Document PostgreSQL fallback host connection strings (#25461)

[deepujain]

Title: Document PostgreSQL fallback host connection strings (#25461)

Summary

Document where Airflow users should look when they need PostgreSQL metadata database URLs with multiple fallback hosts. Airflow delegates this URL handling to SQLAlchemy's PostgreSQL dialects, so the setup guidance now points users to SQLAlchemy's current multiple-host syntax instead of leaving them to infer it from the generic PostgreSQL section.

Changes

• airflow-core/docs/howto/set-up-database.rst -- add a PostgreSQL note that links to SQLAlchemy's documented multiple fallback host URL format.

Evidence it works

• This is a docs-only change that points users to SQLAlchemy's PostgreSQL multiple-host URL syntax, which is the layer Airflow delegates database URL parsing to.
• The reviewer suggestion to avoid psycopg2-specific wording is already applied, so the note now refers to PostgreSQL drivers generally.

Test plan

• git diff --check
• prek run --stage pre-commit --files airflow-core/docs/howto/set-up-database.rst
• CI passes

Was generative AI tooling used to co-author this PR?

• Yes (OpenAI Codex)

Generated-by: OpenAI Codex following the guidelines

Fixes #25461

[shahar1]

Overall LGTM.
Edit: had to take back my approval due to lack of AI attribution, see below.

@Dev-iL - could you please take a second look? (btw, it seems that other parts of the doc might be outdated as they refer to SQL 1.4 docs, but that could be handled in a separate PR)

Created #69164 for tracking.

[Dev-iL]

One suggestion...

[shahar1]

@deepujain please note that you (or your operator) should include AI attribution in the PR as we state in the AI guidelines.
This PR, as well as others, are blocked from being merged until this is corrected.
Please be warned that creating additional PRs except for the 10 you've already created (listed below) without addressing the above might cause in a permanent block from Apache organization on GitHub.

List of PRs:

• #69161
• #69159
• #69158
• #69157
• #69156
• #69154
• #69153
• #69152
• #69151
• #25461

[shahar1]

See above

AI attribution addressed

[deepujain]

Applied the suggestion to avoid making the PostgreSQL fallback-host note specific to psycopg2. The note now refers to PostgreSQL drivers generally while keeping the SQLAlchemy multiple-host URL reference.

Validated locally with git diff --check and prek run --stage pre-commit --files airflow-core/docs/howto/set-up-database.rst.

---

Drafted-by: OpenAI Codex (no human review before posting)

[potiuk]

@deepujain — There are 1 unresolved review thread(s) on this PR, and you have engaged with each one (post-review commits and/or in-thread replies). Could you confirm whether you believe the feedback is fully addressed and the PR is ready for maintainer review confirmation?

If yes, reply here (a short "yes / ready" is fine) and an Apache Airflow maintainer will pick the PR up from the review queue on the next sweep.

If you are still working on a thread, please reply with what is outstanding so the threads stay unresolved on purpose.

---

Note: This comment was drafted by an AI-assisted triage tool and may contain mistakes. Once you have addressed the points above, an Apache Airflow maintainer — a real person — will take the next look at your PR. We use this two-stage triage process so that our maintainers' limited time is spent where it matters most: the conversation with you.

[deepujain]

Yes, ready for maintainer review. The remaining unresolved thread is outdated after the follow-up change: the note now avoids making the fallback-host behavior specific to psycopg2 and refers to PostgreSQL drivers generally, while keeping the SQLAlchemy multiple-host URL reference. No further changes are pending from my side.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased this branch onto current main. The scoped Airflow pre-commit check for airflow-core/docs/howto/set-up-database.rst passed, along with git diff --check. No content changes beyond the rebase.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main so the branch includes the latest dependency and CI fixes. The scoped pre-commit check for airflow-core/docs/howto/set-up-database.rst and git diff --check both pass; there are no content changes.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main at e24f5294. The scoped pre-commit check for airflow-core/docs/howto/set-up-database.rst and git diff --check both pass; no content changes were needed.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main at f9b72d8e. The scoped pre-commit check for airflow-core/docs/howto/set-up-database.rst and git diff --check pass; no content changes were needed.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main at 9ec73bab. The scoped pre-commit check for airflow-core/docs/howto/set-up-database.rst and git diff --check pass; no content changes were needed.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased this branch onto current main (4d3a247f). The scoped pre-commit check for airflow-core/docs/howto/set-up-database.rst and git diff --check both pass; no content changes were needed.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Resolved the two outdated review threads whose requested changes were already incorporated, then rebased onto current main and force-pushed signed head ab116597.

The file-scoped pre-commit suite for airflow-core/docs/howto/set-up-database.rst and git diff --check pass locally. GitHub CI is rerunning for the rebased head.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main and force-pushed signed head c2c8f5f0. The file-scoped pre-commit suite for airflow-core/docs/howto/set-up-database.rst and git diff --check pass locally.

The previous head finished with no failed checks. GitHub CI is rerunning for this head.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main and force-pushed signed head 9c0225ce. The file-scoped pre-commit suite for airflow-core/docs/howto/set-up-database.rst and git diff --check pass locally.

The previous head finished with no failed checks. GitHub CI is rerunning for this head.

---

Drafted-by: OpenAI Codex (no human review before posting)

[deepujain]

Rebased onto current main and force-pushed signed head b19628a4. The file-scoped pre-commit suite for airflow-core/docs/howto/set-up-database.rst and git diff --check pass locally.

The previous head finished with no failed checks. GitHub CI is rerunning for this head.

---

Drafted-by: OpenAI Codex (no human review before posting)