Database Reference
In-Depth Information
Importing Large Objects
Most databases provide the capability to store large amounts of data in a single field.
Depending on whether this data is textual or binary in nature, it is usually represented as a
CLOB
or
BLOB
column in the table. These “large objects” are often handled specially by
the database itself. In particular, most tables are physically laid out on disk as in
Fig-
ure 15-2
. When scanning through rows to determine which rows match the criteria for a
particular query, this typically involves reading all columns of each row from disk. If large
objects were stored “inline” in this fashion, they would adversely affect the performance of
such scans. Therefore, large objects are often stored externally from their rows, as in
Fig-
ure 15-3
. Accessing a large object often requires “opening” it through the reference con-
tained in the row.
