When it runs

Every run of the Health Data Relay transform is the same job, whatever started it: work out which days changed, read them in full from Health, and send them to the pipeline’s destination. A template pipeline reads the range you set under How much instead, such as since the last run, or the last 7 days.

What starts a run

Each pipeline has its own trigger, set when you add or edit it.

Manual, the default: only tapping Run or Run now. With every pipeline manual, Health Data Relay doesn’t ask iOS to wake it at all.

A schedule: every so many minutes, hours, days or weeks after its last run, or every so many seconds while the app is open. It runs at the first chance once due: when iOS gives the app background time, or straight away if the app is open. A failed delivery retries when its wait ends, without waiting for the next interval.

At a set time: a time of day, on the days you choose. iOS decides when background work happens, so this is the earliest it can run.

When Health changes: any of these.

Health records something new. Health Data Relay asks iOS to wake it when data arrives: hourly at most for most types, daily for sleep, stand hours and mindful minutes. Many types arrive together, so wakes within five minutes of the last run are skipped; their changes go with the next one.
Every morning. The app asks iOS for a catch-up around 06:30.
Opening the app, when the last successful run is more than an hour old.

iOS decides exactly when background work runs. It gives more time to apps you use, and less in Low Power Mode. A run started in the background stops starting new work after about 25 seconds, and the next one carries on.

Your iPhone must have been unlocked

iOS encrypts Health data while the phone is locked, and no app can read it. Changes recorded overnight (sleep, for one) are sent after you first unlock the phone in the morning. If a run comes while the data is locked, its card says so and the next run picks the days up; nothing is lost.

Which days a run sends

This is for the Health Data Relay transform, and templates set to Days that changed.

Days with new data. Health Data Relay tracks every type with a bookmark, so it knows exactly which days gained samples since the last run, including a late watch sync for last Tuesday. A pipeline left unused for months still gets the days that changed while it was idle.
Today and yesterday, every time.
The last 35 days, once a week. iOS doesn’t say which day a deleted sample belonged to, so a weekly sweep re-sends the recent past and deletions reach your destinations within a week.

Each day is sent whole: every type, every source, every sample the phone has for it. A receiver can replace what it held for that day, so edits and deletions on the phone land too. See Behaviour for the exact rules.

Re-send on demand

Open a pipeline and tap Re-send recent days to send the last 7, 14 or 35 days again. Use it after fixing a receiver, or after deleting something in Health that you want gone everywhere now rather than at the next weekly sweep.

When a destination fails

Health Data Relay keeps each batch on disk until the destination accepts it, and retries with growing gaps (1 minute, doubling, up to 6 hours). A destination that refuses the token stops until you fix it; see Troubleshooting. Other destinations carry on regardless.