Add temporary cache in lib/acl-checker.js

[michielbdejong]

No description provided.

[michielbdejong]

Cache ACL documents and profiles of owners therein for 5 minutes.
Brings the test I did in #1443 (comment) down from 1 minute to 1 second.

[angelo-v]

That means, if the cache is not hit, it still takes 5 minutes?

[michielbdejong]

That means, if the cache is not hit, it still takes 5 minutes?

No, if the cache is not hit, it will still fetch the document only once instead of 18 times, so it will still be something like 18 times faster.
If the cache is hit it will be up to 1000 times faster, depending on the ratio between CPU and network speed.

[timbl]

Looks good to me. Lots of other cache strategies are possible, but let's put this in now to get over the performance problem we have now.
Not sure also what good coding practice is for where to declare this server-wide variable.

[michielbdejong]

where to declare this server-wide variable.

Yes, good question. It doesn't need to be a singleton though, it doesn't matter if it exists twice, once per execution thread, or even once per http request, just that the less unique it is, the less effective it is. Having it as an in-memory global in the lib/acl-checker.js file feels ok to me now, we can always move it around if our insights change.

Looks good to me. Lots of other cache strategies are possible, but let's put this in now to get over the performance problem we have now.

Thanks!