What do you mean by Multiple Granularity?

What do you mean by Multiple Granularity?

Now Multiple Granularity means hierarchically breaking up the database into blocks that can be locked and can be tracked needs what needs to lock and in what fashion. Such a hierarchy can be represented graphically as a tree.

Under what circumstances is multiple granularity locking used?

Circumstances where Multiple Granularity Locking (MGL) is used: Here, locks are set on objects that contain other objects. MGL exploits the hierarchical nature of the contained relationship. Example: A database may have files, which contain pages, which contain records.

What do you mean by granularity locking?

The granularity of locks in a database refers to how much of the data is locked at one time. In theory, a database server can lock as much as the entire database or as little as one column of data. It can acquire a lock on each row. …

What is meant by granularity in DBMS?

Granularity is the level of detail at which data are stored in a database. When the same data are represented in multiple databases, the granularity may differ.

What is Multiversion schemes in DBMS?

A concurrency control scheme using multiple versions of data objects is presented which allows increased concurrency. The scheme grants an appropriate version to each read request. Transactions issuing write requests which might destroy database integrity are aborted.

What is a six lock?

SIX. Shared intent exclusive locks. SIX (“shared with intent to update”) locks can be considered as combination of S (shared) locks and IX (intent exclusive) locks. SIX locks are used in table locking strategies to minimize the extent of exclusive locking requirements.

Why was the multiple granularity protocol introduced?

The Multiple Granularity protocol enhances concurrency and reduces lock overhead. It maintains the track of what to lock and how to lock. It makes easy to decide either to lock a data item or to unlock a data item. This type of hierarchy can be graphically represented as a tree.

What is data granularity in data warehouse?

In a data warehouse, data granularity is the level of detail in a model or decision making process. It tells you how detailed your data is: Lower levels of detail equal finer, more detailed, data granularity (Ponniah, 2004; Bellahsène, 2008).

What is granularity in data warehouse?

How lock granularity is implemented?

It deals with the cost of implementing locks depending upon the space and time. If a transaction typically accesses many records of the same file it is better to have block or file granularity so that the transaction will consider all those records as one data item. …

What is granularity in datawarehouse?

What is the use of multiple granularity?

Granularity: It is the size of data item allowed to lock. It can be defined as hierarchically breaking up the database into blocks which can be locked. The Multiple Granularity protocol enhances concurrency and reduces lock overhead. It maintains the track of what to lock and how to lock.

How does granularity affect the performance of concurrency control and recovery?

The granularity can affect the performance of concurrency control and recovery. In Section 22.5.1, we discuss some of the tradeoffs with regard to choosing the granularity level used for locking, and in Section 22.5.2 we discuss a multiple granularity locking scheme, where the granularity level (size of the data item) may be changed dynamically.

What is multiple granularity locking (MGL) protocol?

The multiple granularity locking (MGL) protocol consists of the following rules: 1. The lock compatibility (based on Figure 22.8) must be adhered to. 2. The root of the tree must be locked first, in any mode. 3.

Can xacts lock at different levels of granularity?

•Allow Xacts to lock at each level, but with a special protocol using new “intention” locks: •Still need S and X locks, but before locking an item, Xact must have proper intension locks on all its ancestors in the granularity hierarchy. IS – Intent to get S lock(s) at finer granularity. IX – Intent to get X lock(s) at finer granularity.