Re: Explain Plan and Security
Date: Thu, 14 Jun 2018 17:56:09 +0000
Message-ID: <MM1P123MB0842392C5D641C8A3CBB2874A57D0_at_MM1P123MB0842.GBRP123.PROD.OUTLOOK.COM>
Dominic,
There's no question that if the query has executed and you can get there in time then the plan you get from display_cursor() is the plan that actually happened, but we're discussing the point that we can get execution plans into memory (for display_cursor()) to report) that have never executed - which leafs to the point that those are plans that might never actually happen with any real user inputs.
Regards
Jonathan Lewis
From: Dominic Brooks <dombrooks_at_hotmail.com> Sent: 14 June 2018 18:52
To: Jonathan Lewis
Cc: oracle-l_at_freelists.org
Subject: Re: Explain Plan and Security
Well ... dbms_xplan.display_cursor gives you definitively the execution plan you just got for your SQL/child. It might not be the plan you get every execution under all circumstances but you can’t take away that you got that once. You can’t say the same about explain plan. If someone is executing a piece of sql, say they are testing / making a change, and they want to document the execution plan that they got during their test and show that, for one execution at least the plan and performance was ok, then dbms_xplan.display_cursor (or getting the same info direct from v$sql_plan) is the source for that. That’s what I expect developers to provide plus the runtime execution stats. Ditto for extracting the plan information for any particular child cursor that is in memory, display_cursor tells you what it is/was. No doubts.
Sent from my iPhone
> On 14 Jun 2018, at 18:40, Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote:
>
>
> Andy,
>
> I don't think I'd even be that generous. I can't think of any detail where dbms_sql/dbms_xplan.display_cursor() gives you safer information than explain plan / dbms_xplan.display().
> I suppose the extra complexity of using dbms_sql might make you a little more careful as you set up a test, and that could be a benefit.
>
> Regards
> Jonathan Lewis
>
>
> ________________________________________
> From: andyklock_at_gmail.com <andyklock_at_gmail.com> on behalf of Andy Klock <andy_at_oracledepot.com>
> Sent: 14 June 2018 17:15
> To: Jonathan Lewis
> Cc: oracle-l_at_freelists.org
> Subject: Re: Explain Plan and Security
>
> Ah! Indeed. Thanks for that Jonathan. So, the takeaway is that DBMS_SQL is slightly better than EXPLAIN PLAN. But, only slightly?
>
> Thanks!
>
> Andy K
>
> On Thu, Jun 14, 2018 at 12:08 PM, Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk<mailto:jonathan_at_jlcomp.demon.co.uk>> wrote:
>
> Andy,
>
> If you add a "describe columns" to your SQL PARSE TEST BIND you find that you do get a plan before the execute.
>
> DECLARE
> cursor_name INTEGER;
> rows_processed INTEGER;
> m_desc_table dbms_sql.desc_tab;
> m_colcount number;
>
> BEGIN
> cursor_name := dbms_sql.open_cursor;
> dbms_sql.parse(cursor_name, 'select /* SQL_PARSE TEST BIND */ * from parse_test where n = :n', dbms_sql.NATIVE);
> dbms_sql.bind_variable(cursor_name, ':n', 2);
> dbms_sql.describe_columns( cursor_name, m_colcount, m_desc_table );
> END;
> /
>
> SQL> select sql_id, plan_hash_value, sql_text from V$sql where sql_text like '%SQL_PARSE TEST BINDwq%'
> 2 /
>
> SQL_ID PLAN_HASH_VALUE
> ------------- ---------------
> SQL_TEXT
> ------------------------------------------------------------------------------------------------------------------------------------
> 911jt1m3dxrba 903671040
> select sql_id, plan_hash_value, sql_text from V$sql where sql_text like '%SQL_PARSE TEST BINDwq%'
>
>
> Regards
> Jonathan Lewis
>
> ________________________________________
> From: andyklock_at_gmail.com<mailto:andyklock_at_gmail.com> <andyklock_at_gmail.com<mailto:andyklock_at_gmail.com>> on behalf of Andy Klock <andy_at_oracledepot.com<mailto:andy_at_oracledepot.com>>
> Sent: 14 June 2018 16:56
> To: mauro.pagano_at_gmail.com<mailto:mauro.pagano_at_gmail.com>
> Cc: Jonathan Lewis; oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org>; l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch>
> Subject: Re: Explain Plan and Security
>
> Agreed. It's kind of a cool idea, however, BINDs are checked after the DBMS_SQL.PARSE call and is only evaluated after the call to DBMS_SQL.EXECUTE
>
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.oracle.com%2Fdatabase%2F121%2FARPLS%2Fd_sql.htm%23i996870&data=02%7C01%7C%7C7f3f2e59790c49647afd08d5d21ddcb7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636645948067016044&sdata=4kyFobAwG5FlvMc2tloVVZpwaeRzJ%2BpMu7JvwWzxJqo%3D&reserved=0
>
> I ran a quick test to see what shows up in the cursor cache after setting bind_variable, but not calling EXECUTE and as expected you don't get a plan at all.
>
>
> SQL> DECLARE
> cursor_name INTEGER;
> rows_processed INTEGER;
> BEGIN
> cursor_name := dbms_sql.open_cursor;
> dbms_sql.parse(cursor_name, 'select /* SQL_PARSE TEST */ * from parse_test where n = 1', dbms_sql.NATIVE);
> END;
> /
>
> PL/SQL procedure successfully completed.
>
>
> SQL> DECLARE
> cursor_name INTEGER;
> rows_processed INTEGER;
> BEGIN
> cursor_name := dbms_sql.open_cursor;
> dbms_sql.parse(cursor_name, 'select /* SQL_PARSE TEST BIND */ * from parse_test where n = :n', dbms_sql.NATIVE);
> dbms_sql.bind_variable(cursor_name, ':n', 2);
> END;
> /
>
> PL/SQL procedure successfully completed.
>
> SQL> DECLARE
> cursor_name INTEGER;
> rows_processed INTEGER;
> BEGIN
> cursor_name := dbms_sql.open_cursor;
> dbms_sql.parse(cursor_name, 'select /* SQL_PARSE TEST BIND 2 */ * from parse_test where n = :n', dbms_sql.NATIVE);
> dbms_sql.bind_variable(cursor_name, ':n', 2);
> rows_processed := dbms_sql.execute(cursor_name);
> dbms_sql.close_cursor(cursor_name);
> END;
> /
>
> PL/SQL procedure successfully completed.
>
> SQL> _at_findsq SQL_PARSE
>
> SQL_ID PLAN_HASH_VALUE LENGTH(SQL_FULLTEXT) SUB_TEXT EXECUTIONS AVG_ELAPSED
> ------------- --------------- -------------------- -------------------------------------------------- ---------- -----------
> 4wbhzrjq0k7fd 464636435 57 select /* SQL_PARSE TEST */ * from parse_test wher 0 .002671
> 8xbgz1hbjk0vz 0 63 select /* SQL_PARSE TEST BIND */ * from parse_test 0 .000467
> 0bavj3vaszvw2 464636435 65 select /* SQL_PARSE TEST BIND 2 */ * from parse_te 1 .00503
>
> Final note, if you don't actually execute the SQL then you don't get all that other Oracle runtime stuff like cardinality feedback or dynamic sampling, etc which adds to even more headaches.
>
> Andy K
>
> On Thu, Jun 14, 2018 at 11:45 AM, Mauro Pagano <mauro.pagano_at_gmail.com<mailto:mauro.pagano_at_gmail.com><mailto:mauro.pagano_at_gmail.com<mailto:mauro.pagano_at_gmail.com>>> wrote:
> Lothar,
>
> To add on Jonathan's "odd note", because of 9630032 (disabled by default) you might see an even odder behavior (difference between describe vs exec).
> Just saying that DBMS_SQL might translate in some headaches :-(
>
> Cheers,
> Mauro
>
> On Thu, Jun 14, 2018 at 7:13 AM, Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk<mailto:jonathan_at_jlcomp.demon.co.uk><mailto:jonathan_at_jlcomp.demon.co.uk<mailto:jonathan_at_jlcomp.demon.co.uk>>> wrote:
>
> As far as I know explain plan will produce a misleading plan only if:
>
> a) the query uses bind variables - which can't be peeked and are assumed to be character
> or
> b) the literals used in the explain plan are a bad choice compared to what happens in production
> (which includes wrong type, wrong character set, wrong implicit date format etc.)
>
> Using dbms_sql won't (necessarily) be any better. If you supply a statement with a bind variable in the text the call to dbms_parse will assume that it's an unknown varchar - just as explain plan will. This is why you sometimes see systems with lots of statements parsed twice per execute - the first time was a parse call the that used guesses for bind types, the second was with information about the actual bind types.
>
> (I have an odd note from 16 years ago that you don't get the plan on the call to dbms_parse, but have to call dbms_describe_colums as well).
>
> Regards
> Jonathan Lewis
>
> ________________________________________
> From: oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org><mailto:oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>> <oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org><mailto:oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>>> on behalf of l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch><mailto:l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch>> <l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch><mailto:l.flatz_at_bluewin.ch<mailto:l.flatz_at_bluewin.ch>>>
> Sent: 14 June 2018 13:36:46
> To: oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org><mailto:oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org>>
> Subject: Explain Plan and Security
>
> Hi,
>
> you might know Kerry´s classic blog: https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fkerryosborne.oracle-guy.com%2F2008%2F10%2Fexplain-plan-lies%2F&data=02%7C01%7C%7C7f3f2e59790c49647afd08d5d21ddcb7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636645948067016044&sdata=0MfIBWr%2FbqDjJeSA9AMeySqqeQnBo5odXPC8wxYqthY%3D&reserved=0.
> Normally my work around for explain plan issues is to run the query and use dbms_xplan.display_cursor.
> Now I am working in an environment where I must not run a query, but I can do explain plan.
> But still I think I can not tolerate explain plan weaknesses.
> I think it should be possble to use DBMS_SQL to parse a statement and receive a proper plan without actually running the statement.
> Then use dbms_xplan.display_cursor.
> Before I spent time, has anybody done it already?
>
> Regards
>
> Lothar
>
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