Structure
Because a correlation DBMS stores each unique data value only once, the physical database size is significantly smaller than relational or column-oriented databases, without the use of data compression techniques. Above approximately 30GB, a correlation DBMS may become smaller than the raw data set.
The VBS model used by a CDBMS consists of three primary physical sets of objects that are stored and managed:
- a data dictionary (metadata);
- an indexing and linking data set (additional metadata); and
- the actual data values that comprise the stored information.
In the VBS model, each unique value in the raw data is stored only once; therefore, the data is always normalized at the level of unique values. This eliminates the need to normalize data sets in the logical schema.
Data values are stored together in ordered sets based on data types: all integers in one set, characters in another, etc. This optimizes the data handling processes that access the values.
In addition to typical data values, the data value store contains a special type of data for storing relationships between tables. This functions similarly to foreign keys in RDBMS structures, but with a CDBMS, the relationship is known by the dictionary and stored as a data value, making navigation between tables completely automatic.
The data dictionary contains typical metadata plus additional statistical data about the tables, columns and occurrences of values in the logical schema. It also maintains information about the relationships between the logical tables. The index and linking storage includes all of the data used to locate the contents of a record from the ordered values in the data store.
While not a RAM-based storage system, a CDBMS is designed to use as much RAM as the operating system can provide. For large databases, additional RAM improves performance. Generally, 4GB of RAM will provide optimized access times up to about 100 million records. 8GB of RAM is adequate for databases up to 10 times that size. Because the incremental RAM consumed decreases as the database grows, 16GB of RAM will generally support databases containing up to approximately 20 billion records.
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