Skip to content
allanninal.dev/build
Collaborate

Part 6 of 7 · Duplicate contact merger series ~5 min read

What the duplicate contact merger costs

The whole database is re-blocked and re-scored weekly, so the cost scales with contact count rather than with duplicates found. Fourteen thousand contacts is a small business with several years of accumulation. Here is where each cent goes.

Key takeaways

  • About $2 a month at 50k contacts. Roughly $4 at 200k contacts.
  • One Bedrock read per thousand contacts is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • No model. The cost is compute over the whole database once a week, and it scales linearly rather than quadratically because of blocking.
  • The duplicate test runs before the read, so resends are free.
  • The three real risks: a retry loop, storage nobody expires, and a bigger model than the job needs.

The bill at three volumes

These are US East prices at the time of writing, at three volumes that bracket most small businesses. Find the bar closest to your own and read across.

Monthly cost of the duplicate contact merger at three volumesA stacked bar chart with three bars, one per volume tier: 14k contacts totalling about $1, 50k contacts totalling about $2, and 200k contacts totalling about $4. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per thousand contacts, in teal. Then SES for the messages, in pink. Then S3 and DynamoDB storage in green. Then a fixed orange band for Secrets Manager and AWS Budgets, which is eighty-six cents at every volume. Then a grey band for Lambda, SQS and CloudWatch. A note says the read is the only bar that grows with the business and the orange band never moves.$0$2$4$6$8~$1.4314k contacts~$1.9250k contacts~$3.95200k contactsBedrock — one read per thousand contactsSES — asks, results, receiptsLambda — blocking and scoringS3 + DynamoDBFixed — Secrets Manager, BudgetsLambda, SQS, CloudWatchThe read is the only bar that grows with the business. The orange fixed band never moves.
Fig 1. The monthly bill at three volumes. The teal band — one model read per thousand contacts — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 50k contactsHow it scales
Bedrock read$0.00Linear. One call per thousand contacts, roughly 1,800 in and 200 out tokens.
Lambda$0.60Linear at $0.0120 per thousand contacts.
SES$0.03Linear. About 0.3 messages per thousand contacts.
DynamoDB + S3$0.29Storage grows with what you retain, not with throughput.
Lambda + SQS$0.12Linear, and effectively free at this scale.
CloudWatch$0.16Flat, if you set retention. Unbounded if you do not.
Secrets Manager$0.40Flat. One secret, $0.40 a month.
AWS Budgets$0.46Flat. Two actions, so you find out before the bill does.

The compute band is Lambda time to compute keys, build blocks and score pairs across the whole database. There is no model anywhere in this system: matching is exact comparison and weighted evidence.

The three ways this bill surprises you

Every one of these has happened to somebody, and all three are cheap to prevent.

  • Skipping the block size cap. One degenerate key value — four hundred records sharing the company’s own phone number — produces eighty thousand pairs on its own and turns a linear job back into a quadratic one.
  • Re-proposing rejected pairs. Not a cost risk but the one that kills the system: the same six hundred rejections every week means nobody opens the review after the second round.
  • Log retention left at never. A weekly job over the whole database logs a lot if it logs per pair. Log per run, not per comparison.

What it costs when nothing happens

This matters more than the headline number for a seasonal business. In a month with nothing to process the bill is the fixed band: Secrets Manager at forty cents, AWS Budgets at forty-six, and a few cents of storage. Call it a dollar. There is no instance to stop and nothing to remember to turn off.

The monthly bill at four volumes plus one failure modeA horizontal row of five boxes. Quiet month, about one dollar. 14k contacts, about $1. 50k contacts, about $2. 200k contacts, about $4. And one bad retry loop, about two hundred dollars. A note says four of these are the design working and the fifth is a missing dead-letter queue.THE BILL, AT A GLANCEQuiet month~$114k contacts~$150k contacts~$2200k contacts~$4One bad loop~$200Four of these are the design working. The fifth is a missing dead-letter queue.
Fig 2. The bill at a glance, including the one that is not a volume at all. A retry loop with no dead-letter queue costs more than every legitimate use of the system put together.
  • Management
  • Analytics
  • Front-end & mobile

Set these on day one

  • A dead-letter queue on every SQS queue, with a maximum receive count of three.
  • Thirty-day retention on every CloudWatch log group. There is no default that is safe.
  • An S3 lifecycle rule on the object prefix, tiering at 90 days and expiring at your actual record-keeping horizon.
  • Two AWS Budgets actions — one that emails at half your expected spend, one at double it. The second is how you find out about a loop in an hour instead of a month.
  • Provisioned concurrency: none. Nothing here is latency-sensitive enough to justify paying for a warm function.

Next: the same system drawn for engineers — service names, resource identifiers, IAM scopes, table schemas and the model id.

All posts