catalog: change hash-sharded indexes to use md5

[rafiss]

fixes #91109

Release note (sql change): The hash function used by hash-sharded indexes was changed to
mod(fnv32(md5(crdb_internal.datums_to_bytes(columns))), bucket_count). (Previously, it did not use md5.) This change was made to enhance the uniformity of bucket distribution in cases when the bucket count is a power of 2, and the columns being sharded have numerical properties that make the fnv32 function return values with a non-uniformly distributed modulus.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is 

[michae2]

Thank you for looking at this! Some things I'm wondering:

• Do we still need fnv32 if we're also using md5? I guess Andrew was trying fnv32(sha256(...)) so maybe that's what you're thinking?
• Is there any upgrade concern here? Or restore concern? I guess restores should already have the old formula baked into the saved CREATE TABLE?

[rafiss]

Do we still need fnv32 if we're also using md5? I guess Andrew was trying fnv32(sha256(...)) so maybe that's what you're thinking?

we do unfortunately, since md5 (and shaX) return a string.

Is there any upgrade concern here? Or restore concern? I guess restores should already have the old formula baked into the saved CREATE TABLE?

there may be - i was hoping some tests would tell me, but they have not. so i will do a bit more investigation.

[rafiss]

@michae2 this is RFAL. i've confirmed that this is safe for restores and upgrades. the MakeHashShardComputeExpr function is only called by the gateway node at the time of executing a CREATE statement.

[mgartner]

Reviewed 16 of 16 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @michae2)

[michae2]

Could you add one (or both) of the poorly-distributed examples from #91109 to pkg/sql/logictest/testdata/logic_test/hash_sharded_index?

Reviewed 16 of 16 files at r1, all commit messages.
Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @rafiss)

[rafiss]

Could you add one (or both) of the poorly-distributed examples from #91109 to pkg/sql/logictest/testdata/logic_test/hash_sharded_index?

good idea. done!

tftrs!

bors r+

[craig]

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[rafiss]

bors r+

[craig]

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