Hi Dmitry,
On 5/16/11 7:17 AM, Dmitry Shulga wrote:
> #At file:///Users/shulga/projects/mysql/mysql-5.1-bug11749345/ based on
> revid:tatjana.nuernberg@stripped
>
> 3620 Dmitry Shulga 2011-05-16
> Fixed bug#11749345 (formerly bug#38813) - increasing memory consumption
> 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.
>
OK to push. Some minor comments below. Thanks for working on this.
[...]
> - 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 permanent
"on a permanent"
> + statement arena and linked into LEX tree for the current statement
"into the LEX"
> + (this happens even in cases when view is handled through TEMPTABLE
> + algorithm).
> +
> + To prevent this process from unnecessary hogging of memory in permanent
"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;
> +
> + /*
> + Strings in db_name and table_name might be changed by make_table_list()
> + function. In order to pass their unaltered values to process_table()
> + call we save them here.
> + */
> + if (!thd->make_lex_string(&orig_db_name, db_name->str,
> + db_name->length, FALSE) ||
> + !thd->make_lex_string(&orig_table_name, table_name->str,
> + 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').
"tables (only"
> + 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;
> + }
> +
[...]
> + if (!is_show_fields_or_keys&& result&&
> thd->is_error()&&
> + thd->main_da.sql_errno() == ER_NO_SUCH_TABLE)
> + {
> + /*
> + Hide error for not existing table.
"for a non-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.
"For example, this error can occur when we use a where condition with a
db name and table, but the table does not exist."
> +
> + /*
> + For safety reset list of open temporary tables before closing
> + all tables open within this Open_tables_state.
> + */
> + thd->temporary_tables= 0;
0 -> NULL
> + close_thread_tables(thd);
> +
Otherwise, looks good.
Regards,
Davi
