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System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at Airbnb.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Airbnb during technical interviews.

Design an Airbnb wallet with holds and payouts

Quick Overview

This question evaluates a candidate's competency in designing financial transaction systems, covering double-entry append-only ledgers, holds/authorizations and captures, refunds and payouts, multi-currency FX conversion and rounding, idempotency, concurrency safety, and auditable reconciliation.

System Design: Airbnb-Style Wallet with Ledger, Holds, FX, and Idempotency

Context

You are asked to design and implement an Airbnb-style wallet system that supports customer deposits, booking holds and captures, refunds, host payouts, multi-currency balances with FX conversion, and a double-entry append-only ledger. The system must be auditable, concurrency-safe, and idempotent.

Assumptions (explicit and minimal):

Amounts are stored in minor units (integers) to avoid floating-point errors.
Each user has a wallet with per-currency sub-accounts. Platform and hosts are also modeled as accounts.
A double-entry ledger ensures that for every entry, debits equal credits; balances are derived from the ledger. For performance, a materialized balances table is maintained transactionally.
Booking currency is used for hold and capture; users may convert between currencies within their wallet via an explicit convert operation.

Requirements

Create user accounts and allow deposits.
Support booking holds/authorizations and later captures at check-in.
Allow hold release on cancellation or expiry.
Process partial/full refunds.
Pay out hosts after platform fees and taxes.
Enforce spendable vs. total balance with no negative spendable balance.
Support multi-currency balances with FX conversion and rounding rules.
Ensure idempotent operations via client-supplied idempotency keys.
Guarantee concurrency safety for duplicate or overlapping requests.
Maintain an append-only auditable ledger and derive balances from it.
Provide reconciliation to detect inconsistencies.
Define persistence schema (tables or classes) and transaction isolation choices.
Expose clear APIs/methods and include a minimal main() to run sample scenarios.
Write unit tests for happy paths and edge cases (insufficient funds, expired holds, double-capture attempts, partial refunds, FX rate changes). Include core classes (Wallet, Account, Transaction, Hold, Capture, Refund, Payout, LedgerEntry, FXConverter), their relationships, method signatures, and analyze time/space complexity of critical operations.

Quick Overview

Context

Assumptions (explicit and minimal):

Amounts are stored in minor units (integers) to avoid floating-point errors.

Each user has a wallet with per-currency sub-accounts. Platform and hosts are also modeled as accounts.

A double-entry ledger ensures that for every entry, debits equal credits; balances are derived from the ledger. For performance, a materialized balances table is maintained transactionally.

Booking currency is used for hold and capture; users may convert between currencies within their wallet via an explicit convert operation.

Requirements

Create user accounts and allow deposits.

Support booking holds/authorizations and later captures at check-in.

Allow hold release on cancellation or expiry.

Process partial/full refunds.

Pay out hosts after platform fees and taxes.

Enforce spendable vs. total balance with no negative spendable balance.

Support multi-currency balances with FX conversion and rounding rules.

Ensure idempotent operations via client-supplied idempotency keys.

Guarantee concurrency safety for duplicate or overlapping requests.

Maintain an append-only auditable ledger and derive balances from it.

Provide reconciliation to detect inconsistencies.

Define persistence schema (tables or classes) and transaction isolation choices.

Expose clear APIs/methods and include a minimal main() to run sample scenarios.

Write unit tests for happy paths and edge cases (insufficient funds, expired holds, double-capture attempts, partial refunds, FX rate changes). Include core classes (Wallet, Account, Transaction, Hold, Capture, Refund, Payout, LedgerEntry, FXConverter), their relationships, method signatures, and analyze time/space complexity of critical operations.

Design an Airbnb wallet with holds and payouts

Quick Overview

System Design: Airbnb-Style Wallet with Ledger, Holds, FX, and Idempotency

Context

Requirements

Solution

Comments (0)

Design an Airbnb wallet with holds and payouts

Quick Overview

System Design: Airbnb-Style Wallet with Ledger, Holds, FX, and Idempotency

Context

Requirements

Solution

Comments (0)