【GaussDB】数据静止状态下同一个SQL或同一个存储过程执行第6次报错的问题排查
背景
最近有客户遇到了一个问题，原始反馈是
- 客户："我在GaussDB里调用这个sp报错，相同sp在ORACLE里调用不报错"
- 我："报什么错？"
- 客户："invalid input syntax for type numeric: "xxx""
然后我连接上这个报错的GaussDB数据库，执行客户提供的调用sp的例子，却没有报错。
数据库版本：506.0.0.SPC0100
定位过程
- 我到客户工位上，已经开好的连接上执行，的确报错
- 我还是在客户工位上，客户端新开了一个连接，执行不报错
- 检查sp，里面没有使用到任何动态的东西，就是一些局部变量的赋值和判断，连表都没有查
- 难道是sp局部变量有cache没清理？但按sp逻辑来看，就算没清理，也不应该会报这个错。
- 然后客户提供一个重要信息："前面执行也有没报错的时候"
- 我意识到，难道是同一个会话循环调用n次后报错？
- 然后我写了个匿名块循环执行，第6次报错了
- 新开一个窗口再测，同样是第6次就报错了。
为了快速精确定位报错的SQL，我在mogeaver里单步调试这个循环6次调用存储过程的匿名块，前5次step over，第6次step into，跟踪到了一个select case when into语句执行后跳到了exception，其中的else 分支里有to_number(字符串变量)，这个字符串变量是可能不能转换成数字的，但所有不能转换成数字的情况，会被前面的case捕获掉，因此真实业务情况下，这个to_number一定不会报错的。
复现用例
下面是简单的复现用例：
sql
declare
v1 varchar2(20);
v2 number;
begin
v1:='a';
for i in 1..6 loop
select case when v1='a' then 1 else to_number(v1) end from dual into v2;
raise notice '%',v2;
end loop;
exception when others then
raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;
end;
sql
gaussdb=# declare
gaussdb-# v1 varchar2(20);
gaussdb-# v2 number;
gaussdb-# begin
gaussdb$# v1:='a';
gaussdb$# for i in 1..6 loop
gaussdb$# select case when v1='a' then 1 else to_number(v1) end from dual into v2;
gaussdb$# raise notice '%',v2;
gaussdb$# end loop;
gaussdb$# exception when others then
gaussdb$# raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;
gaussdb$# end;
gaussdb$# /
NOTICE: 1
NOTICE: 1
NOTICE: 1
NOTICE: 1
NOTICE: 1
NOTICE: v1:a,sqlerrm:invalid input syntax for type numeric: "a"
ANONYMOUS BLOCK EXECUTE
gaussdb=#原因分析
在PG/OG系数据库中，6是一个必须要记住的数字，同一个SQL从cplan变到gplan的次数正是6次。
加上强制gplan的hint，第一次就会报错
sql
gaussdb=# declare
gaussdb-# v1 varchar2(20);
gaussdb-# v2 number;
gaussdb-# begin
gaussdb$# v1:='a';
gaussdb$# for i in 1..6 loop
gaussdb$# select /*+use_gplan*/ case when v1='a' then 1 else to_number(v1) end from sys_dummy into v2;
gaussdb$# raise notice '%',v2;
gaussdb$# end loop;
gaussdb$# exception when others then
gaussdb$# raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;
gaussdb$# end;
gaussdb$# /
NOTICE: v1:a,sqlerrm:invalid input syntax for type numeric: "a"
ANONYMOUS BLOCK EXECUTE
gaussdb=#加上强制cplan的hint,则一直都不报错
sql
gaussdb=# declare
gaussdb-# v1 varchar2(20);
gaussdb-# v2 number;
gaussdb-# begin
gaussdb$# v1:='a';
gaussdb$# for i in 1..6 loop
gaussdb$# select /*+use_cplan*/ case when v1='a' then 1 else to_number(v1) end from sys_dummy into v2;
gaussdb$# raise notice '%',v2;
gaussdb$# end loop;
gaussdb$# exception when others then
gaussdb$# raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;
gaussdb$# end;
gaussdb$# /
NOTICE: 1
NOTICE: 1
NOTICE: 1
NOTICE: 1
NOTICE: 1
NOTICE: 1
ANONYMOUS BLOCK EXECUTE
gaussdb=#对于同一个SQL，前5次会根据实际的参数值去生成计划执行(cplan)，到第6次(gplan)就不管参数值是什么了，因此对于case when所有的分支都会去判断，此时对于实际不会执行的分支to_number(v1)也执行了计算，因此产生了报错。
使用不报错的参数，跟踪第6次的执行计划和前5次的区别
sql
gaussdb=# set auto_explain_level=notice;
SET
gaussdb=# set enable_auto_explain=on;
SET
gaussdb=#
gaussdb=# declare
gaussdb-# v1 varchar2(20);
gaussdb-# v2 number;
gaussdb-# begin
gaussdb$# v1:='1';
gaussdb$# for i in 1..6 loop
gaussdb$# select case when v1='1' then 1 else to_number(v1) end from sys_dummy into v2;
gaussdb$# raise notice '%',v2;
gaussdb$# end loop;
gaussdb$# exception when others then
gaussdb$# raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;
gaussdb$# end;
gaussdb$# /
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select case when v1='1' then 1 else to_number(v1) end from sys_dummy
Name: primary
Subquery Scan on sys_dummy (cost=0.00..0.02 rows=1 width=0)
Output: 1::numeric, (Expression Flatten Optimized)
-> Result (cost=0.00..0.01 rows=1 width=0)
Output: NULL::text, (Expression Flatten Optimized)
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE:
----------------------------NestLevel:0----------------------------
duration: 0.000 s
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE: 1
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select case when v1='1' then 1 else to_number(v1) end from sys_dummy
Name: primary
Subquery Scan on sys_dummy (cost=0.00..0.02 rows=1 width=0)
Output: 1::numeric, (Expression Flatten Optimized)
-> Result (cost=0.00..0.01 rows=1 width=0)
Output: NULL::text, (Expression Flatten Optimized)
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE:
----------------------------NestLevel:0----------------------------
duration: 0.000 s
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE: 1
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select case when v1='1' then 1 else to_number(v1) end from sys_dummy
Name: primary
Subquery Scan on sys_dummy (cost=0.00..0.02 rows=1 width=0)
Output: 1::numeric, (Expression Flatten Optimized)
-> Result (cost=0.00..0.01 rows=1 width=0)
Output: NULL::text, (Expression Flatten Optimized)
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE:
----------------------------NestLevel:0----------------------------
duration: 0.000 s
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE: 1
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select case when v1='1' then 1 else to_number(v1) end from sys_dummy
Name: primary
Subquery Scan on sys_dummy (cost=0.00..0.02 rows=1 width=0)
Output: 1::numeric, (Expression Flatten Optimized)
-> Result (cost=0.00..0.01 rows=1 width=0)
Output: NULL::text, (Expression Flatten Optimized)
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE:
----------------------------NestLevel:0----------------------------
duration: 0.000 s
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE: 1
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select case when v1='1' then 1 else to_number(v1) end from sys_dummy
Name: primary
Subquery Scan on sys_dummy (cost=0.00..0.02 rows=1 width=0)
Output: 1::numeric, (Expression Flatten Optimized)
-> Result (cost=0.00..0.01 rows=1 width=0)
Output: NULL::text, (Expression Flatten Optimized)
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE:
----------------------------NestLevel:0----------------------------
duration: 0.000 s
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE: 1
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select case when v1='1' then 1 else to_number(v1) end from sys_dummy
Name: primary
Subquery Scan on sys_dummy (cost=0.00..0.03 rows=1 width=0)
Output: CASE WHEN (($10 <param value: 1 type: varchar>)::text = '1'::text) THEN 1::numeric ELSE numeric_in(textout(($10 <param value: 1 type: varchar>)::text), 0::oid, (-1)) END, (Expression Flatten Optimized)
-> Result (cost=0.00..0.01 rows=1 width=0)
Output: NULL::text, (Expression Flatten Optimized)
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE:
----------------------------NestLevel:0----------------------------
duration: 0.000 s
CONTEXT: SQL statement "select case when v1='1' then 1 else to_number(v1) end from sys_dummy"
PL/pgSQL function inline_code_block line 7 at SQL statement
NOTICE: 1
ANONYMOUS BLOCK EXECUTE
gaussdb=#从前5次的执行计划中可以发现，output已经把结果值算出来了，投影列是1::numeric，但第6次的投影列则是带参数的case when表达式CASE WHEN (($10 <param value: 1 type: varchar>)::text = '1'::text) THEN 1::numeric ELSE numeric_in(textout(($10 <param value: 1 type: varchar>)::text), 0::oid, (-1)) END
不过这个用例在openGauss及基于openGauss的商业发行版、还有原生的postgresql上，都不会报错，只有华为的GaussDB会报这个错。
看下报错堆栈
c
(gdb) bt
#0 errstart (elevel=20, filename=0x5648320cb206 "numeric_util.cpp", lineno=175, funcname=0x5648320cb270 <adt_set_var_from_str(char const*, char const*, AdtNumericVar*)::__func__> "adt_set_var_from_str", domain=0x564831dc0004 "plpgsql-9.2") at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/share/error/elog.cpp:238
#1 0x000056482dae8ac8 in adt_set_var_from_str (str=0x7fdeea6be2a0 "a", cp=0x7fdeea6be2a0 "a", dest=0x7fdfda7c3e90) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/share/adt/numeric_util.cpp:171
#2 0x000056482dac2a31 in numeric_in (fcinfo=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/share/adt/numeric.cpp:343
#3 0x000056482dd18bf6 in exec_eval_func_expr_strict (op=0x7fdfd402ad90) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_interp_external.cpp:676
#4 0x000056482dd0fe56 in exec_interp_expr (state=0x7fdfd402a470, econtext=<optimized out>, isnull=<optimized out>, is_done=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_interp.cpp:279
#5 0x000056482dd8d6bd in exec_eval_switch_exprcxt (is_done=0x0, is_null=0x7fdfda7c407c, econtext=<optimized out>, expression=0x7fdfd402a470) at /usr1/GaussDBKernel/server/opengauss/src/include/executor/executor.h:427
#6 optbase_evaluate_expr (expr=<optimized out>, result_type=1700, result_typmod=-1, result_collation=0, can_ignore=<optimized out>, max_length=0, decimals=0) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:5654
#7 0x000056482dd90391 in optbase_evaluate_function (context=0x7fdfda7c4340, func_tuple=0x7fdfcdab30d8, args=0x7fdeea6be398, decimals=0, max_length=0, input_collid=0, result_collid=0, result_typmod=-1, result_type=1700, funcid=1701) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:5069
#8 optbase_simplify_function (funcid=1701, result_type=1700, result_typmod=-1, result_collid=0, input_collid=0, max_length=0, decimals=0, args_p=0x7fdfda7c42b8, process_args=true, allow_non_const=true, context=0x7fdfda7c4340) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:4235
#9 0x000056482dd91127 in optbase_eval_const_expressions_funcexpr (node=0x7fdfd2067bd8, context=0x7fdfda7c4340) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:2795
#10 0x000056482dd91265 in optbase_eval_funcexpr_mutator (node=<optimized out>, context=0x7fdfda7c4340) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:2421
#11 0x000056482dd912d2 in optbase_eval_plan_funcexpr (root=0x0, node=<optimized out>, estate=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:2412
#12 0x000056482dd0e24b in exec_init_expr_rec (node=0x7fdfd2fd79f0, state=0x7fdfd2066b10, resv=0x7fdfd2066c38, resnull=0x7fdfd2066c31, parent_node=0x7fdfd2fd7530) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_internal.cpp:342
#13 0x000056482dd0d29b in exec_init_expr_rec (node=<optimized out>, state=0x7fdfd2066b10, resv=<optimized out>, resnull=<optimized out>, parent_node=0x0) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_internal.cpp:817
#14 0x000056482dd09c22 in exec_build_projinfo_byflt (target_list=<optimized out>, econtext=<optimized out>, slot=<optimized out>, parent=0x7fdfd2066050, input_desc=0x7fdfd3f28610) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_external.cpp:373
#15 0x000056482dd64efe in exec_assign_projinfo (planstate=0x7fdfd2066050, input_desc=0x7fdfd3f28610) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_utils.cpp:940
#16 0x000056482eb73041 in exec_assign_scanprojinfo (node=0x7fdfd2066050) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/executor/rowengine/framework/executor_framework_execscan.cpp:217
#17 0x000056482eb558db in SubqueryScanOperator::init (this=0x7fdfd2066050, node=0x7fdfd2fd7050, estate=0x7fdfd3f52050, eflags=16) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/executor/rowengine/executor_rowopr_subqueryscan.cpp:74
#18 0x000056482eb55954 in exec_init_subqueryscan (node=0x7fdfd2fd7050, estate=0x7fdfd3f52050, eflags=16) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/executor/rowengine/executor_rowopr_subqueryscan.cpp:87
#19 0x000056482dd2d9df in ExecInitNodeByType (node=0x7fdfd2fd7050, estate=0x7fdfd3f52050, eflags=16) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp:3913
#20 0x000056482dd2e658 in ExecInitNode (node=0x7fdfd2fd7050, estate=0x7fdfd3f52050, e_flags=16, bii_state=0x0) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp:4153
#21 0x000056482dd2f2bc in exec_init_plan (queryDesc=0x7fdfd3f50050, eflags=16) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp:1840
#22 0x000056482dd2fa92 in exec_standard_executor_start (queryDesc=0x7fdfd3f50050, eflags=16) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp:572
#23 0x00007fe144da177a in gs_audit_executor_start_hook (queryDesc=0x7fdfd3f50050, eflags=0) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/security/security_plugin/security_policy_plugin.cpp:1849
#24 0x000056482e4fe1a3 in sqlcmd_explain_executor_start (query_desc=0x7fdfd3f50050, eflags=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/commands/auto_explain.cpp:80
#25 0x000056482dd2ffec in exec_executor_start (queryDesc=0x7fdfd3f50050, eflags=0) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp:328
#26 0x000056482ebb03d7 in spi_pquery (from_lock=false, tcount=2, fire_triggers=<optimized out>, query_desc=0x7fdfd3f50050, cplan=0x7fdeea4fb518) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/pl/spi/spi.cpp:2662
#27 spi_execute_plan0 (plan=0x7fdfd3f42450, param_list=0x7fdfd3fad1a0, snapshot=0x0, crosscheck_snapshot=0x0, read_only=false, fire_triggers=true, tcount=2, from_lock=false, dfx_state=0x0) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/pl/spi/spi.cpp:2210
#28 0x000056482ebb0a53 in spi_execute_plan (plan=0x7fdfd3f42450, param_list=0x7fdfd3fad1a0, snapshot=0x0, crosscheck_snapshot=0x0, read_only=false, fire_triggers=true, tcount=2, from_lock=false, dfx_state=0x0) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/pl/spi/spi.cpp:2535
#29 0x000056482ebb207a in SPI_execute_plan_with_paramlist (plan=0x7fdfd3f42450, params=0x7fdfd3fad1a0, read_only=<optimized out>, tcount=2) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/pl/spi/spi.cpp:502
#30 0x000056482e070f22 in gsplsql_exec_stmt_execsql (estate=0x7fdfd3f5e5d0, stmt=0x7fdfd3ee22d0, dfx_state=0x7fe140ab0470, is_open_satetement=false) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_sql.cpp:972
#31 0x000056482e058144 in gsplsql_exec_stmt (estate=0x7fdfd3f5e5d0, stmt=0x7fdfd3ee22d0, dfx_state=0x7fe140ab0470) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:712
#32 0x000056482e058682 in gsplsql_exec_stmts (estate=0x7fdfd3f5e5d0, stmts=0x7fdfd3ee24a0, dfx_state=0x7fdfd3faf490) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:856
#33 0x000056482e067c0e in gsplsql_exec_stmt_fori (estate=0x7fdfd3f5e5d0, stmt=0x7fdfd3ee1d90, dfx_state=0x7fdfd3faf490) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_loop.cpp:492
#34 0x000056482e05830a in gsplsql_exec_stmt (estate=0x7fdfd3f5e5d0, stmt=0x7fdfd3ee1d90, dfx_state=0x7fdfd3faf490) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:681
#35 0x000056482e058682 in gsplsql_exec_stmts (estate=0x7fdfd3f5e5d0, stmts=0x7fdfd3ee16b8, dfx_state=0x7fdfd3faea00) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:856
#36 0x000056482e056ec4 in gsplsql_exec_stmt_block (estate=0x7fdfd3f5e5d0, block=0x7fdfd3ee3420, dfx_state=0x7fdfd3faea00) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:295
#37 0x000056482e058452 in gsplsql_exec_stmt (estate=0x7fdfd3f5e5d0, stmt=0x7fdfd3ee3420, dfx_state=0x7fdfd3faea00) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:648
#38 0x000056482e058682 in gsplsql_exec_stmts (estate=0x7fdfd3f5e5d0, stmts=0x7fdfd3ee1328, dfx_state=0x7fdfd3fad5c0) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:856
#39 0x000056482e058fb0 in gsplsql_exec_stmts_save_cursor (estate=0x7fdfd3f5e5d0, stmts=0x7fdfd3ee1328, dfx_state=0x7fdfd3fad5c0) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_cursor.cpp:66
#40 0x000056482e057b36 in gsplsql_exec_stmt_block (estate=0x7fdfd3f5e5d0, block=0x7fdfd3ee3828, dfx_state=0x7fdfd3fad5c0) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/pl/plsql/pl_exec/pl_exec_stmt_block.cpp:428
#41 0x0000564830230ec5 in gsplsql_exec_function (func=0x7fdfd3f5e170, fcinfo=0x7fdfda7c6230, dynexec_anonymous_block=false, func_runtime_state=0x0, isDstoreAutonomous=false) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/pl/plpgsql/src/pl_exec.cpp:698
#42 0x0000564830242bea in plpgsql_inline_handler (fcinfo=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/pl/plpgsql/src/pl_handler.cpp:1124
#43 0x000056482de839c1 in OidFunctionCall2Coll (function_id=<optimized out>, collation=0, arg1=140599276921936, arg2=0, is_null=0x0) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/share/fmgr/fmgr.cpp:2355
#44 0x000056482e635b39 in sqlcmd_execute_do_stmt (stmt=0x7fdfd1f28ec0, atomic=<optimized out>, is_pkg_anonymous_block=97) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/commands/functioncmds.cpp:4242
#45 0x000056482ea0f27e in sqlcmd_standard_process_utility (parse_tree=0x7fdfd1f28ec0, query_string=0x7fdfd3f34ab8 "declare\nv1 varchar2(20);\nv2 number;\nbegin\n v1:='a';\n for i in 1..6 loop\n select case when v1='a' then 1 else to_number(v1) end from dual into v2;\n raise notice '%',v2;\n end loop;\nexception when others then \n raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;\nend;", params=0x0, is_top_level=true, dest=0x7fdfd3f34fd8, sent_to_remote=<optimized out>, completion_tag=0x7fdfda7ca260 "", isCTAS=false) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/utility.cpp:7283
#46 0x00007fe144da3759 in gsaudit_ProcessUtility_hook (parsetree=0x7fdfd1f28ec0, queryString=0x7fdfd3f34ab8 "declare\nv1 varchar2(20);\nv2 number;\nbegin\n v1:='a';\n for i in 1..6 loop\n select case when v1='a' then 1 else to_number(v1) end from dual into v2;\n raise notice '%',v2;\n end loop;\nexception when others then \n raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;\nend;", params=0x0, isTopLevel=<optimized out>, dest=0x7fdfd3f34fd8, sentToRemote=<optimized out>, completionTag=0x7fdfda7ca260 "", isCTAS=false) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/security/security_plugin/security_policy_plugin.cpp:856
#47 0x000056482ef7ff52 in audit_process_utility (parsetree=0x7fdfd1f28ec0, query_string=0x7fdfd3f34ab8 "declare\nv1 varchar2(20);\nv2 number;\nbegin\n v1:='a';\n for i in 1..6 loop\n select case when v1='a' then 1 else to_number(v1) end from dual into v2;\n raise notice '%',v2;\n end loop;\nexception when others then \n raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;\nend;", params=<optimized out>, is_top_level=<optimized out>, dest=<optimized out>, sent_to_remote=<optimized out>, completion_tag=0x7fdfda7ca260 "", is_ctas=false) at /usr1/GaussDBKernel/server/opengauss/src/gausskernel/security/audit/security_auditfuncs.cpp:1512
#48 0x000056482ea1b71d in sqlcmd_process_utility (parse_tree=0x7fdfd1f28ec0, query_string=0x7fdfd3f34ab8 "declare\nv1 varchar2(20);\nv2 number;\nbegin\n v1:='a';\n for i in 1..6 loop\n select case when v1='a' then 1 else to_number(v1) end from dual into v2;\n raise notice '%',v2;\n end loop;\nexception when others then \n raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;\nend;", params=0x0, is_top_level=<optimized out>, dest=<optimized out>, sent_to_remote=<optimized out>, completion_tag=0x7fdfda7ca260 "", isCTAS=false) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/utility.cpp:1974
#49 0x000056482e9fc83f in PortalRunUtility (portal=0x7fdfcfa7a050, utilityStmt=0x7fdfd1f28ec0, isTopLevel=true, dest=0x7fdfd3f34fd8, completionTag=0x7fdfda7ca260 "") at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/pquery.cpp:2140
#50 0x000056482e9fe0be in PortalRunMulti (portal=0x7fdfcfa7a050, isTopLevel=true, dest=0x7fdfd3f34fd8, altdest=0x7fdfd3f34fd8, completionTag=0x7fdfda7ca260 "", snapshot=0x0, bii_state=0x0) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/pquery.cpp:2326
#51 0x000056482ea022dc in PortalRun (portal=0x7fdfcfa7a050, count=9223372036854775807, isTopLevel=true, dest=0x7fdfd3f34fd8, altdest=0x7fdfd3f34fd8, completionTag=0x7fdfda7ca260 "", snapshot=0x0, bii_state=0x0) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/pquery.cpp:1501
#52 0x000056482e9e8276 in exec_simple_query (query_string=<optimized out>, msg=0x7fdfda7ca530, messageType=QUERY_MESSAGE) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/postgres.cpp:3513
#53 0x000056482e9f4e38 in gs_process_command (firstchar=<optimized out>, input_message=0x7fdfda7ca530, send_ready_for_query=0x7fdfda7ca526) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/postgres.cpp:11743
#54 0x000056482e9fa9c0 in PostgresMain (argc=<optimized out>, argv=0x7fdfd59f5b20, dbname=<optimized out>, username=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/tcop/postgres.cpp:11313
#55 0x000056482e97e2df in backend_run (port=0x7fdfda7ca890) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/postmaster/postmaster.cpp:12482
#56 0x000056482e9bd1b0 in gauss_db_worker_thread_main<(knl_thread_role)2> (arg=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/postmaster/postmaster.cpp:19086
#57 0x000056482e97e39a in internal_thread_func (args=<optimized out>) at /usr1/GaussDBKernel/server/opengauss/src/auxiliary/proc/postmaster/postmaster.cpp:20196
#58 0x00007fe14516ff1b in ?? () from /usr/lib64/libpthread.so.0
#59 0x00007fe1450a7320 in clone () from /usr/lib64/libc.so.6f 21里找到了出错的sql
c
(gdb) f 21
#21 0x000056482dd2f2bc in exec_init_plan (queryDesc=0x7fdfd3f50050, eflags=16) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp:1840
1840 /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_main.cpp: No such file or directory.
(gdb) p *queryDesc
$1 = {operation = CMD_SELECT, plannedstmt = 0x7fdfd405e050, utilitystmt = 0x0, sourceText = 0x7fdfd2fc3778 "select case when v1='a' then 1 else to_number(v1) end from dual", snapshot = 0x7fdfd3f3ca90, crosscheck_snapshot = 0x0, dest = 0x7fe140767020, params = 0x7fdfd3fad1a0, instrument_options = 0, pstmt_idx = 0, tupDesc = 0x0, estate = 0x7fdfd3f52050, planstate = 0x0, aj_states = 0x0, totaltime = 0x0, executed = false, opteval = false, plan_collecting = false, is_parameterized = false, support_operator_reuse = false, psrc_version = -1, stmt_name = '\000' <repeats 63 times>, bii_state = 0x0}从 #19 0x000056482dd2d9df in ExecInitNodeByType起，往里层的栈就在openGauss源码里搜不到了，这意味着GaussDB可能做了特殊的优化
f 12 里跟到了T_FuncExpr节点，它的上一个节点是T_CaseExpr
c
(gdb) f 12
#12 0x000056482dd0e24b in exec_init_expr_rec (node=0x7fdfd2fd79f0, state=0x7fdfd2066b10, resv=0x7fdfd2066c38, resnull=0x7fdfd2066c31, parent_node=0x7fdfd2fd7530) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_internal.cpp:342
342 /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/exec_expr_internal.cpp: No such file or directory.
(gdb) p *node
$3 = {type = T_FuncExpr, selec = 0}
(gdb) p *parent_node
$4 = {type = T_CaseExpr, selec = 0}f 9 里optbase_eval_const_expressions_funcexpr 这里有个关键字const,猜测可能是常量表达式，这里需要提到一个概念，叫常量折叠，即如果一个函数是immutable/stable的，如果入参是固定的常量，不是来自于表，那么就只用计算一次，将这个函数提前算出来，得到一个新的常量，避免每行都要去进行重复的函数计算。虽然复现用例里是个plsql的变量，但是当这个查询sql执行时，它肯定是不会发生变化的，可以视为这个查询sql的常量。
从
c
#8 optbase_simplify_function (funcid=1701, result_type=1700, result_typmod=-1, result_collid=0, input_collid=0, max_length=0, decimals=0, args_p=0x7fdfda7c42b8, process_args=true, allow_non_const=true, context=0x7fdfda7c4340) at /usr1/GaussDBKernel/server/opengauss/src/compatibility/sql_adaptor/utils/opt_clauses.cpp:4235可以看到这里调用了optbase_simplify_function (简单函数？),funcid=1701是numeric_in，即to_number(text)里调用的函数
sql
gaussdb=# select prosrc from pg_proc where proname='to_number' and proargtypes::text='25';
prosrc
--------------------------------------------------------------------
select pg_catalog.numeric_in(pg_catalog.textout($1), 0::Oid, -1)
(1 row)
gaussdb=# select proname from pg_proc where oid=1701;
proname
------------
numeric_in
(1 row)到这里，大概能猜到GaussDB做了什么优化了，即在plsql中，对于单条sql语句里出现的plsql变量，也可以视为常量，使用常量折叠的优化逻辑。
把测试用例稍微改改，to_number里传入字面量，放openGauss里执行,触发openGauss的常量折叠逻辑，看是否会出现报错
sql
openGauss=# declare
openGauss-# v1 varchar2(20);
openGauss-# v2 number;
openGauss-# begin
openGauss$# v1:='a';
openGauss$# for i in 1..6 loop
openGauss$# select case when v1='a' then 1 else to_number('a') end from sys_dummy into v2;
openGauss$# raise notice '%',v2;
openGauss$# end loop;
openGauss$# exception when others then
openGauss$# raise notice 'v1:%,sqlerrm:%',v1,sqlerrm;
openGauss$# end;
openGauss$# /
NOTICE:
QueryPlan
----------------------------NestLevel:0----------------------------
Query Text: select pg_catalog.numeric_in(pg_catalog.textout($1), 0::Oid, -1)
Name: dn_6001
Result (cost=0.00..0.01 rows=1 width=0)
Output: numeric_in(textout($1), 0::oid, (-1))
param1 value: a type: text
CONTEXT: SQL function "to_number" statement 1
referenced column: to_number
SQL statement "select case when v1='a' then 1 else to_number('a') end from sys_dummy"
PL/pgSQL function inline_code_block line 6 at SQL statement
NOTICE: v1:a,sqlerrm:invalid input syntax for type numeric: "a"
ANONYMOUS BLOCK EXECUTE果不其然，v1='a'的值不确定，没有先进行计算，但因为to_number('a')一定是个明确的值，就先进行了常量折叠，触发了报错。
根因总结
GaussDB相较于openGauss，新增支持了对于含有plsql变量的表达式也能支持常量折叠的优化逻辑，以此优化了存储过程内包含函数的sql执行性能，但是由于常量折叠发生在实际执行甚至执行计划生成之前，导致case when 语句里不会执行到的分支逻辑也会提前进行折叠，从而报错。
这不算BUG，因为如果不结合实际业务、不结合上下文，单看SQL，有时候的确无法判断case when会走哪个分支，这种SQL其实算是不规范SQL了。只是由于GaussDB引入了这个性能优化的特性，可能会导致之前不报错的sql在多执行几次后也会报错了。
规避措施
目前观测到在 505.2.0.SPC0100、506.0.0.SPC0100 版本里均存在这个现象，在503.1.0.SPC1700版本里无此现象。
两种处理方法：
1.去掉 from dual ,让其走单个表达式执行，而非可能有多行结果的完整SQL执行。不过如果是select into 两个变量，就变成了单行执行，此时去掉from dual依然还会报错。
2.加上hint /*+use_cplan*/ ,使其每次都强制走cplan
上面两种推荐用1，即去掉from dual 的方式，这样性能最好，但如果的确是要查询表或者into多个变量的情况，则只能使用加hint的方式了。
但是，最理想的代码，还是不要出现这种类型转换，无论是表里的数据作为参数还是使用变量作为参数，只要值可能为不能转换成数字的字符串，就不要尝试去对其转换成数字！
- 本文作者： DarkAthena
- 本文链接： https://www.darkathena.top/archives/Errors-on-the-6th-Run-of-the-Same-SQL-or-Stored-Procedure-in-GaussDB
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