1、問題現象

create database syw_mtr;
use syw_mtr;
CREATE TABLE t1 (f1 VARCHAR(255) CHARACTER SET utf8)engine=tianmu;
CREATE TABLE t2 AS SELECT LEFT(f1,171) AS f2 FROM t1 UNION SELECT LEFT(f1,171) AS f2 FROM t1;
ERROR 2013 (HY000): Lost connection to MySQL server during query

問題issue：https://github.com/stoneatom/stonedb/issues/226

2、問題原因

bug代碼行

Query_result_create::prepare (sql_insert.cc:2753)

create_table->table不為空

assert(create_table->table == NULL);

stonedb堆棧

    libc.so.6!raise (未知源:0)
    libc.so.6!abort (未知源:0)
    libc.so.6!__assert_fail_base (未知源:0)
    libc.so.6!__assert_fail (未知源:0)
    Query_result_create::prepare(Query_result_create * const this, List<Item> & values, SELECT_LEX_UNIT * u) (\opt\litaihong\stonedb\sql\sql_insert.cc:2753)
    st_select_lex::prepare(st_select_lex * const this, THD * thd) (\opt\litaihong\stonedb\sql\sql_resolver.cc:361)
    st_select_lex_unit::prepare_fake_select_lex(st_select_lex_unit * const this, THD * thd_arg) (\opt\litaihong\stonedb\sql\sql_union.cc:441)
    st_select_lex_unit::optimize_for_stonedb(st_select_lex_unit * const this) (\opt\litaihong\stonedb\storage\stonedb\core\engine_execute.cpp:586)
    stonedb::core::Engine::HandleSelect(stonedb::core::Engine * const this, THD * thd, LEX * lex, Query_result *& result, ulong setup_tables_done_option, int & res, int & optimize_after_sdb, int & sdb_free_join, int with_insert) (\opt\litaihong\stonedb\storage\stonedb\core\engine_execute.cpp:181)
    stonedb::dbhandler::SDB_HandleSelect(THD * thd, LEX * lex, Query_result *& result, ulong setup_tables_done_option, int & res, int & optimize_after_sdb, int & sdb_free_join, int with_insert) (\opt\litaihong\stonedb\storage\stonedb\handler\ha_rcengine.cpp:82)
    mysql_execute_command(THD * thd, bool first_level) (\opt\litaihong\stonedb\sql\sql_parse.cc:3265)
    mysql_parse(THD * thd, Parser_state * parser_state) (\opt\litaihong\stonedb\sql\sql_parse.cc:5621)
    dispatch_command(THD * thd, const COM_DATA * com_data, enum_server_command command) (\opt\litaihong\stonedb\sql\sql_parse.cc:1495)
    do_command(THD * thd) (\opt\litaihong\stonedb\sql\sql_parse.cc:1034)
    handle_connection(void * arg) (\opt\litaihong\stonedb\sql\conn_handler\connection_handler_per_thread.cc:313)
    pfs_spawn_thread(void * arg) (\opt\litaihong\stonedb\storage\perfschema\pfs.cc:2197)
    libpthread.so.0!start_thread (未知源:0)
    libc.so.6!clone (未知源:0)

分析過程

assert(create_table->table == NULL);

Query_result_create::prepare (sql_insert.cc:2753)函數prepare階段和optimize階段在被調用了兩次

1、stonedb::core::Engine::HandleSelect函數首先調用

st_select_lex_unit::prepare->prepare_fake_select_lex ->Query_result_create::prepare

此時create_table->table 是NULL。

2、然後調用

st_select_lex_unit::optimize_for_stonedb -> prepare_fake_select_lex -> Query_result_create::prepare

此時create_table->table不為NULL，assert(create_table->table == NULL); 導致資料庫異常退出。

問題出現原因

分析st_select_lex_unit::optimize_for_stonedb函數發現是來源於MySQL的st_select_lex_unit::exec()函數

3、解決辦法

mysql的handle_query函數先有prepare然後是optimize函數，但我們stonedb的optimize函數是根據MySQL的st_select_lex_unit::exec()寫的，不知道為啥沒有正常的optimize流程

兩種解決方案：

1、修改拋異常的代碼行Query_result_create::prepare (sql_insert.cc:2753)函數

assert(create_table->table == NULL);

2、重寫stonedb的st_select_lex_unit::optimize_for_stonedb函數，改動比較大，涉及功能多。

解決方案更新：

A：我們發現，這個問題是由於在優化器的代碼中，Lex unit 兩次prepare造成的。

首先我們拋棄了對assert語句修改的考慮，因為那裡判斷表沒有創建是合理的。

於是解決方案有兩種，

1：考慮在lex unit 的prepare裡加入 is_prepared的判斷。但這個方案，影響面很大，因為這個函數所有的語法都會影響到。

2：針對，select union 或者 select join，以及他們出現的複雜的組合做修改。發現了三處異常點需要進行is_prepared判斷。1：union處。2：join處。3：fake_lex_prepare處。

B：針對我們的修改添加了相應mtr語句進行覆蓋。一併記錄在issue226中。

https://github.com/stoneatom/stonedb/issues/226

ADD test cases to cover these ctas queries for the following reason.

1: From code perspective. There are enough evidences that we want to support these ctas.

2: Our fix can cover these related queries.

CREATE TABLE t2 AS SELECT LEFT(f1,171) AS f2 FROM t1 UNION SELECT LEFT(f1,171) AS f2 FROM t1;

CREATE TABLE t3 AS SELECT t1.f1 AS f3 FROM t1 LEFT JOIN t2 ON t1.f1 = t2.f2;

CREATE TABLE t4 AS SELECT t1.f1 AS f4 FROM t1 INNER JOIN t2 ON t1.f1 = t2.f2;

CREATE TABLE t5 AS SELECT t1.f1 AS f5 FROM t1 RIGHT JOIN t2 ON t1.f1 = t2.f2;

CREATE TABLE t6 AS SELECT t1.f1 AS f6 FROM t1 UNION SELECT t2.f2 AS f6 FROM t2 LEFT JOIN t3 ON t2.f2 = t3.f3;

CREATE TABLE t7 AS SELECT t1.f1 AS f7 FROM t1 UNION SELECT t2.f2 AS f7 FROM t2 INNER JOIN t3 ON t2.f2 = t3.f3;

CREATE TABLE t8 AS SELECT t1.f1 AS f8 FROM t1 UNION SELECT t2.f2 AS f8 FROM t2 RIGHT JOIN t3 ON t2.f2 = t3.f3;

CREATE TABLE t9 AS SELECT t1.f1 AS f9 FROM t1 INNER JOIN t3 ON t1.f1 = t3.f3 UNION SELECT t2.f2 AS f9 FROM t2;

4、MySQL正常流程堆棧

Query_result_create::prepare(Query_result_create * const this, List<Item> & values, SELECT_LEX_UNIT * u) (\opt\litaihong\stonedb\sql\sql_insert.cc:2750)
st_select_lex::prepare(st_select_lex * const this, THD * thd) (\opt\litaihong\stonedb\sql\sql_resolver.cc:361)
st_select_lex_unit::prepare_fake_select_lex(st_select_lex_unit * const this, THD * thd_arg) (\opt\litaihong\stonedb\sql\sql_union.cc:441)
st_select_lex_unit::prepare(st_select_lex_unit * const this, THD * thd_arg, Query_result * sel_result, ulonglong added_options, ulonglong removed_options) (\opt\litaihong\stonedb\sql\sql_union.cc:670)
handle_query(THD * thd, LEX * lex, Query_result * result, ulonglong added_options, ulonglong removed_options, int optimize_after_bh, int free_join_from_bh) (\opt\litaihong\stonedb\sql\sql_select.cc:150)
mysql_execute_command(THD * thd, bool first_level) (\opt\litaihong\stonedb\sql\sql_parse.cc:3266)
mysql_parse(THD * thd, Parser_state * parser_state) (\opt\litaihong\stonedb\sql\sql_parse.cc:5621)
dispatch_command(THD * thd, const COM_DATA * com_data, enum_server_command command) (\opt\litaihong\stonedb\sql\sql_parse.cc:1495)
do_command(THD * thd) (\opt\litaihong\stonedb\sql\sql_parse.cc:1034)
handle_connection(void * arg) (\opt\litaihong\stonedb\sql\conn_handler\connection_handler_per_thread.cc:313)
pfs_spawn_thread(void * arg) (\opt\litaihong\stonedb\storage\perfschema\pfs.cc:2197)
libpthread.so.0!start_thread (未知源:0)
libc.so.6!clone (未知源:0)