Which problems and pitfalls exist in the area of hints?
When using hints you should consider the following problems and pitfalls:
When specifying hints in ABAP it depends on the SAP kernel version which database selector has to be used for SAP HANA:
As a consequence hints with ADABAS stop working when upgrading to SAP kernel >= 7.40 and the performance may degrade. In order to fix this issue you have to specify HDB as database selector:
The following SAP Notes introduce the HDB hint in the SAP standard coding via corrections:
The BW wrapper function RSDU_CREATE_HINT_FAE_HDB for hint generation tends to create very long SQL statements.
In order to come around problems, you should consider the following SAP Notes:
DBSQL_STMNT_TOO_LARGE / DBSQL_SQL_ERROR SQL error 589: too many parameters are set: # of params: 32768 too many input values (32768) - maximum is 32767
The SAP HANA hint OLAP_PARALLEL_AGGREGATION can cause problems:
When feasible it is recommended to disable the OLAP_PARALLEL_AGGREGATION hint or use the hint USE_OLAP_PLAN instead.
While other databases typically ignore invalid hints, SAP HANA fails with the following error:
SQL error 468: hint error: invalid hint
Therefore you have to pay attention that correct hints are specified.
If you specify database specific SAP ABAP hints, no problem will happen, because the specified hints will only be sent to the database(s) indicated with the database selector.
The dbsl_equi_join hint can only be used in restricted contexts (see SAP Notes 1662726 and 1622681). The following main limitations exist:
Not every available SAP HANA hint is supported by every SAP HANA patch level. If you use an unsupported hint, different problems are possible:
Therefore make sure that you only use supported hints. See the SAP HANA SQL and System Views Reference (-> "HINT clause") for more information.
Supported hints can also be identified by SQL: "HANA_SQL_Hints" (SAP Note 1969700) or by directly accessing the HINTS table.
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