# Why is my server lagging?

> Rubber-banding, blocks that reappear after you break them, mobs that teleport, and Can't keep up! Is the server overloaded? in the console all mean the...

Source: https://fadehost.com/docs/server-lag/

Rubber-banding, blocks that reappear after you break them, mobs that teleport, and
`Can't keep up! Is the server overloaded?` in the console all mean the same thing:
the **server thread is falling behind**. A Minecraft server has to finish one tick
every 50 ms (20 ticks per second). When a tick takes longer, everything waits.

Almost always, the reason is **work**, not memory and not the machine: one build,
mod or plugin doing too much every tick. A pipe network that re-scans itself, a
farm with thousands of items, a hopper chain, a quarry, a mob grinder, a mod that
writes to disk on the main thread, a view distance the world cannot afford. More
RAM does not make any of that faster. A kernel out-of-memory kill is a crash, not
lag, and the panel tells you about that separately.

## The tick-health banner

FadeHost measures every online server's tick time once a minute. When the slowest
minutes have been over **100 ms per tick** (that is 10 ticks per second or worse)
for ten minutes with players on, the server page shows an amber banner with the
number, and the owner gets one alert a day on the channels set under
**Settings → Alerts** (event *Slow ticks: the server thread is struggling*).

Idle servers never trigger it: an empty world ticks in a millisecond. A server that
just started spends its first minute catching up and does not trigger it either.
The banner goes away on its own once the ticks have been under 60 ms for fifteen
minutes with players on.

## Profile it

Guessing is slow. A profile shows exactly where each tick's time goes, and the
banner takes one for you:

1. Press **Profile now** on the banner while players are on and the lag is
   happening. The same button lives on the server's **Performance** tab as
   **Run profile**, so you can profile any time, not only while the banner is
   up, and every report you take is listed there to compare before and after
   a change. It uses [spark](https://spark.lucko.me/), the standard Minecraft
   profiler, through the server's console. Paper and Purpur from 1.21 have it
   built in; on Fabric, Forge and NeoForge the banner offers to install the spark
   mod if it is missing (restart the server afterwards, then press the button
   again).
2. Within a minute or two a link to `spark.lucko.me` appears. Open it.
3. Press **flat** at the top, then pick **Server thread**. The list is sorted by
   how much of the tick each thing takes.

Read the list from the top. The deepest entry with a mod or plugin name in it is
your answer:

| You see | It means |
| --- | --- |
| `com.simibubi.create...PumpBlockEntity` | Create pumps re-walking a shared pipe network every tick. Fewer pumps, or split the network. |
| `...tickBlockEntities` dominated by one mod | That mod's machines, hoppers, drawers or quarries. Fewer of them, or spread them out. |
| `...tickEntity` or `EntityCramming` | Too many mobs or items in one place. Clear the farm, cap the grinder. |
| `ServerChunkManager...executeQueuedTasks` or `ThreadedAnvilChunkStorage` while players fly around | Chunk loading and generation. Lower the view distance, or pre-generate the world. |
| `RegionFile...write` every five minutes | Sync chunk writes on save. Turn on *Optimised world saves* in the server settings. |
| Mostly `Thread.run ... park` | The server is idle. The lag is on the network or the client side, or nobody was on during the profile. Profile again while it happens. |

The profile also shows garbage collection at the top. Frequent long "Old" pauses
are the one case where memory is the problem; young pauses of a few milliseconds
are normal.

## Then

Fix the thing the profile named: remove or shrink the build, remove the mod, lower
the view distance, pre-generate the world. Then play a few minutes in the same
place and press **Run profile** on the Performance tab again to see the difference. If the profile names something you do not recognise, send us
the link from **Support** and we will read it with you.