How does the cache stampede problem occur, and what strategies help prevent it in a high traffic PHP application?

A cache stampede occurs when a popular cached item expires and many concurrent requests simultaneously attempt to recompute and repopulate that same expensive cache entry at once, temporarily overwhelming the backend resource the cache was meant to protect, and common prevention strategies include using a locking mechanism so only one request recomputes the value while others wait or serve a slightly stale version, and staggering expiration times slightly so many related cache entries do not all expire at the exact same moment.

if ($lock = $cache->lock('rebuild_top_products', 10)) {
    $lock->get(function () use ($cache) {
        $products = $database->getTopProducts();
        $cache->put('top_products', $products, 3600);
    });
}