Description:
While executing a SELECT ... LIMIT 0 query against patched trunk (to disable PQ filesort optimization, aka. WL#1393), the MySQL server crashed as follows:
Offending query:
SELECT SQL_CALC_FOUND_ROWS `col_varchar_10` AS field1 FROM H AS table1 ORDER BY field1 LIMIT 0;
where table H is an InnoDB table with 100 000 rows.
Stacktrace:
=>[3] my_write_core(sig = 11), line 423 in "stacktrace.c"
[4] handle_segfault(sig = 11), line 2511 in "mysqld.cc"
[5] __sighndlr(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7fff27b076
[6] call_user_handler(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7fff26dfaf
[7] sigacthandler(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7fff26e1be
---- called from signal handler with signal 11 (SIGSEGV) ------
[8] memcpy(0x5c569da, 0xfffffd7fff08dfff, 0xfffffd7fff08e010, 0x5c569eb, 0x11, 0x5c73e90), at 0xfffffd7fff1e6f58
[9] merge_buffers(param = 0xfffffd7fff0898c8, from_file = 0xfffffd7fff089a80, to_file = 0x59e5040, sort_buffer = 0x5a53b70 "P¨^E", lastbuff = 0x5c73e90, Fb = 0x5c73e90, Tb = 0x5c73ec0, flag = 1), line 1507 in "filesort.cc"
[10] merge_index(param = 0xfffffd7fff0898c8, sort_buffer = 0x5a53b70 "P¨^E", buffpek = 0x5c73e90, maxbuffer = 1U, tempfile = 0xfffffd7fff089a80, outfile = 0x59e5040), line 1602 in "filesort.cc"
[11] filesort(thd = 0x5994990, table = 0x5a12430, sortorder = 0x59e2b28, s_length = 1U, select = 0x59e2998, max_rows = 0, sort_positions = false, examined_rows = 0xfffffd7fff089d20, found_rows = 0xfffffd7fff089d18), line 322 in "filesort.cc"
[12] create_sort_index(thd = 0x5994990, join = 0x59e19b0, order = 0x59e18c0, filesort_limit = 0, select_limit = 18446744073709551615ULL, is_order_by = true), line 20223 in "sql_select.cc"
[13] JOIN::exec(this = 0x59e19b0), line 3296 in "sql_select.cc"
[14] mysql_select(thd = 0x5994990, rref_pointer_array = 0x5996db0, tables = 0x59e1270, wild_num = 0, fields = CLASS, conds = (nil), og_num = 1U, order = 0x59e18c0, group = (nil), having = (nil), proc_param = (nil), select_options = 2147748640ULL, result = 0x59e1990, unit = 0x5996590, select_lex = 0x5996bc8), line 3554 in "sql_select.cc"
[15] handle_select(thd = 0x5994990, lex = 0x59964e0, result = 0x59e1990, setup_tables_done_option = 0), line 311 in "sql_select.cc"
[16] execute_sqlcom_select(thd = 0x5994990, all_tables = 0x59e1270), line 4513 in "sql_parse.cc"
[17] mysql_execute_command(thd = 0x5994990), line 2096 in "sql_parse.cc"
[18] mysql_parse(thd = 0x5994990, rawbuf = 0x59e0fe0 "SELECT SQL_CALC_FOUND_ROWS `col_varchar_10` AS field1 FROM H AS table1 ORDER BY field1 LIMIT 0", length = 95U, parser_state = 0xfffffd7fff08d960), line 5550 in "sql_parse.cc"
[19] dispatch_command(command = COM_QUERY, thd = 0x5994990, packet = 0x59d8f91 "SELECT SQL_CALC_FOUND_ROWS `col_varchar_10` AS field1 FROM H AS table1 ORDER BY field1 LIMIT 0", packet_length = 95U), line 1078 in "sql_parse.cc"
[20] do_command(thd = 0x5994990), line 815 in "sql_parse.cc"
[21] do_handle_one_connection(thd_arg = 0x5994990), line 748 in "sql_connect.cc"
[22] handle_one_connection(arg = 0x5994990), line 684 in "sql_connect.cc"
How to repeat:
Patch against trunk:
=== modified file 'sql/filesort.cc'
--- sql/filesort.cc 2011-01-11 09:09:21 +0000
+++ sql/filesort.cc 2011-01-11 14:42:26 +0000
@@ -1146,6 +1146,9 @@
{
DBUG_ENTER("check_if_pq_applicable");
+ /* Fully disable PQ for testing without WL#1393. */
+ DBUG_RETURN(false);
+
/*
How much Priority Queue sort is slower than qsort.
Measurements (see unit test) indicate that PQ is roughly 3 times slower.
Crashing query:
SELECT SQL_CALC_FOUND_ROWS `col_varchar_10` AS field1 FROM H AS table1 ORDER BY field1 LIMIT 0;
Details about the dataset may be made available later.
