compute_ctl: Use 'fast' shutdown for Postgres termination

[ololobus]

Problem

We currently use 'immediate' mode in the most commonly used shutdown path, when the control plane calls a compute_ctl API to terminate Postgres inside compute without waiting for the actual pod / VM termination. Yet, 'immediate' shutdown doesn't create a shutdown checkpoint and ROs have bad times figuring out the list of running xacts during next start.

Summary of changes

Use 'fast' mode, which creates a shutdown checkpoint that is important for ROs to get a list of running xacts faster instead of going through the CLOG. On the control plane side, we poll this compute_ctl termination API for 10s, it should be enough as we don't really write any data at checkpoint time. If it times out, we anyway switch to the slow k8s-based termination.

See https://www.postgresql.org/docs/current/server-shutdown.html for the list of modes and signals.

The default VM shutdown hook already uses fast mode, see [1]

[1]

neon/vm-image-spec.yaml

Lines 30 to 31 in c9fd8d7

	shutdownHook: |
	su -p postgres --session-command '/usr/local/bin/pg_ctl stop -D /var/db/postgres/compute/pgdata -m fast --wait -t 10'

Related to #6211

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[github-actions]

3067 tests run: 2952 passed, 0 failed, 115 skipped (full report)

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Flaky tests (4)

Postgres 14

• test_pg_regress[None]: debug
• test_tenant_creation_fails: debug
• test_pageserver_lsn_wait_error_start: release
• test_pageserver_lsn_wait_error_safekeeper_stop: debug

Code coverage* (full report)

• functions: 32.6% (6933 of 21275 functions)
• lines: 50.0% (54487 of 108970 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
a245fe5 at 2024-07-08T12:18:29.254Z :recycle:}