Hey guys , does anyone know how to limit the heap ...

# kobweb

[Dieter Vaesen]

Hey guys , does anyone know how to limit the heap size for your local kobweb server. I need it so i can test the following issue locally :

I have written code that stores images as base64 (bsonbinary) in mongodb. At first I was just retrieving this base64 code and loading it on my webpage. On my local machine it's working but on my server I get a out of memory exception - java heap size. I use a free render server and it has 512mb memory.

I already tried setting the following in my gradle properties but it only sets the available memory for starting server -- using gradle command

org.gradle.jvmargs=-Xmx256m

Follow up question
Does anyone know how to increase performance when passing these base64 images via json.encode(...)
I'm currently trying to use gzip but it seems i can only use it in my jvmain folder and not my jsmain or commonmain

[David Herman]

Does anyone know how to configure a ktor server to limit its heap?

[David Herman]

I'm trying to find online articles for this and mostly failing

[David Herman]

Also I wonder if the issue is ktor in your case or mongodb?

[Dieter Vaesen]

Uhmm at the moment i linked the same mongodb database to my local and server environment. So if it was mongodb it should also fail locally? 🤔

[CLOVIS]

org.gradle.jvmargs=-Xmx256m

This sets the memory given to Gradle itself, not the memory given to the started apps.

I believe Kobweb uses the application plugin? (Not 100% sure, sorry). In that case, you can use:

application {
    applicationDefaultJvmArgs = listOf("-Xmx256m")
}

[CLOVIS]

Also, keep in mind that MongoDB cannot store a document larger than 16mb. Maybe that is your problem?

[Dieter Vaesen]

Yes indeed jvmargs is only used when setting up server aka using gradle to build

[Dieter Vaesen]

My images are only 2,1mb max. For images over 16mb you have to use Gridfs with mongodb.

[Dieter Vaesen]

My images are stored correctly the memory issue is when I get them from database and format them into json and return them with an api call 🙂

[Dieter Vaesen]

Can't seem to use the application plugin 😞

[S.]

can't you just use

java -jar -Xmx256m file.jar

[Dieter Vaesen]

Not really familiar with setting these things on server. Where would you add this ?

[S.]

I think you can just edit the run config here

[Dieter Vaesen]

Not really sure if it is the same as "kobweb run" but ill give it a try

[Dieter Vaesen]

It's probably the same as this file ? This didn't do anything for me 😛

[S.]

very likely not the same, this sounds like it's vm options for the IDE, you want vm options for the process you're starting

[Dieter Vaesen]

image.png

[Dieter Vaesen]

only have this

[S.]

you can try the kobwebStart gradle task and edit its config

[CLOVIS]

You should be able to add JAVA_OPTIONS="-Xmx256m" in that "environement variables" selector.

However, that will only impact running the app from IntelliJ. It won't do anything to your deployed app.

[S.]

but ultimately it sounds like this issue concerns the underlying ktor layer rather than kobweb. so for debugging it's probably easiest to just create a standalone ktor repro

[Dieter Vaesen]

Doesn't seem to do anything even if i use very little memory

[Dieter Vaesen]

Yeah I was trying to avoid using a separate ktor. but it seems i have to

[CLOVIS]

Is your repository public?

[CLOVIS]

It's hard to say exactly why it doesn't work without seeing everything in action. If it's public, I'll try cloning it tonight to find it

[CLOVIS]

It really shouldn't be too hard, it's just a matter of finding the correct place to put the config

[Dieter Vaesen]

No it's not public 🙂

[CLOVIS]

If you can publish a repository with exactly the same configuration as yours but without the actual code (except maybe a hello world), that should do the trick as well. I assume you started from one of the Kobweb examples?

[Dieter Vaesen]

Yes. I'll try to make a public clone in a few hours 🙂

[Dieter Vaesen]

I found it!! I can use JAVA_TOOL_OPTIONS instead of JAVA_OPTIONS as environment variable in my run. Now I still have to find how to set it for project it self

[Dieter Vaesen]

And then it gives same error as on server

[David Herman]

Yeah, for sure, a problem is going to be that Kobweb is running the ktor server for you.

[David Herman]

But as I'm not sure what actually is causing your problem (mongodb growing in heap size, ktor growing in heap size, something else) we can spend a lot of time trying to give you suggestions for the wrong solution

[David Herman]

You can definitely set environment variables on Render, and I think if you do that, it will be picked up by the ktor server that spins up

[David Herman]

I'm not sure how to do it, but what I might try to do is figure out how to profile a server running locally

[David Herman]

I don't know what OS you're on

[David Herman]

But if you're going over 500MB on Render, then you're also going over 500MB on your local machine too

[David Herman]

https://docs.render.com/configure-environment-variables

[David Herman]

Here is the script that runs the ktor server:

#!/bin/bash

# Find the kobweb project folder, using this file's location to start form
cd "$(dirname "$0")"
cd ../..

args="-Dkobweb.server.environment=PROD -Dkobweb.site.layout=KOBWEB -Dio.ktor.development=false -jar .kobweb/server/server.jar"

if [ -n "$KOBWEB_JAVA_HOME" ]; then
    "$KOBWEB_JAVA_HOME/bin/java" $args
elif [ -n "$JAVA_HOME" ]; then
    "$JAVA_HOME/bin/java" $args
else
    java $args
fi

[David Herman]

which is very similar to what kobweb run does as well

[David Herman]

It's possible I can add hooks for you somewhere to configure stuff that I don't already; but I don't know exactly what that is unfortunately

[David Herman]

It's possible all you need to do is create a Kobweb Server Plugin but again I'm not sure, I'm sorry about that

[Dieter Vaesen]

I tested by changing xmx value locally and my code stops working below -xmx180m. So normally my render server has more than enough memory with 512?

[David Herman]

I believe 512M is quite a lot for a simple web server. But not sure about one dealing with images.

[Dieter Vaesen]

I know 😛. But i needed to increase it on server. Im also going to improve the code managing the images. But for now i wanted to find difference between local and server

[David Herman]

Sure! It's a good idea

[Dieter Vaesen]

JAVA_TOOL_OPTIONS was also solution on render btw

[David Herman]

Have you looked at the Metrics tab for your failed server?

[Dieter Vaesen]

It works. But i'm still curious whats going to happen when i add more pictures

[David Herman]

Oh, your render server is no longer crashing?

[David Herman]

If you limit your heap, you're just going to get more GC collections running, which can slow down the site especially when it is under heavy load.

[David Herman]

I doubt you're ever going to have to need 512MB of images in memory all the same time

[CLOVIS]

Can you reproduce the problem locally? If so, the profiler should help quite a bit

[Dieter Vaesen]

Yeah i can produce it locally now 😛 with java_tool_options. and thats what i set out to find 😛

[Dieter Vaesen]

Now I can improve my code and test quickly

[David Herman]

Good luck!

[Dieter Vaesen]

Thanks for the help guys