AWS SnapStart - Part 19 Measuring cold starts and deployment time with Java 17 using different Lambda memory settings
Tags: aws, java, serverless, coldstart
Published: 2024-04-25 15:13:42

## Introduction
In the [Part 12]( https://dev.to/aws-builders/aws-snapstart-part-12-measuring-cold-starts-and-deployment-time-with-java-21-using-different-lambda-memory-settings-35hl) of our series we measured the cold starts of the Lambda function with Corretto Java 21 runtime without SnapStart enabled, with SnapStart enabled and also applied DynamoDB invocation priming optimization with different Lambda function memory settings .  In this article we’d like to do the same measurement but for Corretto Java 17 runtime and then do comparison between both.

## Measuring cold starts with Java 17 with and without SnapStart enabled using different Lambda memory settings

In our experiment we'll re-use the application introduced in [part 8]( https://dev.to/aws-builders/measuring-lambda-cold-starts-with-aws-snapstart-part-8-measuring-with-java-17-21db) for this. Here is the code for the [sample application](https://github.com/Vadym79/AWSLambdaJavaSnapStart/tree/main/pure-lambda-17). There are basically 2 Lambda functions which both respond to the API Gateway requests and retrieve product by id received from the Api Gateway from DynamoDB. One Lambda function GetProductByIdWithPureJava17Lambda can be used with and without SnapStart and the second one GetProductByIdWithPureJava17LambdaAndPriming uses SnapStart and DynamoDB request invocation priming. We'll measure cold starts using the following memory settings in MBs : 256, 512, 768, 1024, 1536 and 2048.

The results of the experiment below were based on reproducing approximately 100 cold starts for the duration of our experiment which ran for approximately 1 hour. For it (and all experiments from my previous articles) I used the load test tool [hey](https://github.com/rakyll/hey), but you can use whatever tool you want, like [Serverless-artillery](https://www.npmjs.com/package/serverless-artillery) or [Postman](https://www.postman.com/)

**Cold start time without SnapStart in ms:**

| Experiment description                     | p50      | p75      | p90       |p99       | p99.9      | max      
|-----------|----------|-----------|----------|----------|----------|----------|
|256 MB|7309.66|7432.6|7575.51|7662.51|7782.25|7962.01|
|512 MB cold start time w/o SnapStart  |4213.37|4256.07|4325.17|4496.15|4661.23|4786.71|
|768 MB|3310.08|3414.9|3551.82|4271.48|4421.09|4594.42|
|1024 MB| 2880.53|2918.79|2974.45|3337.29|3515.86|3651.65|
|1536 MB|2390.15|2434.52|2464.46|2668.95|2812.15|2987.04|
|2048 MB|2198.02|2272.5|2397.97|2757.06|2892.65|3005.31|

**Cold start time with SnapStart without Priming in ms :**

| Experiment description                     | p50      | p75      | p90       |p99       | p99.9      | max      
|-----------|----------|-----------|----------|----------|----------|----------|
|256 MB|4972.83|5227.66|5754.12|7551.76|7559.31|7562.5|
|512 MB|2550.59|2604.69|2765.67|2942.48|3108.76|3110.69|
|768 MB|1801.28|1887.92|2251.03|2604.69|2681.29|2681.34|
|1024 MB|1521.33|1578.64|1918.35|2113.65|2115.77|2117.42|
|1536 MB|1204.06|1325.32|1507.70|1817.56|1821.19|1821.6|
|2048 MB|1129.45|1286.17|1583.38|1819.37|1998.60|2000.17|

**Cold start time with SnapStart enabled and with DynamoDB invocation Priming in ms :**

| Experiment description                     | p50      | p75      | p90       |p99       | p99.9      | max      
|-----------|----------|-----------|----------|----------|----------|----------|
|256 MB|1126.07|1183.77|1397.42|1608.90|1621.82|1622.23|
|512 MB|831.84|881.49|1136.24|1348.03|1386.29|1387.52|
|768 MB|819.46|891.23|1141.93|1243.19|1808.50|1809.34|
|1024 MB|692.79|758.00|1003.80|1204.06|1216.15|1216.88|
|1536 MB|713.17|773.31|995.80|1124.94|1372.50|1372.73|
|2048 MB|797.64|858.87|1080.86|1296.49|1376.62|1377.05|

I also measured the deployment time of such sample project with all memory settings mentioned above with SnapStart enabled for all functions and GetProductByIdWithPureJava17LambdaAndPriming function additionally using priming. Here are the results: 

| Experiment description | average deployment time in minutes/seconds|
|-----------|----------|
|256 MB deployment time with SnapStart   |2m 57 s|
|512 MB deployment time with SnapStart   |2m 19 s|
|768 MB deployment time with SnapStart   |2m 04 s|
|1024 MB deployment time with SnapStart  |2m 10 s|
|1536 MB deployment time with SnapStart  |2m 12 s|
|2048 MB deployment time with SnapStart  |2m 13 s|

## Conclusions

In this article we measured the cold start time of the Lambda function without SnapStart with SnapStart and for the latter with additional priming of DynamoDB invocation for Java 17 runtime.

In case of not enabling SnapStart we observed that increasing the memory from 256 MB to 2048 MB constantly brought significant reduction of the cold start time. We observed the same with Java 21 runtime, but cold start times with Java 17 runtime  being a bit lower than with Java 21 runtime (for the relative early version of Java 21 used for the measurements)

In case of enabling SnapStart but not using priming we observed that increasing the from 256 MB to 1536 MB brought significant reduction of the cold start time with very low impact of increasing the memory from 1536 MB or even to 2048 MB.  We observed similar with Java 21 runtime, but the impact of increasing memory even beyond 1024 MB already became lower. The cold start times with Java 17 runtime were also a bit lower than with Java 21 runtime (for the relative early version of Java 21 used for the measurements)

In case of enabling SnapStart and with additional priming of DynamoDB invocation we observed that increasing the from 256 MB to 1024 MB brought significant reduction of the cold start time but after that the impact of increasing the memory to 1536 MB or 2048 MB was low or even negative for all percentiles. We observed the same with Java 21 runtime. Also the result of using Java 17 and Java 21 runtimes are very close.

So for the SnapStart-enabled Lambda function and considering our use case with Lambda function reading from the DynamoDB table the Lambda memory setting of 1024 MB is a good choice.

Deployment time for the SnapStart enabled on all 3 Lambda functions and additionally applying priming on one of them also became lower by giving the Lambda function more memory but only until 786 MB. After that we even observed the small increase of the deployment time. With Java 21 runtime we observed  decrease of the deployment time by giving the Lambda function more memory until 1024 MB and then relative stable deployment time by giving Lambda function even more memory.