Issue description @todo.

See discussion at #2217371: Expose cache tags to reverse proxies: X-Drupal-Cache-Tags header (by just slightly changing an existing header).

Comments

drifter’s picture

drifter commented

Sounds good, but couldn't the cache tag header potentially grow very large? Maybe we should use a hash of the tags?

znerol’s picture

znerol commented

In the other discussion it has been pointed out already that cache-tags alone are not enough to generate an ETag. I.e. when content is updated, it is perfectly possible that the list of tags remain the same. In order to generate an ETag, the invalidation counts (or checksum) needs to be included also #2217371-9: Expose cache tags to reverse proxies: X-Drupal-Cache-Tags header (by just slightly changing an existing header).

However, the invalidation count / checksum is an implementation detail. For example there is a PoC of the Redis cache backend (#2233413: Port Redis to Drupal 8), which is solely based on server-side set-operations for invalidation.

I feel that making the checksum mandatory for cache backend implementations in order to unify ETag and X-Drupal-Cache-Tags would make things more complex.

Let's follow common practice and use a hash for the ETag and continue with #2259489: Leverage symfony for HTTP revalidation.

catch’s picture

catch
he/him
Primary language English
commented

Not sure it has to be mandatory, we could add an additional interface for the checksum and decide on the Etag strategy based on that.

Posted in the other issue why I think using a content hash is going to be overly precise.

wim leers’s picture

wim leers
Location Ghent 🇧🇪🇪🇺
commented

Posted in the other issue why I think using a content hash is going to be overly precise.

For this, see #2259489-5: Leverage symfony for HTTP revalidation.

fabianx’s picture

fabianx commented
Title: Consider using cache tags for the ETag » Consider using cache tags (and cache contexts) for the ETag
Related issues: +#2429287: [meta] Finalize the cache contexts API & DX/usage, enable a leap forward in performance

We do have a checksum interface now, which we could use for this.

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wim leers’s picture

wim leers
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commented
Category: Task » Feature request

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