diff --git a/src/tx_dependency.rs b/src/tx_dependency.rs
index 256c91d..0d3edb5 100644
--- a/src/tx_dependency.rs
+++ b/src/tx_dependency.rs
@@ -4,6 +4,8 @@ use std::{
     cmp::{max, min, Reverse},
     collections::{BTreeMap, BTreeSet, BinaryHeap, VecDeque},
 };
+use std::fs::File;
+use std::io::{BufWriter, Write};
 
 pub(crate) type DependentTxsVec = SmallVec<[TxId; 1]>;
 
@@ -35,6 +37,7 @@ pub(crate) struct TxDependency {
 
     pub round: Option<usize>,
     pub block_height: u64,
+    tx_states: SharedTxStates,
 }
 
 impl TxDependency {
@@ -46,6 +49,7 @@ impl TxDependency {
             tx_weight: None,
             round: None,
             block_height: 0,
+            tx_states: Default::default(),
         }
     }
 
@@ -64,6 +68,7 @@ impl TxDependency {
                 last_write_tx.insert(location.clone(), txid);
             }
         }
+        self.tx_states = tx_states;
     }
 
     /// Retrieve the optimal partitions based on the dependency relationships between transactions.
@@ -224,12 +229,14 @@ impl TxDependency {
             counter!("grevm.total_block_cnt").increment(1);
         }
         let mut subgraph = BTreeSet::new();
+        let mut two = false;
         if let Some((_, groups)) = weighted_group.last_key_value() {
             if self.round.is_none() {
                 let largest_ratio = groups[0].len() as f64 / num_remaining as f64;
                 histogram!("grevm.large_graph_ratio").record(largest_ratio);
                 if groups[0].len() >= num_remaining / 2 {
                     counter!("grevm.low_parallelism_cnt").increment(1);
+                    two = true;
                 }
             }
             if groups[0].len() >= num_remaining / 3 {
@@ -240,6 +247,7 @@ impl TxDependency {
             return;
         }
 
+        let mut longest_chain: Vec<TxId> = vec![];
         // ChainLength -> ChainNumber
         let mut chains = BTreeMap::new();
         let mut visited = HashSet::new();
@@ -247,9 +255,11 @@ impl TxDependency {
             if !visited.contains(txid) {
                 let mut txid = *txid;
                 let mut chain_len = 0;
+                let mut curr_chain = vec![];
                 while !visited.contains(&txid) {
                     chain_len += 1;
                     visited.insert(txid);
+                    curr_chain.push(txid);
                     let dep: BTreeSet<TxId> =
                         self.tx_dependency[txid - num_finality_txs].clone().into_iter().collect();
                     for dep_id in dep.into_iter().rev() {
@@ -259,6 +269,9 @@ impl TxDependency {
                         }
                     }
                 }
+                if curr_chain.len() > longest_chain.len() {
+                    longest_chain = curr_chain;
+                }
                 let chain_num = chains.get(&chain_len).cloned().unwrap_or(0) + 1;
                 chains.insert(chain_len, chain_num);
             }
@@ -282,6 +295,47 @@ impl TxDependency {
             counter!("grevm.large_graph", "type" => chain_type, "tip" => tip.clone()).increment(1);
             if self.round.is_none() {
                 info!("Block({}) has large subgraph, type={}", self.block_height, chain_type);
+                if two && chain_type == "chain" {
+                    self.draw_dag(weighted_group, longest_chain);
+                }
+            }
+        }
+    }
+
+    fn draw_dag(&self, weighted_group: &BTreeMap<usize, Vec<DependentTxsVec>>, longest_chain: Vec<TxId>) {
+        let file = File::create(format!("dag/block{}.info", self.block_height)).unwrap();
+        let mut writer = BufWriter::new(file);
+        writeln!(writer, "[dag]").unwrap();
+
+        for txid in (0..self.tx_dependency.len()).rev() {
+            let deps: BTreeSet<TxId> = self.tx_dependency[txid].clone().into_iter().collect();
+            for dep_id in deps.into_iter().rev() {
+                writeln!(writer, "tx{}->tx{}", txid, dep_id).unwrap();
+            }
+        }
+        writeln!(writer, "").unwrap();
+
+        let mut locations: HashSet<LocationAndType> = HashSet::new();
+        info!("Block({}) has large subgraph, longest chain: {:?}", self.block_height, longest_chain);
+        for index in 0..longest_chain.len() - 1 {
+            let txid = longest_chain[index];
+            let dep_id = longest_chain[index + 1];
+            let rs = self.tx_states[txid].read_set.clone();
+            let ws = self.tx_states[dep_id].write_set.clone();
+            let mut intersection = HashSet::new();
+            for l in ws {
+                if rs.contains_key(&l) {
+                    intersection.insert(l);
+                }
+            }
+            if locations.is_empty() {
+                locations = intersection;
+            } else {
+                let join: HashSet<LocationAndType> = locations.intersection(&intersection).cloned().collect();
+                if join.is_empty() {
+                    info!("Block({}) has large subgraph, ==> tx{}: {:?}", self.block_height, txid, locations);
+                }
+                locations = join;
             }
         }
     }