Which BASE concept or concepts explains the following scenario?

Alice who lives in Melbourne posted pictures of her new pet on Instagram. Jane who lives in London, thought she was the first to ask the pet's name, but discovered several hours later that she was the ninth to ask the pet's name.

Question

Which BASE concept or concepts explains the following scenario?

Alice who lives in Melbourne posted pictures of her new pet on Instagram. Jane who lives in London, thought she was the first to ask the pet's name, but discovered several hours later that she was the ninth to ask the pet's name.

BlackTom AI · Accepted Answer

Soft state means the system’s stored state can change over time even without explicit new updates, and eventual consistency means replicas converge to the same state asynchronously—together these explain the scenario.

1) Relevant knowledge points and concepts
- BASE stands for Basically Available, Soft state, and Eventual consistency.  
- Soft state: transient state that can change due to background processes, caches, or replica reconciliation even if no new client writes occur.  
- Eventual consistency: after some time and propagation, all replicas will converge to the same value; in the meantime different clients may observe different states.

2) Step-by-step reasoning
- Alice posts pictures and likely a metadata record (post and comment stream) is written to one or more replicas / data centers (Melbourne).  
- Jane in London queries the Instagram service shortly after Alice’s post. Because replicas are asynchronously replicated, the London replica’s view of the comment count or “first to ask” information might be incomplete. Jane believes she’s the first commenter based on the local replica she contacted.  
- Over time, other clients’ actions and background replication reconcile states across replicas. The authoritative or fully synchronized view shows multiple asks/comments and reveals Jane was actually ninth. That delayed convergence is classic eventual consistency.  
- The fact the observed ordering/contents changed over time without Jane herself writing anything corresponds to soft state (the system’s state changes as replication finishes).

3) Intermediate “steps” (conceptual)
- Write at origin -> asynchronous replication to other datacenters -> client reads from local replica -> later replication updates local replica -> global convergence.

4) Why the correct answer is correct
- The observed behavior (a user’s view changing hours later) requires both the idea that state can be transient/updated in background (soft state) and that replicas converge later (eventual consistency). Both concepts together directly describe the multi-datacenter, asynchronously replicated social feed behavior.

5) Why other options are incorrect
- “Eventually Consistent” alone describes the eventual convergence but omits the soft-state idea that state may change without new direct writes from that client.  
- “Soft State” alone omits the guarantee that replicas will converge later—doesn’t emphasize asynchronous reconciliation.  
- “Basically available and Eventually Consistent” incorrectly includes “Basically Available,” which concerns system responsiveness during partitions; the scenario focuses on inconsistent views and delayed convergence, not on availability guarantees.

6) Conclusion
Both Soft State and Eventually Consistent are required to explain the delayed, changing view experienced by Jane; this matches the provided answer: Soft State and Eventually consistent.

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