Hi all,
I'd like to propose some OCI driver improvement.
1) Enable insert from different client. This could be done by managing the
generation of new FID on DB side instead of client side.
Technically this could be done with an oracle sequence and a trigger to fill
the FID.
This proposition modify the way FID are handled ( I propose to do as in PostGIS
driver). This means that the FID of a feature (i.e. usually the value of the
OGC_FID column for the feature) inserted into a table with CreateFeature() will
be retrieved from the database and can be obtained with GetFID() even if an
non-null FID was provided.
This could be easily implemented in UnboundCreateFeature with a 'returning'
clause.
But I don't known if it's feasible in BoundCreateFeature since truth FIDs will
be know later when OGROCITableLayer::FlushPendingFeatures() is called.
2) By providing true update operation instead of delete + insert operations (cf
SetFeture).
This should provide better performance and enable to develop trigger on update
if needed for other purpose.
With this modification, OCI driver will have the following mapping between OGR
concepts and Oracle operations:
OGRFeature::CreateFeature() <==> INSERT operation
OGRFeature::SetFeature() <==> UPDATE operation
OGRFeature::DeleteFeature() <==> DELETE operation
This modify slightly the actual behavior since it disable the possibility of
inserting a new record through SetFeature (in case of they were no record to
delete, the subsequent insert did the job). With the proposed implementation
it'll be no longer the case. "Update ... set ... where FID = provided FID"
command doesn't insert new record.
3) Add transaction support in the normal SQL sense.
Since transaction is handled within a session and we have a session per
OGROCIDataSource, a transaction will include operation on any layer of that
datasource.
I propose the following operating mode.
Outside a transaction, we'll be in 'auto commit' mode.
This commit on success DeleteFeature, SetFeature and CreateFeature (not in
MULTI_LOAD mode).
For CreateFeature (in MULTI_LOAD mode) data will be commited
- each time the buffer is full (when OGROCITableLayer::FlushPendingFeatures()
is called)
- when OGROCITableLayer::SyncToDisk() is call
- before a new transaction start.
Transaction start (through a call OGRLayer::StartTransaction()) for all layer
in the DataSource.
OGRLayer::CommitTransaction() will call OGROCITableLayer::SyncToDisk() for each
layer of the DataSource and issues one commit command for the session, and
then return in auto commit mode (cf outside transaction mechanism)
OGRLayer::RollbackTransaction() will drop PendingFeature (may be through a
private function that reset nWriteCacheUsed to 0) for each layer of the
datasource and issues one rollback command for the session, and then return to
auto commit mode.
I would like to know if someone else is interested in these improvements ?
Is it the way you want things work ?
An other information is that I'm ready to work for these improvements.
Regards,
Nicolas
==================================================
Nicolas Simon, Informaticien
Service Public de Wallonie (SPW)
Direction générale opérationnelle Agriculture, Ressources Naturelles et
Environnement (DGARNE)
Département des Aides
Direction de l'Octroi des Aides agricoles - Service Informatique
14, Chaussée de Louvain - 4e étage
5000 Namur
BELGIUM
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