Access to the table based on the value of the indexed column(s) (as in a WHERE clause) will use the index to locate the table data. An index is declared on a column or set of columns. Index-An index is a structure created to help retrieve data more quickly and efficiently (just as the index in this book allows you to find a particular section more quickly). Because of the structure of the cluster, related data requires much less I/O overhead if accessed simultaneously. Tables can be accessed separately even though they are part of a clustered table. If data in two or more tables is frequently retrieved together based on data in the common column, using a clustered table can be quite efficient. A table is stored within a tablespace often, many tables share a tablespace.Ĭluster-A cluster is a set of tables physically stored together as one table that shares a common column. Columns are defined by name and data type. Table-A table, which consists of a tablename and rows and columns of data, is the basic logical storage unit in the Oracle database. A tablespace is used to logically group data together. New Term: The database is divided into one or more logical pieces known as tablespaces. The database schema, which consists of items such as tables, clusters, indexes, views, stored procedures, database triggers, sequences, and so on. The logical layer of the database consists of the following elements: Oracle provides a mechanism for storing multiple copies of control files. One or more control files-Control files contain information used to start an instance, such as the location of datafiles and redo log files Oracle needs this information to start the database instance. If redo log information is lost, you cannot recover the system.
#What is oracle 10g software
The redo log files must perform well and be protected against hardware failures (through software or hardware fault tolerance). This information is used in the event of a system failure to reapply changes that have been made and committed but that might not have been made to the datafiles. Redo log files, known as the redo log, store a log of all changes made to the database. Two or more redo log files-Redo log files hold information used for recovery in the event of a system failure. The number of datafiles that can be configured is limited by the Oracle parameter MAXDATAFILES.
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Spreading tablespaces over many datafiles can have a significant positive effect on performance. The information for a single table can span many datafiles or many tables can share a set of datafiles. You can have as few as one datafile or as many as hundreds of datafiles. One or more datafiles-Datafiles store the information contained in the database. The physical layer of the database consists of three types of files: The physical layer consists of the files that reside on the disk the components of the logical layer map the data to these physical components. The Oracle database has a logical layer and a physical layer.