Making pg_rewind faster

Hi Hackers,

I have been using pg_rewind in production for 2 years. One of the things that I noticed in pg_rewind is if it doesn't know what to do with a file "it copies". I understand it's the more safer option. After all, the alternative, pg_basebackup copies all the files from source to target.

However, this is making pg_rewind inefficient when we have a high number of WAL files. Majority of the data (in most of my cases 95%+) that it copies are WAL files which are anyway same between the source and target. Skipping those same WAL files from copying will improve the speed of pg_rewind a lot.

1. Does pg_rewind need to copy WAL files before the WAL that contains the last common check point?

Heikki's presentation https://pgsessions.com/assets/archives/pg_rewind-presentation-paris.pdf gave me a good overview and also explained the behavior what I mentioned.

Thanks,

Vignesh