Temp Table Transformation Cardinality Estimates – 2

Continuing from the previous part - which was about the Temp Table Transformation and join cardinality estimates - using the same simple table setup here is a slight variation of the previously used query to demonstrate the potential impact on single table cardinality estimates:

explain plan for
cte as (
select /* inline */ id from t1 t
where 1 = 1
select /*+
no_merge(a) no_merge(b)
*/ * from cte a, cte (more...)

Temp Table Transformation Cardinality Estimates – 1

Having published recently two notes about the Temp Table Transformation highlighting the heuristics based decision and other weaknesses, for example regarding the projection of columns, it's time to publish some more notes about it.The transformation can also have significant impact on cardinality estimates, both join and single table cardinality.Looking at the difference in the join cardinality estimates of following simple example:

create table t1
rownum as id
, mod(rownum, 10) (more...)

Heuristic Temp Table Transformation – 2

Heuristic Temp Table Transformation - 2 Some time ago I've demonstrated the non-cost based decision for applying the temp table transformation when using CTEs (Common Table/Subquery Expressions). In this note I want to highlight another aspect of this behaviour.Consider the following data creating a table with delibrately wide columns:

create table a
rownum as id
, rownum as id2
, rpad('x', 4000) as large_vc1
, rpad('x', 4000) as large_vc2
, rpad('x', 4000) (more...)

Enabling Edition Based Redefinition On A Schema With Object-Relational Tables

This is just a heads-up for those thinking about using Edition Based Redefinition (EBR) and enabling it on an existing schema with objects. Although EBR isn't exactly a new feature its current adoption level is probably not that high (which probably changes in future as Oracle E-Business Suite uses EBR now as part of their default upgrade procedure as far as I understood).I was recently contacted by someone who enabled EBR on an existing (more...)

Function-Based Indexes And CURSOR_SHARING = FORCE

In general it is known that Function-Based Indexes (FBIs) can no longer be used by the optimizer if the expression contains literals and CURSOR_SHARING = FORCE / SIMILAR (deprecated) turns those literals into bind variables. Jonathan Lewis described the issue quite a while ago here in detail.In a recent OTN thread this issue was raised again, but to my surprise when I played around with a test case that mimicked the OP's problem query (more...)