Outputs where all amounts are known spent can now be pruned

src/blockchain_db/blockchain_db.h

@@ -1405,6 +1405,13 @@ class BlockchainDB
    */
   virtual cryptonote::blobdata get_txpool_tx_blob(const crypto::hash& txid) const = 0;
 
+  /**
+   * @brief prune output data for the given amount
+   *
+   * @param amount the amount for which to prune data
+   */
+  virtual void prune_outputs(uint64_t amount) = 0;
+
   /**
    * @brief runs a function over all txpool transactions
    *

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -1077,6 +1077,60 @@ void BlockchainLMDB::remove_output(const uint64_t amount, const uint64_t& out_in
     throw0(DB_ERROR(lmdb_error(std::string("Error deleting amount for output index ").append(boost::lexical_cast<std::string>(out_index).append(": ")).c_str(), result).c_str()));
 }
 
+void BlockchainLMDB::prune_outputs(uint64_t amount)
+{
+  LOG_PRINT_L3("BlockchainLMDB::" << __func__);
+  check_open();
+  mdb_txn_cursors *m_cursors = &m_wcursors;
+  CURSOR(output_amounts);
+  CURSOR(output_txs);
+
+  MINFO("Pruning outputs for amount " << amount);
+
+  MDB_val v;
+  MDB_val_set(k, amount);
+  int result = mdb_cursor_get(m_cur_output_amounts, &k, &v, MDB_SET);
+  if (result == MDB_NOTFOUND)
+    return;
+  if (result)
+    throw0(DB_ERROR(lmdb_error("Error looking up outputs: ", result).c_str()));
+
+  // gather output ids
+  mdb_size_t num_elems;
+  mdb_cursor_count(m_cur_output_amounts, &num_elems);
+  MINFO(num_elems << " outputs found");
+  std::vector<uint64_t> output_ids;
+  output_ids.reserve(num_elems);
+  while (1)
+  {
+    const pre_rct_outkey *okp = (const pre_rct_outkey *)v.mv_data;
+    output_ids.push_back(okp->output_id);
+    MDEBUG("output id " << okp->output_id);
+    result = mdb_cursor_get(m_cur_output_amounts, &k, &v, MDB_NEXT_DUP);
+    if (result == MDB_NOTFOUND)
+      break;
+    if (result)
+      throw0(DB_ERROR(lmdb_error("Error counting outputs: ", result).c_str()));
+  }
+  if (output_ids.size() != num_elems)
+    throw0(DB_ERROR("Unexpected number of outputs"));
+
+  result = mdb_cursor_del(m_cur_output_amounts, MDB_NODUPDATA);
+  if (result)
+    throw0(DB_ERROR(lmdb_error("Error deleting outputs: ", result).c_str()));
+
+  for (uint64_t output_id: output_ids)
+  {
+    MDB_val_set(v, output_id);
+    result = mdb_cursor_get(m_cur_output_txs, (MDB_val *)&zerokval, &v, MDB_GET_BOTH);
+    if (result)
+      throw0(DB_ERROR(lmdb_error("Error looking up output: ", result).c_str()));
+    result = mdb_cursor_del(m_cur_output_txs, 0);
+    if (result)
+      throw0(DB_ERROR(lmdb_error("Error deleting output: ", result).c_str()));
+  }
+}
+
 void BlockchainLMDB::add_spent_key(const crypto::key_image& k_image)
 {
   LOG_PRINT_L3("BlockchainLMDB::" << __func__);
@@ -2231,11 +2285,19 @@ uint64_t BlockchainLMDB::num_outputs() const
   TXN_PREFIX_RDONLY();
   int result;
 
-  // get current height
-  MDB_stat db_stats;
-  if ((result = mdb_stat(m_txn, m_output_txs, &db_stats)))
+  RCURSOR(output_txs)
+
+  uint64_t num = 0;
+  MDB_val k, v;
+  result = mdb_cursor_get(m_cur_output_txs, &k, &v, MDB_LAST);
+  if (result == MDB_NOTFOUND)
+    num = 0;
+  else if (result == 0)
+    num = 1 + ((const outtx*)v.mv_data)->output_id;
+  else
     throw0(DB_ERROR(lmdb_error("Failed to query m_output_txs: ", result).c_str()));
-  return db_stats.ms_entries;
+
+  return num;
 }
 
 bool BlockchainLMDB::tx_exists(const crypto::hash& h) const

src/blockchain_db/lmdb/db_lmdb.h

@@ -345,6 +345,8 @@ class BlockchainLMDB : public BlockchainDB
 
   void remove_output(const uint64_t amount, const uint64_t& out_index);
 
+  virtual void prune_outputs(uint64_t amount);
+
   virtual void add_spent_key(const crypto::key_image& k_image);
 
   virtual void remove_spent_key(const crypto::key_image& k_image);

src/blockchain_utilities/CMakeLists.txt

@@ -81,6 +81,17 @@ monero_private_headers(blockchain_usage
 
 
 
+set(blockchain_prune_known_spent_data_sources
+  blockchain_prune_known_spent_data.cpp
+  )
+
+set(blockchain_prune_known_spent_data_private_headers)
+
+monero_private_headers(blockchain_prune_known_spent_data
+	  ${blockchain_prune_known_spent_data_private_headers})
+
+
+
 set(blockchain_ancestry_sources
   blockchain_ancestry.cpp
   )
@@ -265,3 +276,25 @@ set_property(TARGET blockchain_stats
 	PROPERTY
 	OUTPUT_NAME "monero-blockchain-stats")
 install(TARGETS blockchain_stats DESTINATION bin)
+
+monero_add_executable(blockchain_prune_known_spent_data
+  ${blockchain_prune_known_spent_data_sources}
+  ${blockchain_prune_known_spent_data_private_headers})
+
+target_link_libraries(blockchain_prune_known_spent_data
+  PRIVATE
+    cryptonote_core
+    blockchain_db
+    p2p
+    version
+    epee
+    ${Boost_FILESYSTEM_LIBRARY}
+    ${Boost_SYSTEM_LIBRARY}
+    ${Boost_THREAD_LIBRARY}
+    ${CMAKE_THREAD_LIBS_INIT}
+    ${EXTRA_LIBRARIES})
+
+set_property(TARGET blockchain_prune_known_spent_data
+	PROPERTY
+	OUTPUT_NAME "monero-blockchain-prune-known-spent-data")
+install(TARGETS blockchain_prune_known_spent_data DESTINATION bin)