User guide

Using ENFORM Search Statistics
Using ENFORM Efficiently
058058 Tandem Computers Incorporated 5–3
The RECORDS
READ Column
The third column, headed RECORDS READ, provides a number that indicates the
number of records that the query processor read in each physical file. The number
indicates logical reads. Logical reads (as opposed to physical reads) count the requests
for records but ignore reads of alternate key data files and index blocks. Logical reads
also ignore the effect of buffering, which might reduce physical reads. For example in
the query shown in Figure 5-1, the query processor logically read a record from
mkt.sample.odetail 124 times. Normally, several times that number of physical reads
occur.
The presence of keys can affect the number of reads performed. If the file read second
has an alternate or primary key field by which it is linked to the file read first, the
query processor positions on that key and then reads only the appropriate subset of
records. If a linking key field does not exist in the file read second, the query
processor must read the entire file for each record selected in the file read first.
The POSITIONS Column The fourth column, headed POSITIONS, provides a number that indicates the total
number of positions that the query processor performs on each physical file. Note the
relationship between the number of records read in the first file and the number of
positions performed on the second and third files. The statistics in Figure 5-1 indicate
that to retrieve the information request in the query the query processor:
1. Positioned $mkt.sample.odetail to beginning of information.
2. Read from $mkt.sample.odetail.
3. Positioned $mkt.sample.order according to the primary key ordernum.
4. Read from $mkt.sample.order.
5. Positioned $mkt.sample.parts according to the primary key partnum.
6. Read from $mkt.sample.parts.
The query processor repeated steps 2 through 6 until it retrieved the requested
information. The query processor retrieved the information in this manner because
both ordernum and partnum are the primary key of their respective files.
The Identification Line The line below the four columns of reported statistics identifies the ENFORM process
(network node number, CPU number, and process number), the date and time the
query was initiated, and the date and time the query terminated.