indexes : SYS_CHANGED_CHRONOS vs SYS_CHANGED_CHRONOS2 performances

Tue, 22 Oct 2019 09:38:06 +0000

Hi everyone,

before giving the context and my observations, here is my question : for what kind of queries the SYS_CHANGED_CHRONOS and SYS_CHANGED_CHRONOS2 indexes are created ?

Yesterday, I observed that the chronos detail was really slow to load.

In the query logs, the chronos detail has generated one query per selected entity (chronos detail options).
The idea is to get the primary key of each entity linked to the entity.
There is no other query in the logs about chronos detail.

So, I guess, but I can’t confirm it without proof, that the primary keys from the previous queries are used by the following SYS_CHANGED queries :

select K_TABLE, D_CHANGE, USERNAME, OPERATION, K_1, K_2, K_3, MILLI,
"COMMENT" from "GERM"."SYS_CHANGED" where ((K_1 = :key and K_TABLE in
(:param1)) or (K_2 = :key and K_TABLE in (:param2, :param3, :param4)))
and (D_CHANGE >= :mindate) and (D_CHANGE < :maxdate) order by D_CHANGE,
K_TABLE, K_2, MILLI, OPERATION;

select distinct USERNAME, D_CHANGE from "GERM"."SYS_CHANGED" where
((K_1 = :key and K_TABLE in (:param1)) or (K_2 = :key and K_TABLE in
(:param2, :param3, :param4))) and (D_CHANGE >= :mindate) and (D_CHANGE
< :maxdate) order by D_CHANGE DESC;

Each of these queries exists in a lot of versions because of a variation in the number of parameters for K_TABLE field.

When I consult the execution plan of the above queries (Oracle - SQL Developer), I observe that the first one is using SYS_CHANGED_CHRONOS (K_2, K_TABLE, D_CHANGE, USERNAME) index and the second one, SYS_CHANGED_CHRONOS2 (D_CHANGE, K_TABLE, K_1, K_2) index.
For each query, I can consult the execution plan with SYS_CHANGED_CHRONOS or SYS_CHANGED_CHRONOS2 index.
The cost is almost the same between these two indexes. So, the choice between them seems to be a really complicated choice for Oracle.
In the database, SYS_CHANGED_CHRONOS is better in a lot of situations.

So, for what kind of queries the SYS_CHANGED_CHRONOS and SYS_CHANGED_CHRONOS2 indexes are created ?

KR,

Eric

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indexes : SYS_CHANGED_CHRONOS vs SYS_CHANGED_CHRONOS2 performances