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BUG#18326: Do not lock table for writing during prepare of statement

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During statement prepare phase the tables were locked as if the
statement is being executed, however this is not necessary.

The solution is to not lock tables on statement prepare phase.
Opening tables is enough to prevent DDL on them, and during statement
prepare we do not access nor modify any data.
This commit is contained in:
kroki/tomash@moonlight.home
2007-03-07 18:51:49 +03:00
parent f0ebefbb8f
commit 3e8bfc83a8
3 changed files with 144 additions and 56 deletions
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106
sql/sql_prepare.cc
View File

@ -34,6 +34,12 @@ When one prepares a statement:
[Params meta info (stubs only for now)] (if Param_count > 0)
[Columns meta info] (if Column_count > 0)
During prepare the tables used in a statement are opened, but no
locks are acquired. Table opening will block any DDL during the
operation, and we do not need any locks as we neither read nor
modify any data during prepare. Tables are closed after prepare
finishes.
When one executes a statement:
- Server gets the command 'COM_STMT_EXECUTE' to execute the
@ -53,6 +59,10 @@ When one executes a statement:
- Execute the query without re-parsing and send back the results
to client
During execution of prepared statement tables are opened and locked
the same way they would for normal (non-prepared) statement
execution. Tables are unlocked and closed after the execution.
When one supplies long data for a placeholder:
- Server gets the long data in pieces with command type
@ -1120,38 +1130,20 @@ static int mysql_test_update(Prepared_statement *stmt,
bool need_reopen;
DBUG_ENTER("mysql_test_update");
if (update_precheck(thd, table_list))
if (update_precheck(thd, table_list) ||
open_normal_and_derived_tables(thd, table_list, 0))
goto error;
for ( ; ; )
if (table_list->multitable_view)
{
if (open_tables(thd, &table_list, &table_count, 0))
goto error;
if (table_list->multitable_view)
{
DBUG_ASSERT(table_list->view != 0);
DBUG_PRINT("info", ("Switch to multi-update"));
/* pass counter value */
thd->lex->table_count= table_count;
/* convert to multiupdate */
DBUG_RETURN(2);
}
if (!lock_tables(thd, table_list, table_count, &need_reopen))
break;
if (!need_reopen)
goto error;
close_tables_for_reopen(thd, &table_list);
DBUG_ASSERT(table_list->view != 0);
DBUG_PRINT("info", ("Switch to multi-update"));
/* pass counter value */
thd->lex->table_count= table_count;
/* convert to multiupdate */
DBUG_RETURN(2);
}
/*
thd->fill_derived_tables() is false here for sure (because it is
preparation of PS, so we even do not check it).
*/
if (mysql_handle_derived(thd->lex, &mysql_derived_prepare))
goto error;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
/* TABLE_LIST contain right privilages request */
want_privilege= table_list->grant.want_privilege;
@ -1209,7 +1201,7 @@ static bool mysql_test_delete(Prepared_statement *stmt,
DBUG_ENTER("mysql_test_delete");
if (delete_precheck(thd, table_list) ||
open_and_lock_tables(thd, table_list))
open_normal_and_derived_tables(thd, table_list, 0))
goto error;
if (!table_list->table)
@ -1268,7 +1260,7 @@ static int mysql_test_select(Prepared_statement *stmt,
goto error;
}
if (open_and_lock_tables(thd, tables))
if (open_normal_and_derived_tables(thd, tables, 0))
goto error;
thd->used_tables= 0; // Updated by setup_fields
@ -1329,7 +1321,7 @@ static bool mysql_test_do_fields(Prepared_statement *stmt,
if (tables && check_table_access(thd, SELECT_ACL, tables, 0))
DBUG_RETURN(TRUE);
if (open_and_lock_tables(thd, tables))
if (open_normal_and_derived_tables(thd, tables, 0))
DBUG_RETURN(TRUE);
DBUG_RETURN(setup_fields(thd, 0, *values, MARK_COLUMNS_NONE, 0, 0));
}
@ -1359,7 +1351,7 @@ static bool mysql_test_set_fields(Prepared_statement *stmt,
set_var_base *var;
if (tables && check_table_access(thd, SELECT_ACL, tables, 0) ||
open_and_lock_tables(thd, tables))
open_normal_and_derived_tables(thd, tables, 0))
goto error;
while ((var= it++))
@ -1385,7 +1377,7 @@ error:
NOTE
This function won't directly open tables used in select. They should
be opened either by calling function (and in this case you probably
should use select_like_stmt_test_with_open_n_lock()) or by
should use select_like_stmt_test_with_open()) or by
"specific_prepare" call (like this happens in case of multi-update).
RETURN VALUE
@ -1413,14 +1405,14 @@ static bool select_like_stmt_test(Prepared_statement *stmt,
}
/*
Check internal SELECT of the prepared command (with opening and
locking of used tables).
Check internal SELECT of the prepared command (with opening of used
tables).
SYNOPSIS
select_like_stmt_test_with_open_n_lock()
select_like_stmt_test_with_open()
stmt prepared statement
tables list of tables to be opened and locked
before calling specific_prepare function
tables list of tables to be opened before calling
specific_prepare function
specific_prepare function of command specific prepare
setup_tables_done_option options to be passed to LEX::unit.prepare()
@ -1430,19 +1422,20 @@ static bool select_like_stmt_test(Prepared_statement *stmt,
*/
static bool
select_like_stmt_test_with_open_n_lock(Prepared_statement *stmt,
TABLE_LIST *tables,
bool (*specific_prepare)(THD *thd),
ulong setup_tables_done_option)
select_like_stmt_test_with_open(Prepared_statement *stmt,
TABLE_LIST *tables,
bool (*specific_prepare)(THD *thd),
ulong setup_tables_done_option)
{
DBUG_ENTER("select_like_stmt_test_with_open_n_lock");
DBUG_ENTER("select_like_stmt_test_with_open");
/*
We should not call LEX::unit.cleanup() after this open_and_lock_tables()
call because we don't allow prepared EXPLAIN yet so derived tables will
clean up after themself.
We should not call LEX::unit.cleanup() after this
open_normal_and_derived_tables() call because we don't allow
prepared EXPLAIN yet so derived tables will clean up after
themself.
*/
if (open_and_lock_tables(stmt->thd, tables))
if (open_normal_and_derived_tables(stmt->thd, tables, 0))
DBUG_RETURN(TRUE);
DBUG_RETURN(select_like_stmt_test(stmt, specific_prepare,
@ -1481,7 +1474,7 @@ static bool mysql_test_create_table(Prepared_statement *stmt)
if (select_lex->item_list.elements)
{
select_lex->context.resolve_in_select_list= TRUE;
res= select_like_stmt_test_with_open_n_lock(stmt, tables, 0, 0);
res= select_like_stmt_test_with_open(stmt, tables, 0, 0);
}
/* put tables back for PS rexecuting */
@ -1541,9 +1534,9 @@ static bool mysql_test_multidelete(Prepared_statement *stmt,
}
if (multi_delete_precheck(stmt->thd, tables) ||
select_like_stmt_test_with_open_n_lock(stmt, tables,
&mysql_multi_delete_prepare,
OPTION_SETUP_TABLES_DONE))
select_like_stmt_test_with_open(stmt, tables,
&mysql_multi_delete_prepare,
OPTION_SETUP_TABLES_DONE))
goto error;
if (!tables->table)
{
@ -1559,15 +1552,16 @@ error:
/*
Wrapper for mysql_insert_select_prepare, to make change of local tables
after open_and_lock_tables() call.
after open_normal_and_derived_tables() call.
SYNOPSIS
mysql_insert_select_prepare_tester()
thd thread handle
NOTE
We need to remove the first local table after open_and_lock_tables,
because mysql_handle_derived uses local tables lists.
We need to remove the first local table after
open_normal_and_derived_tables(), because mysql_handle_derived
uses local tables lists.
*/
static bool mysql_insert_select_prepare_tester(THD *thd)
@ -1624,9 +1618,9 @@ static bool mysql_test_insert_select(Prepared_statement *stmt,
DBUG_ASSERT(first_local_table != 0);
res=
select_like_stmt_test_with_open_n_lock(stmt, tables,
&mysql_insert_select_prepare_tester,
OPTION_SETUP_TABLES_DONE);
select_like_stmt_test_with_open(stmt, tables,
&mysql_insert_select_prepare_tester,
OPTION_SETUP_TABLES_DONE);
/* revert changes made by mysql_insert_select_prepare_tester */
lex->select_lex.table_list.first= (byte*) first_local_table;
return res;