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POMysql cpu usage increasing sorting lat lon distance nearest point
 

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  1. POMysql cpu usage increasing sorting lat lon distance nearest point
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    <p>the question is: Why mysql's cpu usage goes to 300% -> 400% when i add this query in my script php ?</p> <p>I want to find the nearest Point of intereset (poi_id) of certain category (cat_id) from a coordinates point (MYLAT, MYLON)</p> <p>TABLE of <b>POI</b> (poi): </p> <pre><code> | poi_id | name | city_id | lat | lon | </code></pre> <p>TABLE of <b>correlations</b> (corr):</p> <pre><code>| cat_id | poi_id | city_id | </code></pre> <p>TABLE of <b>CITIES</b> (city)</p> <pre><code>| city_id | name | </code></pre> <p><b> SCRIPT: </b></p> <p>$lat = <b>MYLAT</b>; // Latitude of my starting point</p> <p>$lon = <b>MYLON</b>; // Longitude of my starting point</p> <p><b>Bounding box</b>:</p> <p>$lon1 = $lon - ($dist/abs(cos(rad2deg($lat)) * 60 * 1.1515));</p> <p>$lon2 = $lon + ($dist/abs(cos(rad2deg($lat)) * 60 * 1.1515));</p> <p>$lat1 = $lat - ($dist/ 60 * 1.1515);</p> <p>$lat2 = $lat + ($dist/ 60 * 1.1515);</p> <p>When I add this query the CPU usage goes insane:</p> <pre><code>SELECT a.poi_id,a.name,a.city_id,g.name,a.lat, a.lon, ((ACOS(SIN($lat * PI() / 180) * SIN(a.lat * PI() / 180) + COS($lat * PI() / 180) * COS(a.lat * PI() / 180) * COS(($lon - a.lon) * PI() / 180)) * 180 / PI()) * 69.09) AS distance FROM poi a JOIN corr c on a.poi_id = c.poi_id JOIN city g on c.city_id = g.city_id WHERE a.lon &gt; $lon1 and a.lon &lt; $lon2 AND a.lat &gt; $lat1 and a.lat &lt; $lat2 AND c.cat_id = $cat_id HAVING distance &lt; $dist ORDER BY distance LIMIT 20 +----+-------------+-------+--------+----------------------------------+---------+---------+--------------------+------+-----------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+----------------------------------+---------+---------+--------------------+------+-----------------------------+ | 1 | SIMPLE | a | range | poi_id,lat,lon,lat_2 | lat_2 | 14 | NULL | 6924 | Using where; Using filesort | | 1 | SIMPLE | c | eq_ref | city_id_2,cat_id,poi_id,city_id | cat_id | 5 | const,a.poi_id | 1 | | | 1 | SIMPLE | g | eq_ref | PRIMARY | PRIMARY | 4 | c.city_id | 1 | Using where | +----+-------------+-------+--------+----------------------------------+---------+---------+--------------------+------+-----------------------------+ mysql&gt; show profile; +----------------------+----------+ | Status | Duration | +----------------------+----------+ | starting | 0.000138 | | checking permissions | 0.000010 | | checking permissions | 0.000006 | | checking permissions | 0.000008 | | Opening tables | 0.000028 | | System lock | 0.000015 | | init | 0.000043 | | optimizing | 0.000023 | | statistics | 0.000221 | | preparing | 0.000024 | | Creating tmp table | 0.000029 | | executing | 0.000005 | | Copying to tmp table | 0.174197 | | Sorting result | 0.000066 | | Sending data | 0.000065 | | end | 0.000006 | | removing tmp table | 0.000010 | | end | 0.000006 | | query end | 0.000005 | | closing tables | 0.000011 | | freeing items | 0.000077 | | logging slow query | 0.000005 | | cleaning up | 0.000006 | +----------------------+----------+ 23 rows in set (0.00 sec) </code></pre>
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    1. USLuca N.
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    1. CODistance is being computed for 6924 rows. If you might be able to get more performance out of it if you can use other attributes to reduce the size of the set, but short of this you may want to find another option to handle these kind of queries.
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    2. COthose operations are CPU intensive/bound. Asuming query is not optimised by MySQL, can you calculate `SIN($lat * PI() / 180)`, `COS($lat * PI() / 180)` in PHP and substitute float values in Query. See if it makes any difference?
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      1. USSparKot
    3. COLet me check if we can do math ops with less precision.
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      1. USSparKot
 

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