Updating indexes for block model space
If the row fits in the block, users do not see an effect in I/O performance, because no extra I/O operation is required to retrieve the rest of the row.
Each row piece, chained or unchained, contains a A row fully contained in one block has at least 3 bytes of row header.
If an entire row can be inserted into a single data block, then Oracle stores the row as one row piece.
However, if all of a row's data cannot be inserted into a single data block or if an update to an existing row causes the row to outgrow its data block, then Oracle stores the row using multiple row pieces.
Because rowids are constant for the lifetime of a row piece, it is useful to reference rowids in SQL statements such as , then Oracle always stores this column last.
A schema is owned by a database user and has the same name as that user. Schema objects can be created and manipulated with SQL and include the following types of objects: Schema objects are logical data storage structures.A chained row's pieces are chained together using the rowids of the pieces.With intra-block chaining, users receive all the data in the same block.After the row header information, each row contains column length and data.The column length requires 1 byte for columns that store 250 bytes or less, or 3 bytes for columns that store more than 250 bytes, and precedes the column data.After you create a table, insert rows of data using SQL statements.Table data can then be queried, deleted, or updated using SQL. When you create a table, Oracle automatically allocates a data segment in a tablespace to hold the table's future data.After they are assigned, a given row piece retains its rowid until the corresponding row is deleted or exported and imported using Oracle utilities.For clustered tables, if the cluster key values of a row change, then the row keeps the same rowid but also gets an additional pointer rowid for the new values.There is no relationship between schemas and tablespaces: a tablespace can contain objects from different schemas, and the objects for a schema can be contained in different tablespaces.Figure 5-1 illustrates the relationship among objects, tablespaces, and datafiles. This constraint forces the column to contain a value in every row.