Addressing over-eager constraint checking with delete indexes #15092
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# Conflicts: # src/execution/operator/persistent/physical_update.cpp
taniabogatsch
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Mytherin
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test/sql/index/art/constraints/test_art_concurrent_deletes.test
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# Conflicts: # .github/patches/extensions/vss/hnsw.patch
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This was referenced Dec 13, 2024
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when will the next release be? |
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Release is penciled in for mid-january: https://duckdb.org/docs/dev/release_calendar#upcoming-releases |
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Addressing over-eager constraint checking with delete indexes (duckdb/duckdb#15092) Fix update_extensions_ci test (duckdb/duckdb#15310) Move away from upload-artifacts@v3 / download-artifacts@v3 (duckdb/duckdb#15309)
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Addressing over-eager constraint checking with delete indexes (duckdb/duckdb#15092) Fix update_extensions_ci test (duckdb/duckdb#15310) Move away from upload-artifacts@v3 / download-artifacts@v3 (duckdb/duckdb#15309)
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Addressing over-eager constraint checking with delete indexes (duckdb/duckdb#15092) Fix update_extensions_ci test (duckdb/duckdb#15310) Move away from upload-artifacts@v3 / download-artifacts@v3 (duckdb/duckdb#15309) Co-authored-by: krlmlr <krlmlr@users.noreply.github.com>
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#18194) ### Overview #15092 made it possible for ART `PRIMARY/UNIQUE` indexes to have at most two row IDs per (unique) leaf. Currently, the conflict manager (and `ART::VerifyLeaf`) still work with the assumption that there can never be more than one row ID per conflict hit. Since this assumption no longer holds, in some cases, we now have to register conflict hits for up to two row IDs. Related issue: duckdblabs/duckdb-internal#4924. Later in the execution, we need to understand which of the two possible row IDs is visible to the transaction (and the conflict manager). As far as I can tell, this mostly kept working because we use a `vector` for row ID scanning, which is order-preserving, and newer row IDs (more likely the ones visible to the current transaction) overwrote older row IDs. ### Changes in this PR - Exposed `CanFetch` to `DataTable`, `LocalStorage`, `RowGroupCollection` to determine whether a row ID is visible to a transaction/in the local storage, or not. - The conflict manager now has the capacity to register a secondary hit for a conflict. Also, I've refactored basically the entire conflict manager. That refactoring includes removing the `ManagedSelection`, and a lot of code paths. I think the number of lines only went up because I've added the `CanFetch` stuff and because I've also added a lot of comments and some formatting). 😅 This PR is a minor follow-up to #18015 and next up is turning the row ids into an unordered set instead of a vector.
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This PR introduces a new component to duckdb's transaction-local storage: delete indexes.
Let's look at the following snippet:
INSERT OR REPLACEfails with a constraint exception. We do not support out-of-place table updates withUNIQUEconstraints, such as a primary key. An out-of-place update turns anUPDATEintoDELETE + UPDATE.The longstanding limitation of duckdb's over-eager constraint-checking causing this behavior is documented here: https://duckdb.org/docs/sql/indexes.html#over-eager-unique-constraint-checking.
To solve this issue, this PR introduces transaction-local delete indexes. When attempting to remove any data from the global index, we now store this change in the local index. We can not remove the data yet, as other transactions may still depend on it. Subsequent operations within the same local context are then aware of the deletion of that entry. Thus, before throwing a constraint violation, they double-check if the value is still there by performing a lookup against the local delete index.
There are still some limitations to this approach. I.e., concurrent changes of the same key will likely cause a write-write conflict but will no longer cause a constraint violation.