The database replicas are in a different datacenter than Tools Labs. The resulting latency (26ms per query) has a major performance impact on tools that need to make many queries. This prevents the migration of many Toolserver tools (notably crosswiki tools).
This is a tracking ticket for plans to combine the datacenters to address this, mentioned here: http://lists.wikimedia.org/pipermail/labs-l/2013-September/001574.html
The following scripts reproduce the latency issue. They open a connection to each database server, then execute a sample query for each wiki ("use xxwiki").
Toolserver: https://toolserver.org/~pathoschild/accounteligibility/test.php |
Tools Labs: http://tools.wmflabs.org/pathoschild-contrib/accounteligibility/test.php | source: http://pastebin.com/Xi3abGFP
This runs in 0.3 seconds on the Toolserver, but takes a whopping 23 seconds on
Tools Labs. The scripts shows the profiling results at the bottom of the page (click the [+] next to "Page generated in XX seconds").