 }
 
 void Service::Subscribe(CmdArgList args, ConnectionContext* cntx) {

src/server/table.h

@@ -123,6 +123,9 @@ struct DbTable : boost::intrusive_ref_counter<DbTable, boost::thread_unsafe_coun
   // Stores a list of dependant connections for each watched key.
   absl::flat_hash_map<std::string, std::vector<ConnectionState::ExecInfo*>> watched_keys;
 
+  // Keyspace notifications: list of expired keys since last batch of messages was published.
+  mutable std::vector<std::string> expired_keys_events_;
+
   mutable DbTableStats stats;
   std::vector<SlotStats> slots_stats;
   ExpireTable::Cursor expire_cursor;

tests/dragonfly/connection_test.py

@@ -410,6 +410,32 @@ async def test_subscribers_with_active_publisher(df_server: DflyInstance, max_co
     await async_pool.disconnect()
 
 
+@dfly_args({"notify_keyspace_events": "Ex"})
+async def test_keyspace_events(async_client: aioredis.Redis):
+    pclient = async_client.pubsub()
+    await pclient.subscribe("__keyevent@0__:expired")
+
+    keys = []
+    for i in range(10, 50):
+        keys.append(f"k{i}")
+        await async_client.set(keys[-1], "X", px=200 + i * 10)
+
+    # We don't support immediate expiration:
+    # keys += ['immediate']
+    # await async_client.set(keys[-1], 'Y', exat=123) # expired 50 years ago
+
+    events = []
+    async for message in pclient.listen():
+        if message["type"] == "subscribe":
+            continue
+
+        events.append(message)
+        if len(events) >= len(keys):
+            break
+
+    assert set(ev["data"] for ev in events) == set(keys)
+
+
 async def test_big_command(df_server, size=8 * 1024):
     reader, writer = await asyncio.open_connection("127.0.0.1", df_server.port)