Log or raise on unexpected duplicated entry warnings during INSERT IGNORE#100
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tiwilliam
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Looks good to me. I would change the PR title to Log or raise on unexpected duplicated entry warnings during INSERT IGNORE to be more clear.
tiwilliam
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Closes https://github.com/Shopify/shopify/issues/302218
Today when migrating a schema that ends up violating a UNIQUE constraint, the records to the new shadow table is dropped silently. This may cause huge silent data loss when, for example, a column is dropped that is part of a UNIQUE index, without modifying or dropping the index. Same problem can occur if we change collation, causing a unique index to ignore case and drop rows silently.
This PR attempts to make these drops halt the migration and alert the operator that this is happening, making it possible to resolve the issue before migrating again. This is done by inspecting any warnings in-case we can see that the number of inserted rows were lower than we expected, signalling ignored rows. These warnings are in most cases fine, since PK duplicates may occur by design, but other constraints should not.