Java Edition:Update Skipping

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Update skipping is a method that allows block updates to be "skipped" within the new queue-based block update system introduced in snapshot 22w11a (1.19 snapshot). This works as, by default, the game limits each list of updates to contain a maximum of 1,000,000 block positions. Therefore, if the game attempts to schedule more than 1,000,000 block updates, any beyond the first 1,000,000 will be skipped, giving this method its name. This method is much less powerful than its close relative update suppression but still has a variety of useful properties.

General Information

To direct the majority of updates in the direction we want, we still must utilize the game's update order, which is West, East, Down, Up, North, and finally South. By chaining one of these directions into a machine to create a massive amount of block updates, the rest will have their locations skipped and not be processed. However, it is important to note that each successfully scheduled location will also update any blocks directly beside them, effectively creating a barrier of partially updated locations, as any updates blocks in these locations would have created from being processed will not be processed. This effect can easily be seen when slicing nether portals, as the diagram below shows:

The pink concrete represents the obsidian block broken, the red stained glass represents scheduled locations, and the yellow stained glass represents the updates created from processing the scheduled locations. The rail line points into the skipper.

Another important mechanic is how player block breaking is handled. Instead of only one update process being created from the broken block, one will be created for each side of the block, so one must break blocks in such a way that only one of these update chains is important, unless one wishes to build multiple skippers.

A great video for an introduction to update skipping is Igna778's video on the subject.

Skippers

While one can use, for example, the updates of a million BUD-powered rails to skip updates, such designs are not easily resettable. There are two common designs for resettable skippers: the instant update loop skipper, and the wall based skipper.

Wall Based

Wall based skippers rely on BUDing trapdoors next to very tall columns of walls, such that when updated, they schedule thousands of updates each. These designs are bulky, directional, and somewhat tricky to build, but they provide robust skippers. They will work from 22w11a to 25w42a (present).

The wall based skipper above was created by igna778, with a video showcasing it here.

Instant Update Loop Based

A bug was discovered by Nic Nac with redstone dust and trapdoors that allowed for infinite update loops, allowing for very small update skippers and update suppressors. However, the bug these relied on was silently patched in 1.20 Pre-release 2, making its effective range from 22w11a to 1.20 Pre-release 1.

For the above design, make sure the rail is pointing west into the device. The lever may be activated to disable the skipper, which may be useful if one needs to extend or change the BUD line.

Uses

Update skipping is far less powerful than update suppression, but still may be used to create a variety of otherwise impossible block configurations.

Portal Slicing

By far the most useful use of update skipping is the ability to slice portals, allowing for the creation of hyper efficient mob farms in versions without easy access to update suppression. One can use extra layers of portals to absorb the border updates, allowing for portals to be sliced. This is made easier by portals using a slightly different update method, where horizontal updates will always process before vertical ones.

The update diagram from above demonstrates how to slice portals by absorbing the border updates within the portal itself.

This method is not just limited to creating perfect horizontal slices, and can be used to make, for example, 1x1 portals, or very suspicious portals.

Blocks Missing Support

By using snow layers to absorb the border updates, one can create many floating blocks, which include:

Blocks requiring support that are placed on the higher snow layer block will be left floating when the pink concrete is broken. The rail line points into a skipper.

A short video demonstrating the process on a variety of blocks can be found here.

Half Top Doors

One may also create half top doors by replacing the top snow layer buffer with the bottom of the door, allowing the lower half to absorb an update and break, while the top remains intact.

The top of the door will be left floating when the pink concrete is broken. The rail line points into a skipper.