pgsql: Add FLUSH_UNLOGGED option to CHECKPOINT command.

Add FLUSH_UNLOGGED option to CHECKPOINT command.

This option, which is disabled by default, can be used to request
the checkpoint also flush dirty buffers of unlogged relations. As
with the MODE option, the server may consolidate the options for
concurrently requested checkpoints. For example, if one session
uses (FLUSH_UNLOGGED FALSE) and another uses (FLUSH_UNLOGGED TRUE),
the server may perform one checkpoint with FLUSH_UNLOGGED enabled.

Author: Christoph Berg <myon(at)debian(dot)org>
Reviewed-by: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>
Reviewed-by: Dilip Kumar <dilipbalaut(at)gmail(dot)com>
Discussion: https://postgr.es/m/aDnaKTEf-0dLiEfz%40msg.df7cb.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8d33fbacbac93ed70757ea47cd8a4b4fae61528a

Modified Files
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doc/src/sgml/ref/checkpoint.sgml | 26 ++++++++++++++++++++++++++
src/backend/postmaster/checkpointer.c | 4 ++++
src/bin/psql/tab-complete.in.c | 2 +-
src/test/regress/expected/stats.out | 4 ++--
src/test/regress/sql/stats.sql | 4 ++--
5 files changed, 35 insertions(+), 5 deletions(-)