69.2 Space

A Space is a lightweight logical namespace containing serial elements indexed by 32-bit Seids. Each Space belongs to an Partition and is indexed within that partition by a 32-bit SpaceId.

The next Seid used for sequential allocation belongs to the Space, while the RPM owns the radix mapping from Seids to log-record positions:

class Space
{
    SpaceId id;
    Seid nextSeid;
    RPM rpm;
};

A checkpointed or published Space state contains both the allocation state and the corresponding RPM root. Readers use the RPM root; the writer uses nextSeid for allocation.

The allocation state and RPM are separate but coupled. Every explicitly reserved or inserted Seid must be less than nextSeid. Inserting a caller-supplied Seid therefore goes through Space, which advances nextSeid when required as well as updating the RPM.

Affiliate allocation uses RPM-node occupancy and forwarding information to choose a Seid near an existing Seid. It is exposed as a Space allocation operation, with the RPM providing the radix-tree information used by the allocation algorithm.