So I have this method which runs fine + snappy with explicit in-memory
data structures, but I've put it into datamapper and it just takes
forever.
In my Blog class, sometimes I need to do a funky method, foo, that
loops through all the posts, and then further loops through some more
qualities which imply other posts that need to be looped through. It
should take something like O(posts^2) time. So I have a method in the
Blog class which does something like:
def foo
posts.each{|post|
qualities = post.qualities.transform_in_some_way
# number of qualities of each post is bounded by the total # of
posts
qualities.each{|quality|
otherpost = posts.first(:quality => quality)
# I can guarantee otherpost never == post because of the
transform
# I can also guarantee otherpost is unique
x = otherpost.propertya if some_condition?
y = otherpost.propertyb if another_condition?
}
post.update({:propertya => x, :propertyb => y})
}
end
This runs very slowly, but not because of the posts^2 operations. In
particular, 2/3 of the time in foo appears to be taken in the call to
update() (i.e., commenting out the update() call makes it run 3x
faster). I've tried looking at the individual SQL calls corresponding
to the updates with the :debug logger, and they seem to take less than
1/10th the time that DM requires to process them. Any thoughts?
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