Fix: Use merge when updating auto restatements#5016
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Pull Request Overview
This PR fixes the data update strategy for auto restatements by replacing insert_append with merge to prevent duplicate entries when updating existing records.
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insert_appendtomergeoperation for auto restatements updates - Adds a unique key constraint based on snapshot name and version to ensure proper merging
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This PR prevents a race condition that can occur when two runs update auto restatements at the same time. Although the delete + insert happens in a transaction, certain databases and transaction isolation levels can result in duplicate rows being inserted and violate the primary key constraint on the auto restatements table.
For example, the default transaction isolation level for Postgres is READ COMMITTED, and at that level, if the first updater commits, the second updater will ignore the row if the first updater deleted it. In this case, the second updater will be blocked when deleting auto restatements until the first updater commits, but then will not delete any rows even though the first updater has re-inserted matching snapshot name versions.
To get prevent it, auto restatements are updated with a MERGE.