MediaWiki－1.2的内置负载均衡：30秒超时约束对于master／slave两端的影响

On the hardware side, MediaWiki has built-in support for load balancing, added as early as 2004 in MediaWiki 1.2 (when Wikipedia got its second server—a big deal at the time). The load balancer (MediaWiki's PHP code that decides which server to connect to) is now a critical part of Wikimedia's infrastructure, which explains its influence on some algorithm decisions in the code. The system administrator can specify, in MediaWiki's configuration, that there is one master database server and any number of slave database servers; a weight can be assigned to each server. The load balancer will send all writes to the master, and will balance reads according to the weights. It also keeps track of the replication lag of each slave. If a slave's replication lag exceeds 30 seconds, it will not receive any read queries to allow it to catch up; if all slaves are lagged more than 30 seconds, MediaWiki will automatically put itself in read-only mode.