As I said in another thread, I pushed parts 0002,0003,0004. Tomas said he would try to rebase patches 0001,0005,0006 on top of what was committed. My intention is to give that one a look as soon as it is available. So we will have n-distinct and functional dependencies in PG10. It sounds unlikely that we will get MCVs and histograms in, since they're each a lot of code.
I've been working on the MV functional dependencies part of the patch to polish it up a bit. Tomas has been busy with a few other duties.
I've made some changes around how clauselist_selectivity() determines if it should try to apply any extended stats. The solution I came up with was to add two parameters to this function, one for the RelOptInfo in question, and one a bool to control if we should try to apply any extended stats. For clauselist_selectivity() usage involving join rels we just pass the rel as NULL, that way we can skip all the extended stats stuff with very low overhead. When we actually have a base relation to pass along we can do so, along with a true tryextstats value to have the function attempt to use any extended stats to assist with the selectivity estimation.
When adding these two parameters I had 2nd thoughts that the "tryextstats" was required at all. We could just have this controlled by if the rel is a base rel of kind RTE_RELATION. I ended up having to pass these parameters further, down to clauselist_selectivity's singleton couterpart, clause_selectivity(). This was due to clause_selectivity() calling clauselist_selectivity() for some clause types. I'm not entirely sure if this is actually required, but I can't see any reason for it to cause problems.
I've also attempted to simplify some of the logic within clauselist_selectivity and some other parts of clausesel.c to remove some unneeded code and make it a bit more efficient. For example, we no longer count the attributes in the clause list before calling a similar function to retrieve the actual attnums. This is now done as a single step.
I've not yet quite gotten as far as I'd like with this. I'd quite like to see clauselist_ext_split() gone, and instead we could build up a bitmapset of clause list indexes to ignore when applying the selectivity of clauses that couldn't use any extended stats. I'm planning on having a bit more of a look at this tomorrow.
The attached patch should apply to master as of f90d23d0c51895e0d7db7910538e85d3d38691f0.
