spark in FTB Skies 2: Aero

spark is a performance profiler for Minecraft clients, servers and proxies. If your world lags, spark helps you find out why. It has three parts: a CPU profiler for performance problems, memory inspection for memory problems, and server health reporting to keep an eye on overall health.^[1]

The profiler is lightweight and needs no setup. Running it for about 30 seconds is usually enough to show you where the problem is. It samples what the game is doing and builds a call graph, which you then read in an online viewer.^[1]

The health reports cover TPS, tick durations, CPU usage, memory usage and disk usage. spark can also watch individual ticks and send a report whenever one takes longer than a threshold you set.^[1]

In this pack

The pack ships spark 1.10.124 as the NeoForge build. It has been in the pack since version 1.0.3 or earlier.^[2]

Where the quest book mentions it

spark has no quest of its own. It shows up in the very first chapter, "Welcome" (chapter 1 of 31 in the quest book, 4 quests). One of its quests has no title and is a checkmark quest listing handy commands. It includes /spark tps, which checks the server's TPS and is described as useful for seeing whether your world is lagging. See a quest in "Welcome".^[3]

The other quests in that chapter cover teams, bug reports and the welcome message. They are "Creating and Joining a team" quest, "Found A Bug?" quest and "Welcome to FTB Skies 2: Aero!" quest.^[3]

Good news: there is nothing to craft for spark. It's a performance profiler for Minecraft clients, servers and proxies, so you don't build anything with it. In this pack there are no recipes that produce any of its items.^[1]

The mod is made of three parts: a CPU profiler for diagnosing performance issues, memory inspection for memory issues, and server health reporting to track overall server health. The project page says it needs no configuration or setup, you just install it, and the pack already has it installed.^[1]

Your first step: check for lag

The pack's quest book gives you the one command you need right away. In the Welcome chapter, the first chapter of the book, the untitled quest a quest in "Welcome" lists useful commands. For this mod it lists /spark tps, which checks the server's TPS and is useful to see if your world is lagging.^[3]

1. Notice that the world feels laggy, for example when a big machine setup is running.^[3]
2. Type /spark tps in chat to check the server's TPS.^[3]
3. If you want to dig into the cause, the CPU profiler is the tool for it. The project page says running it for about 30 seconds is enough to give useful insights into problem areas.^[1]

Pack config

The pack ships its own config file for the mod, and it sets backgroundProfiler to true.^[4]

Unverified What the background profiler does in this pack, and which other spark commands the pack's quests or docs recommend, is not confirmed by the sources for this section.

Same as in the All the Mods 10: To the Sky 2.0.4 guide

spark works differently from most mods you'll meet in a modpack. It's a performance profiler for Minecraft clients, servers and proxies, so this section covers how its diagnostic tools work, not machines, power or automation.^[1]

It's made up of three separate components: a CPU profiler, memory inspection tools and server health reporting. Install it by adding the jar to the mods directory.^[1]

CPU profiler

The profiler is for diagnosing performance problems such as lag, low tick rate and high CPU usage. It works by sampling statistical data about system activity and building a call graph from it. That graph is then shown in an online viewer, where you can analyse it as a simple tree structure. The viewer can also apply deobfuscation mappings.^[1]

The project page describes the profiler like this:^[1]

• Lightweight: it can be run in production with minimal impact.^[1]
• Easy to use: no configuration or setup is necessary, you just install it.^[1]
• Quick: running for about 30 seconds is enough to give useful insight into problem areas.^[1]
• Customisable: you can target specific threads, sample at a specific interval, or record only "laggy" periods.^[1]

Profiler engines

There are two profiler engines. The first uses native AsyncGetCallTrace and perf_events through async-profiler, and it's only available on Linux x86_64 systems. The second uses the built-in Java ThreadMXBean, an improved version of the WarmRoast profiler by sk89q.^[1]

Memory inspection

For memory problems, spark includes three tools:^[1]

• Heap Summary: a basic snapshot of the server's memory. It shows memory usage and instance counts for each class in the JVM's heap. It's not meant to replace proper memory analysis tools.^[1]
• Heap Dump: a full HPROF snapshot of the JVM's heap, optionally compressed. You can inspect it with conventional analysis tools.^[1]
• GC Monitoring: watches garbage collection activity so you can relate it to server hangs and see how long collections take and how much memory they free. You can also observe how often young and old generation collections happen and how long they last, which helps you pick GC tuning flags.^[1]

Server health reporting

spark can report metrics that summarise the overall health of the server:^[1]

• TPS: ticks per second, with the /tps command giving a more accurate figure.^[1]
• Tick durations: how long each tick takes (min, max and average).^[1]
• CPU usage: how much CPU the server process uses, and how much the overall system uses.^[1]
• Memory usage: how much memory the process is using.^[1]
• Disk usage: how much disk space is free or in use on the system.^[1]

Besides tick rate averages, spark can monitor individual ticks and send a report whenever a single tick's duration goes over a set threshold. That helps you spot trends and the nature of a performance problem relative to other system or game events.^[1]

Good news: spark has no tiers to climb in this pack. It's a utility mod, so there's nothing to craft and no upgrade path to follow. The only place the quest book mentions it is the very first chapter, "Welcome", which is chapter 1 of 31 in the book.^[3]

In that chapter, the untitled quest a quest in "Welcome" lists handy chat commands. It's a simple checkmark quest, so you just read it and tick it off. One of the commands on that list is the spark one.^[3]

• /spark tps checks the server's TPS. It's useful for seeing whether your world is lagging.^[3]

If your skyblock world starts to stutter, run that command first. It tells you whether the server is struggling to keep up.^[3]

Unverified Any other spark commands or profiling features are not covered by the sources for this pack, so they are not described here.

spark only shows up in one place in the quest book: the Welcome chapter, which is the first chapter of the book (chapter 1 of 31). It has 4 quests, and every one of them is a simple checkmark quest, so there is nothing to craft or hand in.^[3]

The quest that matters here is the untitled one, a quest in "Welcome". It is a quick reference card of useful commands for getting around the pack, and one of them is the spark command /spark tps. It checks the server's TPS, which is handy for seeing whether your world is lagging.^[3]

The same quest also lists a few other commands that aren't spark. /sethome (name) sets a home you can return to with /home (name). /ftbteambases home takes you back to your starting island. /back returns you to a previous point, such as where you died or where you teleported from. /spawn takes you back to the lobby.^[3]

The other three quests in the chapter don't involve spark. They are "Welcome to FTB Skies 2: Aero!" quest, "Creating and Joining a team" quest and "Found A Bug?" quest. The team quest explains how to leave your automatic team and invite friends to a shared starting ship or island, and the bug quest tells you where to report problems.^[3]

No other chapter I was given mentions spark, so there are no further spark quests to follow.^[3]

Same as in the All the Mods - Gravitas 4.0 guide

spark is a performance profiler, and this pack ships it with almost nothing configured. The whole config file has just one real setting, so there isn't much to tweak.^[1][5]

Background profiler

The one option that matters is backgroundProfiler. This pack sets it to true.^[5]

spark's profiler is described as lightweight enough to run in production with minimal impact, so leaving it on fits how the mod is meant to be used.^[1]

Unverified The sources don't say what spark's default for backgroundProfiler is, so we can't confirm whether the pack changed it. They also don't say exactly what the option does beyond its name.

The header entry

The file also contains _header. It's only a note pointing you to spark's configuration documentation, and it doesn't change any behavior.^[5]

FTB Skies 2: Aero 1.10.0 ships spark 1.10.124 (the NeoForge build). The mod was already in the pack by FTB Skies 2: Aero 1.0.3 or earlier, so it has been part of Aero for a long time.^[2]

spark 1.10.124

This is the build the pack uses, and it is marked as a backport release. It was manually uploaded to bring some bug fixes to the popular 1.21.1 version of Minecraft.^[6]

It carries the latest spark code from the 1.21.4 version, which was published to Modrinth. For the complete list of fixes, check spark's own changelog on its website.^[6]

Unverified The pack changelogs have no entries for spark, so there is no confirmed record of when or how its version changed between Aero releases.