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Fixed bug#11749345 (formerly bug#38813) - increasing memory consumption

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when selecting from I_S and views exist, in SP.

Symptoms: re-execution of prepared statement (or statement in a stored
routine) which read from one of I_S tables and which in order to fill
this I_S table had to open a view led to increasing memory consumption.

What happened in this situation was that during the process of view
opening for purpose of I_S filling view-related structures (like its
LEX) were allocated on persistent MEM_ROOT of prepared statement (or 
stored routine). Since this MEM_ROOT is not freed until prepared
statement deallocation (or expulsion of stored routine from the cache)
and code responsible for filling I_S is not able to re-use results of
view opening from previous executions this allocation ended up in
memory hogging.

This patch solves the problem by ensuring that when a view opened
for the purpose of I_S filling all its structures are allocated on
non-persistent runtime MEM_ROOT. This is achieved by activating a
temporary Query_arena bound to this MEM_ROOT.
Since this step makes impossible linking of view structures into
LEX of our prepared statement (or stored routine statement) this
patch also changes code filling I_S table to install a proxy LEX
before trying to open a view or a table. Consequently some code
which was responsible for backing-up/restoring parts of LEX when
view/table was opened during filling of I_S table became redundant
and was removed.

This patch doesn't contain test case for this bug as it is hard
to test memory hogging in our test suite.
This commit is contained in:
Dmitry Shulga 2011-05-20 23:52:52 +07:00
parent f633e6f5bb
commit 967cf75819
1 changed files with 177 additions and 137 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

314
sql/sql_show.cc
View File

@ -2428,12 +2428,11 @@ bool schema_table_store_record(THD *thd, TABLE *table)
}
int make_table_list(THD *thd, SELECT_LEX *sel,
LEX_STRING *db_name, LEX_STRING *table_name)
static int make_table_list(THD *thd, SELECT_LEX *sel,
LEX_STRING *db_name, LEX_STRING *table_name)
{
Table_ident *table_ident;
table_ident= new Table_ident(thd, *db_name, *table_name, 1);
sel->init_query();
if (!sel->add_table_to_list(thd, table_ident, 0, 0, TL_READ))
return 1;
return 0;
@ -3003,79 +3002,179 @@ make_table_name_list(THD *thd, List<LEX_STRING> *table_names, LEX *lex,
/**
@brief Fill I_S table for SHOW COLUMNS|INDEX commands
Fill I_S table with data obtained by performing full-blown table open.
@param[in] thd thread handler
@param[in] tables TABLE_LIST for I_S table
@param[in] schema_table pointer to I_S structure
@param[in] open_tables_state_backup pointer to Open_tables_state object
which is used to save|restore original
status of variables related to
open tables state
@param thd Thread handler.
@param is_show_fields_or_keys Indicates whether it is a legacy SHOW
COLUMNS or SHOW KEYS statement.
@param table TABLE object for I_S table to be filled.
@param schema_table I_S table description structure.
@param orig_db_name Database name.
@param orig_table_name Table name.
@param open_tables_state_backup Open_tables_state object which is used
to save/restore original status of
variables related to open tables state.
@return Operation status
@retval 0 success
@retval 1 error
@retval FALSE - Success.
@retval TRUE - Failure.
*/
static int
fill_schema_show_cols_or_idxs(THD *thd, TABLE_LIST *tables,
ST_SCHEMA_TABLE *schema_table,
Open_tables_state *open_tables_state_backup)
static bool
fill_schema_table_by_open(THD *thd, bool is_show_fields_or_keys,
TABLE *table, ST_SCHEMA_TABLE *schema_table,
LEX_STRING *orig_db_name,
LEX_STRING *orig_table_name,
Open_tables_state *open_tables_state_backup)
{
LEX *lex= thd->lex;
bool res;
LEX_STRING tmp_lex_string, tmp_lex_string1, *db_name, *table_name;
enum_sql_command save_sql_command= lex->sql_command;
TABLE_LIST *show_table_list= tables->schema_select_lex->table_list.first;
TABLE *table= tables->table;
int error= 1;
DBUG_ENTER("fill_schema_show");
Query_arena i_s_arena(thd->mem_root,
Query_arena::CONVENTIONAL_EXECUTION),
backup_arena, *old_arena;
LEX *old_lex= thd->lex, temp_lex, *lex;
LEX_STRING db_name, table_name;
TABLE_LIST *table_list;
bool result= true;
lex->all_selects_list= tables->schema_select_lex;
/*
Restore thd->temporary_tables to be able to process
temporary tables(only for 'show index' & 'show columns').
This should be changed when processing of temporary tables for
I_S tables will be done.
When a view is opened its structures are allocated on a permanent
statement arena and linked into the LEX tree for the current statement
(this happens even in cases when view is handled through TEMPTABLE
algorithm).
To prevent this process from unnecessary hogging of memory in the permanent
arena of our I_S query and to avoid damaging its LEX we use temporary
arena and LEX for table/view opening.
Use temporary arena instead of statement permanent arena. Also make
it active arena and save original one for successive restoring.
*/
thd->temporary_tables= open_tables_state_backup->temporary_tables;
old_arena= thd->stmt_arena;
thd->stmt_arena= &i_s_arena;
thd->set_n_backup_active_arena(&i_s_arena, &backup_arena);
/* Prepare temporary LEX. */
thd->lex= lex= &temp_lex;
lex_start(thd);
/* Disable constant subquery evaluation as we won't be locking tables. */
lex->context_analysis_only= CONTEXT_ANALYSIS_ONLY_VIEW;
/*
Some of process_table() functions rely on wildcard being passed from
old LEX (or at least being initialized).
*/
lex->wild= old_lex->wild;
/*
Since make_table_list() might change database and table name passed
to it we create copies of orig_db_name and orig_table_name here.
These copies are used for make_table_list() while unaltered values
are passed to process_table() functions.
*/
if (!thd->make_lex_string(&db_name, orig_db_name->str,
orig_db_name->length, FALSE) ||
!thd->make_lex_string(&table_name, orig_table_name->str,
orig_table_name->length, FALSE))
goto end;
/*
Create table list element for table to be open. Link it with the
temporary LEX. The latter is required to correctly open views and
produce table describing their structure.
*/
if (make_table_list(thd, &lex->select_lex, &db_name, &table_name))
goto end;
table_list= lex->select_lex.table_list.first;
if (is_show_fields_or_keys)
{
/*
Restore thd->temporary_tables to be able to process
temporary tables (only for 'show index' & 'show columns').
This should be changed when processing of temporary tables for
I_S tables will be done.
*/
thd->temporary_tables= open_tables_state_backup->temporary_tables;
}
else
{
/*
Apply optimization flags for table opening which are relevant for
this I_S table. We can't do this for SHOW COLUMNS/KEYS because of
backward compatibility.
*/
table_list->i_s_requested_object= schema_table->i_s_requested_object;
}
/*
Let us set fake sql_command so views won't try to merge
themselves into main statement. If we don't do this,
SELECT * from information_schema.xxxx will cause problems.
SQLCOM_SHOW_FIELDS is used because it satisfies 'only_view_structure()'
SQLCOM_SHOW_FIELDS is used because it satisfies
'only_view_structure()'.
*/
lex->sql_command= SQLCOM_SHOW_FIELDS;
res= open_normal_and_derived_tables(thd, show_table_list,
MYSQL_LOCK_IGNORE_FLUSH);
lex->sql_command= save_sql_command;
result= open_normal_and_derived_tables(thd, table_list,
MYSQL_LOCK_IGNORE_FLUSH);
/*
get_all_tables() returns 1 on failure and 0 on success thus
return only these and not the result code of ::process_table()
We should use show_table_list->alias instead of
show_table_list->table_name because table_name
could be changed during opening of I_S tables. It's safe
to use alias because alias contains original table name
in this case(this part of code is used only for
'show columns' & 'show statistics' commands).
Restore old value of sql_command back as it is being looked at in
process_table() function.
*/
table_name= thd->make_lex_string(&tmp_lex_string1, show_table_list->alias,
strlen(show_table_list->alias), FALSE);
if (!show_table_list->view)
db_name= thd->make_lex_string(&tmp_lex_string, show_table_list->db,
show_table_list->db_length, FALSE);
else
db_name= &show_table_list->view_db;
lex->sql_command= old_lex->sql_command;
error= test(schema_table->process_table(thd, show_table_list,
table, res, db_name,
table_name));
thd->temporary_tables= 0;
close_tables_for_reopen(thd, &show_table_list);
DBUG_RETURN(error);
/*
XXX: show_table_list has a flag i_is_requested,
and when it's set, open_normal_and_derived_tables()
can return an error without setting an error message
in THD, which is a hack. This is why we have to
check for res, then for thd->is_error() and only then
for thd->main_da.sql_errno().
Again we don't do this for SHOW COLUMNS/KEYS because
of backward compatibility.
*/
if (!is_show_fields_or_keys && result && thd->is_error() &&
thd->main_da.sql_errno() == ER_NO_SUCH_TABLE)
{
/*
Hide error for a non-existing table.
For example, this error can occur when we use a where condition
with a db name and table, but the table does not exist.
*/
result= 0;
thd->clear_error();
}
else
{
result= schema_table->process_table(thd, table_list,
table, result,
orig_db_name,
orig_table_name);
}
end:
lex->unit.cleanup();
/* Restore original LEX value, statement's arena and THD arena values. */
lex_end(thd->lex);
if (i_s_arena.free_list)
i_s_arena.free_items();
/*
For safety reset list of open temporary tables before closing
all tables open within this Open_tables_state.
*/
thd->temporary_tables= NULL;
close_thread_tables(thd);
thd->lex= old_lex;
thd->stmt_arena= old_arena;
thd->restore_active_arena(&i_s_arena, &backup_arena);
return result;
}
@ -3300,11 +3399,8 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
{
LEX *lex= thd->lex;
TABLE *table= tables->table;
SELECT_LEX *old_all_select_lex= lex->all_selects_list;
enum_sql_command save_sql_command= lex->sql_command;
SELECT_LEX *lsel= tables->schema_select_lex;
ST_SCHEMA_TABLE *schema_table= tables->schema_table;
SELECT_LEX sel;
LOOKUP_FIELD_VALUES lookup_field_vals;
LEX_STRING *db_name, *table_name;
bool with_i_schema;
@ -3312,20 +3408,14 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
List<LEX_STRING> db_names;
List_iterator_fast<LEX_STRING> it(db_names);
COND *partial_cond= 0;
uint derived_tables= lex->derived_tables;
int error= 1;
Open_tables_state open_tables_state_backup;
uint8 save_context_analysis_only= lex->context_analysis_only;
Query_tables_list query_tables_list_backup;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
Security_context *sctx= thd->security_ctx;
#endif
uint table_open_method;
DBUG_ENTER("get_all_tables");
lex->context_analysis_only|= CONTEXT_ANALYSIS_ONLY_VIEW;
lex->reset_n_backup_query_tables_list(&query_tables_list_backup);
/*
We should not introduce deadlocks even if we already have some
tables open and locked, since we won't lock tables which we will
@ -3340,8 +3430,18 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
*/
if (lsel && lsel->table_list.first)
{
error= fill_schema_show_cols_or_idxs(thd, tables, schema_table,
&open_tables_state_backup);
LEX_STRING db_name, table_name;
db_name.str= lsel->table_list.first->db;
db_name.length= lsel->table_list.first->db_length;
table_name.str= lsel->table_list.first->table_name;
table_name.length= lsel->table_list.first->table_name_length;
error= fill_schema_table_by_open(thd, TRUE,
table, schema_table,
&db_name, &table_name,
&open_tables_state_backup);
goto err;
}
@ -3399,12 +3499,6 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
it.rewind(); /* To get access to new elements in basis list */
while ((db_name= it++))
{
LEX_STRING orig_db_name;
/* db_name can be changed in make_table_list() func */
if (!thd->make_lex_string(&orig_db_name, db_name->str,
db_name->length, FALSE))
goto err;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
if (!(check_access(thd,SELECT_ACL, db_name->str,
&thd->col_access, 0, 1, with_i_schema) ||
@ -3466,64 +3560,14 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
continue;
}
int res;
LEX_STRING tmp_lex_string;
/*
Set the parent lex of 'sel' because it is needed by
sel.init_query() which is called inside make_table_list.
*/
thd->no_warnings_for_error= 1;
sel.parent_lex= lex;
if (make_table_list(thd, &sel, db_name, table_name))
goto err;
TABLE_LIST *show_table_list= sel.table_list.first;
lex->all_selects_list= &sel;
lex->derived_tables= 0;
lex->sql_command= SQLCOM_SHOW_FIELDS;
show_table_list->i_s_requested_object=
schema_table->i_s_requested_object;
DEBUG_SYNC(thd, "before_open_in_get_all_tables");
res= open_normal_and_derived_tables(thd, show_table_list,
MYSQL_LOCK_IGNORE_FLUSH);
lex->sql_command= save_sql_command;
/*
XXX: show_table_list has a flag i_is_requested,
and when it's set, open_normal_and_derived_tables()
can return an error without setting an error message
in THD, which is a hack. This is why we have to
check for res, then for thd->is_error() only then
for thd->main_da.sql_errno().
*/
if (res && thd->is_error() &&
thd->main_da.sql_errno() == ER_NO_SUCH_TABLE)
{
/*
Hide error for not existing table.
This error can occur for example when we use
where condition with db name and table name and this
table does not exist.
*/
res= 0;
thd->clear_error();
}
else
{
/*
We should use show_table_list->alias instead of
show_table_list->table_name because table_name
could be changed during opening of I_S tables. It's safe
to use alias because alias contains original table name
in this case.
*/
thd->make_lex_string(&tmp_lex_string, show_table_list->alias,
strlen(show_table_list->alias), FALSE);
res= schema_table->process_table(thd, show_table_list, table,
res, &orig_db_name,
&tmp_lex_string);
close_tables_for_reopen(thd, &show_table_list);
}
DBUG_ASSERT(!lex->query_tables_own_last);
if (res)
if (fill_schema_table_by_open(thd, FALSE,
table, schema_table,
db_name, table_name,
&open_tables_state_backup))
goto err;
}
}
@ -3539,11 +3583,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
error= 0;
err:
thd->restore_backup_open_tables_state(&open_tables_state_backup);
lex->restore_backup_query_tables_list(&query_tables_list_backup);
lex->derived_tables= derived_tables;
lex->all_selects_list= old_all_select_lex;
lex->context_analysis_only= save_context_analysis_only;
lex->sql_command= save_sql_command;
DBUG_RETURN(error);
}