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.

client/mysqldump.c:
  Pass my_free directly as its signature is compatible with the
  callback type -- which wasn't the case for free_table_ent.

1 files changed, 5 insertions, 5 deletions

diff --git a/sql/log_event_old.cc b/sql/log_event_old.cc
index d9b48cd134e..9263578e0b5 100644
--- a/sql/log_event_old.cc
+++ b/sql/log_event_old.cc
@@ -1017,7 +1017,7 @@ int Delete_rows_log_event_old::do_after_row_operations(TABLE *table, int error)
 {
   /*error= ToDo:find out what this should really be, this triggers close_scan in nbd, returning error?*/
   table->file->ha_index_or_rnd_end();
-  my_free(m_memory, MYF(MY_ALLOW_ZERO_PTR)); // Free for multi_malloc
+  my_free(m_memory); // Free for multi_malloc
   m_memory= NULL;
   m_after_image= NULL;
   m_key= NULL;
@@ -1116,7 +1116,7 @@ int Update_rows_log_event_old::do_after_row_operations(TABLE *table, int error)
 {
   /*error= ToDo:find out what this should really be, this triggers close_scan in nbd, returning error?*/
   table->file->ha_index_or_rnd_end();
-  my_free(m_memory, MYF(MY_ALLOW_ZERO_PTR));
+  my_free(m_memory);
   m_memory= NULL;
   m_after_image= NULL;
   m_key= NULL;
@@ -1360,7 +1360,7 @@ Old_rows_log_event::~Old_rows_log_event()
   if (m_cols.bitmap == m_bitbuf) // no my_malloc happened
     m_cols.bitmap= 0; // so no my_free in bitmap_free
   bitmap_free(&m_cols); // To pair with bitmap_init().
-  my_free((uchar*)m_rows_buf, MYF(MY_ALLOW_ZERO_PTR));
+  my_free(m_rows_buf);
 }
 
 
@@ -2698,7 +2698,7 @@ Delete_rows_log_event_old::do_after_row_operations(const Slave_reporting_capabil
 {
   /*error= ToDo:find out what this should really be, this triggers close_scan in nbd, returning error?*/
   m_table->file->ha_index_or_rnd_end();
-  my_free(m_key, MYF(MY_ALLOW_ZERO_PTR));
+  my_free(m_key);
   m_key= NULL;
 
   return error;
@@ -2797,7 +2797,7 @@ Update_rows_log_event_old::do_after_row_operations(const Slave_reporting_capabil
 {
   /*error= ToDo:find out what this should really be, this triggers close_scan in nbd, returning error?*/
   m_table->file->ha_index_or_rnd_end();
-  my_free(m_key, MYF(MY_ALLOW_ZERO_PTR)); // Free for multi_malloc
+  my_free(m_key); // Free for multi_malloc
   m_key= NULL;
 
   return error;