Bug#34043: Server loops excessively in _checkchunk() when safemalloc is enabled

Essentially, the problem is that safemalloc is excruciatingly
slow as it checks all allocated blocks for overrun at each
memory management primitive, yielding a almost exponential
slowdown for the memory management functions (malloc, realloc,
free). The overrun check basically consists of verifying some
bytes of a block for certain magic keys, which catches some
simple forms of overrun. Another minor problem is violation
of aliasing rules and that its own internal list of blocks
is prone to corruption.

Another issue with safemalloc is rather the maintenance cost
as the tool has a significant impact on the server code.
Given the magnitude of memory debuggers available nowadays,
especially those that are provided with the platform malloc
implementation, maintenance of a in-house and largely obsolete
memory debugger becomes a burden that is not worth the effort
due to its slowness and lack of support for detecting more
common forms of heap corruption.

Since there are third-party tools that can provide the same
functionality at a lower or comparable performance cost, the
solution is to simply remove safemalloc. Third-party tools
can provide the same functionality at a lower or comparable
performance cost. 

The removal of safemalloc also allows a simplification of the
malloc wrappers, removing quite a bit of kludge: redefinition
of my_malloc, my_free and the removal of the unused second
argument of my_free. Since free() always check whether the
supplied pointer is null, redudant checks are also removed.

Also, this patch adds unit testing for my_malloc and moves
my_realloc implementation into the same file as the other
memory allocation primitives.

1 files changed, 9 insertions, 10 deletions

diff --git a/sql/sql_db.cc b/sql/sql_db.cc
index 2e48475f298..1040fc92851 100644
--- a/sql/sql_db.cc
+++ b/sql/sql_db.cc
@@ -94,7 +94,7 @@ extern "C" void lock_db_free_element(void *ptr);
 
 void lock_db_free_element(void *ptr)
 {
-  my_free(ptr, MYF(0));
+  my_free(ptr);
 }
 
 
@@ -136,7 +136,7 @@ static my_bool lock_db_insert(const char *dbname, uint length)
     opt->name_length= length;
     
     if ((error= my_hash_insert(&lock_db_cache, (uchar*) opt)))
-      my_free(opt, MYF(0));
+      my_free(opt);
   }
 
 end:
@@ -209,7 +209,7 @@ extern "C" void free_dbopt(void *dbopt);
 
 void free_dbopt(void *dbopt)
 {
-  my_free((uchar*) dbopt, MYF(0));
+  my_free(dbopt);
 }
 
 #ifdef HAVE_PSI_INTERFACE
@@ -377,7 +377,7 @@ static my_bool put_dbopt(const char *dbname, HA_CREATE_INFO *create)
     
     if ((error= my_hash_insert(&dboptions, (uchar*) opt)))
     {
-      my_free(opt, MYF(0));
+      my_free(opt);
       goto end;
     }
   }
@@ -1438,8 +1438,7 @@ static void mysql_change_db_impl(THD *thd,
       we just call THD::reset_db(). Since THD::reset_db() does not releases
       the previous database name, we should do it explicitly.
     */
-
-    x_free(thd->db);
+    my_free(thd->db);
 
     thd->reset_db(new_db_name->str, new_db_name->length);
   }
@@ -1652,7 +1651,7 @@ bool mysql_change_db(THD *thd, const LEX_STRING *new_db_name, bool force_switch)
   if (check_db_name(&new_db_file_name))
   {
     my_error(ER_WRONG_DB_NAME, MYF(0), new_db_file_name.str);
-    my_free(new_db_file_name.str, MYF(0));
+    my_free(new_db_file_name.str);
 
     if (force_switch)
       mysql_change_db_impl(thd, NULL, 0, thd->variables.collation_server);
@@ -1682,7 +1681,7 @@ bool mysql_change_db(THD *thd, const LEX_STRING *new_db_name, bool force_switch)
              new_db_file_name.str);
     general_log_print(thd, COM_INIT_DB, ER(ER_DBACCESS_DENIED_ERROR),
                       sctx->priv_user, sctx->priv_host, new_db_file_name.str);
-    my_free(new_db_file_name.str, MYF(0));
+    my_free(new_db_file_name.str);
     DBUG_RETURN(TRUE);
   }
 #endif
@@ -1697,7 +1696,7 @@ bool mysql_change_db(THD *thd, const LEX_STRING *new_db_name, bool force_switch)
                           ER_BAD_DB_ERROR, ER(ER_BAD_DB_ERROR),
                           new_db_file_name.str);
 
-      my_free(new_db_file_name.str, MYF(0));
+      my_free(new_db_file_name.str);
 
       /* Change db to NULL. */
 
@@ -1712,7 +1711,7 @@ bool mysql_change_db(THD *thd, const LEX_STRING *new_db_name, bool force_switch)
       /* Report an error and free new_db_file_name. */
 
       my_error(ER_BAD_DB_ERROR, MYF(0), new_db_file_name.str);
-      my_free(new_db_file_name.str, MYF(0));
+      my_free(new_db_file_name.str);
 
       /* The operation failed. */