* functions. In general, objects should assume READ_NORMAL if no flags are explicitly given,
* though certain objects may assume READ_LATEST for common use case or legacy reasons.
*
- * There are three types of reads:
- * - READ_NORMAL : Potentially cached read of data (e.g. from a slave or stale replica)
- * - READ_LATEST : Up-to-date read as of transaction start (e.g. from master or a quorum read)
- * - READ_LOCKING : Up-to-date read as of now, that locks the records for the transaction
+ * There are four types of reads:
+ * - READ_NORMAL : Potentially cached read of data (e.g. from a slave or stale replica)
+ * - READ_LATEST : Up-to-date read as of transaction start (e.g. from master or a quorum read)
+ * - READ_LOCKING : Up-to-date read as of now, that locks (shared) the records
+ * - READ_EXCLUSIVE : Up-to-date read as of now, that locks (exclusive) the records
+ * All record locks persist for the duration of the transaction.
*
* Callers should use READ_NORMAL (or pass in no flags) unless the read determines a write.
* In theory, such cases may require READ_LOCKING, though to avoid contention, READ_LATEST is
*/
interface IDBAccessObject {
// Constants for object loading bitfield flags (higher => higher QoS)
- const READ_LATEST = 1; // read from the master
- const READ_LOCKING = 3; // READ_LATEST and "FOR UPDATE"
+ const READ_LATEST = 1; // read from the master
+ const READ_LOCKING = 3; // READ_LATEST (1) and "LOCK IN SHARE MODE" (2)
+ const READ_EXCLUSIVE = 7; // READ_LOCKING (3) and "FOR UPDATE" (4)
// Convenience constant for callers to explicitly request slave data
const READ_NORMAL = 0; // read from the slave