[POC] EZP-29659: As a v2 User I want support for InMemory SPI cache

[andrerom]

Question	Answer
JIRA issue	EZP-29659
New feature	yes
Target version	master
BC breaks	no
Tests pass	yes
Doc needed	maybe on trouble shooting section, or places explaining caching

As a System Administrator & Developer I'd like SPI cache to re-introduce support for in-memory cache.

However unlike 1.x it must be:

• limited to not eat up all available memory
• time limited so data does not risk becoming stale

Thus allowing it to be used also on long running command line scripts without need to document special ways to run them.

As it it to be limited memory wise it should also be:

• When hitting limits and in need of making space: prefer to use available space for non content cache (meta data) which is frequently needed by the system, and in-frequently changed

---

Brings cache lookups down to the following on clean install in combination with ezsystems/ezplatform-admin-ui#633 & #2444 compared to clean master/2.3-beta1:

• Front: from 74 / 184 to 22 / 59 cache calls => 3x less cache calls
• Admin Dashboard: from 478 / 1452 to 52 / 156 cache calls => 9x less cache calls
• Admin Content structure: from 484 / 1421 to 70 / 204 cache calls => 7x less cache calls

This will especially benefit users on clusters where (Redis) cache server is on different host (latency).

TODO:

• Implement feature / fix a bug.
• Implement tests.
• Fix new code according to Coding Standards ($ composer fix-cs).
• Ask for Code Review.

[andrerom]

Passing ✅ (Travis passing on aeffe2e).

So calling for review here.

EDIT: Will look into how this can be done in external Bundle instead, and cleanup some of the concepts while at it.

[andrerom]

Closing, as we will take another direction on this one.