Slow WordPress Memcached Object Cache with App Engine

I thought it would be a good idea to add a persistent WordPress object cache to this blog, to reduce page load times and increase resilience to spikes in traffic. So I added the WordPress Memcached Object Cache drop-in (AKA wp-memcached), and enabled the legacy App Engine Memcache API. However, adding the Memcache object cache increased page load times by 10s or more! Looking into it further, while the App Engine diagnostics reported a high (90%+) cache hit ratio, the drop-in was getting 0% cache hits. The drop-in was adding keys to the cache only for them not to be found in subsequent reads. There were also hundreds of SQL queries that did not occur with WordPress’s default (request-scoped) object cache.

With some additional debugging and perusing of the source code of PECL’s official Memcached module, the App Engine SDK, and the wp-memcached code, I figured out what was going on and how to fix it.

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WordPress GCS plugin broken thumbnails

The GCS plugin for WordPress lets you use Google Cloud Storage for WordPress’s media and other uploads. This is required on stateless environments like App Engine, where there’s no persistent writable filesystem to store uploads.

However, image thumbnailing and rescaling is broken by default when using the plugin, so while you can upload an image, the thumbnails that usually get automatically generated will never appear in the GCS bucket. So if you add high-resolution images to a post, load times will be massively increased, which is a particularly bad experience for low-resolution mobile devices.

I raised a WordPress ticket and attached a patch that fixes the issue. The patch needs to be applied to the core WordPress installation (rather than being a plugin), so may not be an option for WordPress admins that are using multisite hosting. I think a plugin-based fix would be possible (one that replaced the default image editor with a fixed one), but would involve duplicating a bunch of code from core WordPress.

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Costs of running WordPress using Google Cloud

Self-hosting a WordPress blog gives you the ultimate control over your website and database. However, you may want to utilize cloud IaaS or PaaS offerings to provide the lower-level infrastructure (machines, network, or even the webserver). Google provides resources for running WordPress on Google Cloud Platform, but there is very little upfront information about the costs of the different options. GCP’s complex pricing (with Always Free quota and sustained-use discounts), along with some hidden costs in some configurations, made it difficult to predict the final monthly cost.

Knowing the price of hosting a WordPress blog on Google Cloud Platform is important, because small-time bloggers are going to be comparing these options against options that cost less than $5 a month or even nothing (e.g. the personal and free plans, or even jumping blogging platform completely to Medium or similar).

I’ve recently been through the exercise of measuring the costs of running WordPress on GCP with this blog. The summary of the dominant costs is:

Configuration Breakdown Minimum Cost (USD) per month
App Engine + Cloud SQL
f1-micro App Engine instance ($0) +
db-f1-micro MySQL Cloud SQL instance ($11.50) +
10GB-months low-cost storage ($1.35)
App Engine + GCE + VPC
f1-micro App Engine instance ($0) +
f1-micro GCE instance ($5.42) +
2x f1-micro VPC Connector ($10.84) + PD ($1.45)
App Engine + exposed GCE
1 f1-micro App Engine instance ($0) +
f1-micro GCE instance ($5.42) +
PD ($1.45)
Just GCE
f1-micro GCE instance ($5.42) + PD ($1.45) $6.87
free App Engine + free GCE
f1-micro App Engine instance ($0) +
f1-micro Always Free GCE instance ($0)
almost $0


  • $0 prices assume you’re not already consuming your GCP “Always Free” quota.
  • There are some additional costs not included in the table (storage and network), but they were < $0.10/month for me.
  • I’m not counting Google’s $300 “free trial”, which only lasts 12 months.

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