Memory issue with App Engine and Firestore

I'm developing a MS with Kotlin and Micronaut which access a Firestore database. When I run this MS locally I can make it work with 128M because it's very simple just read and write data to Firestore, and not big amounts of data, really small data like this:

{
    "project": "DUMMY",
    "columns": [
        {
            "name": "TODO",
            "taskStatus": "TODO"
        },
        {
            "name": "IN_PROGRESS",
            "taskStatus": "IN_PROGRESS"
        },
        {
            "name": "DONE",
            "taskStatus": "DONE"
        }
    ],
    "tasks": {}
}

I'm running this in App Engine Standard in a F1 instance (256 MB 600 MHz) with this properties in my app.yaml

runtime: java11
instance_class: F1 # 256 MB 	600 MHz
entrypoint: java -Xmx200m -jar MY_JAR.jar
service: data-connector
env_variables:
  JAVA_TOOL_OPTIONS: "-Xmx230m"
  GAE_MEMORY_MB: 128M

automatic_scaling:
  max_instances: 1
  max_idle_instances: 1

I know all that properties for handling memory are not necessary but I was desperate trying to make this work and just tried a lot of solutions because my first error message was:

Exceeded soft memory limit of 256 MB with 263 MB after servicing 1 requests total. Consider setting a larger instance class in app.yaml.

The error below is not fixed with the properties in the app.yaml, but now everytime I make a call to return that JSON I get this error

2020-04-10 12:09:15.953 CEST
While handling this request, the process that handled this request was found to be using too much memory and was terminated. This is likely to cause a new process to be used for the next request to your application. If you see this message frequently, you may have a memory leak in your application or may be using an instance with insufficient memory. Consider setting a larger instance class in app.yaml.

It always last longer in the first request, I think due to some Firestore configuration, but the thing is that I cannot make that work, always getting the same error.

Do you have any idea what I could be doing wrong or what I need to fix this?

TL;DR The problem was I tried to used a very small instance for a simple application, but even with that I needed more memory.

Ok, a friend helped me with this. I was using a very small instance and even when I didn't get the error of memory limit it was a memory problem.

Updating my instance to a F2 (512 MB 1.2 GHz) solved the problem and testing my app with siege resulted in a very nice performance:

Transactions:		        5012 hits
Availability:		      100.00 %
Elapsed time:		       59.47 secs
Data transferred:	        0.45 MB
Response time:		        0.30 secs
Transaction rate:	       84.28 trans/sec
Throughput:		        0.01 MB/sec
Concurrency:		       24.95
Successful transactions:        3946
Failed transactions:	           0
Longest transaction:	        1.08
Shortest transaction:	        0.09

My sysops friends tells me that this instances are more for python scripting code and things like that, not JVM REST servers.