pgsql: Improve copydir() code for the case that fsync is off.

Improve copydir() code for the case that fsync is off.

We should avoid calling sync_file_range or posix_fadvise in this case,
since (a) we don't really care if the data gets synced, and might as
well save the kernel calls; (b) at least on Linux we know that the
kernel might block us until it's scheduled the write.

Also, avoid making a useless second traversal of the directory tree
if we're not actually going to call fsync(2) after all.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/2d46a57ddcad394e514bbefb193a4a03e766f163

Modified Files
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src/backend/storage/file/copydir.c |    8 ++++++--
src/backend/storage/file/fd.c      |   14 +++++++++-----
2 files changed, 15 insertions(+), 7 deletions(-)