release-23.1: prevent data loss for at risk indexes and add tooling to detect them

[fqazi]

This patch aims at doing the following:

1. Extend the debug doctor / crdb_internal.invalid_objects to detect indexes which could potentially lose data by being dropped specifically when a column is only stored inside them
2. Add a check inside DROP INDEX to prevent dropping indexes with this problem to avoid data loss.

Fixes: #106794
Informs: #106739

Release justification: low risk and prevents a potentially dangerous action by users

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[rafiss]

this is quite nice! just had a minor question about the tests

also, do you think we should forward-port the first commit to master?

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @fqazi)

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pkg/sql/logictest/testdata/logic_test/drop_index line 558 at r1 (raw file):

# Drop INDEX will be blocked
statement error pq: index t_with_idx_data_loss_n_idx cannot be safely dropped, since doing so will lose data in certain columns
DROP INDEX t_with_idx_data_loss@t_with_idx_data_loss_n_idx;

nice test here. just wanted to check if the test already runs for both legacy and new schema changers?

[fqazi]

this is quite nice! just had a minor question about the tests

also, do you think we should forward-port the first commit to master?

That scenario is already blocked by validation on master, so we should no longer have the danger anymore.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @fqazi)

pkg/sql/logictest/testdata/logic_test/drop_index line 558 at r1 (raw file):

# Drop INDEX will be blocked
statement error pq: index t_with_idx_data_loss_n_idx cannot be safely dropped, since doing so will lose data in certain columns
DROP INDEX t_with_idx_data_loss@t_with_idx_data_loss_n_idx;

nice test here. just wanted to check if the test already runs for both legacy and new schema changers?

Yes this test runs in both cases, so we should be covered

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 6c8bd9a to blathers/backport-release-22.2-106863: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.2.x failed. See errors above.

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