I was originally going to ask why it was better to use Memcached vs APC (which is faster) but I did a search, and Memcached is best for distributed systems across multiple web servers, whereas APC is better used for reading/writing on one server.
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ajindia
What if there are more web servers accessing the cache than the database itself. Wouldn't this cause the same problem?
Could it be better to have a cache for each server?
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monster
Cache is far more faster than communicating with database, since dealing with the queries in the database cost more time. Therefore even though more web servers accessing the cache than the database, it will stil save time. If each server has its own cache, it may cost more time when dealing with concurrency and consistency if we modify the database. We can also add some Front-end Cache to cache some web server response.
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briandecost
@ajindia: i imagine contention for the cache would incur a smaller performance hit than contention for the database, because a cache lookup ought to be significantly cheaper than a database lookup. On slide 34 there is an example which uses a set of front-end caches in addition to memcached, which is similar to your suggestion.
You probably wouldn't want to trade the shared cache for front-end or server-specific caches though, because the front-end caches might end up holding replicated data, effectively reducing how much information you can fit in the cache system.
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briandecost
An alternative is to add more caches as shown in slide 32. This could be done either by replication or by partitioning of the data in cache, in the same manner as these links show the replication and partitioning of data across multiple databases.
I was originally going to ask why it was better to use Memcached vs APC (which is faster) but I did a search, and Memcached is best for distributed systems across multiple web servers, whereas APC is better used for reading/writing on one server.
This comment was marked helpful 0 times.
What if there are more web servers accessing the cache than the database itself. Wouldn't this cause the same problem? Could it be better to have a cache for each server?
This comment was marked helpful 0 times.
Cache is far more faster than communicating with database, since dealing with the queries in the database cost more time. Therefore even though more web servers accessing the cache than the database, it will stil save time. If each server has its own cache, it may cost more time when dealing with concurrency and consistency if we modify the database. We can also add some Front-end Cache to cache some web server response.
This comment was marked helpful 0 times.
@ajindia: i imagine contention for the cache would incur a smaller performance hit than contention for the database, because a cache lookup ought to be significantly cheaper than a database lookup. On slide 34 there is an example which uses a set of front-end caches in addition to memcached, which is similar to your suggestion.
You probably wouldn't want to trade the shared cache for front-end or server-specific caches though, because the front-end caches might end up holding replicated data, effectively reducing how much information you can fit in the cache system.
This comment was marked helpful 0 times.
An alternative is to add more caches as shown in slide 32. This could be done either by replication or by partitioning of the data in cache, in the same manner as these links show the replication and partitioning of data across multiple databases.
This comment was marked helpful 0 times.