READ vs SQL SELECT, A Quick Performance Test

READ vs SQL SELECT

With no doubt, SQL is the advanced and efficient way for operations (Read, Write, Update or Delete) on Tables (or Files) on IBM i. 

With the use of Embedded SQL programming (SQLRPGLE), it is efficient to use SELECT to read the data from a table compared to using READ. 

Here is the result from a quick performance test between READ and SELECT to read One million records from a table.

Below are few points to consider about the test before we see the results. 

• Created Physical File (using DDS) for the use in RPGLE with READ Operation. 
• Created Table from SQL Session for the use in SQLRPGLE with SQL SELECT Operation.
• Both the files has same number of fields, length and same number of records.
• Both Programs are called from a new Interactive Session immediately after login.

Let's see the code used to create File/Table and Program. 

Physical File (PPTESTFILE):

Table (PTESTTABL):

Inserted one million records (same data) to both the files. And, Table is occupying less size compared to Physical File. 

Size of Physical File:

Record Length - 40, Total Records - 1,000,000, Size of Physical File - 64,008,192 Bytes

Size of Table:

Record Length - 40, Total Records - 1,000,000, Size of Physical File - 41,951,232 Bytes

Below is the code used for both READ & SELECT. 

for READ (PPREAD):

for SELECT (PPSQL):

Now, coming to the Results, Program with SELECT operation has run in in 30% (approx) less time than with READ (70% of READ).

Program with READ took about 9 seconds to read one million records. 

Program with SELECT took about 6 seconds to read one million records. 

So, It is efficient both in terms of Processing time and Storage to use SQL in place of READ wherever possible. 

Again, Is there a better way of doing this with SQL? Yes, Instead of Fetching one record every time, We can Fetch multiple records into Data Structure and loop through Data Structure for accessing the data. 

This has run > 60% faster than SQL SELECT example listed above. Click Here to see more details on this test.