SQL with BIND_EQUIV_FAILURE repeatedly creates same range over and over again

Dear listers,

I stumbled over an effect today, which I can't explain. Maybe you can help out?

For SQL ID d9k6c3p56r0zc I observe a growing number of child cursors (>500). Reason is BIND_EQUIV_FAILURE/Bind mismatch(33) (except for the first child, where I see LOAD_OPTIMIZER_STATS, which does not surprise me.)

I expect this SQL being a candidate for Extended Cursor Sharing, no discussion, the application profits from this adaption in 99.999% of all cases. But increasing the cursors up to _cursor_obsolete_threshold increases my parsing overhead, which I cannot afford here.

The selectivity in v$sql_shared_cursor is slightly different every time, but "not much". In v$sql_cs_selectivity I can see, that we get new child cursors with the same cardinality range over and over again.

So the question is:
Why does this happen?

Thank you in advance!
Martin Klier

More infos:

The query is basically, an bit obfuscated: SELECT <comma seperated list of all columns of MYVIEW> FROM MYVIEW
WHERE ID = :1 AND (qty - qtyReserved) > :2 AND OtherID = :3

Needless to say, the view is a very complex join all over a normalized schema plus inline queries making up view columns.

See attached a CSV file with the output of

20 =1 0 0.000361 0.000442 
19 =1 0 0.000361 0.000442 
18 =1 0 0.000361 0.000442 
17 =1 0 0.000361 0.000442 
16 =1 0 0.000361 0.000442 
15 =1 0 0.000361 0.000442 
14 =1 0 0.000361 0.000442 
13 =1 0 0.000361 0.000442 
12 =1 0 0.000361 0.000442 

Example for the reason in v$sql_shared_cursor:
<ChildNode><ChildNumber>18</ChildNumber><ID>39</ID><reason>Bind mismatch(33)</reason><size>1x4</size><selectivity>1061987324</selectivity></ChildNode>
<ChildNode><ChildNumber>19</ChildNumber><ID>39</ID><reason>Bind mismatch(33)</reason><size>1x4</size><selectivity>1058633042</selectivity></ChildNode>
<ChildNode><ChildNumber>20</ChildNumber><ID>39</ID><reason>Bind mismatch(33)</reason><size>1x4</size><selectivity>1059681618</selectivity></ChildNode>
(All of them in the other attachment)

DB Version: RU Database Release Update : 19.6.0.0.200114 (30557433), recently upgraded from 11.2.0.4 DB Architecture: Non-Multitenant
OS Platform: Oracle Linux.

-- 
Martin Klier // Performing Databases GmbH 
Managing Partner // Senior DB Consultant 
Oracle ACE Director 

martin.klier_at_performing-db.com // https://www.performing-databases.com 


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