Accessing Data Entities

• US 20090063489A1
• Filed: 08/27/2008
• Published: 03/05/2009
• Est. Priority Date: 08/30/2007
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Neumann, Frank, Pfau, Gerhard
• Granted Patent: US 8,117,159 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/23 Updating
• CPC Class Codes: G06F 16/2329 using versioning
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details
• CPC Class Codes: G06F 16/24552 Database cache management

Abstract

A method of accessing data entities in a client-server system is disclosed. The client-server system comprises a set of clients, a server system, and a repository for storing a plurality of data entities. The server system comprises an inter-transactional cache, the inter-transactional cache being accessible for each client of the set of clients. A first client of the set of clients comprises a first intra-transactional cache. If a copy of a first data entity is in the inter-transactional cache, a version identifier of the original first data entity is read from the repository. If the copy of the first data entity is to be accessed with an exclusive lock, a copy of the copy of the first data entity is added to the first intra-transactional cache. The copy of the copy of the first data entity in the first intra-transactional cache is accessed for further processing of the first data entity by the first client.

Claims

1. A method of accessing data entities in a client-server system, the client-server system comprising a set of clients, a server system, and a repository for storing a plurality of data entities, the first server system comprising an inter-transactional cache, the inter-transactional cache being accessible for each client of the set of clients, a first client of the set of clients being associated with a first intra-transactional cache, the method comprising:

determining whether a copy of a first data entity of the plurality of data entities is held by the inter-transactional cache;

reading a version identifier of the original first data entity from the repository, if the copy of the first data entity is in the inter-transactional cache;

determining whether the copy of the first data entity is associated with an exclusive lock, if the version identifier of the copy and a version identifier of the original first data entity match;

adding a copy of the copy of the first data entity to the first intra-transactional cache, if the copy of the first data entity is associated with an exclusive lock;

accessing the copy of the copy of the first data entity in the first intra-transactional cache for further processing of the first data entity by the first client.

2. The method according to claim 1, further comprising:

adding a reference for the copy of the first data entity to the first intra-transactional cache, if the copy of the first data entity is associated with a non-exclusive lock;

adding a client lock entry in a lock list, the lock list being comprised in the first data entity, the client lock entry indicating the locking level of the first data entity;

removing the client lock entry from the lock list of the first data entity in the inter-transactional cache at the end of a transaction, if the client lock entry relates to a non-exclusive lock.

3. The method according to claim 1, further comprising reading the original first data entity from the repository if the copy of the first data entity is not stored in the inter-transactional cache or if the version identifiers of the original first data entity and the copy of the first data entity in the inter-transactional cache mismatch.

4. The method according to claim 1, further comprising:

determining whether a copy of the first data entity is in the first intra-transactional cache;

accessing the inter-transactional cache if no copy of the first data entity is stored in the first intra-transactional cache.

5. The method according to claim 4, further comprising:

determining the lock level of the copy of the first data entity in the first intra-transactional cache if the copy is stored in the first intra-transactional cache;

accessing the copy of the first data entity in the first intra-transactional cache, if the lock level of the copy of the first data entity is higher than or equal to a requested lock level;

re-reading the original first data entity from the repository by use of an exclusive lock, if the lock level of the copy of the first data entity is lower than the requested lock level;

removing a client lock entry in the copy of the first data entity in the inter-transactional cache, if the original first data entity is re-read and the first data entity is not concurrently referenced by another client.

6. The method according to claim 1, wherein the first data entity comprises a key, the method further comprising getting the key of the first data entity.

7. The method according to claim 1, further comprising:

changing the version identifier of the copy of the copy of the first data entity in the first intra-transactional cache in response to updating the copy of the copy of the first data entity;

writing the copy of the copy of the first data entity to the repository and thereby replacing the original first data entity;

releasing a lock of the first client from the original first data entity;

updating the copy of the copy of the first data entity in the inter-transactional cache;

removing the updated copy of the copy of the first data entity from the first intra-transactional cache.

8. The method according to claim 7, wherein the original first data entity comprises a data object in a raw data format, wherein the first client builds a de-serialized data object from the data object in the raw data format.

9. The method according to claim 8, wherein if the de-serialized data object of the copy of the copy of the first data entity is updated, the updated de-serialized data object is serialized to an updated raw data object.

10. The method according to claim 1, wherein the access to the inter-transactional cache of the first client is synchronized with the other clients of the set of clients.

11. A computer program product for accessing data entities in a client-server system, the client-server system comprising a set of clients, a server system, and a repository for storing a plurality of data entities, the first server system comprising an inter-transactional cache, the inter-transactional cache being accessible for each client of the set of clients, a first client of the set of clients being further associated with a first intra-transactional cache, the computer program product comprising a computer useable medium including a computer readable program, wherein the computer readable program when executed on a computer causes the computer to:

determine whether a copy of a first data entity of the plurality of data entities is held by the inter-transactional cache;

read a version identifier of the original first data entity from the repository, if the copy of the first data entity is in the inter-transactional cache;

determine whether the copy of the first data entity is associated with an exclusive lock if the version identifiers of the copy and the version identifier of the original first data entity match;

add a copy of the copy of the first data entity to the first intra-transactional cache, if the copy of the first data entity is associated with an exclusive lock;

access the copy of the copy of the first data entity in the first intra-transactional cache for further processing of the first data entity by the first client.

12. A client-server system comprising:

a set of clients, a first client of the set of clients being associated with a first intra-transactional cache;

a server system, the server system comprising an inter-transactional cache, the inter-transactional cache being accessible for each client of the set of clients;

a repository for storing a plurality of data entities;

a component for determining whether a copy of a first data entity of the plurality of data entities is held by the inter-transactional cache;

a component for reading a version identifier of the original first data entity from the repository, if the copy of the first data entity is in the inter-transactional cache;

a component for determining whether the copy of the first data entity is associated with an exclusive lock if the version identifier of the copy and the version identifier of the original first data entity match;

a component for adding a copy of the copy of the first data entity to the first intra-transactional cache, if the copy of the first data entity is associated with an exclusive lock;

a component for accessing the copy of the copy of the first data entity in the first intra-transactional cache for further processing of the first data entity by the first client.

13. The client-server system according to claim 12, further comprising:

a component for adding a reference for the copy of the first data entity to the first intra-transactional cache, if the copy of the first data entity is associated with a non-exclusive lock;

a component for adding a client lock entry in a lock list, the lock list being comprised in the first data entity, the client lock entry indicating the locking level of the first data entity;

a component for removing a client lock entry from the lock list of the copy of the first data entity in the inter-transactional cache, if the client lock entry relates to a non-exclusive lock.

14. The client-server system according to claim 12, further comprising a component for reading the original first data entity from the repository if the copy of the first data entity is not stored in the inter-transactional cache or if the version identifiers of the original first data entity and the copy of the first data entity in the inter-transactional cache mismatch.

15. The client-server system according to claim 12, further comprising:

a component for determining whether a copy of the first data entity is in the first intra-transactional cache;

a component for accessing the inter-transactional cache if no copy of the first data entity is stored in the first intra-transactional cache.

16. The client-server system according to claim 15, further comprising:

a component for determining the lock level of the copy of the first data entity in the first intra-transactional cache if the copy is stored in the first intra-transactional cache;

a component for accessing the copy of the first data entity in the first intra-transactional cache, if the lock level of the copy of the first data entity is higher than or equal to a requested lock level;

a component for re-reading the original first data entity from the repository by use of an exclusive lock, if the lock level of the copy of the first data entity is lower than the requested lock level;

a component for removing a client lock entry in the copy of the first data entity in the inter-transactional cache, if the original first data entity is re-read and the data entity is not concurrently referenced by another client.

17. The client-server system according to claim 12, further comprising:

a component for changing the version identifier of the copy of the copy of the first data entity in the first intra-transactional cache in response to updating the copy of the copy of the first data entity;

a component for writing the copy of the copy of the first data entity to the repository and thereby replacing the original first data entity;

a component for releasing a lock of the first client from the original first data entity;

a component for updating a copy of the first data entity in the inter-transactional cache;

a component for removing the updated copy of the copy of the first data entity from the first intra-transactional cache.