While they aren't distributed, Apache Lucene and Apache Lucy (the "loose C" port of Lucene that I work on) both implement MVCC: each index reader object represe

While they aren't distributed, Apache Lucene and Apache Lucy (the "loose C" port of Lucene that I work on) both implement MVCC: each index reader object represents a point-in-time view of the index that persists for the object's lifetime. Core developers such as myself have to deal with some subtleties when implementing MVCC, but I wouldn't say that MVCC is too terribly hard for our users. The thing is, our interface does not look anything like SQL -- you have to use a different mental model when interacting with our data stores, and of course they are not suitable for all applications where you might use SQL. What I took away from the article is that MVCC does not fit well within SQL semantics.