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前几天在写这篇文档的时候，发现sysbench对PostgreSQL libpq绑定变量使用的支持并不好。
《让 sysbench 支持 PostgreSQL 服务端绑定变量》 那么怎样跟踪出错的代码呢？ 通过gdb跟踪是一种手段，但是sysbench在测试PostgreSQL libpq绑定时立即就退出。 通过pid来跟踪不太恰当，可以使用gdb的run指令来跟踪（之前没有仔细研究过gdb，还好有RDS PG内核团队小鲜肉给的方法，靠谱的团队，有问题立即就能找到靠谱的人）。 例如调试data程序gdb date(gdb) runStarting program: /bin/date [Thread debugging using libthread_db enabled]Thu Apr 28 22:32:24 CST 2016Program exited normally.
run后面加参数，实际上就是data命令加参数的效果一样
gdb date(gdb) run +%F%tStarting program: /bin/date +%F%t[Thread debugging using libthread_db enabled]2016-04-28Program exited normally.
对于sysbench_pg，因为出错就立即退出，所以需要先加断点，然后再run，例如我们大概已经分析到sysbench_pg一定会运行的函数，设为断点，然后用单步调试。
(gdb) break [:] (gdb) break [ :]
例子 :
gdb ./sysbench_pg(gdb) b sb_lua_db_execute或(gdb) b script_lua.c:sb_lua_db_executeBreakpoint 1 at 0x40f130: file script_lua.c, line 851.(gdb) run --test=lua/oltp_pg1.lua --db-driver=pgsql --pgsql-host=$PGDATA --pgsql-port=1921 --pgsql-user=postgres --pgsql-password=postgres --pgsql-db=postgres --oltp-tables-count=1 --oltp-table-size=1000000 --num-threads=1 --max-time=120 --max-requests=0 --report-interval=1 run[Thread debugging using libthread_db enabled]sysbench 0.5: multi-threaded system evaluation benchmarkRunning the test with following options:Number of threads: 1Report intermediate results every 1 second(s)Random number generator seed is 0 and will be ignored[New Thread 0x7ffff7e6c700 (LWP 10898)][New Thread 0x7ffff7e5b700 (LWP 10899)]Threads started![Switching to Thread 0x7ffff7e5b700 (LWP 10899)]Breakpoint 1, sb_lua_db_execute (L=0x8ab080) at script_lua.c:851851 script_lua.c: No such file or directory. in script_lua.cMissing separate debuginfos, use: debuginfo-install glibc-2.12-1.80.2.alios6.x86_64 libaio-0.3.107-10.1.alios6.x86_64(gdb) n863 in script_lua.c(gdb) ssb_lua_get_context (L=0x8ab080) at script_lua.c:11091109 in script_lua.c
查看对应的代码 ：
$vi sysbench/scripting/script_lua.c:set nu:11091108 sb_lua_ctxt_t *sb_lua_get_context(lua_State *L)1109 { 打印当前环境的变量值
(gdb) p L$1 = (lua_State *) 0x8ab080(gdb) p *L$2 = {next = 0x7ffff00097b0, tt = 8 '\b', marked = 97 'a', status = 0 '\000', top = 0x8ab3a0, base = 0x8ab390, l_G = 0x8ab138, ci = 0x8a20a0, savedpc = 0x8b6d78, stack_last = 0x8ab560, stack = 0x8ab2f0, end_ci = 0x8a2168, base_ci = 0x8a2050, stacksize = 45, size_ci = 8, nCcalls = 1, hookmask = 0 '\000', allowhook = 1 '\001', basehookcount = 0, hookcount = 0, hook = 0, l_gt = {value = {gc = 0x8aa560, p = 0x8aa560, n = 9086304, b = 9086304}, tt = 5}, env = {value = {gc = 0x8af150, p = 0x8af150, n = 9105744, b = 9105744}, tt = 5}, openupval = 0x0, gclist = 0x0, errorJmp = 0x7ffff7e5ac20, errfunc = 0}(gdb) p *L->savedpc$3 = 147525 一路回车，在这个位置抛出异常
sb_lua_db_execute (L=0x8ab080) at script_lua.c:943943 script_lua.c: No such file or directory. in script_lua.c(gdb) 942 in script_lua.c(gdb) 943 in script_lua.c(gdb) 946 in script_lua.c(gdb) 945 in script_lua.c(gdb) 946 in script_lua.c(gdb) 948 in script_lua.c(gdb) lua_error (L=0x8ab080) at lapi.c:957957 lapi.c: No such file or directory. in lapi.c(gdb) 960 in lapi.c(gdb) luaG_errormsg (L=0x8ab080) at ldebug.c:600600 ldebug.c: No such file or directory. in ldebug.c(gdb) 601 in ldebug.c(gdb) 610 in ldebug.c(gdb) 609 in ldebug.c(gdb) 610 in ldebug.c(gdb) 609 in ldebug.c(gdb) luaD_throw (L=0x8ab080, errcode=2) at ldo.c:9494 ldo.c: No such file or directory. in ldo.c(gdb) 95 in ldo.c(gdb) 94 in ldo.c(gdb) 95 in ldo.c(gdb) 96 in ldo.c(gdb) 97 in ldo.c(gdb) FATAL: failed to execute function `event': (null)[Thread 0x7ffff7e5b700 (LWP 11124) exited][Thread 0x7ffff7e6c700 (LWP 11123) exited]
重来一遍，直接跟踪行号