Gear6 Web Cache Server FAQ

1. Why is the effective Memcached capacity bigger than memory size of the Amazon machine that’s running it (e.g. 1.7GB “m1.small” machine offers 6.17GB of Memcached storage)?
A: Gear6 Memcached Server uses Amazon’s attached block devices to transparently add Memcached capacity to the server. It also overcomes the 4GB memory size limitation of 32bit architectures.
 
2. How does that work? Do I need to change anything in my Memcached application?
A: No need to change anything. The system automatically makes a bigger server available by intelligently using the Amazon instance’s RAM and block device(s).
 
3. Does it cost any more to use these block devices for extra Memcached capacity?
A: No. Our Memcached server uses the included block devices which come with each Amazon instance type from m1.small all the way to m2.4xlarge. These are built-in to in the base cost of running the Amazon instance and do not incur additional charges (like EBS or S3 services).
 
4. How is performance? Aren’t block devices slower than RAM?
A: Our Memcached server intelligently places frequently used items in RAM (fast) and moves less frequently used items onto slower block devices. It constantly auto tunes placement and will evict the least interesting items to make room for new data using frequency of access and other criteria. Overall performance should be comparable to a memory-only server. The web user interface shows the block device utilization under the “Storage” tab.
 
5. Is your server multithreaded? Can it take advantage of multi-processor (high CPU) instances?
A: Yes. The server auto tunes to the container it is started in and will automatically adjust concurrency and threading internally to take advantage of the hardware platform. That said, it really cares more about memory than CPU, so high memory instances (e.g. m2.4xlarge) are perfect for it.
 
6. How far back does the web UI go when showing data?
A: The web UI provides a rolling 24-hour look back into stats.
 
7. I see some Memcached stats I didn’t recognize. What are these?
A: The server provides some new synthetic stats describing health and response time. They are on the “health” tab. It also shows the block device utilization under “Storage”.
 
8. How about APIs – can I talk to the server and get management data such as stats? Do you have a REST API?
A: Yes. Normal Memcached telnet stats are available, but also a REST API for all stats is available under http://< instance ip >/api/MemcacheServer/latest/self/stats/{basic, items, storage, health,...}
 
9. How does that work?
A: Say you wanted to read the amount of evictions and feed that into an auto scaling application. By reading http://< instance ip >/api/MemcacheServer/latest/self/stats/basic/evictions you’ll get the current number of evictions returned as an XML document. Your scaling system could react to that by turning on or off Memcached servers dynamically as needed.
 
10. Is this free? How about support? Do you provide support?
A: Yes. 32 bit versions are free to run. 64 bit versions incur small charges paid through Amazon. Support is available for the free 32-Bit versions on our forums.  The 64-Bit versions include paid 24x7 email support and forums.