experimental support for query batching

[garypen]

Things needing attention

• Configuration to match the design
• Decide if cloning parts is acceptable (in review) It isn't, so not cloned but re-built.
• Decide if cloning context for each SupergraphRequest is acceptable (in review)
• Should we do special handling if @defer or subscription detected in batch?
• Metrics
• Find someone happy to test from an appropriately configured Apollo Client and verify it works
• Modify Apollo telemetry to create separate root traces for each batch entry

Fixes #126

---

Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• Changes are compatible¹
• Documentation² completed
• Performance impact assessed and acceptable
• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

Exceptions

Manual testing was performed with curl and apollo client

Notes

Footnotes

1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩

2. Configuration is an important part of many changes. Where applicable please try to document configuration examples. ↩

3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩

[router-perf]

CI performance tests

• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events - Stress test for events with a lot of users and deduplication ENABLED
• large-request - Stress test with a 1 MB request payload
• step - Basic stress test that steps up the number of users over time
• xlarge-request - Stress test with 10 MB request payload
• reload - Reload test over a long period of time at a constant rate of users
• no-graphos - Basic stress test, no GraphOS.
• xxlarge-request - Stress test with 100 MB request payload
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• const - Basic stress test that runs with a constant number of users

[BrynCooke]

There are a couple of things that need to be verified:

1. What to traces look like in studio?
2. Are we OK with the metrics being generated and sent to Apollo e.g. op counts?