Class CombineUnsupportedMemo

java.lang.Object
org.frontcache.include.combine.CombineUnsupportedMemo
public class CombineUnsupportedMemo extends Object
Remembers, per batch group, that the origin does not implement combining. See docs/archive/combine-reduce-proposal.md section 9.1. Without it, an origin that has the combine attribute in its markup but not the handler behind it pays one wasted request per group on every single page view, forever. With it, that cost is one probe per group per TTL, and a rolling origin deploy converges within one TTL rather than staying degraded until someone notices.

Why a TTL and not a permanent flag

The answer changes. An origin gains combine support mid-deploy, and half the fleet answers one way while the other half answers the other. A permanent flag would pin the edge to whichever node it happened to ask first.

Bounding it

The key space is endpoints named in the origin's own markup, so it is small and not attacker-chosen - but it is written from include threads and never otherwise read, so an entry for a group that stops appearing would live forever. mark(String, long) sweeps expired entries once the map grows past SWEEP_THRESHOLD, which is cheap because the sweep only ever runs on the already-slow unsupported path.

  • Constructor Details

    • CombineUnsupportedMemo

      public CombineUnsupportedMemo()

  • Method Details

    • isUnsupported

      public boolean isUnsupported(String groupKey)
      Is combining known to be unsupported for this group right now?

    • mark

      public void mark(String groupKey, long ttlMillis)
      Record that this group's origin did not understand a combined request.

    • clear

      public void clear()
      Forget everything - for tests, and for a config reload that changes the TTL.

    • size

      public int size()