Unable to Lock Row

A DML operation could not acquire a lock on the target record(s) because another transaction is concurrently updating the same record or one of its parents. Retry the operation, typically with backoff.

References

developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_dml_exception_handling.htm

In this namespace

← previous STORAGE_LIMIT_EXCEEDED Storage Limit Exceeded

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MIXED_DML_OPERATION QUERY_TIMEOUT REQUEST_LIMIT_EXCEEDED REQUIRED_FIELD_MISSING STORAGE_LIMIT_EXCEEDED UNABLE_TO_LOCK_ROW