TTL-cache CMS (WordPress) reads — removes the ~3s per-request floor

[anuveyatsu]

Follow-up to #256. That PR cached CKAN's organization_list and took the ODDK home page from 11.7s to ~2.4s in production — but ~2.4s is still slow, and the remaining time is not CKAN.

The measurement

The ODDK theme awaits a CMS call in global app.use middleware on every non-static request, so every page pays a WordPress round trip before its own work starts:

path	time	notes
/static/js/home_page.js	0.44s	express.static, mounted before the middleware
/robots.txt	2.9s	trivial route, still pays the middleware
any 404	13.3s	middleware + 404 render

A ~3s floor on anything routed through the app. /robots.txt returns a few hundred bytes and touches no data source, so that time is essentially all WordPress.

The specific call is CmsModel.getListOfPosts({ type: 'page' }), used to build the navbar.

What this does

Every method on CmsModel is a read of slow-changing blog content, so this caches them using the same TtlCache already shipped for CKAN actions in #256:

• single-flight — concurrent misses collapse into one upstream call rather than each hitting WordPress
• stale-on-error — a WordPress blip serves the last good value. This is a real improvement on today's behaviour: the theme catches CMS errors and falls back to [], so a WP outage currently silently empties the navbar
• opt-in via CMS_CACHE_TTL (default 0), so portals that have not asked for it are unaffected

Cached: getListOfPostsWithMeta (which getListOfPosts and getListOfPages both route through), getPost, getCategories, getSiteInfo.

Two correctness fixes that fall out

Keying a cache on the query exposed argument mutation:

• getListOfPostsWithMeta did Object.assign(query, this.baseQuery) — mutating the caller's object and writing status into it. A caller reusing an object would therefore produce a different cache key on the second call. Now Object.assign({}, query, ...).
• getListOfPages likewise set query.type = 'page' on the caller's object.

Both are covered by tests asserting the passed object is untouched.

Design note

The cache instance is injectable so tests get isolation; at runtime every model shares one, which is the point — plugins/wp and plugins/ckan_pages each construct their own CmsModel and should not each hold a private copy of the same blog content. (The first draft of the tests failed precisely because they assumed isolation from a shared cache — worth knowing if you add more.)

Testing

tests/plugins/wp-cache.test.js — 8 tests, all passing: the middleware call is cached, distinct queries stay separate, getSiteInfo/getCategories cached, caching is a no-op at TTL 0, concurrent reads collapse to one call, a failed refresh serves stale, and neither list method mutates its argument.

tests/plugins/wp.test.js has 4 pre-existing failures on this branch — verified identical with and without this commit by stashing it, so not introduced here.

Rollout

Nothing changes until a portal sets CMS_CACHE_TTL. For ODDK I would suggest 300s: the navbar and featured posts are editorial content where a few minutes of staleness is unremarkable, and even 300s removes essentially every per-request call under real traffic.

Expected effect on ODDK, based on the numbers above: the ~3s floor collapses, so the cached home page should drop from ~2.4s to well under a second, and /robots.txt and other light routes become near-instant.

Worth noting separately: the 13.3s 404 path is not addressed here and looks like its own liability.

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