MySQL Selecting million records to generate urls - php

Question

I currently getting a 2 million records from different tables to generate a url to create a sitemap. The script eat too much resources and use 100% of the servers performance
query
SELECT CONCAT("/url/profile/id/",u.id,"/",nickname) as url FROM users AS u
UNION ALL
Select CONCAT("url/city/", c.id, "/paramId/",p.id,"/",Replace(p.title, " ", "+"),"/",r.region_Name,"/",c.city_Name) AS url
From city c
Join region r On r.id = c.id_region
Join country country On country.id = c.id_country
cross join param p
Where country.used = 1
And p.active = 1
//i store it on an array $url_list then process for creating a sitemap..but it takes time and to much resources
//i tried to get the data by batch using LIMIT 0,50000
but getting the maxrow for paging takes time. also the code doesn't look good for i have to run a two query that has a large data
$url_list = array();
$maxrow = SELECT COUNT(*) AS max from (
SELECT CONCAT("/url/profile/id/",u.id,"/",nickname) as url FROM users AS u
UNION ALL
Select CONCAT("url/city/", c.id, "/paramId/",p.id,"/",Replace(p.title, " ", "+"),"/",r.region_Name,"/",c.city_Name) AS url
From city c
Join region r On r.id = c.id_region
Join country country On country.id = c.id_country
cross join param p
Where country.used = 1
And p.active = 1) as tmp
$limit = 50,000;
$bybatch = ceil($maxrow/$limit);
$start = 0;
for($i = 0;$i < $bybatch; $i++){
// run query and store to $result
(SELECT CONCAT("/url/profile/id/",u.id,"/",nickname) as url FROM users AS u
UNION ALL
Select CONCAT("url/city/", c.id, "/paramId/",p.id,"/",Replace(p.title, " ", "+"),"/",r.region_Name,"/",c.city_Name) AS url
From city c
Join region r On r.id = c.id_region
Join country country On country.id = c.id_country
cross join param p
Where country.used = 1
And p.active = 1 LIMIT $start,$limit);
$start += $limit;
//push to $url_list
$url_list = array_push($result);
}
//when finish i use this to create a site map
$linkCount = 1;
$fileNomb = 1;
$i = 0;
foreach ($url_list as $ul) {
$i += 1;
if ($linkCount == 1) {
$doc = new DOMDocument('1.0', 'utf-8');
$doc->formatOutput = true;
$root = $doc->createElementNS('http://www.sitemaps.org/schemas/sitemap/0.9', 'urlset');
$doc->appendChild($root);
}
$url= $doc->createElement("url");
$loc= $doc->createElement("loc", $ul['url']);
$url->appendChild($loc);
$priority= $doc->createElement("priority",1);
$url->appendChild($priority);
$root->appendChild($url);
$linkCount += 1;
if ($linkCount == 49999) {
$f = fopen($this->siteMapMulti . $fileNomb .'.xml', "w");
fwrite($f,$doc->saveXML());
fclose($f);
$linkCount = 1;
$fileNomb += 1;
}
}
Any better way to do this? or to speed up the performance?
Added
Why is this faster than sql query but consumes 1 hundred percent of the servers resources and performance
$this->db->query('SELECT c.id, c.city_name, r.region_name, cr.country_name FROM city AS c, region AS r, country AS cr WHERE r.id = c.id_region AND cr.id = c.id_country AND cr.id IN (SELECT id FROM country WHERE use = 1)');
$arrayCity = $this->db->recordsArray(MYSQL_ASSOC);
$this->db->query('SELECT id, title FROM param WHERE active = 1');
$arrayParam = $this->db->recordsArray(MYSQL_ASSOC);
foreach ($arrayCity as $city) {
foreach ($arrayParam as $param) {
$paramTitle = str_replace(' ', '+', $param['title']);
$url = 'url/city/'. $city['id'] .'/paramId/'. $param['id'] .'/'. $paramTitle .'/'. $city['region_name'] .'/'. $city['city_name'];
$this->addChild($url);
}
}

Answer 1

I suggest you not to use UNION and just issue two separated queries. It will speed up a query itself.
Also as you mentioned above it's good idea to get data by batches.
And finally, don't collect all data in memory. Immediately write it to file in your loop.
Just open file in beginning, write each URL entry in loop and close file in end.
— open file for writing
— count query users table
— do several selects with LIMIT in loop (as you already done)
— right here in loop while ($row = mysql_fetch_array()) write each row to file
and than repeat such algorithm for another table.
It would be useful to implement a function for writing data to file, so you can call that function and adhere to the DRY principle.