Merge adventure.(none):/home/thek/Development/cpp/bug28249/my50-bug28249

into  adventure.(none):/home/thek/Development/cpp/mysql-5.0-runtime


mysql-test/t/query_cache.test:
  Auto merged
sql/ha_myisam.cc:
  Auto merged
sql/handler.h:
  Auto merged
mysql-test/r/query_cache.result:
  SCCS merged

1 files changed, 74 insertions, 0 deletions

diff --git a/sql/ha_myisam.cc b/sql/ha_myisam.cc
index 5e953092436..18c9e6feb34 100644
--- a/sql/ha_myisam.cc
+++ b/sql/ha_myisam.cc
@@ -1921,3 +1921,77 @@ uint ha_myisam::checksum() const
   return (uint)file->state->checksum;
 }
 
+#ifdef HAVE_QUERY_CACHE
+/**
+  @brief Register a named table with a call back function to the query cache.
+
+  @param thd The thread handle
+  @param table_key A pointer to the table name in the table cache
+  @param key_length The length of the table name
+  @param[out] engine_callback The pointer to the storage engine call back
+    function, currently 0
+  @param[out] engine_data Engine data will be set to 0.
+
+  @note Despite the name of this function, it is used to check each statement
+    before it is cached and not to register a table or callback function.
+
+  @see handler::register_query_cache_table
+
+  @return The error code. The engine_data and engine_callback will be set to 0.
+    @retval TRUE Success
+    @retval FALSE An error occured
+*/
+
+my_bool ha_myisam::register_query_cache_table(THD *thd, char *table_name,
+                                              uint table_name_len,
+                                              qc_engine_callback
+                                              *engine_callback,
+                                              ulonglong *engine_data)
+{
+  /*
+    No call back function is needed to determine if a cached statement
+    is valid or not.
+  */
+  *engine_callback= 0;
+
+  /*
+    No engine data is needed.
+  */
+  *engine_data= 0;
+
+  /*
+    If a concurrent INSERT has happened just before the currently processed
+    SELECT statement, the total size of the table is unknown.
+
+    To determine if the table size is known, the current thread's snap shot of
+    the table size with the actual table size are compared.
+
+    If the table size is unknown the SELECT statement can't be cached.
+  */
+  ulonglong actual_data_file_length;
+  ulonglong current_data_file_length;
+
+  /*
+    POSIX visibility rules specify that "2. Whatever memory values a
+    thread can see when it unlocks a mutex <...> can also be seen by any
+    thread that later locks the same mutex". In this particular case,
+    concurrent insert thread had modified the data_file_length in
+    MYISAM_SHARE before it has unlocked (or even locked)
+    structure_guard_mutex. So, here we're guaranteed to see at least that
+    value after we've locked the same mutex. We can see a later value
+    (modified by some other thread) though, but it's ok, as we only want
+    to know if the variable was changed, the actual new value doesn't matter
+  */
+  actual_data_file_length= file->s->state.state.data_file_length;
+  current_data_file_length= file->save_state.data_file_length;
+
+  if (current_data_file_length != actual_data_file_length)
+  {
+    /* Don't cache current statement. */
+    return FALSE;
+  }
+
+  /* It is ok to try to cache current statement. */
+  return TRUE;
+}
+#endif