proxy: reduce number of concurrent connections

[khanova]

Problem

Usually, the connection itself is quite fast (bellow 10ms for p999: https://neonprod.grafana.net/goto/aOyn8vYIg?orgId=1).

It doesn't make a lot of sense to wait for a lot of time for the lock, if it takes a lot of time to acquire it, probably, something goes wrong.

We also spawn a lot of retries, but they are not super helpful (0 means that it was connected successfully, 1, most probably, that it was re-request of the compute node address https://neonprod.grafana.net/goto/J_8VQvLIR?orgId=1). Let's try to keep a small number of retries.

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[skyzh]

LGTM, could you please remove the changes to Postgres? thanks!

[khanova]

LGTM, could you please remove the changes to Postgres? thanks!

Yep, it was accidental, forgot to do git submodule update

[github-actions]

2928 tests run: 2807 passed, 0 failed, 121 skipped (full report)

---

Flaky tests (3)

Postgres 16

• test_vm_bit_clear_on_heap_lock: debug

Postgres 15

• test_partial_evict_tenant[relative_spare]: release
• test_delete_tenant_exercise_crash_safety_failpoints[real_s3-tenant-delete-before-remove-deleted-mark-False-Check.RETRY_WITH_RESTART]: release

Code coverage* (full report)

• functions: 31.4% (6237 of 19865 functions)
• lines: 47.1% (46739 of 99266 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
7734e90 at 2024-05-06T19:10:57.593Z :recycle:}