add histogram for links on level 0

* also add stats for current config

3 files changed, 40 insertions, 16 deletions

diff --git a/searchlib/src/vespa/searchlib/tensor/hnsw_graph.cpp b/searchlib/src/vespa/searchlib/tensor/hnsw_graph.cpp
index 6f902a30861..b6b3e670f08 100644
--- a/searchlib/src/vespa/searchlib/tensor/hnsw_graph.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/hnsw_graph.cpp
@@ -50,21 +50,32 @@ HnswGraph::set_link_array(uint32_t docid, uint32_t level, const LinkArrayRef& ne
     links.remove(old_links_ref);
 }
 
-std::vector<uint32_t>
-HnswGraph::level_histogram() const
+HnswGraph::Histograms
+HnswGraph::histograms() const
 {
-    std::vector<uint32_t> result;
+    Histograms result;
     size_t num_nodes = node_refs.size();
     for (size_t i = 0; i < num_nodes; ++i) {
-        uint32_t levels = 0;
         auto node_ref = node_refs[i].load_acquire();
         if (node_ref.valid()) {
-            levels = nodes.get(node_ref).size();
+            uint32_t levels = 0;
+            uint32_t l0links = 0;
+            auto level_array = nodes.get(node_ref);
+            levels = level_array.size();
+            if (levels > 0) {
+                auto links_ref = level_array[0].load_acquire();
+                auto link_array = links.get(links_ref);
+                l0links = link_array.size();
+            }
+            while (result.level_histogram.size() <= levels) {
+                result.level_histogram.push_back(0);
+            }
+            ++result.level_histogram[levels];
+            while (result.links_histogram.size() <= l0links) {
+                result.links_histogram.push_back(0);
+            }
+            ++result.links_histogram[l0links];
         }
-        while (result.size() <= levels) {
-            result.push_back(0);
-        }
-        ++result[levels];
     }
     return result;
 }
diff --git a/searchlib/src/vespa/searchlib/tensor/hnsw_graph.h b/searchlib/src/vespa/searchlib/tensor/hnsw_graph.h
index 233b9087af7..f38f5ca0baf 100644
--- a/searchlib/src/vespa/searchlib/tensor/hnsw_graph.h
+++ b/searchlib/src/vespa/searchlib/tensor/hnsw_graph.h
@@ -70,7 +70,11 @@ struct HnswGraph {
 
     size_t size() const { return node_refs.size(); }
 
-    std::vector<uint32_t> level_histogram() const;
+    struct Histograms {
+        std::vector<uint32_t> level_histogram;
+        std::vector<uint32_t> links_histogram;
+    };
+    Histograms histograms() const;
 };
 
 }
diff --git a/searchlib/src/vespa/searchlib/tensor/hnsw_index.cpp b/searchlib/src/vespa/searchlib/tensor/hnsw_index.cpp
index b08d862ae6d..c1f6589b025 100644
--- a/searchlib/src/vespa/searchlib/tensor/hnsw_index.cpp
+++ b/searchlib/src/vespa/searchlib/tensor/hnsw_index.cpp
@@ -383,18 +383,27 @@ HnswIndex::get_state(const vespalib::slime::Inserter& inserter) const
     StateExplorerUtils::memory_usage_to_slime(memory_usage(), object.setObject("memory_usage"));
     object.setLong("nodes", _graph.size());
     auto& histogram_array = object.setArray("level_histogram");
-    auto level_histogram = _graph.level_histogram();
-    for (uint32_t hist_val : level_histogram) {
+    auto& links_hst_array = object.setArray("level_0_links_histogram");
+    auto histograms = _graph.histograms();
+    uint32_t valid_nodes = 0;
+    for (uint32_t hist_val : histograms.level_histogram) {
         histogram_array.addLong(hist_val);
+        valid_nodes += hist_val;
     }
-    uint32_t reachable = count_reachable_nodes();
-    uint32_t unreachable = _graph.size() - reachable;
-    if (level_histogram.size() > 0) {
-        unreachable -= level_histogram[0];
+    object.setLong("valid_nodes", valid_nodes);
+    for (uint32_t hist_val : histograms.links_histogram) {
+        links_hst_array.addLong(hist_val);
     }
+    uint32_t reachable = count_reachable_nodes();
+    uint32_t unreachable = valid_nodes - reachable;
     object.setLong("unreachable_nodes", unreachable);
     object.setLong("entry_docid", _graph.entry_docid);
     object.setLong("entry_level", _graph.entry_level);
+    auto& cfgObj = object.setObject("cfg");
+    cfgObj.setLong("max_links_at_level_0", _cfg.max_links_at_level_0());
+    cfgObj.setLong("max_links_on_inserts", _cfg.max_links_on_inserts());
+    cfgObj.setLong("neighbors_to_explore_at_construction",
+                   _cfg.neighbors_to_explore_at_construction());
 }
 
 std::unique_ptr<NearestNeighborIndexSaver>