spark in All the Mods - Gravitas

spark is a performance profiler for Minecraft clients, servers and proxies. It doesn't add blocks, items or mobs. It helps you work out why a world or server is lagging, so it's handy for a big modpack like this one.^[1]

This pack ships spark 1.10.38 (the Forge jar), and it has been part of the pack since version 1.1 or earlier.^[2]

What it does

spark is made up of three components, each covering a different kind of problem:^[1]

• CPU Profiler: diagnoses performance issues such as lag, low tick rate and high CPU usage. It samples what the system is doing and builds a call graph, which is shown in an online viewer. Running it for about 30 seconds is enough to give useful insights.^[1]
• Memory Inspection: includes a heap summary, a full heap dump, and garbage collection monitoring, so you can diagnose memory issues.^[1]
• Server Health Reporting: reports TPS, tick durations, CPU usage, memory usage and disk usage. It can also watch individual ticks and send a report when one takes longer than a threshold you set.^[1]

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

spark is different from most mods you'll meet in this pack: there's nothing to craft and no machine to place. It's a performance profiler for Minecraft clients, servers and proxies, so it helps you find out why the game is lagging.^[1]

The mod page says spark needs no configuration or setup, you just install it. That makes your first steps more about knowing what it can do than building anything.^[1]

What you can do with it

1. Start with the CPU profiler when you notice lag, a low tick rate or high CPU usage. Those are the problems it's meant to diagnose.^[1]
2. Let the profiler run for about 30 seconds. The mod page says that's enough to give useful insight into the problem areas.^[1]
3. Read the results as a call graph. spark samples what the system is doing, builds the graph from that, and shows it in an online viewer for you to analyse.^[1]
4. Check overall health. spark can report TPS, tick durations (min, max and average), CPU usage, memory usage and disk usage.^[1]
5. If you suspect a memory problem, use the memory tools: a heap summary, a full heap dump, and garbage collection monitoring.^[1]

The mod page also mentions a /tps command for checking ticks per second more accurately. It is the only command named in the sources I have.^[1]

Unverified This section describes spark as its project page does. The sources I have show no pack-specific changes, extra commands or permission settings for spark in this pack, so check in-game before relying on any of those.

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]

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][3]

Background profiler

The one option that matters is backgroundProfiler. This pack sets it to true.^[3]

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.^[3]

There isn't much version history to tell for spark in this pack. All the Mods - Gravitas 4.0 ships spark 1.10.38 (the Forge jar), and the mod has been in the pack since All the Mods - Gravitas 1.1 or earlier.^[2]

The mod's own changelog for 1.10.38 is short: it is a backported version of spark v1.10.x for Minecraft 1.18.2.^[4]

The pack changelogs have no entries for this mod, so there are no pack-specific changes to report here.^[2]