Custom Fetcher Memory Loading is really slow

[vanniktech]

I have the same behavior as here: #629

Basically when you scroll down and up, the image is recycled and then needs to be loaded again. However, it takes a considerable amount of time (at least 2-3 seconds on my Pixel 6) which is too much for a memory cache, right?

I can see in logcat that the Memory Cache is used: 🧠 Successful (MEMORY)

This is how I return the image that I want to display from my custom fetcher:

  private suspend fun inMemory(statement: HttpStatement) = SourceFetchResult(
    source = ImageSource(
      source = statement.execute().bodyAsChannel().toBufferedSource(),
      fileSystem = options.fileSystem,
    ),
    mimeType = profileAvatarRequest.mimeType,
    dataSource = DataSource.MEMORY,
  )

Am I doing something wrong?

I'd expect the image to be rendered instantly when I scroll up again, instead I see my placeholder being shown for 2-3 seconds.

[colinrtwhite]

This sounds like it could be a case where the image isn't being returned from the memory cache. What do the extra debug logs say?

I can see in logcat that the Memory Cache is used: 🧠 Successful (MEMORY)

This actually means the image was returned from a memory source i.e. your fetcher as it returns DataSource.MEMORY. There's a separate DataSource.MEMORY_CACHE that indicates the memory cache.

[vanniktech]

I've added .logger(DebugLogger()) and I'm not seeing much more than this. I'm only using io.coil-kt.coil3:coil-compose though.

[colinrtwhite]

It sounds like your request is missing the memory cache and is loading via your custom fetcher which takes 2-3 seconds, though it's not possible to say without a way to repro locally. It's possible it could be this, but there would be a log indicating why the memory cache result was ignored in that case.

[vanniktech]

Yes the override suspend fun fetch(): FetchResult? { is called multiple times but there is no log statement. No worries, I've managed to reproduce this here: vanniktech/playground#308

If you scroll down, and up again you can see that requests are loaded again and the fetcher is called.

[vanniktech]

@colinrtwhite have you had time to check out the reproducer?

[colinrtwhite]

@vanniktech I took a look at the repro sample and the issue is you need to also register a Keyer<Int> to ensure a memory cache key is created based on the Int. This is mentioned in the docs here, but I've added more docs here to make it more prominent.

[vanniktech]

Ah yes, now i'm getting: 🧠 Successful (MEMORY_CACHE)

Isn't possible to emit a warning if you have a custom fetcher, but you haven't provided a keyer for the same type? Coil has all of the information, so it should be fairly trivial, right?

[colinrtwhite]

@vanniktech Agreed. I can't remember why we don't default to data.toString() in the case of a missing Keyer, but I feel like there's a good reason. Going to think through changing the default on this, but it's tough as changing it could break someone's use case.

In the meantime I've added a more prominent warning here: #2816