Experimenting with SimpleDB (Flagthis.com)
The initial version of this tool used MySQL database. The original application architecture was very simple, and other than the database it could have scaled horizontally. Over the weekend I played a little with SimpleDB and was able to convert my code to use SimpleDB in a matter of hours.
Here are some things I observed during my experimentation
- Its not a relational database.
- Can’t do joins in the database. If joins have to be done, it has to be done at the application which can be very expensive .
- De-normalizing data is recommended.
- Schemaless: You can add new columns (which are actually just new row attributes) anytime you want.
- You have to create your own unique row identifiers. SimpleDB doesn’t have a concept of auto-increment
- All attributes are auto-Indexed. I think in Google App Engine you had to specify which columns need indexing. I’m wondering if this would increase cost of using SimpleDB.
- Data is automatically replicated across Amazon’s huge SimpleDB cloud. But they only guarantee something called “Eventually Consistent”. Which means data which is “put” into the system is not guaranteed to be available in the next “get”.
- I couldn’t find a GUI based tool to browse my SimpleDB like the way some S3 browsers do. I’m sure someone will come up with something soon. [Updated: Jeff blogged about some simpleDB tools here]
- There are limits imposed by SimpleDB on the amount of data you can put in. Look at the tables below.
|domains||100 active domains|
|size of domains||10GB|
|attributes per domain||250,000,000|
|attributes per item||256 attributes|
|size per attribute||1024 characters|
|items returned in a query response||250 items|
|seconds a query may run||5 seconds|
|attribute names per query predicate||1 attribute name|
|comparisons per predicate||10 operators|
|predicates per query expression||10 predicates|
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