Re: Query with Bind variables hangs but hard coded literals works fine

There's so many differences in these plans that it's hard to pick out what's important, that and the plans we've got to look at may have no relation to the real plans means we are just stabbing in the dark. I suggest you get the real execution plans with row source statistics so we can see what's really important here.

One thing to note is that
colloq_name like '%ACTUATOR%'
Is not the same as
 colloq_name like '%ACTUATOR% '

There's a possibility that the optimizer really won't like your LIKE :bind filter and that seems like the most likely problem to me. The optimizer would be right to fear this predicate as it can't be used at all to access an index (it can only be used to filter down what you've already read from the index as it starts with a wildcard). You can lie to the optimizer with the _like_with_bind_as_equality hidden parameter, but because you are starting with a wildcard, this should be treated the same as index cost adj = 1.

Your first explain plan manages to use the index MSF12001I1 when it does this colloq_name filter, this is actually a little more clever than it immediately seems - it's doing two different scans with the colloq_name filter starting with two different points, the scan is on at least the third key of the index. One thing that has changed between 12.1.0.2 and 18.8 (well, 12.2.0.1 is when the change was made) is how the optimizer decides to do this - have a read of
https://jonathanlewis.wordpress.com/2018/11/15/num_index_keys/ . This is something you can hint at, but I know that's not on the menu.

You should be easily able to put together SQL Plan Baseline to force the SQL to execute using your desired plan, but you'll have to note that index filters are not included in the baseline - Oracle might decide to effectively do a full scan of the index rather than the two accesses.

This is why I'd suggest going for a SQL Patch - you can create them straight from dbms_Sqldiag now with dbms_sqldiag.create_sql_patch passing either your sql_id or the sql_text.

With that said, the first plan you shared with an index fast full scan and a full table scan hash joined together to produce an estimated 1 row seems quite unexpected. From what you've said, it sounds like joining MSF100 and MSF170 shouldn't cut down many rows - I guess you've got some wildly different low and high value stats for stock_code in these tables? The second plan changes how it does this join into a nested loop plan which visits MSF100 twice, this could be particularly bad. I suggest you investigate why the optimizer thinks this join is such a strong filter.

Hope this gets you started,
Andy

On Tue, 26 Nov 2019 at 10:12, Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote:

>
> One other point I forgot to mention.
>
> It's a little unusual to see "rownum < :bindvariable". Do the bind
> variables take the form :SYS_B_nnnn ? This would indicate that they have
> been created by Oracle in response to the cursor_sharing parameter being
> set to something other than EXACT.
>
> Regards
> Jonathan Lewis
>
>
> ________________________________________
> From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on
> behalf of Steve Wales (AddOns) <steve.wales_at_addonsinc.com>
> Sent: 26 November 2019 01:23
> To: oracle-l_at_freelists.org
> Subject: Query with Bind variables hangs but hard coded literals works fine
>
> Sorry for the length of this up front. Trying to get as much relevant
> info into the initial post as people might need to point me where I’m
> getting the problem
>
> I have an Oracle 18c (18.8 if it matters) Standard Edition 2 database on
> Linux 7..
>
> There’s a query from the ERP system that’s hanging the online screen and
> getting http timeouts because it’s not completing in a timely fashion.
>
> I pulled the text of the query from v$sqltext and the bind variables from
> v$sql_bind_capture.
>
> The query is searching a parts catalog for colloquial names for parts.
>
> If I take the query, replace the bind variables from the query with string
> values and run it through SQLPLUS, it runs in about 0.7 seconds and returns
> the expected values.
>
> If I instead leave the bind variables in the query, and in SQLPLUS define
> variables and then assign values via exec :v1 := ‘SOMEVALUE’, then it sits
> and spins 57 MINUTES before returning the exact same result set.
>
> The execution plans change slightly but significantly as well.
>
> The tables:
> MSF100 is a stock catalog table. Contains all stock items that the
> business catalogs across all properties
> MSF170 is a table that busts up the global catalog among assorted business
> units
> MSF120 contains the colloquial names. If I search on “ACTUATOR” it can
> return me all the stock codes that have “ACTUATOR” as a colloquial name.
> I assume rownum <= 20 is specified because that’s how many rows fit on a
> screen at a time.
>
> select * from( select * from MSF100 CATALOG where (CATALOG.stock_code in
> (select MSF170Rec.stock_code from MSF170 MSF170Rec, MSF100 MSF100Rec
> where (MSF100Rec.stock_code = MSF170Rec.stock_code))) and ( exists (select
> 1 from MSF120 MSF120Rec where (MSF120Rec.colloq_code = CATALOG.stock_code
> and MSF120Rec.colloq_name like '%ACTUATOR%' and MSF120Rec.colloq_type =
> 'S' )) or exists (select 1 from MSF120 MSF120Rec
> where (MSF120Rec.colloq_code = CATALOG.template_id and
> MSF120Rec.colloq_name like '%ACTUATOR%' and MSF120Rec.colloq_type = 'I' )))
> and (CATALOG.stock_status <> 'X' ) order by CATALOG.stock_code ) where
> ROWNUM <= 20;
>
> When using the static values (and I apologize in advance for what
> proportional fonts do the formatting below)
>
> (Estimated plans generated just by doing good old “explain plan for”)
>
>
> ---------------------------------------------------------------------------------------------------
> | Id | Operation | Name | Rows | Bytes
> |TempSpc| Cost (%CPU)| Time |
>
> ---------------------------------------------------------------------------------------------------
> | 0 | SELECT STATEMENT | | 1 | 3243 |
> | 5756 (1)| 00:00:01 |
> |* 1 | COUNT STOPKEY | | | |
> | | |
> | 2 | VIEW | | 1 | 3243 |
> | 5756 (1)| 00:00:01 |
> |* 3 | SORT ORDER BY STOPKEY | | 1 | 3243 |
> | 5756 (1)| 00:00:01 |
> | 4 | VIEW | VM_NWVW_2 | 1 | 3243 |
> | 5756 (1)| 00:00:01 |
> | 5 | HASH UNIQUE | | 1 | 785 |
> | 5756 (1)| 00:00:01 |
> |* 6 | FILTER | | | |
> | | |
> | 7 | NESTED LOOPS SEMI | | 1 | 785 |
> | 5751 (1)| 00:00:01 |
> |* 8 | HASH JOIN | | 1 | 775 |
> 5632K| 5751 (1)| 00:00:01 |
> | 9 | INDEX FAST FULL SCAN| MSF170_PK | 262K| 2559K|
> | 265 (1)| 00:00:01 |
> |* 10 | TABLE ACCESS FULL | MSF100 | 74750 | 54M|
> | 2466 (1)| 00:00:01 |
> |* 11 | INDEX UNIQUE SCAN | MSF100_PK | 83735 | 817K|
> | 0 (0)| 00:00:01 |
> | 12 | INLIST ITERATOR | | | |
> | | |
> |* 13 | INDEX RANGE SCAN | MSF12001I1 | 1 | 49 |
> | 4 (0)| 00:00:01 |
>
> ---------------------------------------------------------------------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 1 - filter(ROWNUM<=20)
> 3 - filter(ROWNUM<=20)
> 6 - filter( EXISTS (SELECT 0 FROM "MSF120" "MSF120REC" WHERE
> ("MSF120REC"."COLLOQ_CODE"=:B1 AND
> "MSF120REC"."COLLOQ_TYPE"='S' OR
> "MSF120REC"."COLLOQ_CODE"=:B2 AND
> "MSF120REC"."COLLOQ_TYPE"='I') AND
> "MSF120REC"."COLLOQ_NAME" LIKE '%ACTUATOR%'))
> 8 - access("CATALOG"."STOCK_CODE"="MSF170REC"."STOCK_CODE")
> 10 - filter("CATALOG"."STOCK_STATUS"<>'X')
> 11 - access("MSF100REC"."STOCK_CODE"="MSF170REC"."STOCK_CODE")
> 13 - access(("MSF120REC"."COLLOQ_CODE"=:B1 AND
> "MSF120REC"."COLLOQ_TYPE"='S' OR
> "MSF120REC"."COLLOQ_CODE"=:B2 AND
> "MSF120REC"."COLLOQ_TYPE"='I'))
> filter("MSF120REC"."COLLOQ_NAME" LIKE '%ACTUATOR%')
>
>
> When using bind variables (Yes, I know that the columns are all defined as
> CHAR instead of VARCHAR2. No, I don’t know why the vendor of this
> application insists on presenting their database that way):
>
> variable v1 char(24 char)
> variable v2 char(1 char)
> variable v3 char(24 char)
> variable v4 char(1 char)
> variable v5 char(1 CHAR)
> variable v6 number
>
> exec :v1 := '%ACTUATOR% ';
> exec :v2 := 'S';
> exec :v3 := '%ACTUATOR% ';
> exec :v4 := 'I';
> exec :v5 := 'X';
> exec :v6 := 20;
>
> select * from( select * from MSF100 CATALOG where (CATALOG.stock_code in
> (select MSF170Rec.stock_code from MSF170 MSF170Rec, MSF100 MSF100Rec
> where (MSF100Rec.stock_code = MSF170Rec.stock_code))) and ( exists (select
> 1 from MSF120 MSF120Rec where (MSF120Rec.colloq_code = CATALOG.stock_code
> and MSF120Rec.colloq_name like :v1 and MSF120Rec.colloq_type = :v2 )) or
> exists (select 1 from MSF120 MSF120Rec
> where (MSF120Rec.colloq_code = CATALOG.template_id and
> MSF120Rec.colloq_name like :v3 and MSF120Rec.colloq_type = :v4 )))
> and (CATALOG.stock_status <> :v5 ) order by CATALOG.stock_code ) where
> ROWNUM <= :v6;
>
>
> ------------------------------------------------------------------------------------------
> | Id | Operation | Name | Rows | Bytes | Cost
> (%CPU)| Time |
>
> ------------------------------------------------------------------------------------------
> | 0 | SELECT STATEMENT | | 1 | 3243 | 192K
> (1)| 00:00:08 |
> |* 1 | COUNT STOPKEY | | | |
> | |
> | 2 | VIEW | | 1 | 3243 | 192K
> (1)| 00:00:08 |
> |* 3 | SORT ORDER BY STOPKEY | | 1 | 755 | 192K
> (1)| 00:00:08 |
> |* 4 | FILTER | | | |
> | |
> | 5 | NESTED LOOPS SEMI | | 3 | 2265 | 192K
> (1)| 00:00:08 |
> |* 6 | TABLE ACCESS FULL | MSF100 | 63173 | 45M| 2466
> (1)| 00:00:01 |
> | 7 | VIEW PUSHED PREDICATE | VW_NSO_1 | 12 | 24 | 3
> (0)| 00:00:01 |
> | 8 | NESTED LOOPS | | 262K| 5120K| 3
> (0)| 00:00:01 |
> |* 9 | INDEX UNIQUE SCAN | MSF100_PK | 1 | 10 | 1
> (0)| 00:00:01 |
> |* 10 | INDEX RANGE SCAN | MSF17001I1 | 262K| 2560K| 2
> (0)| 00:00:01 |
> |* 11 | INDEX FAST FULL SCAN | MSF120_PK | 1 | 49 | 476
> (1)| 00:00:01 |
>
> ------------------------------------------------------------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 1 - filter(ROWNUM<=TO_NUMBER(:V6))
> 3 - filter(ROWNUM<=TO_NUMBER(:V6))
> 4 - filter( EXISTS (SELECT 0 FROM "MSF120" "MSF120REC" WHERE
> "MSF120REC"."COLLOQ_TYPE"=:V2 AND "MSF120REC"."COLLOQ_NAME"
> LIKE :V1 AND
> "MSF120REC"."COLLOQ_CODE"=:B1 OR
> "MSF120REC"."COLLOQ_TYPE"=:V4 AND
> "MSF120REC"."COLLOQ_NAME" LIKE :V3 AND
> "MSF120REC"."COLLOQ_CODE"=:B2))
> 6 - filter("CATALOG"."STOCK_STATUS"<>:V5)
> 9 - access("MSF100REC"."STOCK_CODE"="CATALOG"."STOCK_CODE")
> 10 - access("MSF170REC"."STOCK_CODE"="CATALOG"."STOCK_CODE")
> filter("MSF100REC"."STOCK_CODE"="MSF170REC"."STOCK_CODE")
> 11 - filter("MSF120REC"."COLLOQ_TYPE"=:V2 AND "MSF120REC"."COLLOQ_NAME"
> LIKE
> :V1 AND "MSF120REC"."COLLOQ_CODE"=:B1 OR
> "MSF120REC"."COLLOQ_TYPE"=:V4 AND
> "MSF120REC"."COLLOQ_NAME" LIKE :V3 AND
> "MSF120REC"."COLLOQ_CODE"=:B2)
>
> The CPU cost on this second query is orders of magnitude greater than the
> other way. I can only assume that this is why my CPU on the server goes
> into overdrive as it sits and thinks forever before the http server throws
> it’s hands up and gets sick of waiting.
>
> This database was just upgraded to 18.8 from 12.1.0.2 over the weekend.
> (Vendor hasn’t certified the product for 19c yet, hence the upgrade to 18c).
> This was not a problem with 12.1.0.2 SE2.
>
> One last thing, since this is an ERP package, I can’t change the code /
> insert hints / build new indexes (well I suppose I could do that but the
> next release upgrade would blow it away anyway). Any solution really has
> to be about a config / parameter change (but if an index would work, I
> suppose I’d be willing to try it as a work around for the time being).
>
> Thanks in advance for any pointers. I’m hoping that there’s an init
> parameter or something that was new in the 12.2 engine from 12.1 that might
> be causing the problem.
>
> Steve
>
>
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