Optimizing a Server: prelink

When most people think about server optimization, it’s almost always a question of tuning MySQL, deciding how many HTTPD processes should be running, limiting the maximum connections to the server, and installing a caching proxy like Varnish or Squid.

While all of these optimizations should be performed, they’re not the only optimizations we can perform on a server. In fact, there’s something simple that can improve performance of the system globally, without any configuration!

When a program is run, there are a few things that have to happen before it can actually start doing work. First, the program is loaded into server memory. Next, ld.so processes the binary, loading all of the libraries (.so files, shared objects) that it needs–a step called dynamic linking. Finally, the program will start running from its main() function.

While there’s not much that can be done to speed up loading the binary into memory, other than getting faster disks, the dynamic linking step can be made faster. How? With prelink.

prelink is run on every binary and library on the system, pre-computing the locations of all of the libraries, so that they can be loaded into the same place in memory (barring no conflicts) every time a program starts. This significantly reduces the amount of time needed for the dynamic linking step of the program loading process, allowing programs to reach execution much faster.

To install prelink, run:

yum install prelink

Next, force prelink to pre-link all binaries on the system right now by running:

/usr/sbin/prelink --all

All programs on the system are now prelink'd. The prelink package adds a cron job that runs daily to check for any binaries that may have changed since the last prelink run, and updates them as needed.

Enjoy faster process start up times, thanks to prelink.

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