spark in FTB Skies 2

spark is a performance profiler for Minecraft clients, servers and proxies. You won't craft anything with it. It's a diagnostic tool that helps you find out why a world is lagging.^[1]

This pack ships spark 1.10.124 (the NeoForge jar), and it has been in the pack since 1.0.1 or earlier.^[2]

What it does

• CPU Profiler: diagnoses performance problems like lag, low tick rate and high CPU usage. Running it for about 30 seconds is enough to give useful results.^[1]
• Memory Inspection: includes a heap summary, a full heap dump and garbage collection monitoring.^[1]
• Server Health Reporting: tracks TPS, tick durations, CPU usage, memory usage and disk usage. It can also report whenever a single tick runs longer than a threshold you set.^[1]

Where the quest book mentions it

The pack's quest book brings spark up in the Welcome chapter, which is chapter 1 of 41 and has 4 quests. The mention is in the untitled quest a quest in "Welcome", a checkmark quest that lists handy commands. Its spark entry is /spark tps, which checks the server's TPS and is useful for seeing whether your world is lagging.^[3]

The other quests in that chapter are "Welcome to FTB Skies 2!" quest, "Creating and Joining a team" quest and "Found A Bug?" quest.^[3]

spark is a performance profiler for Minecraft clients, servers and proxies. It isn't a machine or a tool you build. It's a set of commands you use when the game feels laggy, and it needs no configuration or setup beyond being installed.^[1]

Step 1: Check your TPS

The first thing to learn is the TPS check. The quest book's Welcome chapter, the very first chapter in the book, has an untitled quest called a quest in "Welcome" that lists useful commands. For this mod it gives /spark tps, which checks the server's TPS. It's handy for seeing whether your world is lagging.^[3]

TPS means ticks per second. spark also reports tick durations (min, max and average), CPU usage, memory usage and disk usage as part of its server health reporting.^[1]

Step 2: Profile when something is wrong

If the TPS looks bad, the CPU profiler is the next tool. It's meant to diagnose lag, low tick rate and high CPU usage. Running it for just around 30 seconds is enough to give useful insights into problem areas. The results are shown as a call graph in an online viewer.^[1]

For memory trouble, spark also has a heap summary, a full heap dump and garbage collection monitoring.^[1]

What the pack sets

The pack ships a spark config file. In it, backgroundProfiler is set to true.^[4]

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]

The sources here show no tier ladder for spark. It appears in the "Welcome" chapter of the quest book, as one entry in a list of commands.^[3]

The untitled command-list quest a quest in "Welcome" in that chapter lists /spark tps. It checks the server's TPS, which is handy for seeing whether your world is lagging. The quest is a simple checkmark task, so there are no items to collect or machines to build for it.^[3]

In the quest book, spark is mentioned in the "Welcome" chapter, the very first chapter. Every quest in it is a simple checkmark quest, so you just read it and tick it off.^[3]

The quest that mentions spark is a quest in "Welcome", which has no title of its own in the book. It is a list of handy commands, and for spark it tells you to use /spark tps to check the server's TPS. The quest says this is useful to see if your world is lagging.^[3]

That same quest also lists other commands besides spark's, for example /sethome and /back. Nothing needs to be crafted or collected for it.^[3]

The other quests in the chapter are "Creating and Joining a team" quest, "Found A Bug?" quest and "Welcome to FTB Skies 2!" quest. Their texts are about teams, bug reports and a welcome to the pack, and they do not mention spark. The text of the Mekanism chapter does not mention spark either.^[3][5]

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][6]

Background profiler

The one option that matters is backgroundProfiler. This pack sets it to true.^[6]

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.^[6]

FTB Skies 2 1.22.0 ships spark 1.10.124, using the NeoForge jar. The mod has been part of the pack since FTB Skies 2 1.0.1 or earlier.^[2]

spark 1.10.124

This build is a backport release. It was uploaded manually to bring some bug fixes to the popular 1.21.1 version of Minecraft.^[7]

It carries the latest spark for Minecraft 1.21.4. The full list of changes is on spark's own changelog page.^[7]

Unverified No pack changelog entries for spark were available, so changes to the mod between earlier FTB Skies 2 releases and 1.22.0 are unverified.