Why is My Sim Taking Longer to Run?
The Really Quick Answer
If your sim is taking way longer usual, you probably have "Replace Existing Gems/Enchants" enabled in Top Gear. "Replace Existing" will usually significantly increase sim time. It's recommended to keep this off by default and just briefly turn it on to double check your gem/enchant loadout.
The reason why it takes so much longer is due to how Smart Sim works. Gems and enchants provide a small amount of DPS which means that there will be more combinations close to your best option - any combinations that are near the top get run at higher precision which requires a lot more time.
The Detailed Version
The total time a sim will take depends on a variety of factors:
- Number of combinations/actors
- The number of combinations that are sidegrades
- Fight style, fight duration, number of enemies
- Class/spec
All of these aspects can affect how long a sim takes - they also all stack up, sometimes multiplicatively. If you run a huge sim with lots of sidegrades using a complex fight style, it might require 10-20x more time than a smaller sim without sidegrades using a simpler fight style.
Number of Combinations
The overall size of the sim (number of combinations/actors) is a pretty obvious aspect - testing 1,000 options will take longer than testing 10 options.
Raidbots uses some techniques to make some of these large sims faster (Smart Sim) but reducing the number of combinations will always speed things up.
Reducing combinations can be achieved by selecting fewer items/talents/etc or disabling options that create a lot more options (like "Replace Existing").
Sidegrades
"Sidegrades" are basically any gearsets/combinations that are very close to the top result in a Top Gear sim. If your sim has a lot of combinations that are very close to the top result, it's going to take much longer than one where the combinations are more spread out.
The most common example is "Replace Existing Gems/Enchants" in Top Gear. Gems and enchants provide a relatively small amount of DPS - when you select this option, you end up with a lot of potential combinations that are very close to your best one. Each of those combinations will need to be run at the highest precision to determine which of them is the best (or is a sidegrade).
Under the hood, this is all based on how Smart Sim works. The trick of Smart Sim is that it's able to identify sub-optimal combinations very quickly and then remove them from later, higher precision stages. If you have a bunch of options that only change gems and enchants, there will be way more options than make it to the last stage which takes the most time to run.
Fight Configuration
A fight like Patchwerk is very simple - there's just one boss that is not moving. This is simpler and faster to simulate than something more complex like DungeonSlice - DS has lots of mobs, many pulls, and require more CPU time to figure it all out.
Longer sims (e.g. 10 minutes vs 5 minutes) also take more time. Increasing the boss/enemy count also requires more time.
Class and Spec Differences
Different classes and specs require different amounts of time to simulate. You might notice this if you usually play a character that has faster sims and then start playing an alt that takes a longer time.
There's not much to be done about this but it's worth noting if you end up playing a bunch of different characters.
The difference in time can be pretty significant - the fastest-to-sim spec might be 3-4x faster than the slowest. Under the hood, there can be a variety of technical reasons for the differences that are difficult to summarize (pets tend to be slower, high variance specs require more time, etc). This doesn't indicate anything about good a class/spec is, it's just a side effect of the computational complexity.