Database Reference
In-Depth Information
The catch is that this application has two significant shortcomings. First, it is a
memory-only database. If the power goes out, then all the data is lost. Second, you can't
actually search for data using memcached; you can only request specific keys.
These might sound like serious limitations; however, you must remember the
problems that memcached is designed to solve. First and foremost, memcached is a
data cache. That is, it's not supposed to be a permanent data store, but only to provide
a caching layer for your existing database. When you build a dynamic web page, you
generally request very specific data (such as the current top ten articles). This means you
can specifically ask memcached for that data—there is no need to perform a search. If the
cache is out-of-date or empty, you would query your database as normal, build up the
data, and then store it in memcached for future use.
Once you accept these limitations, you can see how memcached offers superb
performance by implementing a very limited feature set. This performance, by the way,
is unmatched by that of a traditional database. That said, memcached certainly can't
replace an RDBMS. The important thing to keep in mind is that it's not supposed to.
Compared to memcached, MongoDB is itself feature-rich. To be useful, MongoDB
must offer a strong set of features, such as the ability to search for specific documents.
It must also be able to store those documents on disk, so that they can survive a reboot.
Fortunately, MongoDB provides enough features to be a strong contender for most web
applications and many other types of applications as well.
Like memcached, MongoDB is not a one-size-fits-all database. As is usually the case
in computing, tradeoffs must be made to achieve the intended goals of the application.
Running the Database Anywhere
MongoDB is written in C++, which makes it relatively easy to port and/or run the
application practically anywhere. Currently, binaries can be downloaded from the
MongoDB website for Linux, Mac OS, Windows, and Solaris. There are also various
official versions available for Fedora and CentOS, among other platforms. You can even
download the source code and build your own MongoDB, although it is recommended
that you use the provided binaries wherever possible. All the binaries are available in
both 32-bit and 64-bit versions.
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the 32-bit version of MongodB is limited to databases of 2gB or less. this is
because MongodB uses memory-mapped files internally to achieve high performance.
anything larger than 2gB on a 32-bit system would require some fancy footwork that wouldn't
be fast and would also complicate the application's code. the official stance on this limitation
is that 64-bit environments are easily available; therefore, increasing code complexity is not a
good tradeoff. the 64-bit version for all intents and purposes has no such restriction.
Caution
MongoDB's modest requirements allow it to run on high-powered servers or virtual
machines, and even to power cloud-based applications. By keeping things simple and
focusing on speed and efficiency, MongoDB provides solid performance wherever you
choose to deploy it.
