Here is the logic that I am trying to achieve. I have a User Model and
the business rule is that user can accept maximum 5 friends requests.
for this I have an accept method in User Model which looks similar to
below code snippet
raise ArgumentError if self.friends.count >= MAX_FRIENDS_ALLOWED
#code to add friend to friends list
As you can see that I basically query for count of friends for a user
and if the count is greater then or equal to MAX_FRIENDS_ALLOWED the
friend accept request should not go through.
From the UI perspective I have a link_to_remote, “Accept” link that
calls an action which calls the User Model’s “accept” method. Basically
UI looks like
FRIEND NAME | Action
AAAAA | Accept
BBBBB | Accept
CCCCC | Accept
DDDDD | Accept
EEEEE | Accept
FFFFF | Accept
Now from UI I try to accept multiple friends requests by clicking on
“Accept” link (which makes an ajax request) quickly.
When I run this in under normal development environment (running single
mongrel), everything works fine i.e. the validation put in User Model’s
“accept” method works.
After that I configured 4 mongrel in a cluster and ran it behind
lighttpd and then ran in to trouble.
I guess the problem here is that since I run cluster of mongrels each
mongrel executes the request in separate process because of which before
the a friend is accepted, another process executes “self.friends.count”
and it will not reflect the updated count. I tried to enclose the above
statements in Activerecord transaction, but it did not work and the
reason I think is that transaction is per-database connection and each
process will spawn a separate connection.
Please suggest any workarounds or probably solution to this issue.