miniob调试篇

– by caizj

调试c/c++程序，常用的有两种方式，一是打印日志调试，二是gdb调试，调试不仅可以定位问题，也可以用来熟悉代码。

miniob关键代码

首先，拿到一份陌生的代码，要先确定代码的大致结构，一些关键数据结构和方法，这里的技巧和经验不展开了

miniob的关键数据结构

部分关键数据结构：

parse_def.h:
	struct Selects;//查询相关
	struct CreateTable;//建表相关
	struct DropTable;//删表相关
	enum SqlCommandFlag;//sql语句对应的command枚举
	union Queries;//各类dml和ddl操作的联合
table.h
	class Table;
db.h
	class Db;

miniob的关键接口

部分关键接口

RC parse(const char *st, Query *sqln);//sql parse入口
ExecuteStage::handle_request
ExecuteStage::do_select
DefaultStorageStage::handle_event
DefaultHandler::create_index
DefaultHandler::insert_record
DefaultHandler::delete_record
DefaultHandler::update_record
Db::create_table
Db::find_table
Table::create
Table::scan_record
Table::insert_record
Table::update_record
Table::delete_record
Table::scan_record
Table::create_index

打印日志调试

miniob提供的日志接口

deps/common/log/log.h:
#define LOG_PANIC(fmt, ...)
#define LOG_ERROR(fmt, ...)
#define LOG_WARN(fmt, ...)
#define LOG_INFO(fmt, ...)
#define LOG_DEBUG(fmt, ...)
#define LOG_TRACE(fmt, ...)

日志相关配置项observer.ini

LOG_FILE_NAME = observer.log
#  LOG_LEVEL_PANIC = 0,
#  LOG_LEVEL_ERR = 1,
#  LOG_LEVEL_WARN = 2,
#  LOG_LEVEL_INFO = 3,
#  LOG_LEVEL_DEBUG = 4,
#  LOG_LEVEL_TRACE = 5,
#  LOG_LEVEL_LAST
LOG_FILE_LEVEL=5
LOG_CONSOLE_LEVEL=1

gdb调试

Attach进程

 [caizj@localhost run]$ gdb -p `pidof observer` 
    
 GNU gdb (GDB) Red Hat Enterprise Linux 8.2-15.el8 Copyright (C) 2018 Free Software Foundation, Inc.
    
 (gdb)

设置断点

 (gdb) break do_select
 Breakpoint 1 at 0x44b636: file /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp, line 526.
 (gdb) info b
 Num     Type           Disp Enb Address            What
 1       breakpoint     keep y   0x000000000044b636 in ExecuteStage::do_select(char const*, Query*, SessionEvent*)
                                                    at /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp:526

 (gdb) break Table::scan_record
 Breakpoint 2 at 0x50b82b: Table::scan_record. (2 locations)
 (gdb) inf b
 Num     Type           Disp Enb Address            What
 1       breakpoint     keep y   0x000000000044b636 in ExecuteStage::do_select(char const*, Query*, SessionEvent*)
                                                    at /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp:526
 2       breakpoint     keep y   <MULTIPLE>
 2.1                         y     0x000000000050b82b in Table::scan_record(Trx*, ConditionFilter*, int, void*, void (*)(char const*, void*))
                                                    at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:421
 2.2                         y     0x000000000050ba00 in Table::scan_record(Trx*, ConditionFilter*, int, void*, RC (*)(Record*, void*))
                                                    at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:426
 (gdb)

继续执行
```
 (gdb) c
 Continuing.
```

触发断点

执行：miniob > select * from t1;

 [Switching to Thread 0x7f51345f9700 (LWP 54706)]
    
 Thread 8 "observer" hit Breakpoint 1, ExecuteStage::do_select (this=0x611000000540,
     db=0x6040000005e0 "sys", sql=0x620000023080, session_event=0x608000003d20)
     at /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp:526
 526	  RC rc = RC::SUCCESS;
 (gdb)

单步调式

 575	  std::vector<TupleSet> tuple_sets;
 (gdb) next
 576	  for (SelectExeNode *&node: select_nodes) {
 (gdb) n
 577	    TupleSet tuple_set;
 (gdb)
 578	    rc = node->execute(tuple_set);
 (gdb)

跳入跟踪到函数内部

 (gdb) s
 SelectExeNode::execute (this=0x60700002ce80, tuple_set=...)
     at /home/caizj/source/stunning-engine/src/observer/sql/executor/execution_node.cpp:43
 43	  CompositeConditionFilter condition_filter;
 (gdb)
    

打印变量

 (gdb) p tuple_set
 $3 = (TupleSet &) @0x7f51345f1760: {tuples_ = std::vector of length 0, capacity 0, schema_ = {
     fields_ = std::vector of length 0, capacity 0}}
 (gdb)

watch变量

 (gdb) n
 443	  RC rc = RC::SUCCESS;
 (gdb) n
 444	  RecordFileScanner scanner;
 (gdb) n
 445	  rc = scanner.open_scan(*data_buffer_pool_, file_id_, filter);
 (gdb) watch -l rc
 Hardware watchpoint 3: -location rc
 (gdb) c
 Continuing.
    
 Thread 8 "observer" hit Hardware watchpoint 3: -location rc
    
 Old value = SUCCESS
 New value = RECORD_EOF
 0x000000000050c2de in Table::scan_record (this=0x60f000007840, trx=0x606000009920,
     filter=0x7f51345f12a0, limit=2147483647, context=0x7f51345f11c0,
     record_reader=0x50b74a <scan_record_reader_adapter(Record*, void*)>)
     at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:454
 454	  for ( ; RC::SUCCESS == rc && record_count < limit; rc = scanner.get_next_record(&record)) {
 (gdb)

结束函数调用

 (gdb) finish
 Run till exit from #0  0x000000000050c2de in Table::scan_record (this=0x60f000007840,
     trx=0x606000009920, filter=0x7f51345f12a0, limit=2147483647, context=0x7f51345f11c0,
     record_reader=0x50b74a <scan_record_reader_adapter(Record*, void*)>)
     at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:454

结束调试

(gdb) quit
A debugging session is active.
    
	Inferior 1 [process 54699] will be detached.
    
Quit anyway? (y or n) y
Detaching from program: /home/caizj/local/bin/observer, process 54699
[Inferior 1 (process 54699) detached]