Developer workshop on I/O and persistence evolutionLAL,Orsay, 20-22 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

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Evolution of Converters

Orsay 21/2/2012Marcin Nowak BNL (PAS)

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AthenaPoolCnv T

Object Store

T POOL

T->P

P->T

AthenaPoolCustCnv P

Object Store

T POOL

T->PN

P2->T PN->TP1->TAthenaPoolCustomCnv

PN

P1,2..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

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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

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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

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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

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Extending T/P Converters Overview

Orsay 21/2/2012Marcin Nowak BNL (PAS)

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Orsay 21/2/2012Marcin Nowak BNL (PAS) 8

T->PN

P2->T PN->TP1->TAthenaPoolCnv

PN

P1,2..N

Object Store

T

POOL

T->PN

P2->T PN->TP1->TExtending AthenaPoolCnv

PN

T->PN

P2->T PN->TP1->TExtending AthenaPoolCnv

PN

P1,2..N

P1,2..N

Initi

aliz

atio

n

Merge