Problem

• the interface, wire protocol and storage all support 64 bits ledger id.

• however, the ledger id generation on zookeeper only generate 32 bits ledger id.
• the zookeeper-based ledger metadata store uses 2-4-4 split to store 32 bits ledger id.
• we need to find a solution to support 64 bits in zookeeper-based ledger metadata store.

Proposal

• there are 3 major concerns for this problem
  • how to store metadata for 64-bits-id ledgers in zookeeper?
  • how to generate 64-bits ledger id using zookeeper?
  • how to achieve backward compatibility?
• how to store?
  • Salesforce built a Long Hierarchical Ledger Manager
  • Ledger ID is split in 3-4-4-4-4 components.
  • No backward compatible on initial built
  • backward compatibility?
    • for ledger id whose higher 32 bits are zero, use split 2-4-4
    • for ledger id whose higher 32 bits are higher than zero, use split 3-4-4-4-4
    • since the first component has different characters (2 vs 3), it is easy to achieve backward compatibility
  • negative ledger id discussion

• how to generate?

• use zookeeper sequence znode to create lower 32 bits

• use another znode to create sequential buckets, the buckets are used for higher 32 bits.
• when to create bucket?
  • when lower 32-bits generation is approaching 31 bits, create a new bucket.
  • creating a new bucket and the id generation will happen under one zookeeper 'multi' transaction call to guarantee there is only one bucket is created.

Action