chore: disable persistent journaling feature (#1549)

1. We have not worked on it for many months
2. It's not on the short term roadmap
3. It complicates the code around the replication.

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

src/server/dflycmd.cc

@@ -104,9 +104,9 @@ void DflyCmd::Run(CmdArgList args, ConnectionContext* cntx) {
   ToUpper(&args[0]);
   string_view sub_cmd = ArgS(args, 0);
 
-  if (sub_cmd == "JOURNAL" && args.size() >= 2) {
+  /*if (sub_cmd == "JOURNAL" && args.size() >= 2) {
     return Journal(args, cntx);
-  }
+  }*/
 
   if (sub_cmd == "THREAD") {
     return Thread(args, cntx);
@@ -139,6 +139,7 @@ void DflyCmd::Run(CmdArgList args, ConnectionContext* cntx) {
   rb->SendError(kSyntaxErr);
 }
 
+#if 0
 void DflyCmd::Journal(CmdArgList args, ConnectionContext* cntx) {
   DCHECK_GE(args.size(), 2u);
   ToUpper(&args[1]);
@@ -201,6 +202,8 @@ void DflyCmd::Journal(CmdArgList args, ConnectionContext* cntx) {
   return rb->SendError(reply, kSyntaxErrType);
 }
 
+#endif
+
 void DflyCmd::Thread(CmdArgList args, ConnectionContext* cntx) {
   RedisReplyBuilder* rb = static_cast<RedisReplyBuilder*>(cntx->reply_builder());
   util::ProactorPool* pool = shard_set->pool();
@@ -472,8 +475,9 @@ OpStatus DflyCmd::StartFullSyncInThread(FlowInfo* flow, Context* cntx, EngineSha
     flow->saver.reset();
   };
 
+  sf_->journal()->StartInThread();
+
   // Shard can be null for io thread.
-  CHECK(!sf_->journal()->OpenInThread(false, ""sv));  // can only happen in persistent mode.
   if (shard != nullptr) {
     flow->saver->StartSnapshotInShard(true, cntx->GetCancellation(), shard);
   }

src/server/dflycmd.h

@@ -133,7 +133,7 @@ class DflyCmd {
  private:
   // JOURNAL [START/STOP]
   // Start or stop journaling.
-  void Journal(CmdArgList args, ConnectionContext* cntx);
+  // void Journal(CmdArgList args, ConnectionContext* cntx);
 
   // THREAD [to_thread]
   // Return connection thread index or migrate to another thread.

src/server/journal/journal.cc

@@ -28,9 +28,20 @@ thread_local JournalSlice journal_slice;
 Journal::Journal() {
 }
 
-error_code Journal::OpenInThread(bool persistent, string_view dir) {
+void Journal::StartInThread() {
   journal_slice.Init(unsigned(ProactorBase::GetIndex()));
 
+  ServerState::tlocal()->set_journal(this);
+  EngineShard* shard = EngineShard::tlocal();
+  if (shard) {
+    shard->set_journal(this);
+  }
+}
+
+#if 0
+error_code Journal::OpenInThread(bool persistent, string_view dir) {
+
+
   error_code ec;
 
   if (persistent) {
@@ -40,14 +51,9 @@ error_code Journal::OpenInThread(bool persistent, string_view dir) {
     }
   }
 
-  ServerState::tlocal()->set_journal(this);
-  EngineShard* shard = EngineShard::tlocal();
-  if (shard) {
-    shard->set_journal(this);
-  }
-
   return ec;
 }
+#endif
 
 error_code Journal::Close() {
   CHECK(lameduck_.load(memory_order_relaxed));
@@ -65,12 +71,12 @@ error_code Journal::Close() {
       shard->set_journal(nullptr);
     }
 
-    auto ec = journal_slice.Close();
+    /*auto ec = journal_slice.Close();
 
     if (ec) {
       lock_guard lk2(ec_mu);
       res = ec;
-    }
+    }*/
   };
 
   shard_set->pool()->AwaitFiberOnAll(close_cb);

src/server/journal/journal.h

@@ -23,11 +23,15 @@ class Journal {
   // and false otherwise.
   bool EnterLameDuck();  // still logs ongoing transactions but refuses to start new ones.
 
+  void StartInThread();
+
   // Requires: journal is in lameduck mode.
   std::error_code Close();
 
+#if 0
   // Opens journal inside a Dragonfly thread. Must be called in each thread.
   std::error_code OpenInThread(bool persistent, std::string_view dir);
+#endif
 
   //******* The following functions must be called in the context of the owning shard *********//
 

src/server/journal/journal_slice.cc

@@ -20,9 +20,11 @@ namespace fs = std::filesystem;
 
 namespace {
 
+/*
 string ShardName(std::string_view base, unsigned index) {
   return absl::StrCat(base, "-", absl::Dec(index, absl::kZeroPad4), ".log");
 }
+*/
 
 }  // namespace
 
@@ -42,17 +44,18 @@ JournalSlice::JournalSlice() {
 }
 
 JournalSlice::~JournalSlice() {
-  CHECK(!shard_file_);
+  // CHECK(!shard_file_);
 }
 
 void JournalSlice::Init(unsigned index) {
-  if (ring_buffer_)  // calling this function multiple times is allowed and it's a no-op.
-    return;
+  // if (ring_buffer_)  // calling this function multiple times is allowed and it's a no-op.
+  //   return;
 
   slice_index_ = index;
-  ring_buffer_.emplace(128);  // TODO: to make it configurable
+  // ring_buffer_.emplace(128);  // TODO: to make it configurable
 }
 
+#if 0
 std::error_code JournalSlice::Open(std::string_view dir) {
   CHECK(!shard_file_);
   DCHECK_NE(slice_index_, UINT32_MAX);
@@ -111,15 +114,17 @@ error_code JournalSlice::Close() {
 
   return ec;
 }
+#endif
 
 void JournalSlice::AddLogRecord(const Entry& entry, bool await) {
-  DCHECK(ring_buffer_);
-
+  // DCHECK(ring_buffer_);
   if (entry.opcode != Op::NOOP) {
-    // TODO: This is preparation for AOC style journaling, currently unused.
-    RingItem item;
-    item.lsn = lsn_;
     lsn_++;
+// TODO: This is preparation for AOC style journaling, currently unused.
+#if 0
+    RingItem item;
+    item.lsn = prev_lsn;
+
     item.opcode = entry.opcode;
     item.txid = entry.txid;
     VLOG(1) << "Writing item [" << item.lsn << "]: " << entry.ToString();
@@ -131,6 +136,7 @@ void JournalSlice::AddLogRecord(const Entry& entry, bool await) {
       CHECK_EC(ec);
       file_offset_ += line.size();
     }
+#endif
   }
 
   {

src/server/journal/journal_slice.h

@@ -8,7 +8,6 @@
 #include <string_view>
 
 #include "base/ring_buffer.h"
-#include "core/uring.h"
 #include "server/common.h"
 #include "server/journal/types.h"
 
@@ -23,9 +22,11 @@ class JournalSlice {
 
   void Init(unsigned index);
 
+#if 0
   std::error_code Open(std::string_view dir);
 
   std::error_code Close();
+#endif
 
   // This is always the LSN of the *next* journal entry.
   LSN cur_lsn() const {
@@ -36,9 +37,9 @@ class JournalSlice {
     return status_ec_;
   }
 
-  // Whether the file-based journaling is open.
+  // Whether the journaling is open.
   bool IsOpen() const {
-    return bool(shard_file_);
+    return slice_index_ != UINT32_MAX;
   }
 
   void AddLogRecord(const Entry& entry, bool await);
@@ -53,9 +54,9 @@ class JournalSlice {
  private:
   struct RingItem;
 
-  std::string shard_path_;
-  std::unique_ptr<LinuxFile> shard_file_;
-  std::optional<base::RingBuffer<RingItem>> ring_buffer_;
+  // std::string shard_path_;
+  // std::unique_ptr<LinuxFile> shard_file_;
+  // std::optional<base::RingBuffer<RingItem>> ring_buffer_;
 
   mutable util::SharedMutex cb_mu_;
   std::vector<std::pair<uint32_t, ChangeCallback>> change_cb_arr_ ABSL_GUARDED_BY(cb_mu_);