Domain.DLS: document that creating a high number of DLS keys may not be a good idea

[gasche]

The current implementation of Domain.DLS was made with "singleton states" in mind: each library/module would have at most a handful of DLS keys to store various bits of global state. It provides fairly efficient access, but the memory representation is wasteful when there are many keys

I believe that we should document this limitation / intent, so that users avoid using Domain.DLS in unsuitable scenarios, for example "each instance of my data-structure will store per-domain information in its own DLS key, I can have tens of thousands of them". (See for example the discussion in #11625; @lyrm confirmed in a discussion that they had to give up on Domain.DLS.)

(I guess this is a follow-up on the question of basic documentation for Domain.DLS: #11905.)

[github-actions]

This issue has been open one year with no activity. Consequently, it is being marked with the "stale" label. What this means is that the issue will be automatically closed in 30 days unless more comments are added or the "stale" label is removed. Comments that provide new information on the issue are especially welcome: is it still reproducible? did it appear in other contexts? how critical is it? etc.

[Octachron]

It is probably best to revisit (and close) the issue once we switch to TLS.