Developer workshop on I/O and persistence evolution LAL,Orsay, Feb 2012 Marcin Nowak (PAS BNL) Extended T/P Converters

T/P Converters Implemented in /Database/AthenaPOOL/AthenaPoolCnvSvc  Basic T/P converter  A simple method converting data between Transient and Persistent representations 1 – 1 direct conversion stateless  Independent of any framework Unless dependency is required by the conversion process Dependency on the transient store Unfortunately has MessageSvc as parameter (in the default interface)  Simple and easy concept, but problematic for: Polymorphism Schema evolution of complex types (chain effect!)  T/P EDM Separation was introduced for Schema Evolution Orsay 21/2/2012Marcin Nowak BNL 2

Evolution of Converters Orsay 21/2/2012Marcin Nowak BNL (PAS) 3 AthenaPoolCnv T Object Store T POOL T->P P->T AthenaPoolCustCnv P Object Store T POOL T->P N P 2 ->T P N ->T P 1 ->T AthenaPoolCustomCnv PNPN P 1,2..N Object Store T POOL

TLP Converters Top Level T/P (TLP) converter: AthenaPoolTopLevelTPConverter  Aggregation of basic T/P converters  Manages conversion process Persistent types used only in declarations, never in the code Provides automatic choice of basic T/P converters Enforces uniform API in basic converters Type safe conversion Supports polymorphism and eliminates schema evolution chain effect Owns the persistent object Therefore has state  Still 1 – 1 conversion  No additional dependencies (!) Using 2 predefined persistent types from AthenaPoolUtilites  Extending TLP converters invented to handle cross-package polymorphism Orsay 21/2/2012Marcin Nowak BNL 4

Extending TLP Converters  (it is the same converter type, only extensions are not always used)  The principal TLP converter can be extended with other TLP converters  Extending enlarges the combined set of types that the converter understands  But each converter has its own persistent object (storage object)  Resulting in 1 (transient) – N (persistent) objects conversion  The extra persistent objects don’t have any corresponding StoreGate objects  They need fake AthenaPool converters as their interface/anchor to the I/O framework  The principal TLP object stores navigational information for extending objects  In a string format  Nesting foreseen but never fully implemented  Management of the extending TLP converters is in the AthenaPoolCnv layer  T/P conversion layer does not depend on AthenaPool  but TLP converter management layer is in AthenaPool  needs to be reimplemented if moving to a different I/O framework Orsay 21/2/2012Marcin Nowak BNL 5

AthenaPoolCnv Layer Responsibilities  Extended TLP converter management : AthenaPoolCnvTPExtension Self-contained, no dependencies  Specialization of AthenaPoolCustomCnv: T_AthenaPoolExtendingCnv  Connects extensions at initialization runtime Dependencies needs to be explicitly added in the principal AthenaPool converter  On the AthenPool level for I/O  On the T/P level for conversion  The principal AthenaPool converter is responsible for reading and writing of the entire group of persistent objects Because the extending AthenePool converters (for fake SG objects) are never called by the I/O framework directly Order of writing is important because navigational information needs to be stored in the principal TLP object  Extensions used by more than one principal converter need to clone their AthenaPool converter (!) Orsay 21/2/2012Marcin Nowak BNL 6

Schema Evolution  Persistent object versioning is supported on AthenaPoolCnv level  X persistent representations - > 1 transient type  TLP converters work on 1 1 principle Need X different TLP converters  For extended converters, each version (X) needs to clone its extensions The same principle as for a shared extension But for schema evolution case this is done only on demand  The extensions can be versioned as well The principal TLP converter needs to be extended with the current version of the extending TLP converter Orsay 21/2/2012Marcin Nowak BNL 7

Extending T/P Converters Overview Orsay 21/2/2012Marcin Nowak BNL (PAS) 8 Orsay 21/2/2012Marcin Nowak BNL (PAS) 8 T->P N P 2 ->T P N ->T P 1 ->T AthenaPoolCnv PNPN P 1,2..N Object Store T POOL T->P N P 2 ->T P N ->T P 1 ->T Extending AthenaPoolCnv PNPN T->P N P 2 ->T P N ->T P 1 ->T Extending AthenaPoolCnv PNPN P 1,2..N Merge