Greetings all, I am looking for some insight from some of the more
experienced with has_many :through relationships as I am having a hard
time reconciling the performance I am seeing.
I have 2 tables that are linked together via has_many :through
Table 1: urls ( there are about 7,000 records )
2 fields, id and url
Table 2: phrases ( there are about 87,000 records )
2 fields, id and phrase (w/ an index defined on phrase)
A given url can be associated w/ many phrases and a given phrase can be
associated with many urls.
Table 3: relations ( there are about 235,000 records )
id, url_id, phrase_id and isrel (int)
w/ an index created on url_id,phrase_id
In Relation model I have
In Url model I have
has_many :phrases, :through => :relations
In Phrase model I have
has_many :urls, :through => :relations
For a given phrase I can access phrase.urls wthout any performance
issues, I see this in my Lighttpd console:
Url Load (0.423328) SELECT urls.* FROM urls INNER JOIN relations ON
urls.id = relations.url_id WHERE (relations.phrase_id = 12)
The problem is apparent when I try to access url.phrases for any url
object, my console screen fills up with these:
Phrase Load (0.006682) SELECT phrases.* FROM phrases INNER JOIN
relations ON phrases.id = relations.phrase_id WHERE (relations.url_id =
one of those messages for each url, and there can be up to 7k urls for a
I know little about optimizing MySQL databases and I am wondering if I
need to tweak the way the tables are structured or if its something I
can fine-tune in rails.
If it helps the indices were defined on the relations table as follows:
CREATE unique index phrase_url on relations (phrase_id, url_id)
CREATE unique index url_phrase on relations (url_id,phrase_id)
( started with just the first index and added the second when these
issues started popping up )
I am hoping someone can spot the problem and suggest a modification to
either the DB or the relationship in rails that leads to a solution.
Thanks for any suggestions!