way, is kept in the dictionary cache to avoid unnecessary recursive queries.The SYS.SEG$ table is the source of location-related information for the oracle server process and will be constantly checked in order to know where to find things in the data file.While table SYS.SEG$ acts like a GPS for the oracle server process, who tells the Oracle Server process where SYS.SEG$ is? As it turns out, SYS.SEG$ is a special type of segment and its location is defined somewhere else.
9) Oracle data blocks (describe important features).Oracle manages the storage space in the datafiles of a database in units called data blocks. A data block is the smallest unit of data used by a database. In contrast, at the physical, operating system level, all data is stored in bytes. Each operating system has a block size. Oracle requests data in multiples of Oracle data blocks, not operating system blocks.The standard block size is specified by the DB_BLOCK_SIZE initialization parameter. In addition, you can specify of up to five nonstandard block sizes. The data block sizes should be a multiple of the operating system's block size within the maximum limit to avoid unnecessary I/O. Oracle data blocks are the smallest units of storage that Oracle can use or allocate.Two types of statements can increase the free space of one or more data blocks: DELETE statements, and UPDATE statements that update existing values to smaller values.The released space from these types of statements is available for subsequent INSERT statements under the following conditions:If the INSERT statement is in the same transaction and subsequent to the statement thatfrees space, then the INSERT statement can use the space made available.If the INSERT statement is in a separate transaction from the statement that frees space (perhaps being run by another user), then the INSERTstatement can use the space made available only after the other transaction commits and only if the space is needed.Block Size AdvantagesSmaller blocksize:- Good for small rows with lots of random access.- Reduces block contention.Larger blocksize:- Has lower overhead, so there is more room to store data.- Permits reading several rows into the buffer cache with a single I/O (depending on row size and block size).
10) How can space within a block be managed for a data segment with PCTFREE = 20 and PCTUSED = 40 (describe important features with suitable diagrams)?