How many searches per day can be served?
Searching an index of ten thousand documents takes between 0.5 and 4.0 seconds for a normal 500 MHz processor. The search activity tends to be CPU bound and scales linearly with CPU speed and also linearly with multiple processors.
For a basic traffic estimate, lets assume that each search takes 2 seconds to complete (average of the observed 0.5 to 4.0 second range).
We know that traffic is not spread out evenly during the day. At peak times, there might be about 4 times more traffic than average. So, at peak times, FDSE can handle one search per 2 seconds, which maps to 1800 searches / hour. A site that gets about 1800 searches / hour at peak is probably serving 1/4th that, or 500 searches/hour, as a daily average. 500 searches / hour maps to 12,000 search queries per day.
Your experience will vary, probably by an order of magnitude. FDSE on your site might serve 1200 daily queries, or 120,000 daily queries. The purpose of this analysis is just to give some very rough numbers to reassure those whose sites will have less than 1200 daily searches, and to warn off those whose sites get more than 120,000 daily searches.
The search speed is highly dependent on content and on the power of the server. A faster-than-average server and a smaller-than-average search index will be able to serve more visitors more quickly. A collection of all the known speed-enhancement tips can be found at:
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