pgsql: doc: Clarify the logging collector's guarantees.

doc: Clarify the logging collector's guarantees.

Presently, the documentation for logging_collector says that the
collector "is designed to never lose messages," which reads as a
stronger promise than we actually make. The collector does not
fsync the log file or retry failed writes, so log messages can go
missing after an operating system crash, power loss, or a write
error. Reword that sentence and add a note about what is not
guaranteed.

Author: Daniel Bauman <danielbaniel(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Zhenwei Shang <a934172442(at)gmail(dot)com>
Reviewed-by: Robert Treat <rob(at)xzilla(dot)net>
Discussion: https://postgr.es/m/CAMtj0_a86DdDKkW-ReVpQpqjndVS6GMrwXVpQY4G3-SGY7saMQ%40mail.gmail.com
Backpatch-through: 14

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/247ef8481d89c04554702a0d18ec5455fb19f321

Modified Files
--------------
doc/src/sgml/config.sgml | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)