doc: improve description of synchronous_commit modes

Bruce Momjian <bruce@momjian.us>

Commit: a97e85f2be400a08d863c1d65f172eb48af3e9b5
Author: Bruce Momjian <bruce@momjian.us>
Date: 2020-10-15T19:15:29Z
Releases: 14.0
doc:  improve description of synchronous_commit modes

Previously it wasn't clear exactly what each of the synchronous_commit
modes accomplished.  This clarifies that, and adds a table describing it.
Only backpatched through 9.6 since 9.5 doesn't have all the options.

Reported-by: kghost0@gmail.com

Discussion: https://postgr.es/m/159741195522.14321.13812604195366728976@wrigleys.postgresql.org

Backpatch-through: 9.6

Files

PathChange+/−
doc/src/sgml/config.sgml modified +114 −30
src/include/access/xact.h modified +2 −1

Documentation touched