Sitecore index rebuilding practices
lucene, sitecore, sitecore6
Solution
If you have multiple servers you can take out one of them from the load balancer (or stop it from delivering content in any other way) and rebuild the index on this server. While it's done, just put it back in load balancer.
You can also try to use Sitecore Lucene Refresher.
Take a look at how to maintain sitecore lucene indexes in huge content delivery webfarm for more options.
Problem
In our sitecore project (6.6.0 rev. 130404), we have more than 2 million total sitecore items. We have several Lucene indexes (each for a subset of these items) configured. The issue we face is the time it takes to freshly rebuild these indexes. Specially with the Sitecore's QuickSearch index, it might take nearly a full day to rebuild that index, in addition to our custom indexes. What are the usual practices followed with maintenance of large sitecore indexes in day-to-day operations? How often would you need to rebuild indexes? and when you do, how to cope with long website down-time (index rebuilding makes the index offline)?