[HarrisonFisk]

Right, PG calls the REDO log the WAL (for most purposes they are the same thing). I did not know that 9.4 can do partial page writes to the WAL now. Guess I will have more reading to do, thanks for pointing it out! A nice blog post by a colleague recently showing how large writes to redo logs matter is (not about PG, but why it is significant in the context of size of entries):

http://smalldatum.blogspot.com/2014/03/redo-logs-in-mongodb-...

As far as when clustering a table is useful, see the CLUSTER command in PG. It is roughly the same places you would want to do it, except it is automatically maintained. You do need to realize what is going on to minimize impact on inserts, but in a lot of cases, data in inserted in generally ascending order so it mostly 'free'. This does make GUIDs really bad for PKs in InnoDB.

Clustered indexes are like covering indexes (which PG got recently). You don't quite realize how useful they are until you get access to it ;)

InnoDB compression for us is primarily for non-lob objects, so TOAST is quite a bit different than the cross-row compression that we get. We will normally do compression of large objects outside of the DB whenever possible.

I'm not saying that InnoDB is always better than PG, but in a lot of cases that I have tested it with, it is indeed better. PG has come a long way recently, including options such as covering indexes to close the gap.