Where can the indexer claim completeness?
Find the earliest missing result in a parallel processing report.
The question
A mock indexer processes finalized blocks in parallel. Its checkpoint advances only through consecutive blocks with durable, reconciled results. The last verified complete checkpoint is block 200.
| Status | |
|---|---|
| Block 201 | Seen |
| Block 202 | Seen |
| Block 203 | Seen |
| Block 204 | Seen |
Seen means a worker reported the block. The dashboard gives no stored result.
“What would you tell the incident owner about progress?”
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A strong answer, step by step
Open each step in turn. This is one strong answer, not the only one.
Step 1: Read the report
What would you do here? Open the move you’d make.
Report the maximum seen height and leave the complete checkpoint open.
The strong move. A worker can see or parse a block without completing its durable result.
Advance the verified checkpoint to the highest seen height.
Tempting, but it misses something. The dashboard shows input progress. It does not show which block results are complete.
See how a strong candidate says it
“The workers have seen block 204. That is the highest reported height. I’d check the durable results before advancing the checkpoint.”
Why it works: A worker can see or parse a block without completing its durable result.
Step 2: Ask for stored results
What would you do here? Open the move you’d make.
Check only the result for block 204.
Tempting, but it misses something. A stored result at 204 could arrive ahead of a result at an earlier height.
Check the durable result for each block in the range.
The strong move. The case checkpoint needs evidence for each block in order.
See how a strong candidate says it
“I’d ask for the stored and reconciled result at every height after 200, including a record for a block with zero relevant events.”
Why it works: The case checkpoint needs evidence for each block in order.
Step 3: Find the first gap
Readback verifies durable, reconciled results for 201, 203 and 204. Block 202 was parsed but has no verified durable result.
What would you do here? Open the move you’d make.
Report 204 as complete because its result is durable.
Tempting, but it misses something. The missing result for 202 breaks the consecutive range before 204.
Report checkpoint 201 and the missing result at 202.
The strong move. Later results can be durable even when one earlier block leaves a gap in the consecutive record.
See how a strong candidate says it
“The highest durable height is 204, but the contiguous checkpoint stops at 201. Three seen heights are beyond that checkpoint. Only 202 lacks a verified result.”
Why it works: Later results can be durable even when one earlier block leaves a gap in the consecutive record.
Step 4: Explain the recovery boundary
What would you do here? Open the move you’d make.
Keep the verified results and name the exact evidence still needed.
The strong move. If 202 is verified and the later records still agree, the complete range can reach 204.
Treat all three blocks beyond the checkpoint as unverified.
Tempting, but it misses something. The readback confirms 203 and 204. The gap at 202 limits the checkpoint.
See how a strong candidate says it
“I’d report the gap at 202, keep the verified records for 203 and 204, and ask the owner to verify 202 without double-counting earlier results.”
Why it works: If 202 is verified and the later records still agree, the complete range can reach 204.
The answer, in short
- Decision
- Report block 201 as the last complete checkpoint.
- Because
- Block 202 lacks a verified durable result even though 203 and 204 are complete.
- What would change it
- A verified result at 202, with the later records still reconciled, would allow the checkpoint to reach 204.
Common traps
- Using the highest seen block as the checkpoint.
- Treating every record after a gap as missing.
Check your answer
- I read the progress report.
- I asked for durable results.
- I identified the first gap.
- I kept the verified later records visible.
Last reviewed Nov 11, 2026