Collection + Concurrent Update
Dustin Sallings
dustin at spy.net
Thu Feb 21 21:45:20 UTC 2008
cas was created for this scenario.
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Dustin Sallings (mobile)
On Feb 21, 2008, at 13:23, "Rakesh Rajan" <rakeshxp at gmail.com> wrote:
> Hi,
>
> I am using memcached to store a lot of collections. An example would
> be, for a given item, a collection of integers representing various
> attributes. Now, since there can be concurrent update to the
> collection ( addition / deletion / updation ), there are times when
> the cached data gets stale/dirty. Example
> Current Cache [ 1,2]
>
> Thread 1 ( Added 3 ) : [1,2,3]
> Thread 2 ( Added 4 ) : [1,2,4]
> Thread 3 ( Removed 2 ) : [1]
>
> Now when all 3 threads tries to update the cache, cache becomes
> dirty. One way to solve this is, for every set operation, I would
> need to get the current cached collection and then perform operation
> ( addition/deletion/updation) on it before setting it back ( with
> the write operation acquiring a lock first ).
>
> For a typical write, I do
> -> Take a lock ( with ~1-2 secs timeout)
> -> Fetch the current cache value ( if any)
> -> Perform the operation between the cached data and the
> newer data ( addition/deletion/updation)
> -> Update the cache with the newer collection
> -> Release the lock ( this is purely a safety mechanism : in the
> finally block of the java code )
>
> So every write operation, I need to make 4 memcached calls which I
> believe is not a good solution ( since it is in the same thread).
> One possible solution that I was thinking was making the cache
> update async process. Would love to hear how this case is generally
> solved / opinions ? ( In my case collections are either Set / List )
>
> -Rakesh
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