Saturday afternoon, a bike shop. At ten past four the last blue cargo bike is wheeled out of the door by a customer who paid at the counter. At twenty to ten the same evening, the webshop sells that same bike to someone two towns away. On Monday morning, somebody has to make an apologetic phone call.
The owner believed the till and the webshop were “linked”. They were. The link ran every night at three. Nothing was broken. Nobody had ever decided how out of date the stock figures were allowed to be.
Three speeds, in plain words
Once a night
A scheduled job copies everything across at a quiet hour, usually between two and five in the morning. It is the cheapest and most predictable option, and it is easy to run again if something goes wrong. The price is that any number can be up to a day old.
Every few minutes
One system asks the other “anything new since last time?” every five, ten or fifteen minutes. This is called polling, and most links in small businesses live here for good reason: near-current data without much added complexity.
The moment it happens
The source system pushes a message the second something changes. The technical word is a webhook: a short message system A sends to system B as soon as it has news, instead of waiting to be asked. Fastest, and the most moving parts.
The question that picks the speed
Not “how fast can this go”. Ask instead: what does a wrong answer cost during the gap?
Finish this sentence for each link: “If this number is an hour old, the worst that happens is ___.”
For stock of one-off or expensive items, the answer is an order you have to cancel, an apologetic call, sometimes a refund and an unhappy review. That means minutes. For purchase invoices going into the bookkeeping, nobody looks until the accountant does, so nightly is fine and weekly is often fine too. For an online booking arriving while the phone rings about the same slot, it has to be instant, or you are double-booked.
Once you write that sentence down, the speed usually chooses itself. And mixed speeds inside one business are completely normal: stock every five minutes, prices and product texts nightly, invoices nightly, appointments instantly.
Faster is not free
Some platforms charge per call, or cap how often you may ask — a rate limit, which is simply the supplier’s rule about how many requests per minute they will accept. Instant links need a queue and a retry for the moments when the receiving system is briefly unavailable; a nightly job you can just run again tomorrow. And the more often something runs, the more small error messages it produces, which only helps if someone actually reads them.
In our experience the regret is rarely “we should have made it faster”. It is usually “we made everything instant and now nobody knows which system is right”.
Decide who wins, and who gets told
Two agreements make a link boring in the best sense.
First, decide per field which system is the master. Price lives in the webshop, stock lives in the till, the customer address lives in the diary or the customer system. Without that, edits ping-pong between systems and the price you corrected is back to the old figure by morning.
Second, links fail silently. Nothing turns red. Both systems carry on working and the numbers drift slowly apart. So ask for a visible line — “last successful sync at …” — somewhere you actually look, plus an alert to a named person when that time is older than agreed. A link nobody watches is a link you hear about from a customer.
What to do this week
- Pick your two most important links and finish the sentence for both: “if this number is an hour old, what happens is …”.
- Ask your supplier or installer two things: how often does it run now, and where can I see the last successful run?
- Put one name against each link: the person who gets told when it stalls.
If you would like to think out loud about which of your systems should be talking faster — and which can happily sleep until three in the morning — that is the kind of conversation we enjoy at ITSysPro, with nothing required afterwards.