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How to insert into multiple table using JPA @Query only?

I believe you might be facing this issue, which is pretty likely especially if both transactions attempt to insert the same SKUs.

If that's the case, I can think of two ways to mitigate it:

Partial solution: try sorting the SKUs in List<CreateSkuRequest> SKUs by SKU.code and (if that's not enough) using saveAndFlush() to store them, ensuring the order of insertion. This should eliminate the circular wait, meaning that now, at least one of the transactions should succeed (the other will probably get a unique constraint violation)

Full solution: if you prefer both transactions to succeed, you would have to acquire a table-level lock for the SKU table. You should be able to do this using a custom update query:

@Query(value = "LOCK TABLE SKU IN EXCLUSIVE MODE", nativeQuery = true)

@Modifying

void lockTable();

then, just call the method as the first operation inside createSku. Note that this might turn out to be only marginally more efficient than putting the transactions in a queue, so if I were you, I'd probably still just go with that approach.