How are extents allocated to a segment in oracle?An extent is stored some specific information. This information is stored using specific number of adjoining data blocks. A collection of extent is called as a segment stored in the same tablespace. Space for segments is in units of one extent. Extents are allocated as needed. When allocated, Oracle8 and above rounds off extents to a multiple of 5 blocks when more than 5 blocks are requested. If one requests 16K or 2 blocks (assuming a 8K block size), Oracle doesn't round it up to 5 blocks, but it allocates 2 blocks or 16K as requested. If one asks for 8 blocks, Oracle will round it up to 10 blocks. Certainly this is not the case always. For locally managed tablespaces, the extent size is 64K, then Oracle allocates 64K or 8 blocks assuming 8K-block size.