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Expose Kartotherian version as an HTTP header to help in selective purges
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We have a few cases where cache-maps needed to be fully wiped to correct from bad tiles put in cache. We need better ways to do selective caching. A first proposal is to add an HTTP header identifying the version of kartotherian. This could be used if bad tiles are generated as a result of a bug in kartotherian to selectively wipe cache.

Event Timeline

Gehel created this task.Oct 28 2016, 7:22 PM
Restricted Application added a subscriber: Aklapper. · View Herald TranscriptOct 28 2016, 7:22 PM
Yurik added a comment.Oct 30 2016, 5:59 PM

I guess the only time this is useful is if we catch a problem within the 1 day cache period. If it is longer, like happened on Friday, all objects would already have the new version number, and we would need to purge objects based on other criteria, like the zoom.

MaxSem added a subscriber: MaxSem.Oct 30 2016, 6:28 PM

We also want to raise the cache lifetime...

Yurik added a comment.Oct 30 2016, 6:34 PM

@MaxSem that's a tricky one - because we don't have any good way to invalidate the tiles on update. It might actually make sense to reduce the cache time rather than increase it, so that Varnish would solve the hot load areas, but any kind of severe problems would self-solve themselves in hours, removing the need to purge cache. Cache's value is in optimizing very expensive calls, whereas Kartotherian has a relatively low tile generation cost (especially if we move to the client-side rendering).

Gehel added a comment.Oct 31 2016, 3:57 PM

I still hope that we will catch problems faster than what happened on Friday, at least some of the times. The goal should be to solve severe problems in minutes, not hours.

It looks to me like the implementation of this should be relatively simple, so it might make sense to do it "just in case". The larger issue of cache invalidation, we should try to find good natural keys to expose to the caching infrastructure (but I have no idea what those keys might be).

Yurik removed a project: Maps.Dec 15 2016, 4:37 AM
Abbe98 moved this task from Backlog to Done on the User-Abbe98 board.
Pnorman closed this task as Resolved.Jul 10 2018, 4:53 PM