doc: improve description of synchronous_commit modes

Bruce Momjian <bruce@momjian.us>

Commit: ee59f669b666e62b7e769ece97ef74ef621acd8d
Author: Bruce Momjian <bruce@momjian.us>
Date: 2020-10-15T19:15:28Z
Releases: 9.6.20
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 −2

Documentation touched