[WIP] chore: add tx queue head debug info in AnalyzeTxQueue

src/server/engine_shard.cc

@@ -795,7 +795,7 @@ bool EngineShard::ShouldThrottleForTiering() const {  // see header for formula
          (UsedMemory() > tiering_redline + tiered_storage_->CoolMemoryUsage());
 }
 
-auto EngineShard::AnalyzeTxQueue() const -> TxQueueInfo {
+EngineShard::TxQueueInfo EngineShard::AnalyzeTxQueue() const {
   const TxQueue* queue = txq();
 
   ShardId sid = shard_id();
@@ -810,6 +810,12 @@ auto EngineShard::AnalyzeTxQueue() const -> TxQueueInfo {
 
   auto& db_slice = namespaces.GetDefaultNamespace().GetCurrentDbSlice();
 
+  {
+    auto value = queue->At(cur);
+    Transaction* trx = std::get<Transaction*>(value);
+    info.head.debug_id_info = trx->DebugId();
+  }
+
   do {
     auto value = queue->At(cur);
     Transaction* trx = std::get<Transaction*>(value);

src/server/engine_shard.h

@@ -155,6 +155,10 @@ class EngineShard {
 
   void StopPeriodicFiber();
 
+  struct TxQueueItem {
+    std::string debug_id_info;
+  };
+
   struct TxQueueInfo {
     // Armed - those that the coordinator has armed with callbacks and wants them to run.
     // Runnable - those that could run (they own the locks) but probably can not run due
@@ -174,6 +178,9 @@ class EngineShard {
 
     // the lock fingerprint with maximum contention score.
     uint64_t max_contention_lock;
+
+    // We can use a vector to hold debug info for all items in the txqueue
+    TxQueueItem head;
   };
 
   TxQueueInfo AnalyzeTxQueue() const;

src/server/transaction.cc

@@ -61,6 +61,7 @@ void AnalyzeTxQueue(const EngineShard* shard, const TxQueue* txq) {
         absl::StrAppend(&msg, " continuation_tx: ", cont_tx->DebugId(), " ",
                         cont_tx->DEBUG_IsArmedInShard(shard->shard_id()) ? " armed" : "");
       }
+      absl::StrAppend(&msg, "\nTxQueue head debug info ", info.head.debug_id_info);
 
       LOG(WARNING) << msg;
     }