Remove serialization non C41 constructors from stats

With this change in, PR #4685 and others to follow should:

a) remove Subarray::set_stats and respective call from serialization/query.cc
b) where Subarray is constructed in serialization/query.cc, change constructor
call with the following code snippet:
 auto &stats_data = stats_from_capnp(reader.getStats());
 Subarray subarray(array, layout, query_stats, stats_data, dummy_logger, true);
c) The constructor calls parent_stats->create_child(prefix, stats_data);
d) When all migrations are done, make Stats::populate_with_data private

tiledb/sm/query/query.cc

@@ -1663,6 +1663,10 @@ stats::Stats* Query::stats() const {
   return stats_;
 }
 
+void Query::set_stats(const stats::StatsData& data) {
+  stats_->populate_with_data(data);
+}
+
 shared_ptr<Buffer> Query::rest_scratch() const {
   return rest_scratch_;
 }

tiledb/sm/query/query.h

@@ -655,6 +655,11 @@ class Query {
   /** Returns the internal stats object. */
   stats::Stats* stats() const;
 
+  /** Populate the owned stats instance with data.
+   * To be removed when the class will get a C41 constructor.
+   */
+  void set_stats(const stats::StatsData& data);
+
   /** Returns the scratch space used for REST requests. */
   shared_ptr<Buffer> rest_scratch() const;
 

tiledb/sm/query/strategy_base.cc

@@ -65,6 +65,10 @@ stats::Stats* StrategyBase::stats() const {
   return stats_;
 }
 
+void StrategyBase::set_stats(const stats::StatsData& data) {
+  stats_->populate_with_data(data);
+}
+
 /* ****************************** */
 /*       PROTECTED METHODS        */
 /* ****************************** */

tiledb/sm/query/strategy_base.h

@@ -208,6 +208,11 @@ class StrategyBase {
   /** Returns `stats_`. */
   stats::Stats* stats() const;
 
+  /** Populate the owned stats instance with data.
+   * To be removed when the class will get a C41 constructor.
+   */
+  void set_stats(const stats::StatsData& data);
+
   /** Returns the configured offsets format mode. */
   std::string offsets_mode() const;
 

tiledb/sm/serialization/query.cc

@@ -118,27 +118,27 @@ Status stats_to_capnp(Stats& stats, capnp::Stats::Builder* stats_builder) {
   return Status::Ok();
 }
 
-Status stats_from_capnp(
-    const capnp::Stats::Reader& stats_reader, Stats* stats) {
+StatsData stats_from_capnp(const capnp::Stats::Reader& stats_reader) {
+  std::unordered_map<std::string, uint64_t> counters;
+  std::unordered_map<std::string, double> timers;
+
   if (stats_reader.hasCounters()) {
-    auto counters = stats->counters();
     auto counters_reader = stats_reader.getCounters();
     for (const auto entry : counters_reader.getEntries()) {
       auto key = std::string_view{entry.getKey().cStr(), entry.getKey().size()};
-      (*counters)[std::string{key}] = entry.getValue();
+      counters[std::string(key)] = entry.getValue();
     }
   }
 
   if (stats_reader.hasTimers()) {
-    auto timers = stats->timers();
     auto timers_reader = stats_reader.getTimers();
     for (const auto entry : timers_reader.getEntries()) {
       auto key = std::string_view{entry.getKey().cStr(), entry.getKey().size()};
-      (*timers)[std::string{key}] = entry.getValue();
+      timers[std::string(key)] = entry.getValue();
     }
   }
 
-  return Status::Ok();
+  return stats::StatsData(counters, timers);
 }
 
 void range_buffers_to_capnp(
@@ -328,11 +328,8 @@ Status subarray_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (reader.hasStats()) {
-    stats::Stats* stats = subarray->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(reader.getStats());
+    subarray->set_stats(stats_data);
   }
 
   if (reader.hasRelevantFragments()) {
@@ -566,11 +563,8 @@ Status subarray_partitioner_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (reader.hasStats()) {
-    auto stats = partitioner->stats();
-    // We should always have stats
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(reader.getStats());
+    partitioner->set_stats(stats_data);
   }
 
   return Status::Ok();
@@ -1146,11 +1140,8 @@ Status reader_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (reader_reader.hasStats()) {
-    stats::Stats* stats = reader->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(reader_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(reader_reader.getStats());
+    reader->set_stats(stats_data);
   }
 
   return Status::Ok();
@@ -1187,11 +1178,8 @@ Status index_reader_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (reader_reader.hasStats()) {
-    stats::Stats* stats = reader->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(reader_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(reader_reader.getStats());
+    reader->set_stats(stats_data);
   }
 
   return Status::Ok();
@@ -1229,11 +1217,8 @@ Status dense_reader_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (reader_reader.hasStats()) {
-    stats::Stats* stats = reader->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(reader_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(reader_reader.getStats());
+    reader->set_stats(stats_data);
   }
 
   return Status::Ok();
@@ -1252,11 +1237,8 @@ Status delete_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (delete_reader.hasStats()) {
-    stats::Stats* stats = delete_strategy->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(delete_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(delete_reader.getStats());
+    delete_strategy->set_stats(stats_data);
   }
 
   return Status::Ok();
@@ -1341,11 +1323,8 @@ Status writer_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (writer_reader.hasStats()) {
-    stats::Stats* stats = writer->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(writer_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(writer_reader.getStats());
+    writer->set_stats(stats_data);
   }
 
   if (query.layout() == Layout::GLOBAL_ORDER &&
@@ -2270,11 +2249,8 @@ Status query_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (query_reader.hasStats()) {
-    stats::Stats* stats = query->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      RETURN_NOT_OK(stats_from_capnp(query_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(query_reader.getStats());
+    query->set_stats(stats_data);
   }
 
   if (query_reader.hasWrittenFragmentInfo()) {
@@ -3212,11 +3188,8 @@ void ordered_dim_label_reader_from_capnp(
 
   // If cap'n proto object has stats set it on c++ object
   if (reader_reader.hasStats()) {
-    stats::Stats* stats = reader->stats();
-    // We should always have a stats here
-    if (stats != nullptr) {
-      throw_if_not_ok(stats_from_capnp(reader_reader.getStats(), stats));
-    }
+    auto stats_data = stats_from_capnp(reader_reader.getStats());
+    reader->set_stats(stats_data);
   }
 }
 

tiledb/sm/stats/global_stats.h

@@ -49,6 +49,71 @@
 #include "tiledb/common/heap_memory.h"
 #include "tiledb/sm/stats/stats.h"
 
+/**
+ * Documenting the current stats behavior and architecture as close as
+ * possible to the code so it's helpful next time some tries to refactor.
+ *
+ * Statistics collection is done at the top level via the GlobalStats class
+ * defined in this file.
+ * We maintain a global object called `all_stats` which is used to register
+ * Stats objects, enable/disable collection, reset or dumping the collected
+ * stats.
+ *
+ * The TileDB C API uses the `all_stats` object directly to execute the
+ * actions iterated above.
+ *
+ * The GlobalStats class owns a list called `registered_stats` that has one
+ * Stats object registered for each Context used. In consequence,
+ * ContextResources register a Stats object for each Context created, this
+ * object serves as the root for the tree of all children Stats used in a
+ * Context.
+ *
+ * As mentioned above, the Stats objects used under a Context form a tree.
+ * Each Stats object mentains a list of children Stats and a pointer to the
+ * parent Stats object.
+ * The Stats object created by ContextResources(named "Context.StorageManager")
+ * is the only Stats constructed in a standalone fashion using the Stats
+ * constructor, all the other objects under this root Stats are created via
+ * the Stats::create_child API.
+ *
+ * The (current, please update if not accurate anymore) exhaustive list of
+ * Stats we maintain under a Context is:
+ * ---------------------------
+ * ContextResources
+ *    - Query
+ *    - Reader
+ *    - Writer
+ *        - DenseTiler
+ *        - Subarray
+ *    - Deletes
+ *    - Subarray
+ *    - subSubarray
+ *        - SubarrayPartitioner
+ *    - VFS
+ *        - S3
+ *        - ArrayDirectory
+ *    - RestClient
+ *    - Consolidator
+ * ---------------------------
+ * Please visualize this as a tree, it was much easier to write
+ * like this, the tree is too wide.
+ *
+ *
+ * Observed issues:
+ * - Stats objects currently are created via Stats::create_child API from a
+ *   parent stats object. Child objects such as e.g. Subarray only hold a
+ *   pointer to the Stats object, this means that the Stats objects outlive
+ *   the objects they represent and are kept alive by the tree like structure
+ *   defined by the Stats class.
+ *   In theory, a Context running for a long time would OOM the machine with
+ *   Stats objects.
+ *
+ * - Stats::populate_flattened_stats aggregate the collected statistic via
+ *   summing. But we also collect ".min", ".max" statistics as well,
+ *   sum-aggregating those is incorrect. Currently the dump function just
+ *   doesn't print those statistics.
+ */
+
 namespace tiledb {
 namespace sm {
 namespace stats {
@@ -158,8 +223,7 @@ class GlobalStats {
 /* ********************************* */
 
 /**
- * The singleton instance holding all global stats counters. The report will
- * be automatically made when this object is destroyed (at program termination).
+ * The singleton instance holding all global stats counters and timers.
  */
 extern GlobalStats all_stats;
 

tiledb/sm/stats/stats.cc

@@ -48,9 +48,14 @@ namespace stats {
 /* ****************************** */
 
 Stats::Stats(const std::string& prefix)
+    : Stats(prefix, StatsData{}) {
+}
+
+Stats::Stats(const std::string& prefix, const StatsData& data)
     : enabled_(true)
     , prefix_(prefix + ".")
     , parent_(nullptr) {
+  this->populate_with_data(data);
 }
 
 /* ****************************** */
@@ -246,8 +251,12 @@ Stats* Stats::parent() {
 }
 
 Stats* Stats::create_child(const std::string& prefix) {
+  return create_child(prefix, StatsData{});
+}
+
+Stats* Stats::create_child(const std::string& prefix, const StatsData& data) {
   std::unique_lock<std::mutex> lck(mtx_);
-  children_.emplace_back(prefix_ + prefix);
+  children_.emplace_back(prefix_ + prefix, data);
   Stats* const child = &children_.back();
   child->parent_ = this;
   return child;
@@ -272,15 +281,26 @@ void Stats::populate_flattened_stats(
   }
 }
 
-std::unordered_map<std::string, double>* Stats::timers() {
+const std::unordered_map<std::string, double>* Stats::timers() const {
   return &timers_;
 }
 
 /** Return pointer to conters map, used for serialization only. */
-std::unordered_map<std::string, uint64_t>* Stats::counters() {
+const std::unordered_map<std::string, uint64_t>* Stats::counters() const {
   return &counters_;
 }
 
+void Stats::populate_with_data(const StatsData& data) {
+  auto timers = data.timers();
+  for (const auto& timer : timers) {
+    timers_[timer.first] = timer.second;
+  }
+  auto counters = data.counters();
+  for (const auto& counter : counters) {
+    counters_[counter.first] = counter.second;
+  }
+}
+
 }  // namespace stats
 }  // namespace sm
 }  // namespace tiledb