Has anyone experienced an ActiveRecord query being much much slower than
running the equivalent
query in the MySql console?
I am running a simple “group by” query with one condition on a table
million records. When
I run EXPLAIN it says that it will have to scan over all the records -
that’s OK. In the MySQL
query it takes 1min 40secs which is OK for me - this is not a web app.
when I run exactly
the same query in a ruby script using ActiveRecord it takes about 45
far too long.
I am running all this on my work PC, 3 gig of memory. Windows PerfMon
I have 2 gig available
and 1 gig on standyby. I am using ruby 1.8.7; rails 3; mysql2 gem;
7 and MySql 5.5.
I have also set the INNODB buffer pool size to 480M.
What seems to be happening is that the MySQL process uses all the memory
to 500M and
there is a lot of page swapping. PerfMon shows that the disk activity
very high (99%). So
that explains the bottleneck. But I still don’t know why this happens
I run the code from
Ruby and yet from the MySQL console it is fine.
I even tried just using the MySQL2 gem directly in my ruby code using
but still very very slow.
I know this probably doesn’t explain everything but I just wondered if
anyone had a similar experience.
p.s. also posed on StackOverflow.