System performance tuning involves optimizing software configurations, SQL queries, and application code. Common issues include inefficient pagination and the N+1 query problem. Pagination addresses fetching large result sets by breaking them into multiple pages. The N+1 query problem occurs when querying for related data rows causes multiple roundtrips to the database. Solutions include batching queries to retrieve related data in one query rather than many sequential queries.

1. System Performance Tuning

2. What is Performance Tuning
• Performance tuning can involve configuration
changes to software components.
• Performance tuning can also include tuning SQL
queries and tuning an applications underlying code
to cater for concurrency and to improve efficiency.

3. Common Problems in SQL Queries

4. Pagination
• Fetching lots of records can cause slow down
the speed of system but its necessary because
database is systematically organized or
structure repository of indexed information.

5. Pagination
Example:
Without pagination fetching all data
SELECT * FROM cats

6. Pagination
Two things you must do:
• Decide on the maximum number of database
rows that can be included in each page. You
may hard code this value, or (my preferred
method) you can define it in a variable so that
the value may be changed at runtime.

7. Pagination
• You then need to inform the user that other
'pages' are available and provide a mechanism
whereby the user is able to select a different
'page' of details. I currently use a set of
hyperlinks in a separate pagination area which
looks like this:

8. Pagination
How to do it :
1. Obtain the required page number.
- if(isset($_GET[‘pageno’])) {
$pageno = $_GET[‘pageno’];
} else {
$pageno = 1;
}

9. Pagination
2. Identify how many database rows are
available:
-$query = “SELECT count(1) FROM table
WHERE…”;
$result = mysql_query($query, $db);
$query_data = mysql_fetch_row($result);
$numrows = $query_data[0];

10. Pagination
3. Calculate number of $lastpage:
- $rows_per_page = 15;
$lastpage = ceil($numrows/$rows_per_page);
4.Ensure that $pageno is within range:
-$pageno = (int)$pageno;
If ($pageno > $lastpage) {
$pageno = $lastpage;
}
If ($pageno < 1 ){
$pageno = 1;
}

11. Pagination
5. Construct LIMIT clause:
- $limit = ‘LIMIT’ .($pageno - 1) *
$rows_per_page.’,’.$rows_per_page;
6. Issue the database query:
- $query = “SELECT * FROM table $limit”
$result = mysql_query($query,$db);

12. Pagination
7. Construct pagination hyperlinks:
- If ($pageno == 1) {
echo “PREV”;
} else {
echo " <a href='{$_SERVER['PHP_SELF']}?pageno=1'>FIRST</a> ";
$prevpage = $pageno-1;
echo " <a href='{$_SERVER['PHP_SELF']}?pageno=$prevpage'>PREV</a> ";
}

13. Pagination
if ($pageno == $lastpage) {
echo " NEXT";
} else {
$nextpage = $pageno+1;
echo " <a
href='{$_SERVER['PHP_SELF']}?pageno=$nextpage'>NEXT
</a> ";
echo " <a
href='{$_SERVER['PHP_SELF']}?pageno=$lastpage'>LAST<
/a> ";
}

14. Performance: N+1 Query Problem
• Select N+1 is a data access anti-pattern
where the database is accessed in a
suboptimal way.
• Detecting Select N+1 problem usually means
that the data fetch strategy of the application
can be optimized.

15. Performance: N+1 Query Problem
Example:
$test = new test();
$hats = $test->getHats();
$cats = [];
foreach ($hats as $value) {
$cats[] = $test->getCats($value['id']);
}

16. Performance: N+1 Query Problem
Assuming $hats() has an implementation that boils
to:
SELECT * FROM hats WHERE …
.. And $cats($hats_id) has an implementation like
this:
SELECT * FROM cats WHERE hats_id = ..

17. Performance: N+1 Query Problem
.. You will issue “N+1” queries when the code executes, Where
N is the number of cats:
SELECT * FROM cats WHERE ..
SELECT * FROM cats WHERE hats_id = 1
SELECT * FROM cats WHERE hats_id = 2
SELECT * FROM cats WHERE hats_id = 3
SELECT * FROM cats WHERE hats_id = 4
….

18. Performance: N+1 Query Problem
Solution :
Batching Queries
$cats=getCats();

19. Performance: N+1 Query Problem
That is issue these queries:
SELECT * FROM cats WHERE …
SELECT cats.id, cats.name, cats.created
FROM cats INNER JOIN hats
ON hats.id = cats.hats_id

20. Performance: N+1 Query Problem
• It is much faster to issue 1 query which
returns thousands results than to issue t
queries which each thousands return 1
result.

21. Thank You