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Memory measurement

Decode benchmarks measure time, not memory. CI containers are memory constrained, so peak memory usage on large inputs is measured explicitly and reported per input size.

Running the measurement

cargo run --release -p devkit-xdr --example mem_profile

Pass comma-separated input sizes in bytes to override the defaults (1024,65536,1048576):

cargo run --release -p devkit-xdr --example mem_profile -- 1024,262144,1048576

The example prints CSV:

size_bytes,base64_bytes,decoded_json_bytes,current_bytes,peak_bytes,delta_current_bytes
1024,1376,2060,5595136,5595136,290816
262144,349536,524300,6590464,6848512,0
Column Meaning
size_bytes Size of the ScVal::Bytes payload used to build the input.
base64_bytes Length of the base64 XDR input that is decoded.
decoded_json_bytes Length of the decoded JSON, proving the decode ran.
current_bytes Resident memory after decoding (or n/a).
peak_bytes Peak resident memory observed by the process (or n/a).
delta_current_bytes Current-memory growth across the decode (or n/a).

Methodology

  1. Build a ScVal::Bytes payload of the requested size and encode it to base64 XDR.
  2. Sample memory before the call.
  3. Decode with devkit_xdr::inspect_scval_base64.
  4. Sample memory after the call and serialise the result to JSON.

Each size is measured in the same process. Peak memory is monotonic, so later rows report the running maximum; use the current-memory column, or a fresh process, for isolated per-input figures.

Platform APIs and fallback

Platform Current Peak Source
Linux VmRSS VmHWM /proc/self/status
Windows WorkingSetSize PeakWorkingSetSize GetProcessMemoryInfo
Other n/a n/a documented fallback

On unsupported platforms the example still builds and runs and prints a note to stderr; memory columns are reported as n/a.

Limits

  • Figures are process-wide: they include the allocator, the toolchain runtime, and the decoded JSON value, not just XDR buffers.
  • Decoding to JSON expands bytes substantially (each byte becomes a decimal array element), so JSON size dominates the large-input measurements.
  • Numbers are representative, not exact: run in --release and compare runs on the same platform to detect regressions.
  • Measurement is not cross-platform normalised; compare Linux to Linux.