Create benchmark & approach for testing Lucene's near real-time performance [LUCENE-2061]

With the improvements to contrib/benchmark in #3126, it's now
possible to create compelling algs to test indexing & searching
throughput against a periodically reopened near-real-time reader from
the IndexWriter.

Coming out of the discussions in #2600, I think to properly
characterize NRT, we should measure net search throughput as a
function of both reopen rate (ie how often you get a new NRT reader
from the writer) and indexing rate. We should also separately measure
pure adds vs updates (deletes + adds); the latter is much more work
for Lucene.

This can help apps make capacity decisions... and can help us test
performance of pending improvements for NRT (eg #2390,
LUCENE-2047).

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Migrated from [LUCENE-2061](https://issues.apache.org/jira/browse/LUCENE-2061) by Michael McCandless (@mikemccand), updated Nov 29 2009
Attachments: [LUCENE-2061.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-2061/LUCENE-2061.patch) (versions: 3)