Write handling

...

of WORM object

All data are stored as regular(hierarchical) objects initially, because it is very challenging to handle write in flattened format (MVCC, ilog, DTX…). In addition, even for WORM object, application can still submit writes in multiple RPCs, e.g., appends, in this case, it is complex to add new keys and values to flattened buffer. To avoid these complexities, this design does not change the write handler, which creates trees to index keys and values for write request.

...

Flattening service

DAOS can provide API to allow user to indicate write completion immutability of WORM objects:

• Application/middleware calls write(obj) with “DONE” flag.

• Application/middleware calls flatten(obj).

• Set container property and convert all objects within a container to WORM.

...

DAOS will have a new read handler for flattened object, it can find locate the requested key and value from the flattened object format by leaner search. Because flattened object is stored in DT-blob and it can be evicted from DRAM. If , if storage engine receives a read request against an evicted object, it can bring the entire object back to DRAM by one SSD read.

...