First off, I’ve looked at several other questions about optimizing sql queries, but I’m still unclear for my situation what is causing my problem. I read a few articles on the topic as well and have tried implementing a couple possible solutions, as I’ll describe below, but nothing has yet worked or even made an appreciable dent in the problem.
The application is a nutrition tracking system – users enter the foods they eat and based on an imported USDA database the application breaks down the foods to the individual nutrients and gives the user a breakdown of the nutrient quantities on a (for now) daily basis.
here’s
A PDF of the abbreviated database schema
and here it is as a (perhaps poor quality) JPG. I made this in open office – if there are suggestions for better ways to visualize a database, I’m open to suggestions on that front as well! The blue tables are directly from the USDA, and the green and black tables are ones I’ve made. I’ve omitted a lot of data in order to not clutter things up unnecessarily.
Here’s the query I’m trying to run that takes a very long time:
SELECT listing.date_time,listing.nutrdesc,data.total_nutr_mass,listing.units
FROM
(SELECT nutrdesc, nutr_no, date_time, units
FROM meals, nutr_def
WHERE meals.users_userid = '2'
AND date_time BETWEEN '2009-8-12' AND '2009-9-12'
AND (nutr_no <100000
OR nutr_no IN
(SELECT nutr_def_nutr_no
FROM nutr_rights
WHERE nutr_rights.users_userid = '2'))
) as listing
LEFT JOIN
(SELECT nutrdesc, date_time, nut_data.nutr_no, sum(ingred_gram_mass*entry_qty_num*nutr_val/100) AS total_nutr_mass
FROM nut_data, recipe_ingredients, food_entries, meals, nutr_def
WHERE nut_data.nutr_no = nutr_def.nutr_no
AND ndb_no = ingred_ndb_no
AND foods_food_id = entry_ident
AND meals_meal_id = meal_id
AND users_userid = '2'
AND date_time BETWEEN '2009-8-12' AND '2009-9-12'
GROUP BY date_time,nut_data.nutr_no ) as data
ON data.date_time = listing.date_time
AND listing.nutr_no = data.nutr_no
ORDER BY listing.date_time,listing.nutrdesc,listing.units
So I know that’s rather complex – The first select gets a listing of all the nutrients that the user consumed within the given date range, and the second fills in all the quantities.
When I implement them separately, the first query is really fast, but the second is slow and gets very slow when the date ranges get large. The join makes the whole thing ridiculously slow. I know that the ‘main’ problem is the join between these two derived tables, and I can get rid of that and do the join by hand basically in php much faster, but I’m not convinced that’s the whole story.
For example: for 1 month of data, the query takes about 8 seconds, which is slow, but not completely terrible. Separately, each query takes ~.01 and ~2 seconds respectively. 2 seconds still seems high to me.
If I try to retrieve a year’s worth of data, it takes several (>10) minutes to run the whole query, which is problematic – the client-server connection sometimes times out, and in any case we don’t want I don’t want to sit there with a spinning ‘please wait’ icon. Mainly, I feel like there’s a problem because it takes more than 12x as long to retrieve 12x more information, when it should take less than 12x as long, if I were doing things right.
Here’s the ‘explain’ for each of the slow queries: (the whole thing, and just the second half).
Whole thing:
+----+--------------------+--------------------+----------------+-------------------------------+------------------+---------+-----------------------------------------------------------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+--------------------+----------------+-------------------------------+------------------+---------+-----------------------------------------------------------------------+------+----------------------------------------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 5053 | Using temporary; Using filesort |
| 1 | PRIMARY | <derived4> | ALL | NULL | NULL | NULL | NULL | 4341 | |
| 4 | DERIVED | meals | range | PRIMARY,day_ind | day_ind | 9 | NULL | 30 | Using where; Using temporary; Using filesort |
| 4 | DERIVED | food_entries | ref | meals_meal_id | meals_meal_id | 5 | nutrition.meals.meal_id | 15 | Using where |
| 4 | DERIVED | recipe_ingredients | ref | foods_food_id,ingred_ndb_no | foods_food_id | 4 | nutrition.food_entries.entry_ident | 2 | |
| 4 | DERIVED | nutr_def | ALL | PRIMARY | NULL | NULL | NULL | 174 | |
| 4 | DERIVED | nut_data | ref | PRIMARY | PRIMARY | 36 | nutrition.nutr_def.nutr_no,nutrition.recipe_ingredients.ingred_ndb_no | 1 | |
| 2 | DERIVED | meals | range | day_ind | day_ind | 9 | NULL | 30 | Using where |
| 2 | DERIVED | nutr_def | ALL | PRIMARY | NULL | NULL | NULL | 174 | Using where |
| 3 | DEPENDENT SUBQUERY | nutr_rights | index_subquery | users_userid,nutr_def_nutr_no | nutr_def_nutr_no | 19 | func | 1 | Using index; Using where |
+----+--------------------+--------------------+----------------+-------------------------------+------------------+---------+-----------------------------------------------------------------------+------+----------------------------------------------+
10 rows in set (2.82 sec)
Second chunk (data):
+----+-------------+--------------------+-------+-----------------------------+---------------+---------+-----------------------------------------------------------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+--------------------+-------+-----------------------------+---------------+---------+-----------------------------------------------------------------------+------+----------------------------------------------+
| 1 | SIMPLE | meals | range | PRIMARY,day_ind | day_ind | 9 | NULL | 30 | Using where; Using temporary; Using filesort |
| 1 | SIMPLE | food_entries | ref | meals_meal_id | meals_meal_id | 5 | nutrition.meals.meal_id | 15 | Using where |
| 1 | SIMPLE | recipe_ingredients | ref | foods_food_id,ingred_ndb_no | foods_food_id | 4 | nutrition.food_entries.entry_ident | 2 | |
| 1 | SIMPLE | nutr_def | ALL | PRIMARY | NULL | NULL | NULL | 174 | |
| 1 | SIMPLE | nut_data | ref | PRIMARY | PRIMARY | 36 | nutrition.nutr_def.nutr_no,nutrition.recipe_ingredients.ingred_ndb_no | 1 | |
+----+-------------+--------------------+-------+-----------------------------+---------------+---------+-----------------------------------------------------------------------+------+----------------------------------------------+
5 rows in set (0.00 sec)
I’ve ‘analyzed’ all the tables involved in the query, and added an index on the datetime field that is joining meals and food entries. I called it ‘day_ind’. I hoped that would accelerate things, but it didn’t seem to make a difference. I also tried removing the ‘sum’ function, as I understand that having a function in the query will frequently mean a full table scan, which is obviously much slower. Unfortunately removing the ‘sum’ didn’t seem to make a difference either (well, about 3-5% or so, but not the order magnitude that I’m looking for).
I would love any suggestions and will be happy to provide any more information you need to help diagnose and improve this problem. Thanks in advance!
Okay, so I eventually figured out what I’m gonna end up doing. I couldn’t make the ‘data’ query any faster – that’s still the bottleneck. But now I’ve made it so the total query process is pretty close to linear, not exponential.
I split the query into two parts and made each one into a temporary table. Then I added an index for each of those temp tables and did the join separately afterwards. This made the total execution time for 1 month of data drop from 8 to 2 seconds, and for 1 year of data from ~10 minutes to ~30 seconds. Good enough for now, I think. I can work with that.
Thanks for the suggestions. Here’s what I ended up doing: