Realms changes worlds to simulation distance 10

My realm is absolutely wrecked right now. Performance has tanked for everyone. Started yesterday. Hoping this is why.

I noticed a lot of lag on my realm today. This was all with one player online. Mob movement was stuttering a lot. Mining blocks was difficult, block lag was worse than usual, chunk loading was very slow as well. I'd suggedt changing to Sim6 and allow us to evaluate that.

Corner tweeted that it's official. Unbelievable https://twitter.com/CornerHardMC/status/1349951720969785348

No new bugs were found by me. However, the server speed dropped significantly. Example for demonstration:
Until yesterday, 4 players could join my realm and my farm with pistons worked +- ok. Now, when I am ONE on the server, the pistons are moving 3 times slower than usual. And so it lags absolutely everything - hoppers transfer objects much slower, objects despawn more slowly, chunks are barely loaded. It's impossible to play.

Why can't you just increase server performance? Why, after so many bugs (REALMS-4642, REALMS-1887), you still haven't done anything to fix it?

P.S. My PC is working absolutely fine (RAM 32, 12CPUs ~3.2GHz, GTX 1080), internet connection is stable. Can show other characteristics if needed

Ever since 24-28 hours ago, my realm speed has dropped significantly. My Xbox One S can not handle gameplay. My movement was stuttering, opening inventory, and other inventories takes ages and trading with villagers is virtually impossible. Please add a sim distance slider or at least change it back to 4. 

I think sim 10 is a step in the right direction, but it was a bit too much. It was about 10-20% laggier than normal. I would suggest sim 6 or sim 8 because mobs can spawn and despawn better than they do with sim 4, but it also doesn’t load nearly as many chunks as sim 10, so it could be a happy medium between mob spawning/ despawning mechanics and performance.

I'm sorry, but I hate the change. Simulation distance 10 brought lag and everything lag brings with it. With the sim distance being on 10, that means players also have to spawnproof way bigger areas, wich I honestly definitly do not want to do. I'd like to be able to play, and not spend an entire month spawnproofing everything around my base. We joked around that from now on all bases will become skybases to not load mobs on the ground, but that's like the only viable option right now. I was perfectly happy with a sim distance of 4, I don't need more. If the realms would get a bigger sim distance, that should've been anounced weeks in advance. Think of all the mobfarms that are designed and spawnproofed for sim distance 4! All those need tweaking. I hope this change will get reversed, but as for now, I will stay of the realm as much as I can. Totally not playable.

Realms have already been laggy on a simulation distance of 4. Unless the entire game has been optimized AND realm specs have been raised (neither of which have happened), realms should not be raised to any simulation distance other than 4 or 6 (which is ideal). Simulation distance 10 loads 4 times as many chunks (see @Amuhn Ra's breakdown) per player. Realms simply aren't built to handle anywhere near this: I have no idea what testing you did, but this does not seem thought out to me.

On top of that, this not only added a lot more lag to both realms AND clients (devices stuttering, mobs "teleporting", mob caps filling up nearly instantly, etc), but it also broke the majority of farms on the platform as virtually all farms are built for sim 6 or sim 4. 

Players typically don't even play on sim 10 on their local worlds: I don't understand why it's being forced on realms. 

Especially on realms with addons or realms with many players, it's impossible to play: almost half of my players have protested this change and started playing on other servers rather than our realm, simply because it's such a massively negative change. Some other realm owners I know switched immediately from realms to servers. Please, revert this change, or switch it to simulation 6, or open it up to player changing. 

On my realm even when there is just one player on it the TPS(ticks per second) drops below the normal 20. Then when 4+ people join it drops to almost half or a third. The world is still playable, but flying with elytra is impossible.  Once the realm fills to its max of 10 players, I would classify the TPS as unplayable as it probably dips below 5. This was not at all how it was before and only started happening when this change was introduced. Also I am not 100% sure but I have built multiple farms that rely on sim distance 4, and if the mob spawning radius changed I would have to rebuild the farm.

Umm.. can we do something about getting 79 phantoms in 1 minute after coming up from the mine.

Phantoms spawn, they move over to the closets player, open up spawn cap, and keep spawning... It is impossible to survive if you dont sleep. and you cant sleep easily on multi player servers 

Client: all 

It is sim 10 related and having sim 10 is just broken right now. Sim 6 and Sim 4 is fine

To many mobs spawning when coming up from mines, not to mention the 70 phantoms coming at me. Not to mention this lags out the game when we have any more then 6 people if different areas of the map just makes the game unplayable. (Unless we slab or light up a radios of 96 blocks around areas were we are working) it's ridiculous. Either dedicate more Ram to the Realms or fix the issues cause if not you gonna lose people to servers.

On Win 10 but don't get how this matters 

It was requested to provide the client device, I have tested on Windows 10 PC (Ryzen3 2600) and Android (Samsung Galaxy S7), both had noticeable lag. 

Advanced Automation is one of the best places to test things (most importantly lag) for Realms. We're a tech server that's been running on the same realm world for nearly two years now and have taken large steps to reduce lag while working on the world. It's a given to most of the players that the world will always be a little laggy. Simulation distance 10 brought standard lag that has new effects like fairly common block lag with non-instabreak blocks, slower redstone (gameticks have slowed down–my guess is around 10-15 gt/s), and restricted flight due to slower chunk loading (aside from it being more difficult to take off, even when being the only player on I reach unloaded chunks every 200 blocks or so). NinjaPigeon is correct when he says the lag is about 15-20% worse than normal even when staying in the same area (not loading new chunks). My internet runs over 200mbps download and 50mbps upload speed so the lag I experience is nearly all from the server.
I believe the best long term and agreed-upon solution is to give Realms owners the ability to change the world simulation distance between 4, 6, 8, and 10. Before that's implemented, setting Realms to simulation distance 6 would be the best solution to reduce lag while keeping the larger spawn/despawn radii. We as a server love that you're working on higher simulation distances for Realms, thank you!

This change was extremely noticeable. Everyone on my realm has been complaining about severe lag the last 2 days.

It takes multiple attempts to successfully join the realm now. Trying to take off and fly with elytra is very hard, you have to spam jump and fireworks for up to 20seconds before it works typically. Lot of frame drops and laggy gameplay. People on my realm keep dying because of lag spikes while flying in particular. When we run any farms on the realm, the game becomes near unplayable.

People can't eat food properly. You hold the button to eat and the eating animation just goes on indefinitely without ever actually consuming the food. This is because the realms are so incredibly laggy now.

Also issues with picking up dropped items on the floor. We have lost some shulker boxes full of materials because it won't pick it up into our inventory due to the lag.

Please please please revert this change, or at least give us the option to choose our preferred simulation distance. This is such a terrible game ruining change you have made.

Edit: I play on ps4. Typically 4 people on my realm when I play. All are either playstation or Xbox. 

Noticable increase in realm lag. No issues when playing solo, but all joining players have raised that it is now lagging. Mainly seeing this with eating (Hunger does not fill), there is a delay to hitting and breaking blocks, items in water jitter when floating and smelting takes significantly longer.

Will 3+ players it there is a significant amount of lag, up to the point of it not being feasible to play without constantly being impacted.

Edit - This has only been an issue since last night. Faced by all players (Up to 7) across PS5/PS4/Switch

The lag on realms is crazy now since it changed, very noticeable. It never used to get it like this. Here is a basic example of something flowing in water.

Device Information

Model: HP Z230 Desktop Computer 
OS: Windows 10 Pro (64-bit)
CPU: Intel(R) Core(TM) i7-4770
GPU: AMD Radeon Pro WX 4100
Memory: 16GB
HD Free Space: 1.47TB
Internet Access: Wired/Ethernet - Fibre Broadband

I've advocated for the increase of sim distance on Realms for several months now, so I'm glad for the change. Because of spawning mechanics and view distances, I would rather be running on sim 10 than sim 4. However, making such a big jump on existing realms is going to cause lag. Players have not designed their realm worlds for sim 10, and if they placed a lot of their farms, storage systems, and redstone too close together, then all of those farms will now be loaded at once. This is the source of lag. There is also increased memory and disk usage from increasing the sim distance. This would also contribute to lag.

In my experience with playing on technical servers with BDS, sim 8 and sim 10 struggled when multiple players were on. Sim 6 seemed like the sweet spot.

I can confirm that lag on the realm increased this week with the change over.
The number of players online does affect it (more players means more chunks getting simulated).
I'm joining realms from a PC, and I haven't tested different devices.

Code Analysis: Sim distances are implemented in a rather simple way in the game. Based on sim distance, the game creates a list of offsets representing all the ticked chunks relative to an active player. Every game tick, the game loops through all players and loops through all offsets for every player, and combines the player's position and the offsets to determine every chunk that needs to be simulated. It also includes the chunks in every ticking area as well.

It would not be difficult to allow realms/bds to dynamically scale sim distance based on load or number of players. By loading multiple lists of offsets into memory, the game can dynamically switch between sim distances. Alternatively, multiple lists can be used to prioritize certain chunks over others, such as the sim4 chunks being simulated before sim6, sim8, etc. This way the game can skip simulating outer chunks if a game tick is taking longer than 50 milliseconds.

I'm actually sorry: THERE IS a new bug. I think, its not normal amount of phantoms (Survival, Hard mode):

As this is broken i think i will suspend my realm sub until it is fixed. It is unplayable on Xbox one, phone, or windows 10 pc. even with 1 or 2 players online.

PC

I7-8700
32 gigs ram
RTX 2080

My family realm is unplayable, especially on Android and Switch, which is how the kids play there.  I might need to move it to a local game or a server.  If this was at Sim6, I think it would be tolerable.

Please give us the option to change this back to 4 if we want to. The game is completely unplayable at the moment. It is the same on both Nintendo Switch and PC - but the problem seems a little bit less noticeable when moving away from the base/builds. 
I never experienced this before the change. It does not matter if we are 1 or 2 players online. 

I believe this is an adverse change and needs to be reverted immediately. I own a public invite-only realm, and most of the users can’t join because of the extreme lag that sim 10 is causing. Normal tasks like eating food and taking off with elytra are increasingly difficult due to lag. I believe that realms should be at sim 6, as that seems to be the optimal sim distance.

It causes so much lag and breaks farms.  Please revert it back.  In the future, just let the realm owners have the option to set the simulation distance on their own.  Thanks

I too have horrid lag on realms. My friends and I tested by flying to an area we had not built in and firing an arrow. The arrow travelled slow and staggered. The lag is from the server, not you.