Reading Session Variables I/O

ishmael437

This is a little lower level topic but here it goes.

For performance reasons, I want to know when the sess_XXXXXXXXXXXXXX file is read. Is it read, thus causing IO, each time the php page is parsed or each time a session variable is evaluated.

Here is a very simple example:

$SESSION['VAR1']=5;
for ($i = 0; $i < $SESSION['VAR1']; $i++)
{
echo $i . " " . $_SESSION['VAR1'] . "\n";
}

The sess_XXXXXXX file be read how many times:
a. 1
b. 2
c. 3
d. 10
e. I can't count properly

Ishi

Garth_Farley

AFAIK, the session file is read & stored in memory every time the PHP script is run with the SESS_ID variable set. Then upon script completion, the file is rewritten.

It would be highly inefficient to keep doing filesystem IO each time a session variable is requested.

So my answer is a.

Garth Farley

ishmael437

You appear to be correct Garth. After I did the post I remembered about a little utility I last used about a year or two ago, File Monitor. There was not any difference in the number of IOs between the two following scripts:

<?php
session_start();
$SESSION['var1']=10;
$SESSION['var2']=20;
echo $SESSION['var1'] . " <p>";
echo $SESSION['var2'] . " <p>";
for ($i = 0; $i < $SESSION['var1']; $i++)
{
echo $i . " " . $SESSION['var1'] . " ";
$SESSION['var2']++;
echo $SESSION['var2'] . "<p>";
}
?>

as compared to :

<?php
session_start();
$_SESSION['var1']=10;
?>

ishi