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

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