Reload Analyzer Manual

Tandem Reload Analyzer Manual Page 23 of 42
block has no records. When the records from that block were deleted, it became
empty.
Remember that a condition of an organized file is to have the fewest possible index
levels. If you compare Figure 1-3 and Figure 1-2, you will notice that there is one more
index level in Figure 1-3. (The dashed line above the second level index block points to
the other index blocks on this index level.) The more index levels, the longer the disk
access time and the disk space required.
When a file is disorganized, the data blocks are not contiguous or not physically
adjacent. Disorganized files cannot take advantage of certain performance features,
such as bulk reads for sequential prefetch or bulk writes for sequential updates in files.
Consequently, sequential performance slows down. To improve application
performance and disk space utilization, the file must be reorganized.
Determining when disk space is not properly utilized requires the right database
management tool. Reload Analyzer gives you this information.
Data Chains
One key piece of information Reload Analyzer gives about a file is the number of
contiguous data blocks. The number of contiguous data blocks helps you determine
whether a file needs to be reorganized.
Reload Analyzer counts the data blocks in contiguous order and reports the number of
data chains. A data chain is a set of physically and logically contiguous data blocks in
a file.
You can determine whether a file is disorganized by how many data chains a file has
and how long each chain is. An organized file will have one long data chain. If a file
has a few long chains, it is better organized than a file with many short chains. The
number of data chains and the length of each chain are key factors in deciding whether
to reorganize a file. Section 2, “Using Tandem Reload Analyzer,” explains how the
program gives this information.
Summary
You now know what a key-sequenced file is, the difference between an organized and
disorganized file, and what a data chain is. From here, turn to Section 2: Using
Tandem Reload Analyzer to learn how to run the program and analyze the output.