Remember last written LSN when it is first requested

[knizhnik]

Problem

See https://neondb.slack.com/archives/C03QLRH7PPD/p1712529369520409

In case of statements CREATE TABLE AS SELECT... or INSERT FROM SELECT... we are fetching data from source table and storing it in destination table. It cause problems with prefetch last-written-lsn is known for the pages of source table
(which for example happens after compute restart). In this case we get get global value of last-written-lsn which is changed frequently as far as we are writing pages of destination table. As a result request-isn for the prefetch and request-let when this page is actually needed are different and we got exported prefetch request. So it actually disarms prefetch.

Summary of changes

Proposed simple patch stores last-written LSN for the page when it is not found. So next time we will request last-written LSN for this page, we will get the same value (certainly if the page was not changed).

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

[github-actions]

2754 tests run: 2636 passed, 0 failed, 118 skipped (full report)

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Flaky tests (1)

Postgres 14

• test_timeline_size_quota_on_startup: release

Code coverage* (full report)

• functions: 28.1% (6429 of 22866 functions)
• lines: 46.8% (45139 of 96400 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
ee6591f at 2024-04-10T19:01:19.074Z :recycle:}

[MMeent]

Please ping me after PG's PRs are merged & the references here are updated.

[knizhnik]

Please ping me after PG's PRs are merged & the references here are updated.

Extra spaces are removed, PG versions are bumped

[MMeent]

Looks good.