pgsql: Add support for --jobs in reindexdb

Add support for --jobs in reindexdb

When doing a schema-level or a database-level operation, a list of
relations to build is created which gets processed in parallel using
multiple connections, based on the recent refactoring for parallel slots
in src/bin/scripts/.  System catalogs are processed first in a
serialized fashion to prevent deadlocks, followed by the rest done in
parallel.

This new option is not compatible with --system as reindexing system
catalogs in parallel can lead to deadlocks, and with --index as there is
no conflict handling for indexes rebuilt in parallel depending in the
same relation.

Author: Julien Rouhaud
Reviewed-by: Sergei Kornilov, Michael Paquier
Discussion: https://postgr.es/m/CAOBaU_YrnH_Jqo46NhaJ7uRBiWWEcS40VNRQxgFbqYo9kApUsg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5ab892c391c6bc54a00e7a8de5cab077cabace6a

Modified Files
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doc/src/sgml/ref/reindexdb.sgml    |  23 ++
src/bin/scripts/Makefile           |   2 +-
src/bin/scripts/reindexdb.c        | 416 ++++++++++++++++++++++++++++++++-----
src/bin/scripts/t/090_reindexdb.pl |  44 +++-
4 files changed, 432 insertions(+), 53 deletions(-)