DB Projects Help >> Time stamp ordering
In computer research, in the area of directories, timestamp-based concurrency management is a non-lock concurrency management technique, used in relational directories to properly manage dealings, using timestamps.
Assumptions
Every timestamp value is exclusive and effectively signifies a quick at some point.
No two timestamps can be the same.
A higher-valued timestamp takes place later at some point than a lower-valued timestamp.
Creating Timestamp
A variety of different techniques have been used to produce timestamp
Use the value of the body time at the begin of a purchase as the timestamp.
Use a thread-safe discussed table that is small at the begin of a purchase as the timestamp.
A mixture of the above two techniques.
Each purchase (Ti) is a requested record of measures (Aix). Before the purchase works its first actions (Ai1), it is noticeable with the present timestamp, or any other just completely requested sequence: TS (Ti) = NOW (). Every purchase is also given an at first clear set of dealings upon which this will depend, DEP (Ti) = [], and an at first clear set of old physical objects which it modified, OLD (Ti) = [].
Each subject (OJ) in the collection is given two timestamp areas which are not used other than for concurrency control: RTS (OJ)'s time at which the value of subject was last used by a purchase, WTS (OJ)'s time at which the value of the subject was last modified by a purchase.
Granularity of data items
In computer research, multiple granularity locking (MGL), sometimes known as the Bob Rayner secure technique, is a secure technique used in collection control techniques (DBMS) and relational directories.
In MGL, hair is set on physical objects that contain other physical objects. MGL uses the ordered characteristics of the contains marriage. For example, a collection may have information, which contains websites, which further contain information. This can be believed of as a hardwood of physical objects, where each node contains its kids. A secure hair a node and its enfant.
Multiple granularity secure is usually used with non-strict two-phase secure to assurance serializability. MGL uses secure escalation to figure out granularity secure on a node and its forefathers.
Lock Modes
Moreover to discussed (S) hair and unique (X) hair from other lock plans, like demanding two-phase lock, MGL also uses objective discussed and objective unique hair. IS hair issue with X hair, while IX hair issue with S and X hair. The zero secure (NL) is appropriate with everything.
To secure a node in S (or X), MGL has the purchase secure all of its forefathers with IS (or IX), so if a purchase hair a node in S (or X), no other purchase can accessibility its forefathers in X (or S and X).
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