race condition might happen when use memcached in such scenario
biao zhang
I found a question on Stack Overflow which is about race condition which is not easy to solve:
http://stackoverflow.com/questions/7802772/cache-consistency-when-using-memcached-and-a-rdbms-like-mysql
the question is:
I have taken a database class this semester and we are studying about maintaining cache consistency between the RDBMS and a cache server such as memcached. The consistency issues arise when there are race conditions. For example: 1. Suppose I do a get(key) from the cache and their is a cache miss. Because I get a cache miss, I fetch the data from the database, and then do a put(key,value) into the cache. 2. But, a race condition might happen, where some other user might delete the data I fetched from the database. This delete might happen before I do a put into the cache.
Thus, ideally the put into the cache should not happen, since the data is longer present into the database.
If the cache entry has a TTL, the entry in the cache might expire. But still, their is a window where the data in the cache is inconsistent with the database.
Does anyone know how to prevent race condition in that scenario?
Thanks in advance.
Best Regards,
Steve
Brian Moon
> maintaining cache consistency between the RDBMS and a cache server such
> as memcached. The consistency issues arise when there are race
> conditions. For example: 1. Suppose I do a get(key) from the cache and
> their is a cache miss. Because I get a cache miss, I fetch the data from
> the database, and then do a put(key,value) into the cache. 2. But, a
> race condition might happen, where some other user might delete the data
> I fetched from the database. This delete might happen before I do a put
> into the cache.
>
> Thus, ideally the put into the cache should not happen, since the data
> is longer present into the database.
>
> If the cache entry has a TTL, the entry in the cache might expire. But
> still, their is a window where the data in the cache is inconsistent
> with the database.
>
>
> Does anyone know how to prevent race condition in that scenario?
on the memcache data.
Sounds like maybe you are doing query based caching which is caching 101
and only holds up for a very short time or can last when you understand
the caveats and are willing to live with them.
Brian.
abinesh td
- Gumball technique developed at USC
- http://abineshtd.blogspot.com/2012/09/gumball-race-condition-prevention.html
- http://dblab.usc.edu/Users/papers/GumballTR.pdf
- A solution in McDipper developed at Facebook
biao zhang
Best Regards,
Steve
charles merto
Suppose that we have a message passing system using mailboxes. When sending to a full mail box or trying to receive from an empty one, a process does not block, instead, it gets an error code back. The process responds to the error code by just trying again, over and over, until it succeeds. Does this lead to RACE CONDITION?
Ryan McElroy
Suppose that we have a message passing system using mailboxes. When sending to a full mail box or trying to receive from an empty one, a process does not block, instead, it gets an error code back. The process responds to the error code by just trying again, over and over, until it succeeds. Does this lead to RACE CONDITION?can someone help me pls :(
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