feat(pageserver): support synthetic size calculation for invisible branches

[skyzh]

Problem

ref #11279

Imagine we have a branch with 3 snapshots A, B, and C:

base---+---+---+---main
        \-A \-B \-C
base=100G, base-A=1G, A-B=1G, B-C=1G, C-main=1G

at this point, the synthetic size should be 100+1+1+1+1=104G.

after the deletion, the structure looks like:

base---+---+---+
       \-A \-B \-C

If we simply assume main never exists, the size will be calculated as size(A) + size(B) + size(C)=300GB, which obviously is not what the user would expect.

The correct way to do this is to assume part of main still exists, that is to say, set C-main=1G:

base---+---+---+main
       \-A \-B \-C

And we will get the correct synthetic size of 100G+1+1+1=103G.

Summary of changes

• Do not generate gc cutoff point for invisible branches.
• Use the same LSN as the last branchpoint for branch end.
• Remove test_api_handler for mark_invisible.

[github-actions]

8030 tests run: 7647 passed, 0 failed, 383 skipped (full report)

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Flaky tests (8)

Postgres 17

• test_pgdata_import_smoke[8-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: debug-x86-64-without-lfc
• test_pgdata_import_smoke[None-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: debug-x86-64-without-lfc
• test_deletion_queue_recovery[validate-keep]: release-arm64-without-lfc
• test_isolation[v1-4]: release-x86-64-without-lfc

Postgres 16

• test_sliding_working_set_approximation: release-arm64-with-lfc

Postgres 15

• test_sliding_working_set_approximation: release-arm64-with-lfc
• test_password_hack: release-x86-64-with-lfc

Postgres 14

• test_lfc_working_set_approximation: release-arm64-with-lfc

Code coverage* (full report)

• functions: 32.5% (8778 of 27040 functions)
• lines: 48.9% (76054 of 155496 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
03b98b9 at 2025-03-31T20:32:44.986Z :recycle:}

[Copilot]

Pull Request Overview

This PR adds support for synthetic size calculation for invisible branches, ensuring that size computation correctly handles branches marked as invisible.

• Added an is_invisible helper on Timeline to propagate branch visibility information.
• Adjusted lease point and branch endpoint selection logic in size calculation based on branch visibility.
• Updated the API route for marking a timeline as invisible and added tests for the new synthetic size logic.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
pageserver/src/tenant/timeline.rs	Added a helper function to check branch invisibility.
pageserver/src/tenant/size.rs	Updated synthetic size calculation to handle invisible branches and adjusted lease point/endpoint logic.
pageserver/src/tenant.rs	Added test coverage for synthetic size calculation with invisible branches.
pageserver/src/http/routes.rs	Changed the mark_invisible handler from testing_api_handler to api_handler.