Lambda SnapStart reduces cold start latency (java)

1. What Lambda SnapStart Is

• AWS Lambda functions, especially Java, can have long cold start times because the runtime has to initialize the code and dependencies.
• SnapStart solves this by initializing the function ahead of time and taking a snapshot of the initialized execution environment.
• When a new invocation occurs, Lambda reuses the snapshot instead of starting from scratch.

In short: cold starts become much faster.

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2. How It Works

1. Deploy your Lambda function with SnapStart enabled.
2. When you publish a version:

• Lambda runs the function once.

• Lambda takes a snapshot of the memory, execution environment, and initialized state.

  1. On subsequent invocations:

• Lambda restores the snapshot.

• Skips the normal initialization phase (runtime boot + static initializations).
  

Without SnapStart:   Cold Start → Runtime Init → Code Init → Handler Execute
With SnapStart:      Cold Start → Snapshot Restore → Handler Execute

• Result: cold start latency can drop from seconds to milliseconds, especially for Java and other slow-start runtimes.

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3. Key Points

Feature	SnapStart
Supported Runtimes	Java (as of now), others may be added
Applies To	Lambda function versions (not aliases directly)
Use Case	Functions with heavy initialization (DB connections, libraries, frameworks)
Cold Start Improvement	70–95% faster in typical cases
Cost Impact	Minimal — you still pay normal Lambda invocation charges

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4. Comparison With Other Optimizations

Optimization	How It Helps	Notes
Provisioned Concurrency	Keeps pre-initialized instances warm	Fixed cost even if unused
Lambda SnapStart	Creates snapshots for new invocations	Only triggers on version publish, cheaper than provisioned concurrency
Both	Can be combined	Maximize performance and minimize cold starts

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5. TL;DR

Lambda SnapStart = pre-initialized snapshot of your Lambda function,
which dramatically reduces cold start time, especially for Java functions.