5800 System Overview
The metadata associated with an object is immutable. There is no operation to modify the metadata associated with an object after the object has been stored. Instead, the storeMetadata operation can be used to create a completely new object by associating new user metadata with the underlying data and
When creating a new object using storeMetadata, a new system.object_id and new system.object_ctime are generated, to indicate that a new object has been created. The metadata computed from the object data itself (system.object_length, system.object_hash_alg, and system.object_hash) does not change. Both the storeObject and the storeMetadata operations return a SystemRecord value that includes all of the
While retrieving the OID is the most common use of the SystemRecord, the other system fields can also be helpful. For example, the customer application might use the system.object_length, the system.object_hash_alg and the system.object_hash fields to verify that the data as stored matches the data as present in the customer application. If a hash independently computed on the client matches the hash stored on the 5800 system, then the data store has been validated.
The metadata values associated with an object can be retrieved using the retrieveMetadata operation. The retrieveMetadata operation takes an OID as input, and returns the entire set of user, system, and
The 5800 System Query Model
One of the primary methods for retrieving data is to specify the characteristics of the desired data and then let the system find it for you. In the 5800 system, a query expression specifies a set of conditions on metadata field values. The system then returns a list of all the objects whose metadata values match the query conditions. Each object is considered individually without reference to any other objects. There are no queries that compare fields in one object with fields in a different object.
20 | Sun StorageTek 5800 System Client API Reference Manual • June 2008 |
