What's the best way to run (many) complex queries in a rake task ?

rubyonrails-talk
1

Hi everyone,

I'm currently working on a project which will execute a rake task from time to time, and said taks involves a complex recommendation algorithm that can be accomplished with a complex SQL query.

I may use a single one to do everything, or a lot of them, one per item to be computed. The nature of the query isn't in cause here, it's just

2

Hi everyone,

I'm currently working on a project which will execute a rake task from time to time, and said taks involves a complex recommendation algorithm that can be accomplished with a complex SQL query.

I may use a single one to do everything, or a lot of them, one per item to be computed. The nature of the query isn't in cause here, it's just

################# ######## ONE SINGLE QUERY query "INSERT INTO deviations(pivot_id, deviant_id, value) SELECT ratings.content_id as pivot_id, ratings2.content_id as deviant_id, AVG(ratings.rate - ratings2.rate) as value FROM ratings INNER JOIN ratings as ratings2 ON ratings.viewer_id = ratings2.viewer_id AND ratings.viewer_type = ratings2.viewer_type AND ratings.content_id < ratings2.content_id GROUP BY pivot_id, deviant_id"

ActiveRecord::Base.connection().execute(query)

######## MULTIPLE QUERIES sql = ActiveRecord::Base.connection() ids.each do |id| query = "INSERT INTO deviations(pivot_id, deviant_id, value) SELECT #{id.to_i} as pivot_id, ratings2.content_id as deviant_id, AVG(ratings.rate - ratings2.rate) as value FROM ratings INNER JOIN ratings as ratings2 ON ratings.viewer_id = ratings2.viewer_id AND ratings.viewer_type = ratings2.viewer_type AND ratings.content_id = #{id.to_i} AND ratings.content_id < ratings2.content_id GROUP BY deviant_id" sql.execute(query) end #################

Just for curiosity sake, I have an index on [viewer_id, viewer_type, content_id]

I teste performance, for the single query variant and the multiple queries variant, and then changed MySQL so I can have more memory and the temp tables aren't stored in the hard drive. After changing MySQL settings, the single query variant improved, (268sec vs 80sec) but the multiple queries variant took almost twice the time. (190sec vs 390sec) What the...??

hard to say without knowing what you changed. Take a look at your query plans (use explain) to see if your queries could be better. If your tables are innodb you'll might also want to increase the innodb buffer pool size

I checked process info, and it's just using one of the four available CPUs.

What can I do to improve this performance? How to use all the available CPUs?

Is it to create multiple threads inside the rake task, and then use a connection per task with multiple queries?? Am I doing something fundamentally wrong here?

Running multiple queries in parallel won't help if you are IO bound (also unfortunately running a mysql query with the standard ruby mysql gem will block all threads in the ruby interpreter).

Fred

3

Use the spawn plugin to fork new processes for each query once you address the database optimizations.

4

Just for curiosity sake, I have an index on [viewer_id, viewer_type, content_id]

Maybe, you want to include the rate in the index as well? That way, everything is in the index, and I would presume, MYSQL will not have to access the table at all.