Running a last db server jersey applications and I need to start thinking about memory caching.
The majority of the db commands are only updated once a day. There is an opportinity to cache these queries at the server level.
What options do I have? I know quite a few large applications use memcached. Others??
Any of the Java memcached libraries is probably your best best.
Spymemcached
Memcached-Java-Client
Xmemcached
Memcached is a good default. Redis can be used to. It offers richer functionality should you choose to use it, but if you're use case will always be what memcached offers then there's no particular advantage.
Note that PostgreSQL has an internal cache (the buffer cache) and uses the kernel's disk cache. So tuning the PostgreSQL config for your needs may be a good idea.
In addition to this you could use materialized views for some queries.
Related
I have a java enterprise application that does a lot of fetching of cached data.
The data is stored in a 3 server redis cluster and is accessed by 5 backend api nodes.
I am seeing that we are putting alot of stress on the redis caches, which is why I am wondering if it is dumb to put a in-mem cache such as Ehcache in front of redis. With this solution I would set the TTL to be very short in the Ehcache.
Is this a common solution or is it more reasonable to look into expanding the redis cluster?
Thing you are talking about is called near cache. It's absolutely legit solution in some cases. It provides trade-off between performance and freshness of the values. However you can only consider this option if seeing a bit stale values is tolerable in your case. Just FYI, Apache Ignite supports this feature out of the box.
We are trying to develop a system for distributed caching. Right now, we have 12 applications and they all load same cache. So each jvm loads cache in its in-memory. Problem with this system is redundant data. All 12 applications are loading same cache.
We want to develop a system where you add one or two(for failover) JVM's which load cache and the other 12 applications call these new Cache JVM's.
Can someone suggest me if there are any technologies/frameworks that has solution for my needs?
Thanks
Have a look at Memcached. It may offer a solution to your distributed cache needs.
Also, as #Guy Bouallet mentioned, ehcache is also a viable solution.
Ehcache is a good alternative. It can be used to cache data loaded from database, Web pages or other key/value elements in a distributed environment.
I personally used it in several professional applications and it had shown to be an efficent solution.
I'm looking for a solution to share a cache between two tomcat web apps running on different hosts. The cache is being used for data synchronization, so the cache must be guaranteed to be up-to-date at all times between the two tomcat instances. (Sorry, I'm not 100% sure if the correct terminology for this requirement is "consistency" or something more specific like having ACID property). Another requirement is of course is that it should be fast to access the cache, with about equal numbers of writes as reads. I do have access to a shared filesystem so that is a consideration.
I've looked at something like ehcache but in order to get a shared cache between the webapps I would either need to implement on top of a Terracotta environment or using the new ehcache cache server. The former (Terracotta) seems like overkill for this, while the cache web server seems like it wouldn't provide the fast performance that I want.
Another solution I've looked at is building something simple on top of a fast key-value store like Redis or memcachedb. Redis is in-memory but can easily be configured to be a centralized cache, while memcachedb is a disk-based persistent cache which could work because I have a shared filesystem.
I'm looking for suggestions on how to best solve this problem. The solution needs to be a relatively mature technology as it will be used in a production environment.
Thanks in advance!
I'm quite sure that you don't require terracotta or ehcache server if you need a distributed cache. Ehcache with one of the four replication mechanisms would do.
However, based on what you've written I guess that you're looking for more than just a cache. Memcached/Ehcache are examples of what you might call a caching layer for your application - nothing more.
If you find yourself using words like 'guaranteed' 'up-to-date' 'ACID' you're better off using an in-memory DB like Oracle Times Ten/MySQL Cluster/Redis with a disk-based persistent storage.
You can use memcached (not memcachedb) for fast and efficient caching. Redis or memcachedb could be an overkill unless you want persistent caching. Memcached can be clustered very easily and you can use spymemcached java client to access it. Memcacached is very mature and is running in several hundred thousands, if not millions of production servers. It can be monitored through Nagios and Munin systems when in production.
I am new to memcached and caching in general. I have a java web application running on Ubuntu + Tomcat + MySQL on a VPS Server with 1GB of memory.
Does it make sense to add a memcached layer with about 256MB for caching? Will this be too much load on the server? Which is more appropriate caching rendered html pages or database objects?
Please advise.
If you're going to cache pages, don't use memcached, use Varnish. However, there's a good chance that's not a great use of memory. Cacheing pages trades memory for computation and database work, but it does cost quite a lot of memory per page, so it's best for cases where the computation and database work needed to produce a single page amounts to a lot (or the pages are very small!). Also, consider that page cacheing won't be effective, or even possible, if you want to use per-user customisation on your pages (eg showing the number of items in a shopping cart). At least not without getting into some truly hairy shenanigans (edge-side includes, anyone?).
If you're not going to cache pages, and your app is on a single machine, then there's no point using memcached or similar. The point of cache servers like that is to make the memory on one machine work as a cache for another - like how a file server shares a disk, they're essentially memory servers. On a single machine, you might as well give all the memory to Java and cache objects on the heap.
Are you using an object-relational mapper? If so, see if it has any support for a second-level cache. The big three implementations (Hibernate, OpenJPA, and EclipseLink) all support in-memory caches. They're likely to do a much better job than you would if you did the cacheing yourself.
But, if you're not using a mapper, you have no choice but to do the cacheing yourself. There are extension points in LinkedHashMap for building LRU caches, and then of course there's the people's favourite, SoftReference, in combination with a HashMap. Plus, there are probably cache implementations out there you could download and use - i'd be shocked if there wasn't something in the Apache Commons libraries.
memcached won't add any noticeable load on your server, but it will be memory your app can't use. If you only plan to have a single app server for a while, you're better off using an in-JVM cache.
As far what to cache, the answer falls somewhere in the middle of the above. You don't want to cache exactly what's in your database and you certainly don't want to cache the final output. You have a data model representation in your application that isn't exactly what's in the DB (e.g. a User object might be made up of multiple queries from a few different tables). Cache that kind of thing as it's most reusable.
There's lots of info in the memcached site that should help you understand and get going with caching in general and memcached specifically.
It might make sense to do that, why don't try a smaller size like 64 MB and see how that goes. When you use more resources for the memcache, there is less for everything else. You should try it and see what will give you the best performance.
Not really a question but I'm looking for comments/suggestions from anyone who has experiences using one or more of the following:
EhCache with RMI
EhCache with JGroups
EhCache with Terracotta
Gigaspaces Data Grid
A bit of background: our applications is read only for the most part but there is some user data that is read-write and some that is only written (and can also be reasonably inaccurate). In addition, it would be nice to have tools that enable us to flush and fill the cache at intervals or by admin intervention.
Regarding the first option - are there any concerns about the overhead of RMI and performance of Java serialization?
I'm working with EhCache for Hibernate and for application level cache since 3 years ago.
We use it with RMI for cache invalidation and it works really good. If you use the cache for replication you should take care about the object graph, it could turn very heavy with high cardinality relations.
If you use EhCache for Hibernate you could use it for Query cache (it's a good improvement for read-only tables) and it the table is modified it cleans the cache automatically.
Using EhCache to cache collections is a good idea too, to avoid joins a sub-selects.
To clean the caches at time intervals you could implement a cache extension of EhCache that cleans the caches. We did it, it works well.
Also check out Hazelcast, Coherence and GemStone. These are distributed caching solutions with Query support. They also have ready-to-go second level cache plug-in for Hibernate. Hazelcast is open source.