Performance is something we are constantly working on improving. Marvin is a complex app and depending on how you are using it there are a lot of calculations being run in the background that can slow things down.
Here are some tips on what you can do to try and speed things up.
The limiting factor in how quickly Marvin can run is your free memory on your computer. If you haven't restarted your computer in a while, are running other applications or have lots of tabs open... all these things take up memory on your computer, slowing things down.
Restart & Close
So the first measure if Marvin feels slow is to restart your computer. You also might want to make sure you don't have any applications open that you are not using. And closing tabs might further help.
Deleting unused Smart Lists
If you have a lot of Smart Lists that you no longer use, delete them.
Avoid long lists
If a Smart List contains thousands of items it can be too much to render them at once. In that case reduce the smart list. We will improve this in the future.
If you have a lot of tasks, the Custom Alerts strategy can cause slowness, since Marvin needs to check which items are in the alert, especially if you have many alerts set up. Try disabling this strategy to see how much it is affecting performance. If you notice a big difference, try moving some of the smart lists to your sidebar, which has similar utility so long as smart list counts are enabled.
If you use a lot of Marker strategies (Line Marker, Icon Marker, etc.), and especially if you use complex Smart Lists, then the performance of drawing long task lists will suffer.
Daily Recurring Tasks
If you have a lot of recurring tasks, especially daily recurring tasks, this can massively affect Marvin's performance. This includes both sync performance, and performance within Marvin. This is one reason why we plan to introduce Habits.
turn as many of your daily recurring tasks into a single task with subtasks
use "repeat X days after completion" (with X=1)
use the Separate Habits snippet to keep your day list manageable in terms of number of tasks