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Patch for Bug#13805127: Stored program cache produces wrong result in same THD.

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Background:

  - as described in MySQL Internals Prepared Stored
    (http://forge.mysql.com/wiki/MySQL_Internals_Prepared_Stored),
    the Optimizer sometimes does destructive changes to the parsed
    LEX-object (Item-tree), which makes it impossible to re-use
    that tree for PS/SP re-execution.

  - in order to be able to re-use the Item-tree, the destructive
    changes are remembered and rolled back after the statement execution.

The problem, discovered by this bug, was that the objects representing
GROUP-BY clause did not restored after query execution. So, the GROUP-BY
part of the statement could not be properly re-initialized for re-execution
after destructive changes.

Those objects do not take part in the Item-tree, so they can not be saved
using the approach for Item-tree.

The fix is as follows:

  - introduce a new array in st_select_lex to store the original
    ORDER pointers, representing the GROUP-BY clause;

  - Initialize this array in fix_prepare_information().

  - restore the list of GROUP-BY items in reinit_stmt_before_use().
This commit is contained in:
Tor Didriksen 2012-03-29 15:07:54 +02:00
commit ed41846161
8 changed files with 485 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

23
sql/sql_lex.cc
View file

@ -389,6 +389,8 @@ void lex_start(THD *thd)
lex->select_lex.sql_cache= SELECT_LEX::SQL_CACHE_UNSPECIFIED;
lex->select_lex.init_order();
lex->select_lex.group_list.empty();
if (lex->select_lex.group_list_ptrs)
lex->select_lex.group_list_ptrs->clear();
lex->describe= 0;
lex->subqueries= FALSE;
lex->context_analysis_only= 0;
@ -1773,6 +1775,8 @@ void st_select_lex::init_select()
{
st_select_lex_node::init_select();
group_list.empty();
if (group_list_ptrs)
group_list_ptrs->clear();
type= db= 0;
having= 0;
table_join_options= 0;
@ -3100,6 +3104,8 @@ static void fix_prepare_info_in_table_list(THD *thd, TABLE_LIST *tbl)
The passed WHERE and HAVING are to be saved for the future executions.
This function saves it, and returns a copy which can be thrashed during
this execution of the statement. By saving/thrashing here we mean only
We also save the chain of ORDER::next in group_list, in case
the list is modified by remove_const().
AND/OR trees.
The function also calls fix_prepare_info_in_table_list that saves all
ON expressions.
@ -3111,6 +3117,19 @@ void st_select_lex::fix_prepare_information(THD *thd, Item **conds,
if (!thd->stmt_arena->is_conventional() && first_execution)
{
first_execution= 0;
if (group_list.first)
{
if (!group_list_ptrs)
{
void *mem= thd->stmt_arena->alloc(sizeof(Group_list_ptrs));
group_list_ptrs= new (mem) Group_list_ptrs(thd->stmt_arena->mem_root);
}
group_list_ptrs->reserve(group_list.elements);
for (ORDER *order= group_list.first; order; order= order->next)
{
group_list_ptrs->push_back(order);
}
}
if (*conds)
{
prep_where= *conds;
@ -3362,3 +3381,7 @@ void binlog_unsafe_map_init()
BINLOG_DIRECT_OFF & TRX_CACHE_NOT_EMPTY);
}
#endif
#ifdef HAVE_EXPLICIT_TEMPLATE_INSTANTIATION
template class Mem_root_array<ORDER*, true>;
#endif