pgsql: Retry short writes when flushing WAL.

Retry short writes when flushing WAL.

We don't normally bother retrying when the number of bytes written by
write() is short of what was requested. It is generally assumed that a
write() to disk doesn't return short, unless you run out of disk space.
While writing the WAL, however, it seems prudent to try a bit harder,
because a failure leads to PANIC. The write() is also much larger than most
write()s in the backend (up to wal_buffers), so there's more room for
surprises.

Also retry on EINTR. All signals used in the backend are flagged SA_RESTART
nowadays, so it shouldn't happen, but better to be defensive.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/79ce29c734c6a652b2f7193bda537cff0c8eb8c1

Modified Files
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src/backend/access/transam/xlog.c | 32 ++++++++++++++++++++------------
1 file changed, 20 insertions(+), 12 deletions(-)