From a11a10191adcf4307ed0d400ef872b74c492d192 Mon Sep 17 00:00:00 2001
From: Dave Gosselin <dave.gosselin@mariadb.com>
Date: Fri, 29 Mar 2024 10:25:21 -0400
Subject: [PATCH] accrue statistics to correct handler

---
 sql/handler.cc     |  5 +++--
 sql/handler.h      |  8 +++++++-
 sql/sql_explain.cc | 14 +++++++-------
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/sql/handler.cc b/sql/handler.cc
index b52551fee31..f2310a1489d 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -6995,6 +6995,7 @@ extern "C" check_result_t handler_index_cond_check(void* h_arg)
   check_result_t res;
 
   DEBUG_SYNC(thd, "handler_index_cond_check");
+  DBUG_ASSERT(h->handler_stats);
 
   enum thd_kill_levels killed= thd_kill_level(thd);
   if (unlikely(killed != THD_IS_NOT_KILLED))
@@ -7008,13 +7009,13 @@ extern "C" check_result_t handler_index_cond_check(void* h_arg)
   if (unlikely(h->end_range) && h->compare_key2(h->end_range) > 0)
     return CHECK_OUT_OF_RANGE;
   h->increment_statistics(&SSV::ha_icp_attempts);
-  h->active_handler_stats.icp_attempts++;
+  h->handler_stats->icp_attempts++;
   res= CHECK_NEG;
   if  (h->pushed_idx_cond->val_int())
   {
     res= CHECK_POS;
     h->fast_increment_statistics(&SSV::ha_icp_match);
-    h->active_handler_stats.icp_match++;
+    h->handler_stats->icp_match++;
   }
   return res;
 }
diff --git a/sql/handler.h b/sql/handler.h
index 0224313924c..0b6a8151311 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -3211,7 +3211,13 @@ protected:
 
   ha_rows estimation_rows_to_insert;
   handler *lookup_handler;
-  /* Statistics for the query. Updated if handler_stats.in_use is set */
+  /*
+    Statistics for the query.  Prefer to use the handler_stats pointer
+    below rather than this object directly as the clone() method will
+    modify how stats are accounted by adjusting the handler_stats
+    pointer.  Referring to active_handler_stats directly will yield
+    surprising and possibly incorrect results.
+  */
   ha_handler_stats active_handler_stats;
   void set_handler_stats();
 public:
diff --git a/sql/sql_explain.cc b/sql/sql_explain.cc
index 48fe7ab01c2..274f107c0ce 100644
--- a/sql/sql_explain.cc
+++ b/sql/sql_explain.cc
@@ -1938,13 +1938,13 @@ static void trace_engine_stats(handler *file, Json_writer *writer)
 
 static void print_r_icp_filtered(handler *file, Json_writer *writer)
 {
-  if (file && file->handler_stats && file->pushed_idx_cond)
-  {
-    ha_handler_stats *hs= file->handler_stats;
-    double r_icp_filtered = hs->icp_attempts ?
-      (double)(hs->icp_match) / (double)(hs->icp_attempts) : 1.0;
-    writer->add_member("r_icp_filtered").add_double(r_icp_filtered * 100);
-  }
+  if (!file || !file->handler_stats || !file->pushed_idx_cond)
+    return;
+
+  ha_handler_stats *hs= file->handler_stats;
+  double r_icp_filtered = hs->icp_attempts ?
+    (double)(hs->icp_match) / (double)(hs->icp_attempts) : 0.0;
+  writer->add_member("r_icp_filtered").add_double(r_icp_filtered * 100);
 }
 
 void Explain_table_access::print_explain_json(Explain_query *query,