How Fast Should Your POS Sync?

A customer checks your website: “Is the last pair of running shoes in size 10 available at the downtown store?” The site says yes. They drive 30 minutes across town. When they arrive, the shelf is empty.

“Sorry, someone must have bought it this morning. Our inventory updates every few hours.”

This scenario plays out in retail every day. It wastes customers’ time. It damages trust. And it’s entirely preventable—if your inventory actually syncs in real time.

The batch sync trap

Most POS systems sync inventory on a schedule. Every 15 minutes. Every 30 minutes. Some systems sync hourly or even once per shift.

The logic seems reasonable. Constant syncing would hammer the servers. Batch updates are more efficient. And for most products, a 15-minute delay doesn’t matter.

But when a customer is deciding whether to drive to your store based on inventory data? That delay is the difference between a sale and a frustrated ex-customer.

The problem is that inventory changes cluster around events—flash sales, social media mentions, seasonal rushes. These are exactly the moments when accurate cross-channel visibility matters most.

Consider a product that goes viral on TikTok. For the next few hours, it’s selling both online and in-store at unprecedented rates. A 15-minute sync interval means your website shows inventory that’s 15 minutes behind reality. Customers see “in stock,” make the trip, and find empty shelves.

Where stale inventory actually hurts

The real cost of slow sync isn’t at the register—it’s in the decisions customers make before they ever walk through your door.

The wasted trip: A customer checks online, sees “3 in stock” at your location, drives across town, and finds zero. They’re not just disappointed—they’re angry. They wasted their time because your data was wrong.

The missed visit: A customer checks online, sees “out of stock,” and doesn’t bother coming. But you actually have five on the shelf. That’s a lost sale you’ll never know about.

The cross-store letdown: A customer at Store A asks about an item. Staff checks inventory at Store B: “Yes, they have two!” Customer drives to Store B. They have zero. Now you’ve disappointed them twice.

The online oversell: Two online orders come in for your last unit. One gets fulfilled, one gets cancelled with an apology email. That cancelled customer isn’t coming back.

What “real-time” actually means

True real-time sync is technically impossible. Data has to travel from the source of truth to your device, and that takes time—even if it’s just milliseconds.

When people talk about real-time sync, they mean “fast enough that humans don’t notice the delay.” For retail, this means inventory changes should propagate in seconds, not minutes.

There are three main approaches to achieving this speed:

Webhooks: The source of truth notifies your system when something changes. Efficient and fast, but depends on reliable delivery. If a webhook fails, you miss the update until the next poll.

Push notifications: Similar to webhooks, but designed for mobile devices. The server can wake up your app to deliver updates, even if the app isn’t actively running.

Polling: Your POS checks for updates on a regular interval. Simple but inefficient. You’re constantly asking “anything new?” even when nothing has changed.

A robust sync architecture uses all three. Webhooks provide the primary update mechanism. Push notifications wake the mobile app for immediate processing. Polling serves as a safety net, catching anything the other two missed.

The three-layer approach

Here’s how a properly designed sync system works:

Layer 1: Webhooks for speed

When a product changes in your e-commerce platform—a sale, an inventory adjustment, a price update—the platform sends a webhook to your POS backend. This happens within seconds of the change.

The backend receives the webhook, validates it, and stores a change notification. It doesn’t try to push the full updated product to every device immediately. That would be too slow and resource-intensive.

Instead, it records: “Product X changed at timestamp Y. Devices should fetch the latest.”

Layer 2: Push for immediacy

After logging the change, the backend sends a push notification to all active POS devices. This notification is lightweight—just a signal that says “sync now.”

The device receives the push, wakes up, and queries the backend: “What changed since my last sync?” The backend returns a list of product IDs. The device fetches just those products and updates its local database.

From webhook to device update: typically under 5 seconds.

Layer 3: Polling for reliability

Push notifications aren’t 100% reliable. Sometimes they’re delayed. Sometimes they’re dropped. Sometimes the device is in a state where it can’t receive them.

So in the background, the device also polls for changes on a regular interval—say, every 2 minutes. This catches anything the push notifications missed.

If a push came through, the poll finds nothing new and does minimal work. If a push was missed, the poll catches the change within 2 minutes. Either way, you’re covered.

The real cost of stale data

Let’s quantify the impact. Say you’re a mid-size retailer with 10 stores, a busy online channel, and “check store availability” on your website.

With 30-minute sync intervals, every inventory number on your site could be up to 30 minutes old. During peak hours, this might mean 5-10 products per store showing incorrect availability at any given time.

Now consider the customer journeys:

• 50 customers per day check online before visiting
• 20% see inaccurate inventory (10 customers)
• Half make wasted trips, half skip visits they should have made
• Average order value: $75

That’s 5 wasted trips (angry customers who won’t return) plus 5 missed visits (lost sales). At $75 per order, you’re losing $375 per day in missed revenue—plus the incalculable cost of customers who write you off after a wasted trip.

Over a year: $136,000 in lost sales. And that’s conservative.

With sub-10-second sync, your website shows accurate inventory. Customers trust the data. They make trips when items are actually there. They don’t make trips when they’re not. Everyone’s time is respected.

Implementation matters

Fast sync is technically achievable, but many POS vendors don’t invest in it because it’s hard to do right.

You need infrastructure that can handle high webhook volumes without dropping messages. You need a push notification system that works reliably across iOS and Android. You need a local database on each device that can efficiently update specific products without re-downloading the entire catalog.

You also need to handle the edge cases. What if a webhook arrives out of order? What if a product update conflicts with an in-progress transaction? What if the device is offline when a push arrives?

These aren’t insurmountable challenges, but they require careful engineering and thorough testing.

What to look for

When evaluating a POS system’s sync capabilities, ask:

1. How quickly does an in-store sale update your online “check store availability” feature? (Target: under 10 seconds)
2. If I sell the last item in Store A, how fast does Store B know about it?
3. What mechanisms trigger sync? (Look for webhooks + push + polling)
4. How does the system handle missed updates? (Should have automatic recovery)
5. How do you monitor sync health? (Should have visibility into sync status)

The answers reveal whether the vendor understands the problem or is just checking a feature box.

Fast sync isn’t glamorous. It doesn’t make for exciting demos. But it’s the invisible foundation that makes omnichannel retail actually work—accurate inventory across every touchpoint, so customers can trust what they see and staff can confidently answer “do you have this?”

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Kynetik POS syncs inventory in under 5 seconds—so your website, your stores, and your staff all see the same accurate data. See how offline mode works or explore all features.