Top 20 Reconciliation Interview Questions
Browse 20 real-world technical and behavioral interview questions about Reconciliation. Review scenarios, edge cases, and architectural best practices.
A transform has been writing wrong revenue figures for three days and six downstream tables have consumed it. How do you backfill the corrected data without double-counting anything?
Make the write idempotent before you make it correct: partition-level replace rather than append, so rerunning a day produces the same result whether it runs once or five times. Then work out how far the contamination spread, because a downstream table that accumulated rather than recomputed will not fix itself when the source is repaired.
A small percentage of your transaction reports are rejected every day and the team resubmits them the next morning. Is that acceptable?
A steady rejection rate that is cleared daily is not a healthy control - it is a known defect being absorbed by people, and it says nothing about the reports that were accepted while being wrong. Rejections you can see are the smaller half of the problem.
How would you aggregate exposure across a portfolio so that the number can still be defended a year later?
Aggregation is easy arithmetic over hard inputs, so the design work is agreeing what may be added together, storing positions bi-temporally so a figure can be rebuilt as it was known on the day, and carrying lineage from every reported number back to the transaction that produced it.
The clearing house has called far more initial margin than your own risk system predicted. How do you find out why before the deadline?
Reconcile the positions before questioning the model, because most differences are in the population and not the model. Then attribute the remainder in layers, prices, parameters, netting scope and add-ons, and treat margin as a contractual number you must reproduce rather than a risk number you can dispute.
You are moving a sharded datastore to Cassandra with no maintenance window. How do you cut over, and how do you know both copies agree before you do?
Replicate from the source's change log rather than dual-writing from application code, backfill with each row's original write timestamp so history can never overwrite live data, then run continuous range checksums and shadow reads until divergence is understood rather than merely small. The read flip and the write flip are separate steps, each reversible.
A user deletes the second row of an editable list and the wrong row now shows the text they typed. What is going on?
A React index key bug happens when list positions are used as identity. Deleting, sorting or filtering shifts positions, so React reuses the wrong component instance and local state appears beside the wrong row.
A fill arrives for an order your system has already marked cancelled. What do you do?
Book the fill. The venue decides what happened, so a fill against a cancelled order means your state was wrong, and the position, risk headroom and client record all have to be corrected from the venue's version. The design fix is to make cancelled a state only the venue can grant.
You forecast every store and also the national total, and the store forecasts do not sum to it. What do you do?
Forecast at whichever levels have signal, then reconcile so the numbers are coherent by construction. Bottom-up preserves detail but accumulates noise, top-down is stable but allocates by an assumed proportion, and optimal reconciliation projects independent forecasts onto the set that adds up.
Your nostro reconciliation shows a break this morning. How do you investigate it, and how do you know when the money has actually gone?
You classify the break before chasing it, because most differences are timing rather than error: match in layers from exact reference down to grouped and tolerance matching, age what remains, and remember that your ledger being updated is not the same event as settlement becoming final and irrevocable.
The MES is unreachable for four hours and the line keeps producing. What happens to the production record, and how do you reconcile afterwards?
The line survives on cached work orders and locally queued events, so the difficulty is the merge, not the outage. Reconciliation has to be idempotent, ordered by source timestamp rather than arrival, and honest about units that passed a gate nobody could evaluate. It also connects degraded mode to the point an interviewer is testing.
How would you model physical and logical network resources, and what do you do when discovery disagrees with the inventory?
Logical network inventory should separate physical equipment, logical resources and services, then reconcile discovery as observed state against intended inventory. Do not overwrite the record blindly; classify gaps as faults, drift or orphaned resources. It also connects resource management to the point an interviewer is testing.
A subscriber's service is working on the network but no subscription exists in billing. How did that happen, and what do you do about it?
An activation half-succeeded and nobody owns the divergence. Detect it by reconciling the network's view against the subscription record, classify which side is wrong, re-drive fulfilment from stored intent rather than patching either side, and treat the unbilled period as a decided commercial policy.
A client says your position does not match their custodian statement. How do you work out who is right, and what does a corporate action do to that answer?
A position is what you have traded, a holding is what the custodian says you own, and they legitimately differ by unsettled trades and pending entitlements. Reconciliation compares both against the custodian's statements, and corporate actions break it when an election deadline is missed. Use this custody answer to show the decision, trade-off, and evidence rather than a memorised definition.
A payment API times out and the client retries. How do you guarantee the customer is not charged twice?
Prevent a double charge on payment retry with an idempotency key tied to the purchase intent, a unique constraint, atomic charge recording, honest in-flight retry responses and settlement reconciliation.
You have to release a change to the order-routing path. Walk me through the release, and tell me what makes it different from deploying any other service.
The gateway owns state you cannot drain, namely resting orders at the venue and sequenced sessions, so a rolling deployment leaves a mixed fleet holding live obligations. Verification has to be a position reconciliation rather than a health check, rollback does not undo executions, and dead code must be deleted rather than disabled.
How do you replace a system that cannot be switched off?
Put a routing facade in front of the old system, migrate one business capability at a time, and treat dual-write as a reconciliation problem rather than two inserts: name a writer of record at every moment, shadow-compare before flipping reads, and sequence slices so value lands early.
A figure in a regulatory return you already submitted turns out to be wrong. What happens next, and what should the system have been built to do?
You quantify the error, decide materiality, tell the supervisor and resubmit with an explained delta. Building for that means an immutable snapshot of what was submitted, a re-run that reproduces it exactly, per-line lineage back to the ledger, and completeness asserted against a declared manifest rather than assumed.
The system says four units are in that location and there is one on the shelf. What do you do, and how do you stop it happening again?
Block the location first so nothing allocates against a figure you have just disproved, then correct it as a recorded adjustment with a reason rather than an edit. Accuracy is maintained continuously by cycle counting, because stock records drift even in a well-run warehouse. It also connects inventory accuracy to the point an interviewer is testing.
A customer's bank shows the money left their account and you have no order. How does your checkout make that impossible, and how do you find the ones that already happened?
Write the order before you call the payment provider and key both with the same idempotency token, so a timeout leaves a record you can resolve. Then reconcile the provider's ledger against your orders daily in both directions, because a lost outcome is silent by default. Use this payment orchestration answer to show the decision, trade-off, and evidence rather than a memorised definition.
Finance and Operations quote different figures for the same monthly number and both insist they are right. How do you settle it?
Usually both are correct and they are answering different questions, so stop comparing totals and reconcile down to the first point of divergence. Publish a bridge that explains the gap in named components, then have one definition made authoritative with a named owner instead of declaring a winner.