Game Lag White Paper › L10 Memory

Allocation surge Allocation storms

Cause ID mem-alloc · Primary owner Game team (Server development)

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Creating large numbers of temporary objects during an event makes GC run far more often than usual.

Why Item drops, combat logs, and event rewards create a flood of temporary objects → Effect GC runs several times as often, and objects not yet discarded get promoted to the old generation, so full GCs come sooner too → On screen Periodic hitches only during events

Symptoms

Stutter, Freeze

Factors

Stall

Who’s affected

Whole server, Specific zone/channel

When

When crowds gather

Owner

Primary owner Game team (Server development)

Game team action items

Use object pools and reusable buffers, profile allocations.

On the graph

Rises with load · GC count, allocation rate

Where to look

Count GCs per minute from GC logs (Java -Xlog:gc, Go GODEBUG=gctrace=1); on .NET, check allocation volume and GC count in dotnet-counters (dotnet.gc.heap.total_allocated and dotnet.gc.collections on .NET 9 and later, Allocation Rate and Gen 0 GC Count on 8 and earlier). Overlay with concurrent users and event times

Confirmed if

When the event starts, allocation rate and GC count climb faster than player count, and short pauses become frequent. Back to normal once the event ends

Ruled out if

GC count unchanged but each pause gets longer: live data has grown (mem-gc-thrash, mem-leak)

Check with

Infra tools (no game code needed)

Sources

1. Garbage Collector Implementation Oracle
   Minor GC when the young generation fills; some surviving objects move to the old generation, and when the old generation fills, the whole heap is collected (much slower than a minor GC); -Xlog:gc writes one line per GC
2. A Guide to the Go Garbage Collector Go
   The higher the allocation rate, the more often GC cycles run; GODEBUG=gctrace=1 prints GC trace output
3. dotnet-counters diagnostic tool .NET
   .NET 9 and later show dotnet.gc.heap.total_allocated and dotnet.gc.collections; .NET 8 and earlier show Allocation Rate and Gen 0 GC Count

See also

Same layer: L10 Memory

• Server GC stop-the-world pause
• Script engine GC pause
• Memory leak
• GC thrashing (too little heap headroom)
• Swap
• Cache miss
• Memory fragmentation
• Remote NUMA memory

Same symptom (Stutter), other layers

• Frame time spike L1 Client game process
• Client garbage collection L1 Client game process
• Synchronous loading and shader compilation on the main thread L1 Client game process
• Slow storage delays asset streaming L1 Client game process
• Rendering load from large crowds L1 Client game process
• Missing or too-short interpolation buffer L1 Client game process
• Excessive extrapolation (dead reckoning) L1 Client game process
• Fixed-timestep catch-up spiral L1 Client game process

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