Magento indexers: real optimization and when to run them

Two modes:
- Update on save (small stores)
- Schedule (mid/enterprise stores)

In production, the recommended mode is `schedule`.
It prevents spikes on catalog requests.

Useful commands:
```
bin/magento indexer:show-mode
bin/magento indexer:set-mode schedule
```

If cron is misconfigured, your catalog becomes inconsistent.
Fix: review `cron_schedule` and monitor cron failures.

Typical symptom: products “appear late” or prices don’t update. That’s almost always cron.

Healthy ops:
- Cron every minute.
- Controlled retries.
- Alerts when `cron_schedule` fills with pending jobs.