Re: [WIP] Effective storage of duplicates in B-tree index.

Please, find the new version of the patch attached. Now it has WAL
functionality.

Detailed description of the feature you can find in README draft
https://goo.gl/50O8Q0

This patch is pretty complicated, so I ask everyone, who interested in
this feature,
to help with reviewing and testing it. I will be grateful for any feedback.
But please, don't complain about code style, it is still work in progress.

Next things I'm going to do:
1. More debugging and testing. I'm going to attach in next message
couple of sql scripts for testing.
2. Fix NULLs processing
3. Add a flag into pg_index, that allows to enable/disable compression
for each particular index.
4. Recheck locking considerations. I tried to write code as less
invasive as possible, but we need to make sure that algorithm is still
correct.
5. Change BTMaxItemSize
6. Bring back microvacuum functionality.

--
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company