What Happens When You Run 10,000 Concurrent Lambda Functions Against a Single DynamoDB Table (The Throttling Cascade Nobody Simulates) | by Illya Yalovoy | Jun, 2026 | MediumSitemapOpen in appSign up<br>Sign in
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What Happens When You Run 10,000 Concurrent Lambda Functions Against a Single DynamoDB Table (The Throttling Cascade Nobody Simulates)
Illya Yalovoy
16 min read·<br>6 days ago
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The exact sequence of failures when serverless scale meets partition throughput limits, and why your SDK retries make everything worse.<br>I ran a load test last year that taught me more about DynamoDB than three years of production use. Ten thousand concurrent Lambda invocations, one table, one hot partition key. The whole thing collapsed in under 4 seconds — not because DynamoDB is broken, but because every safety mechanism built into the AWS SDK made the problem exponentially worse. The dashboard showed nothing. CloudWatch’s 1-minute granularity smoothed a catastrophic cascade into a barely visible blip.<br>The Setup That Looks Perfectly Reasonable<br>This is the architecture I have seen in at least four production systems, and it looks completely fine until it does not.<br>You have an event source — SQS queue, EventBridge rule, S3 notification — that fans out to Lambda. Each Lambda invocation writes an event record to DynamoDB. The partition key is something time-based: a date string, an hour bucket, a campaign ID that thousands of users hit simultaneously. IoT telemetry ingestion at midnight UTC rollover. Flash sale events where every purchase lands on the same campaign key. Marketing platforms where a scheduled push notification triggers 50,000 user actions in the same second. These are not…
Written by Illya Yalovoy<br>10 followers<br>·8 following
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