Yes, I said InnoDB+ with a plus sign at the end (also see the first comment here).

Please note that this blog post is only based on public information. It has absolutely nothing in it that I only could have learned from back when I worked at Sun or MySQL AB. Everything has links or pointers to where you can find the information out on the Internet and all thoughts are based on stringing these things together.

There was a lot of talk around the acquisition of Sun Microsystems by Oracle about MySQL (MySQL AB was bought by Sun). Some of the talk centred around Oracle and their ability to make a closed source version of MySQL with added bits that wouldn’t be released as GPL. They’ve since proved that they’re quite willing to do this to an open source project (see OpenSolaris).

Relatively recently, a bunch of history from the old InnoDB SVN trees was imported into the MySQL source tree. You can pull the revision of the SVN tree as of InnoDB Plugin 1.0.6 release by using revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/zip:6263  from the MySQL repository – or just use a branch I’ve put up on launchpad for it (lp:~stewart/haildb/innodb-1.0.6-from-svn).

The first revision from the SVN tree was created on 2005-10-27, which you may remember was not too long after Oracle acquired Innobase on the 7th of October that year. The next two revisions were importing the 5.0 innodb code base, and then the 5.1 code base. Previous history can be found according to this blog post on Transactions on InnoDB.

According to Monty in the comment on the Pythian blog:

Oracle did work on a closed source version of InnoDB, codename InnoDB+, but they never released it, probably because our contract with them stopped them.

and from Eben Moglen’s letter to the EU Commission (via Baron Schwartz’s blog post):

Innobase could therefore have provided an enhanced version of InnoDB, like Oracle’s current InnoDB+, under non-GPL license

Most tellingly is a lot of references in the revision history to “branches/innodb+” as well as this commit:

revno: 0.5.148
revision-id: svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6329
parent: svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6322
committer: vasil
timestamp: Thu 2009-12-17 11:00:17 +0000
message:
branches/innodb+: change name and version
Change name from “InnoDB Plugin” to “InnoDB+” and
version from 1.0.5 to 1.0.0.

So, from the revision history I’ve managed to work out that it likely was going to have the following features:

• innodb_change_buffering (for values other than inserts)
  See revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/zip:4061
  Or, more tellingly revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:4053
  The latter tells about the merge of change buffering for delete-mark and delete in addition to the default of inserts.
• Possibly compressed tables.
  revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:2316 seems to show that it may have been copied across: “branches/innodb+: Copy from branches/zip r2315” in the comment.  There’s a lot of other merges of branches/zip as well
• Something named FTS
  There is “branches/fts” in revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:2325 and revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:2324  (there’s an import of a red-black tree implementation)
  If you also look at revid: svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6776
  you’ll see references to a innofts+ branch with ha_innodb.cc in it.
  So between a red-black tree and handler changes, this is surely something interesting.
• Persistent statistics (also revid: svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6776)
• Metrics Table (also revid: svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6776)
• posix_fadvise() hints to temp files used in creating indexes (revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:2342 )
• Improved recovery performance
  See revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:2989
  Talks about using the red-black tree for sorted insertion into the flush_list
• native linux aio (revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:3913 )
• group commit (revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:3923 )
• New mutex to protect flush_list (revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6330)

and finally, in revid:svn-v4:16c675df-0fcb-4bc9-8058-dcc011a37293:branches/innodb%2B:6819 you can see the change from “InnoDB+” back to “InnoDB” for being the built in default for MySQL 5.5