pgsql: Clarify resource utilization of parallel query.

Clarify resource utilization of parallel query.

temp_file_limit is a per-process limit, not a per-session limit across
all cooperating parallel processes; change wording accordingly, per a
suggestion from Tom Lane.

Also, document under max_parallel_workers_per_gather the fact that each
process involved in a parallel query may use as many resources as a
separate session. Caveat emptor.

Per a complaint from Peter Geoghegan.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d1f822e58597cac5000bf69b893cc236c5ef5fcb

Modified Files
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doc/src/sgml/config.sgml | 20 ++++++++++++++++++--
src/backend/utils/misc/guc.c | 2 +-
src/backend/utils/misc/postgresql.conf.sample | 2 +-
3 files changed, 20 insertions(+), 4 deletions(-)