Add multi-GPU parallelization for dataset generation

* Added process_qa_chunk() function to handle parallel processing on individual GPUs
* Modified make_dataset() to distribute QA pairs across available GPUs using multiprocessing
* Each GPU process creates its own embedding model and backend directory
* Added per-GPU progress bars for real-time monitoring

Author: ssubhanjali

CHANGELOG.md

@@ -84,6 +84,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added a check that confirms that custom edge types of `NumNeighbors` actually exist in the graph ([#9807](https://github.com/pyg-team/pytorch_geometric/pull/9807))
 - Automatic num_params in LLM + update `GRetriever` default llm ([#9938](https://github.com/pyg-team/pytorch_geometric/pull/9938))
 - Updated calls to NumPy's deprecated `np.in1d` to `np.isin` ([#10283](https://github.com/pyg-team/pytorch_geometric/pull/10283))
+- Added multi-GPU parallelization using multiprocessing for accelerated RAG dataset generation in `txt2kg_rag.py`, distributing QA pair processing across GPUs ([#10474](https://github.com/pyg-team/pytorch_geometric/pull/10474))
 
 ### Deprecated
 

examples/llm/txt2kg_rag.py

@@ -1,6 +1,7 @@
 import argparse
 import gc
 import json
+import multiprocessing as mp
 import os
 import random
 import re
@@ -424,6 +425,112 @@ def update_data_lists(args, data_lists):
     return data_lists
 
 
+def process_qa_chunk(chunk_data):
+    """Process a chunk of QA pairs on a specific GPU."""
+    (qa_chunk, gpu_id, fs_path, gs_path, graph_data, triples, model_name,
+     dataset_path) = chunk_data
+
+    # Set the GPU for this process
+    torch.cuda.set_device(gpu_id)
+    device = torch.device(f"cuda:{gpu_id}")
+    print(f"Process {mp.current_process().pid} using GPU {gpu_id} "
+          f"to process {len(qa_chunk)} QA pairs")
+    sys.stdout.flush()  # Force flush to see logs immediately
+
+    # Create embedding model for this process
+    sent_trans_batch_size = 256
+    model = SentenceTransformer(
+        model_name=ENCODER_MODEL_NAME_DEFAULT).to(device).eval()
+
+    # Load graph and feature stores with unique path for each GPU
+    backend_path = f"backend_gpu_{gpu_id}"
+    fs, gs = create_remote_backend_from_graph_data(
+        graph_data=graph_data, path=backend_path,
+        graph_db=NeighborSamplingRAGGraphStore,
+        feature_db=KNNRAGFeatureStore).load()
+
+    # Create subgraph filter for this process
+    subgraph_filter = make_pcst_filter(
+        triples,
+        model,
+        topk=5,  # nodes
+        topk_e=5,  # edges
+        cost_e=.5,  # edge cost
+        num_clusters=10)  # num clusters
+
+    # Load document retriever
+    model_kwargs = {
+        "output_device": device,
+        "batch_size": int(sent_trans_batch_size / 4),
+    }
+    doc_retriever_path = os.path.join(dataset_path, "document_retriever.pt")
+    vector_retriever = DocumentRetriever.load(doc_retriever_path,
+                                              model=model.encode,
+                                              model_kwargs=model_kwargs)
+
+    # Query loader config
+    fanout = 100
+    num_hops = 2
+    query_loader_config = {
+        "k_nodes": 1024,
+        "num_neighbors": [fanout] * num_hops,
+        "encoder_model": model,
+    }
+
+    # Create query loader for this process
+    query_loader = RAGQueryLoader(graph_data=(fs, gs),
+                                  subgraph_filter=subgraph_filter,
+                                  vector_retriever=vector_retriever,
+                                  config=query_loader_config)
+
+    # Process the chunk
+    chunk_data_list = []
+    chunk_triple_sizes = []
+    max_answer_len = 0
+
+    # Add tqdm progress bar for this GPU
+    from tqdm import tqdm
+
+    # Create a progress bar for this GPU with position offset to avoid overlap
+    gpu_pbar = tqdm(qa_chunk, desc=f"GPU {gpu_id}", position=gpu_id,
+                    leave=True, total=len(qa_chunk))
+
+    for idx, data_point in enumerate(gpu_pbar):
+        if data_point["is_impossible"]:
+            continue
+        q = data_point["question"]
+        a = data_point["answer"]
+        max_answer_len = max(len(a), max_answer_len)
+
+        # Update progress bar description with current item
+        gpu_pbar.set_postfix({'QA': idx + 1})
+
+        subgraph = query_loader.query(q)
+        subgraph.label = a
+        chunk_data_list.append(subgraph)
+        chunk_triple_sizes.append(len(subgraph.triples))
+
+    gpu_pbar.close()
+
+    # Log completion
+    print(
+        f"GPU {gpu_id}: Completed processing {len(chunk_data_list)} QA pairs!")
+    sys.stdout.flush()
+
+    # Clean up
+    del model
+    del query_loader
+    gc.collect()
+    torch.cuda.empty_cache()
+
+    # Clean up GPU-specific backend directory
+    import shutil
+    if os.path.exists(backend_path):
+        shutil.rmtree(backend_path)
+
+    return chunk_data_list, chunk_triple_sizes, max_answer_len
+
+
 def make_dataset(args):
     qa_pairs, context_docs = get_data(args)
     print("Number of Docs in our VectorDB =", len(context_docs))
@@ -447,6 +554,13 @@ def make_dataset(args):
         triples = index_kg(args, context_docs)
 
     print("Number of triples in our GraphDB =", len(triples))
+
+    # Determine number of GPUs to use
+    num_gpus = (args.num_gpus
+                if args.num_gpus is not None else torch.cuda.device_count())
+    num_gpus = min(num_gpus, torch.cuda.device_count())
+    print(f"Using {num_gpus} GPUs for dataset generation")
+
     device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
 
     # creating the embedding model
@@ -496,52 +610,65 @@ def make_dataset(args):
                                              model_kwargs=model_kwargs)
         vector_retriever.save(doc_retriever_path)
 
-    subgraph_filter = make_pcst_filter(
-        triples,
-        model,
-        topk=5,  # nodes
-        topk_e=5,  # edges
-        cost_e=.5,  # edge cost
-        num_clusters=10)  # num clusters
-
-    # number of neighbors for each seed node selected by KNN
-    fanout = 100
-    # number of hops for neighborsampling
-    num_hops = 2
-
-    query_loader_config = {
-        "k_nodes": 1024,  # k for Graph KNN
-        "num_neighbors": [fanout] * num_hops,  # number of sampled neighbors
-        "encoder_model": model,
-    }
-
-    # GraphDB retrieval done with KNN+NeighborSampling+PCST
-    # PCST = Prize Collecting Steiner Tree
-    # VectorDB retrieval just vanilla vector RAG
+    # Distribute QA pairs across GPUs for parallel subgraph retrieval
+    # Each process loads its own embedding model, graph/feature stores,
+    # and query loader
     print("Now to retrieve context for each query from "
-          "our Vector and Graph DBs...")
-
-    query_loader = RAGQueryLoader(graph_data=(fs, gs),
-                                  subgraph_filter=subgraph_filter,
-                                  vector_retriever=vector_retriever,
-                                  config=query_loader_config)
-
-    # pre-process the dataset
+          "our Vector and Graph DBs using multiprocessing...")
+
+    # Filter out impossible QA pairs first
+    valid_qa_pairs = [dp for dp in qa_pairs if not dp["is_impossible"]]
+
+    # Split QA pairs into chunks for each GPU
+    chunk_size = len(valid_qa_pairs) // num_gpus
+    qa_chunks = []
+    for i in range(num_gpus):
+        start_idx = i * chunk_size
+        end_idx = start_idx + chunk_size if i < num_gpus - 1 else len(
+            valid_qa_pairs)
+        qa_chunks.append(valid_qa_pairs[start_idx:end_idx])
+
+    # Prepare data for multiprocessing
+    chunk_data_list = []
+    for i, chunk in enumerate(qa_chunks):
+        chunk_data_list.append((
+            chunk,  # QA pairs chunk
+            i % torch.cuda.device_count(),  # GPU ID
+            "backend/fs",  # fs path
+            "backend/gs",  # gs path
+            graph_data,  # graph data
+            triples,  # triples
+            ENCODER_MODEL_NAME_DEFAULT,  # model name
+            args.dataset  # dataset path
+        ))
+
+    # Use multiprocessing to process chunks in parallel
+    mp.set_start_method('spawn', force=True)
+
+    print(f"\nProcessing {len(valid_qa_pairs)} QA pairs "
+          f"across {num_gpus} GPUs...")
+    print("=" * 60)
+
+    with mp.Pool(processes=num_gpus) as pool:
+        results = list(pool.imap(process_qa_chunk, chunk_data_list))
+
+    # Clean up main backend directory if it exists
+    import shutil
+    if os.path.exists("backend"):
+        shutil.rmtree("backend")
+
+    # Combine results from all processes
     total_data_list = []
     extracted_triple_sizes = []
     global max_chars_in_train_answer
-    for data_point in tqdm(qa_pairs, desc="Building un-split dataset"):
-        if data_point["is_impossible"]:
-            continue
-        QA_pair = (data_point["question"], data_point["answer"])
-        q = QA_pair[0]
-        max_chars_in_train_answer = max(len(QA_pair[1]),
-                                        max_chars_in_train_answer)
-        # (TODO) make this batch queries for retrieving w/ CuVS+CuGraph
-        subgraph = query_loader.query(q)
-        subgraph.label = QA_pair[1]
-        total_data_list.append(subgraph)
-        extracted_triple_sizes.append(len(subgraph.triples))
+    max_chars_in_train_answer = 0
+
+    for chunk_data_list, chunk_triple_sizes, chunk_max_answer_len in results:
+        total_data_list.extend(chunk_data_list)
+        extracted_triple_sizes.extend(chunk_triple_sizes)
+        max_chars_in_train_answer = max(max_chars_in_train_answer,
+                                        chunk_max_answer_len)
+
     random.shuffle(total_data_list)
 
     # stats