What kind of database should I use because MySQL is not meeting my need?
Currently, I am using MySQL but I feel it is not keeping up with the stream data that is coming. I have memcached in front of MySQL for caching, but most the data is accessed for single time so the cache is not helping much. The other problem is the ibdata file keeps getting bigger and even deleting data won't claim disk space. 

The data is short, average 200 charers. I just want store the data and retrieve it using a key. There is no complex data relationship. There are about 100,000 insert and get in hour but getting much bigger. I even tried Amazon RDS service, but the latency between EC2 and RDS within the same region is slow I started getting MySQL too many connection error.

I know that I have to use Nosql type of database, but not sure which one. Disk space is important that I need to claim it when I delete data.
What kind of database should I use because MySQL is not meeting my need?
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Currently, I am using MySQL but I feel it is not keeping up with the stream data that is coming. I have memcached in front of MySQL for caching, but most the data is accessed for single time so the cache is not helping much. The other problem is the ibdata file keeps getting bigger and even deleting data won't claim disk space. 

The data is short, average 200 charers. I just want store the data and retrieve it using a key. There is no complex data relationship. There are about 100,000 insert and get in hour but getting much bigger. I even tried Amazon RDS service, but the latency between EC2 and RDS within the same region is slow I started getting MySQL too many connection error.

I know that I have to use Nosql type of database, but not sure which one. Disk space is important that I need to claim it when I delete data.