Timestamp-based concurrency control
In computer science, a timestamp-based concurrency control algorithm is a non-lock concurrency control method. It is used in some databases to safely handle transactions, using timestamps.
Operation
Each transaction ({\displaystyle T_{i}}
) is an ordered list of actions ({\displaystyle A_{ix}}
). Before the transaction performs its first action ({\displaystyle A_{i1}}
), it is marked with the current timestamp, or any other strictly totally ordered sequence: {\displaystyle TS(T_{i})=NOW()}
. Every transaction is also given an initially empty set of transactions upon which it depends, {\displaystyle DEP(T_{i})=[]}![DEP(T_{i})=[]](https://wikimedia.org/api/rest_v1/media/math/render/svg/7d815e65d336bc8cab691a1110a371787f6d11de)
, and an initially empty set of old objects which it updated, {\displaystyle OLD(T_{i})=[]}![OLD(T_{i})=[]](https://wikimedia.org/api/rest_v1/media/math/render/svg/911907b187ee4936ee803d14c7a0bbe3bd9ee233)
.
Each object {\displaystyle (O_{j})}
in the database is given two timestamp fields which are not used other than for concurrency control: {\displaystyle RTS(O_{j})}
is the time at which the value of object was last used by a transaction, {\displaystyle WTS(O_{j})}
is the time at which the value of the object was last updated by a transaction.
For all {\displaystyle T_{i}}:
To abort: