Which of the following are considered limitations of the legacy LOB implementation?
A.
Legacy LOBs are not available in a RAC environment.
B.
DML access is multi-threaded.
C.
User-defined version control
D.
Randomly writing data to LOBs was preferable to reading LOB data.
Explanation:
LOBs were first implemented in Oracle8i, and the assumptions at the time were as follows:
LOBs would not be more than a few megabytes in size.
LOBs were typically “write-once, read-many” types of objects.
There would be no OLTP access.
Undo retention was difficult to manage using the initialization parameters PCTVERSION and
RETENTION.
Chunk sizes are uniform; in other words, data was expected to be written in the same size blocks,
and each block was 32K or less.
Multiple concurrency in a RAC environment was not anticipated.
Versioning was not an important requirement, and user-defined version control solutions were not
optimal.
These assumptions no longer apply in an environment with XML documents and images that are
gigabytes in size and are frequently read and
written to, in a RAC environment no less.
Large amounts of application data (much greater than 4K bytes in size) can be classified into three
areas: structured, semi-structured, and
unstructured. You may have all three types in a database, or even within the same table. For
example, XML documents are highly structured
and may be several gigabytes in size; on the other end of the spectrum, unstructured image data
may require hundreds of megabytes or
even gigabytes for each image. The recent enhancements to LOBs, SecureFile LOBs, makes
processing these objects even more scalable,
even in a RAC environment.
Answer D is incorrect. Random writes to LOB were expected to be rare or non-existent; only
sequential reads were expected after a
LOB was first written.
Answer B is incorrect. Legacy LOBs are not efficient at concurrent DML access; locking usually occurs
at the LOB level.
Answer A is incorrect. Legacy LOBs are available in a RAC environment, but high concurrency writes
are very inefficient in a RAC
environment.