目錄一、問(wèn)題發(fā)現(xiàn)二、問(wèn)題調(diào)查過(guò)程三、問(wèn)題解決方案四、問(wèn)題總結(jié)一、問(wèn)題發(fā)現(xiàn)

在一次開(kāi)發(fā)中在sp中使用MySQL PREPARE以后，使用match AGAINST語(yǔ)句作為prepare stmt的參數(shù)后，發(fā)現(xiàn)執(zhí)行第二遍call會(huì)導(dǎo)致數(shù)據(jù)庫(kù)crash，于是開(kāi)始動(dòng)手調(diào)查問(wèn)題發(fā)生的原因。

注：本次使用的 MySQL 數(shù)據(jù)庫(kù)版本為最新的debug版本。

SQL語(yǔ)句示例：

CREATE TABLE t1 (a INT, b VARCHAR(10));DELIMITER $$CREATE PROCEDURE p1()begin declare a VARCHAR(200); declare b TEXT; set a = 'Only MyISAM tables'; set b ='support collections'; set @bb := match(a,b) AGAINST ('collections'); prepare stmt1 from 'select * from t1 where ?'; execute stmt1 using @bb; end$$DELIMITER ;執(zhí)行結(jié)果：mysql> call p1;ERROR 1210 (HY000): Incorrect arguments to MATCHmysql> call p1; 這里發(fā)現(xiàn)代碼crash了ERROR 2013 (HY000): Lost connection to MySQL server during query二、問(wèn)題調(diào)查過(guò)程

1、首先查看錯(cuò)誤堆棧信息，可以看到Item_func_match::val_real函數(shù)的item->real_item()->type()不等于FIELD_ITEM引起的，打印堆棧看了一下，此時(shí)的item->real_item()為Item_splocal，明顯不是FIELD_ITEM。

#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50#1 0x00007ffff7568859 in __GI_abort () at abort.c:79#2 0x00007ffff7568729 in __assert_fail_base (fmt=0x7ffff76fe588 '%s%s%s:%u: %s%sAssertion `%s' failed.\n%n', assertion=0x55555bd2e340 'std::all_of(args, args + arg_count, [](const Item *item) { return item->real_item()->type() == FIELD_ITEM; })', file=0x55555bd2a9e0 '/mysql/sql/item_func.cc', line=9769, function=<optimized out>) at assert.c:92#3 0x00007ffff7579fd6 in __GI___assert_fail ( assertion=0x55555bd2e340 'std::all_of(args, args + arg_count, [](const Item *item) { return item->real_item()->type() == FIELD_ITEM; })', file=0x55555bd2a9e0 '/mysql/sql/item_func.cc', line=9769, function=0x55555bd2e300 'virtual double Item_func_match::val_real()') at assert.c:101#4 0x0000555558f9e17e in Item_func_match::val_real (this=0x7fff2cc86928) 這里導(dǎo)致的crash at /mysql/sql/item_func.cc:9769#5 0x0000555558f97f7e in Item_func_set_user_var::check (this=0x7fff2cc88200, use_result_field=false) at /mysql/sql/item_func.cc:8238#6 0x00005555592d74d3 in set_var_user::check (this=0x7fff2cc88388) at /mysql/sql/set_var.cc:1874#7 0x00005555592d5cd6 in sql_set_variables (thd=0x7fff2c001050, var_list=0x7fff2cc87210, opened=true) at /mysql/sql/set_var.cc:1442#8 0x00005555594d89ed in mysql_execute_command (thd=0x7fff2c001050, first_level=false) at /mysql/sql/sql_parse.cc:4051#9 0x000055555930c7a8 in sp_instr_stmt::exec_core (this=0x7fff2cc883d8, thd=0x7fff2c001050, nextp=0x7fffe02ed8b4) at /mysql/sql/sp_instr.cc:1039#10 0x000055555930ae0b in sp_lex_instr::reset_lex_and_exec_core (this=0x7fff2cc883d8, thd=0x7fff2c001050, nextp=0x7fffe02ed8b4, open_tables=false) at /mysql/sql/sp_instr.cc:457#11 0x000055555930bc74 in sp_lex_instr::validate_lex_and_execute_core (this=0x7fff2cc883d8, thd=0x7fff2c001050, nextp=0x7fffe02ed8b4, open_tables=false) at /mysql/sql/sp_instr.cc:771#12 0x000055555930c3ad in sp_instr_stmt::execute (this=0x7fff2cc883d8, thd=0x7fff2c001050, nextp=0x7fffe02ed8b4) at /mysql/sql/sp_instr.cc:956#13 0x00005555592fa772 in sp_head::execute (this=0x7fff2cc76da0, thd=0x7fff2c001050, merge_da_on_success=true) at /mysql/sql/sp_head.cc:2279#14 0x00005555592fcec2 in sp_head::execute_procedure (this=0x7fff2cc76da0, thd=0x7fff2c001050, args=0x0) at /mysql/sql/sp_head.cc:2995#15 0x00005555593661c9 in do_execute_sp (thd=0x7fff2c001050, sp=0x7fff2cc76da0, args=0x0) at /mysql/sql/sql_call.cc:86

2、要想獲取sp參數(shù)的實(shí)際item，應(yīng)該調(diào)用this_item()方法，但是也許作者本來(lái)就不想讓match支持sp參數(shù)，因此這里的寫(xiě)法是對(duì)的。但是本來(lái)代碼不應(yīng)該運(yùn)行到這里，因?yàn)楸緛?lái)應(yīng)該直接報(bào)錯(cuò)。

double Item_func_match::val_real() { assert(fixed); assert(!has_rollup_expr()); assert(std::all_of(args, args + arg_count, [](const Item *item) { return item->real_item()->type() == FIELD_ITEM; ==>這里的item->real_item()->type()說(shuō)明不支持Item_splocal }));

3、接著繼續(xù)調(diào)查，查看第一次報(bào)錯(cuò)的地方的代碼，找到Item_func_match::fix_fields，看到了第一次報(bào)錯(cuò)的地方的代碼item->type() != Item::FIELD_ITEM，因此代碼運(yùn)行應(yīng)該在這里報(bào)錯(cuò)。但是為何第二次執(zhí)行會(huì)運(yùn)行到Item_func_match::val_real而不是在Item_func_match::fix_fields就直接報(bào)錯(cuò)返回呢？仔細(xì)查看下面的代碼，發(fā)現(xiàn)下面的代碼有1個(gè)地方有錯(cuò)誤。

bool Item_func_match::fix_fields(THD *thd, Item **ref) { if (Item_func::fix_fields(thd, ref) || fix_func_arg(thd, &against) || 上面這里Item_func::fix_fields執(zhí)行完后使fixed=true 但是如果后面有任何報(bào)錯(cuò)的地方導(dǎo)致返回的話，這個(gè)值沒(méi)有修改回false 會(huì)導(dǎo)致第二次call sp不會(huì)再次執(zhí)行Item_func_match::fix_fields。 !against->const_for_execution()) { thd->mark_used_columns = save_mark_used_columns; my_error(ER_WRONG_ARGUMENTS, MYF(0), 'AGAINST'); return true; } for (uint i = 0; i < arg_count; i++) { item = args[i] = args[i]->real_item(); if (item->type() != Item::FIELD_ITEM || /* Cannot use FTS index with outer table field */item->is_outer_reference()) { my_error(ER_WRONG_ARGUMENTS, MYF(0), 'MATCH'); return true; }三、問(wèn)題解決方案

通過(guò)以上代碼解析后作如下修改，正確給fixed賦值，這樣就可以保證每次call sp的時(shí)候如果遇到報(bào)錯(cuò)再次運(yùn)行還會(huì)重新執(zhí)行fix_fields。

bool Item_func_match::fix_fields(THD *thd, Item **ref) { if (Item_func::fix_fields(thd, ref) || fix_func_arg(thd, &against) || !against->const_for_execution()) { fixed = false; ==>這里需要重新把fixed賦值為false thd->mark_used_columns = save_mark_used_columns; my_error(ER_WRONG_ARGUMENTS, MYF(0), 'AGAINST'); return true; } thd->mark_used_columns = save_mark_used_columns; fixed = false; ==>這里需要重新把fixed賦值為false for (uint i = 0; i < arg_count; i++) { item = args[i] = args[i]->real_item()->this_item(); if (item->type() != Item::FIELD_ITEM ||/* Cannot use FTS index with outer table field */item->is_outer_reference()) { my_error(ER_WRONG_ARGUMENTS, MYF(0), 'MATCH'); return true; } 中間省略 fixed = true; ==>最后沒(méi)有問(wèn)題了再賦值為true return false;

現(xiàn)在重新執(zhí)行call sp，沒(méi)有問(wèn)題了。

mysql> call p1;ERROR 1210 (HY000): Incorrect arguments to MATCHmysql> call p1;ERROR 1210 (HY000): Incorrect arguments to MATCH四、問(wèn)題總結(jié)

本次只是解決了match的fix_fields問(wèn)題，但是如果想讓 match 支持 sp 的參數(shù)，即Item_splocal的參數(shù)的話，代碼里面還要做相應(yīng)修改，包括set @bb := match(a,b) AGAINST ('collections'); 這里面生成的Item_func_match會(huì)在這句執(zhí)行完以后被 cleanup 掉，等到下一句 prepare 想再次使用它的時(shí)候會(huì)因?yàn)檎也坏皆搃tem發(fā)生問(wèn)題，這個(gè)是重構(gòu) match函數(shù)支持 sp 參數(shù)需要注意的點(diǎn)。

Enjoy GreatSQL :)

## 關(guān)于 GreatSQL

GreatSQL是由萬(wàn)里數(shù)據(jù)庫(kù)維護(hù)的MySQL分支，專注于提升MGR可靠性及性能，支持InnoDB并行查詢特性，是適用于金融級(jí)應(yīng)用的MySQL分支版本。

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