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+--- Thread: CI_DB_result methods are time and space inefficient (/showthread.php?tid=15638)
CI_DB_result methods are time and space inefficient - El Forum - 02-10-2009
[eluser]voidstar[/eluser]
PHP 5.2.6, CI 1.7.0 (DB_result.php unchanged in SVN 1631)
result_array() returns a copy of a CI_DB_result data member ($result_array). So a query like
Code:
$query = $this->db->query("YOUR QUERY");
$rows = $query->result_array();produces two copies of each row ('field'=>'value' pairs) generated by the query. For any query, but particularly for a large query, this consumes twice as much space as one might expect, and, of course, it takes time to copy the array.
The situation is worse for first_row('array'), last_row('array'), next_row('array'), and previous_row('array'). These methods make an internal copy of the $result_array data member, e.g.
Code:
$result = $this->result($type);and then return a single row from the copy. Clearly this unnecessarily consumes time and space. These methods could easily access the data member $result_array directly and avoid this expense.
Also, it would be helpful if the documentation encouraged the use of 'object' instead of 'array'. In PHP5+ the data member $result_object will be an array of object handles, so 'object' versions of these methods will manipulate and return handles, making them much less expensive in terms of time and space.
CI_DB_result methods are time and space inefficient - El Forum - 02-11-2009
[eluser]gh0st[/eluser]
If there is a better way to do the above, please give an example.
For example, before CI I used to use the ez_mysql library by Justin Vincent.
And of course there is the ADODB library.
If there's a better way to do the search results, please show some examples.
CI_DB_result methods are time and space inefficient - El Forum - 02-11-2009
[eluser]m4rw3r[/eluser]
Usually PHP makes a copy by reference, until the copy is changed - then the real copy occurs (so called copy-on-write).
So the same arrays won't take twice the space, as long as they are unchanged (after the copy has been made).
Example:
Code:
$a = array(1, 2, ... , 1475137425428354); // allocates a lot of memory
$b = $a; // doesn't allocate any memory at all (except for the reference)
$b[0] = -2; // allocates new memory for a copy of a, with one changed value
// or:
$a[0] = -5; // does the same as above, provided $b hasn't been changedBTW, I'm doing a remake of CI's db for PHP 5, so if anybody has ideas of improvement, I'm all ears.
CI_DB_result methods are time and space inefficient - El Forum - 02-11-2009
[eluser]TheFuzzy0ne[/eluser]
[quote author="m4rw3r" date="1234382538"]BTW, I'm doing a remake of CI's db for PHP 5, so if anybody has ideas of improvement, I'm all ears.[/quote]
http://ellislab.com/forums/viewthread/102489/
CI_DB_result methods are time and space inefficient - El Forum - 02-11-2009
[eluser]voidstar[/eluser]
I did not know that PHP used COW. Cool!
I retract my complaint about the space/time inefficiencies in DB_result, although in my case COW doesn't help. In this particular application it's very convenient in the Model to modify a field in the database records before returning them to the Controller.
Thanks for the help!
CI_DB_result methods are time and space inefficient - El Forum - 02-11-2009
[eluser]m4rw3r[/eluser]
Well, DB_result is still a bit inefficient, because it loops the resultset more than necessary.
But it is unavoidable in PHP 4 (solving it with iterator interface in PHP 5).
CI_DB_result methods are time and space inefficient - El Forum - 02-11-2009
[eluser]m4rw3r[/eluser]
Is it really necessary to cache the result in the resultset?
How often does the user call result() more than once on the same resultset? I certainly don't.
(And don't blame it on "foreach() calls the result() method for each row", it doesn't (at least not on PHP 5))