From 124cb126fa65fc1099256be5e269277bde815703 Mon Sep 17 00:00:00 2001 From: unknown Date: Mon, 19 Jun 2006 13:22:42 +0300 Subject: * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big tables Currently in INSERT ... SELECT ... LIMIT ... the compiler uses a temporary table to store the results of SELECT ... LIMIT .. and then uses that table as a source for INSERT. The problem is that in some cases it actually skips the LIMIT clause in doing that and materializes the whole SELECT result set regardless of the LIMIT. This fix is limiting the process of filling up the temp table with only that much rows that will be actually used by propagating the LIMIT value. mysql-test/r/insert_select.result: * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big tables - a test demonstrating the code path mysql-test/t/insert_select.test: * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big tables - a test demonstrating the code path sql/sql_select.cc: * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big tables - pass through the real LIMIT number if the temp table is created for buffering results. - set the counter for all the cases when the temp table is not used for grouping --- sql/sql_select.cc | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) (limited to 'sql') diff --git a/sql/sql_select.cc b/sql/sql_select.cc index 5a7e9e52aed..709ff9726bb 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -888,8 +888,9 @@ JOIN::optimize() group_list ? 0 : select_distinct, group_list && simple_group, select_options, - (order == 0 || skip_sort_order) ? select_limit : - HA_POS_ERROR, + (order == 0 || skip_sort_order || + test(select_options & OPTION_BUFFER_RESULT)) ? + select_limit : HA_POS_ERROR, (char *) ""))) DBUG_RETURN(1); @@ -5530,6 +5531,11 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List &fields, keyinfo->key_length+= key_part_info->length; } } + else + { + set_if_smaller(table->max_rows, rows_limit); + param->end_write_records= rows_limit; + } if (distinct && field_count != param->hidden_field_count) { @@ -5544,8 +5550,6 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List &fields, null_pack_length-=hidden_null_pack_length; keyinfo->key_parts= ((field_count-param->hidden_field_count)+ test(null_pack_length)); - set_if_smaller(table->max_rows, rows_limit); - param->end_write_records= rows_limit; table->distinct=1; table->keys=1; if (blob_count) -- cgit v1.2.1