"CONCAT" or "||" (these two are in fact the same thing) are
blocked from being pushed down since V97 GA. This can cause
various operations like predicates or other parts of query not
being pushed down, hence result in performance problems.
They are blocked since "CONCAT" in Oracle has different
semantics in handling NULL values, that is, e.g. a CONCAT(C1,
NULL) will return NULL in Federation Server / DB2, but will
return C1 in Oracle. In V95, we tolerate such difference and
pushed down CONCAT predicate to Oracle. But in V97, we decided
to block it.
In fact, it is tolerable to pushdown the function in most cases.
The problem may happen when all of the following conditions are
met:
1. The query contains nicknames from Oracle datasource, or DB2
datasource that is in Varchar2 compatibility mode
2. The query has one or both of following expressions
1) predicate with CONCAT, e.g. CONCAT(C1, C2)
2) predicate with "||", e.g. C1 || "A" |
****************************************************************
* USERS AFFECTED: *
* all platforms *
****************************************************************
* PROBLEM DESCRIPTION: *
* "CONCAT" or "||" (these two are in fact the same thing) are *
* *
* blocked from being pushed down since V97 GA. This can cause *
* *
* various operations like predicates or other parts of query *
* not *
* being pushed down, hence result in performance problems. *
* *
* *
* *
* They are blocked since "CONCAT" in Oracle has different *
* *
* semantics in handling NULL values, that is, e.g. a *
* CONCAT(C1, *
* NULL) will return NULL in Federation Server / DB2, but will *
* *
* return C1 in Oracle. In V95, we tolerate such difference and *
* *
* pushed down CONCAT predicate to Oracle. But in V97, we *
* decided *
* to block it. *
* *
* *
* *
* In fact, it is tolerable to pushdown the function in most *
* cases. *
* *
* *
* The problem may happen when all of the following conditions *
* are *
* met: *
* *
* 1. The query contains nicknames from Oracle datasource, or *
* DB2 *
* datasource that is in Varchar2 compatibility mode *
* *
* 2. The query has one or both of following expressions *
* *
* 1) predicate with CONCAT, e.g. CONCAT(C1, C2) *
* *
* 2) predicate with "||", e.g. C1 || "A" *
****************************************************************
* RECOMMENDATION: *
* upgrade to v98fp4 *
**************************************************************** |
