amadan
Say what a cold thumbnail render actually costs
The budget comment asserted 40 was a reasonable bound without a number behind it. Measured on the seeded documents: a miss is ~1.9ms, so 36 documents render cold in 68ms and warm in 3.4ms, and the bound puts a cold landing page at roughly 75ms of layout — paid only after a restart. Recorded with the date, the machine and what would move it, because a bare number ages into a wrong fact.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_014JM96sbqzZLJgqYmAs4j5y
internal/docs/preview.go+10 −0
CI passed — run details
Intent
<task-notification> <task-id>b59vpf1mm</task-id> <tool-use-id>toolu_01StrSLqrXfpZ6wzzFMnVF7t</tool-use-id> <output-file>/home/paulca/.cache/tmp/claude-1001/-home-paulca-amadan-net-oficina-docs/e1e74ec8-0576-474e-8564-a71365101816/tasks/b59vpf1mm.output</output-file> <status>completed</status> <summary>Background command "Wait for remote CI to settle" completed (exit code 0)</summary> </task-notification>
Attributed to this commit: 16.0 g CO₂e (1985555 tokens). This is an attribution, not a measurement — usage counted from this commit's own marker forward to the next one on list-thumbnails, never backward from it. A turn that produced more than one commit books all of its tokens to the last one, and a concurrent session on this branch can add to the same figure. Some of it was priced using the shared default rate, because no model-specific factor row exists yet for at least one model involved. The Carbon view has the repo total, which is never derived from this attribution.
diff --git a/internal/docs/preview.go b/internal/docs/preview.go| index 23b8823..597d415 100644 |
| --- a/internal/docs/preview.go |
| +++ b/internal/docs/preview.go |
| @@ -221,6 +221,16 @@ func (h *handlers) thumbnail(ctx context.Context, doc *Document) []previewBar { |
| // is written. With one, a cold cache costs a bounded amount and warms |
| // over the next few renders; a warm cache never reaches the bound at |
| // all, because a hit does not spend from it. |
| +// |
| +// Measured rather than guessed, on the seeded sample documents |
| +// (2026-09-02, this machine): a miss is about 1.9ms — replay through |
| +// the snapshot and its tail, then one page of layout — and a hit is |
| +// far under that. 36 documents rendered cold in 68ms and warm in |
| +// 3.4ms. So this bound puts a cold landing page at roughly 75ms of |
| +// layout, which is a page load rather than a stall, and it is only |
| +// ever paid after a restart. Re-measure before raising it; the number |
| +// that matters is the miss, and it grows with a document's update log |
| +// between snapshots. |
| const thumbnailBudget = 40 |
| // thumbnailer returns the function the row builders call for each |