blockchain: speedup fetching pruned contiguous tx blobs

About twice as fast, very roughly

src/blockchain_db/blockchain_db.h

@@ -1252,6 +1252,22 @@ public:
    */
   virtual bool get_pruned_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const = 0;
 
+  /**
+   * @brief fetches a number of pruned transaction blob from the given hash, in canonical blockchain order
+   *
+   * The subclass should return the pruned transactions stored from the one with the given
+   * hash.
+   *
+   * If the first transaction does not exist, the subclass should return false.
+   * If the first transaction exists, but there are fewer transactions starting with it
+   * than requested, the subclass should return false.
+   *
+   * @param h the hash to look for
+   *
+   * @return true iff the transactions were found
+   */
+  virtual bool get_pruned_tx_blobs_from(const crypto::hash& h, size_t count, std::vector<cryptonote::blobdata> &bd) const = 0;
+
   /**
    * @brief fetches the prunable transaction blob with the given hash
    *

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -3033,6 +3033,48 @@ bool BlockchainLMDB::get_pruned_tx_blob(const crypto::hash& h, cryptonote::blobd
   return true;
 }
 
+bool BlockchainLMDB::get_pruned_tx_blobs_from(const crypto::hash& h, size_t count, std::vector<cryptonote::blobdata> &bd) const
+{
+  LOG_PRINT_L3("BlockchainLMDB::" << __func__);
+  check_open();
+
+  if (!count)
+    return true;
+
+  TXN_PREFIX_RDONLY();
+  RCURSOR(tx_indices);
+  RCURSOR(txs_pruned);
+
+  bd.reserve(bd.size() + count);
+
+  MDB_val_set(v, h);
+  MDB_val result;
+  int res = mdb_cursor_get(m_cur_tx_indices, (MDB_val *)&zerokval, &v, MDB_GET_BOTH);
+  if (res == MDB_NOTFOUND)
+    return false;
+  if (res)
+    throw0(DB_ERROR(lmdb_error("DB error attempting to fetch tx from hash", res).c_str()));
+
+  const txindex *tip = (const txindex *)v.mv_data;
+  const uint64_t id = tip->data.tx_id;
+  MDB_val_set(val_tx_id, id);
+  MDB_cursor_op op = MDB_SET;
+  while (count--)
+  {
+    res = mdb_cursor_get(m_cur_txs_pruned, &val_tx_id, &result, op);
+    op = MDB_NEXT;
+    if (res == MDB_NOTFOUND)
+      return false;
+    if (res)
+      throw0(DB_ERROR(lmdb_error("DB error attempting to fetch tx blob", res).c_str()));
+    bd.emplace_back(reinterpret_cast<char*>(result.mv_data), result.mv_size);
+  }
+
+  TXN_POSTFIX_RDONLY();
+
+  return true;
+}
+
 bool BlockchainLMDB::get_prunable_tx_blob(const crypto::hash& h, cryptonote::blobdata &bd) const
 {
   LOG_PRINT_L3("BlockchainLMDB::" << __func__);

src/blockchain_db/lmdb/db_lmdb.h

@@ -254,6 +254,7 @@ public:
 
   virtual bool get_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const;
   virtual bool get_pruned_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const;
+  virtual bool get_pruned_tx_blobs_from(const crypto::hash& h, size_t count, std::vector<cryptonote::blobdata> &bd) const;
   virtual bool get_prunable_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const;
   virtual bool get_prunable_tx_hash(const crypto::hash& tx_hash, crypto::hash &prunable_hash) const;
 

src/blockchain_db/testdb.h

@@ -69,6 +69,7 @@ public:
   virtual cryptonote::blobdata get_block_blob(const crypto::hash& h) const override { return cryptonote::blobdata(); }
   virtual bool get_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const override { return false; }
   virtual bool get_pruned_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const override { return false; }
+  virtual bool get_pruned_tx_blobs_from(const crypto::hash& h, size_t count, std::vector<cryptonote::blobdata> &bd) const { return false; }
   virtual bool get_prunable_tx_blob(const crypto::hash& h, cryptonote::blobdata &tx) const override { return false; }
   virtual bool get_prunable_tx_hash(const crypto::hash& tx_hash, crypto::hash &prunable_hash) const override { return false; }
   virtual uint64_t get_block_height(const crypto::hash& h) const override { return 0; }

src/cryptonote_core/blockchain.cpp

@@ -2498,10 +2498,17 @@ bool Blockchain::find_blockchain_supplement(const uint64_t req_start_block, cons
     block b;
     CHECK_AND_ASSERT_MES(parse_and_validate_block_from_blob(blocks.back().first.first, b), false, "internal error, invalid block");
     blocks.back().first.second = get_miner_tx_hash ? cryptonote::get_transaction_hash(b.miner_tx) : crypto::null_hash;
-    std::vector<crypto::hash> mis;
     std::vector<cryptonote::blobdata> txs;
-    get_transactions_blobs(b.tx_hashes, txs, mis, pruned);
+    if (pruned)
-    CHECK_AND_ASSERT_MES(!mis.size(), false, "internal error, transaction from block not found");
+    {
+      CHECK_AND_ASSERT_MES(m_db->get_pruned_tx_blobs_from(b.tx_hashes.front(), b.tx_hashes.size(), txs), false, "Failed to retrieve all transactions needed");
+    }
+    else
+    {
+      std::vector<crypto::hash> mis;
+      get_transactions_blobs(b.tx_hashes, txs, mis, pruned);
+      CHECK_AND_ASSERT_MES(!mis.size(), false, "internal error, transaction from block not found");
+    }
     size += blocks.back().first.first.size();
     for (const auto &t: txs)
       size += t.size();