The default transaction processing behavior, table-level snapshot versioning, allows multiple writers to modify a table serially—that is, one after the other, never more than one at a time—while multiple readers continue to work on an original copy of the table.
Without table-level snapshot versioning, concurrent read and write operations might cause inconsistencies in the IQ main store. The table-level versioning provided by SAP Sybase IQ prevents inconsistencies both by serializing transactions, and by making the table the version level.
While any transaction processing system is designed to ensure that the database remains consistent, the SAP Sybase IQ approach means that users need not worry about placing their queries and updates in appropriate transactions. SAP Sybase IQ begins and ends transactions automatically, and ensures that read and write operations do not interfere with each other.
When table-level snapshot versioning is enabled but the table is configured for RLV storage, concurrent read and write operations are still disallowed. The table-level snapshot versioning setting overrides a table's RLV setting.