Timings

Every row carries both.

execution_time — per run

rows[0].execution_time
// { stages: { PdfToImage: 412, PaddleTextRecognizer: 1830 }, total: 2244 }

One number per stage, covering every row that stage processed, and the same object on every row. This is what Python's ScaleDP records, and it keeps that meaning exactly. It cannot say how long page 7 took, because each stage's number covers every page at once.

Two stages of the same class disambiguate by position:

// { PdfToImage: 412, ImageDrawBoxes: 22, 'ImageDrawBoxes#3': 19 }

row_time — per row

for (const row of rows) console.log(row.page, row.row_time.total)
// 0 259
// 1 190
// 2 192

Time spent on that row alone. This is an addition to the Python model, not a change to it — the question "which page was slow" has no answer in execution_time, so the answer lives beside it.

Why the row totals do not sum to execution_time.total

The difference is stage.init(): downloading models and creating sessions, once for the whole run rather than per page. A pipeline whose first run downloads 333 MB of GLiNER weights will show a total far larger than the sum of its rows, and every subsequent run on a warm cache will show them close.

That is the number to watch when deciding whether to pre-warm a model.

Expanding stages split evenly

PdfToImage renders five pages in one call and returns five rows. Its elapsed time is divided by five and charged to each. No finer attribution exists from outside the stage, so a slow page 3 in a five-page render is invisible in row_time — it shows up in execution_time as a large PdfToImage.

Stages that do not expand attribute exactly.

Live progress

transform also takes an onStage callback, which fires as each stage completes rather than at the end:

await pipeline.transform(file, {
    onStage: (name, ms, rows) => console.log(`${name}: ${ms}ms over ${rows} rows`),
})

The worker client exposes the same callback, so a pipeline running off the main thread reports the same shape. See Workers.

Model downloads are a separate channel — configure({ onProgress }) — because they happen inside init() and are measured in bytes rather than stages.