Bug#10178 - failure to find a row in heap table by concurrent UPDATEs

Moved the key statistics update to info().
The table is not locked in open(). This made wrong stats possible.

No test case for the test suite.
This happens only with heavy concurrency.
A test script is added to the bug report.


mysql-test/r/heap_hash.result:
  Bug#10178 - failure to find a row in heap table by concurrent UPDATEs
  Updated test results to reflect the new  statistics behaviour.
mysql-test/t/heap_hash.test:
  Bug#10178 - failure to find a row in heap table by concurrent UPDATEs
  Added a FLUSH TABLES to avoid statistics differences between normal 
  and ps-protocol tests.
sql/ha_heap.cc:
  Bug#10178 - failure to find a row in heap table by concurrent UPDATEs
  Moved the key statistics update to info().
  The table is not locked in open(). This made wrong stats possible.
sql/ha_heap.h:
  Bug#10178 - failure to find a row in heap table by concurrent UPDATEs
  Added an element to track the validity of the key statistics.

1 files changed, 26 insertions, 5 deletions

diff --git a/sql/ha_heap.cc b/sql/ha_heap.cc
index 4fc0116a26a..f8c2e6cc338 100644
--- a/sql/ha_heap.cc
+++ b/sql/ha_heap.cc
@@ -60,7 +60,15 @@ int ha_heap::open(const char *name, int mode, uint test_if_locked)
   {
     /* Initialize variables for the opened table */
     set_keys_for_scanning();
-    update_key_stats();
+    /*
+      We cannot run update_key_stats() here because we do not have a
+      lock on the table. The 'records' count might just be changed
+      temporarily at this moment and we might get wrong statistics (Bug
+      #10178). Instead we request for update. This will be done in
+      ha_heap::info(), which is always called before key statistics are
+      used.
+    */
+    key_stats_ok= FALSE;
   }
   return (file ? 0 : 1);
 }
@@ -112,6 +120,8 @@ void ha_heap::update_key_stats()
     }
   }
   records_changed= 0;
+  /* At the end of update_key_stats() we can proudly claim they are OK. */
+  key_stats_ok= TRUE;
 }
 
 int ha_heap::write_row(byte * buf)
@@ -125,7 +135,7 @@ int ha_heap::write_row(byte * buf)
   res= heap_write(file,buf);
   if (!res && ++records_changed*HEAP_STATS_UPDATE_THRESHOLD > 
               file->s->records)
-    update_key_stats();
+    key_stats_ok= FALSE;
   return res;
 }
 
@@ -138,7 +148,7 @@ int ha_heap::update_row(const byte * old_data, byte * new_data)
   res= heap_update(file,old_data,new_data);
   if (!res && ++records_changed*HEAP_STATS_UPDATE_THRESHOLD > 
               file->s->records)
-    update_key_stats();
+    key_stats_ok= FALSE;
   return res;
 }
 
@@ -149,7 +159,7 @@ int ha_heap::delete_row(const byte * buf)
   res= heap_delete(file,buf);
   if (!res && table->tmp_table == NO_TMP_TABLE && 
       ++records_changed*HEAP_STATS_UPDATE_THRESHOLD > file->s->records)
-    update_key_stats();
+    key_stats_ok= FALSE;
   return res;
 }
 
@@ -262,6 +272,13 @@ void ha_heap::info(uint flag)
   delete_length= info.deleted * info.reclength;
   if (flag & HA_STATUS_AUTO)
     auto_increment_value= info.auto_increment;
+  /*
+    If info() is called for the first time after open(), we will still
+    have to update the key statistics. Hoping that a table lock is now
+    in place.
+  */
+  if (! key_stats_ok)
+    update_key_stats();
 }
 
 int ha_heap::extra(enum ha_extra_function operation)
@@ -273,7 +290,7 @@ int ha_heap::delete_all_rows()
 {
   heap_clear(file);
   if (table->tmp_table == NO_TMP_TABLE)
-    update_key_stats();
+    key_stats_ok= FALSE;
   return 0;
 }
 
@@ -433,7 +450,11 @@ ha_rows ha_heap::records_in_range(uint inx, key_range *min_key,
       max_key->flag != HA_READ_AFTER_KEY)
     return HA_POS_ERROR;			// Can only use exact keys
   else
+  {
+    /* Assert that info() did run. We need current statistics here. */
+    DBUG_ASSERT(key_stats_ok);
     return key->rec_per_key[key->key_parts-1];
+  }
 }