Change JSONB's on-disk format for improved performance.

The original design used an array of offsets into the variable-length
portion of a JSONB container.  However, such an array is basically
uncompressible by simple compression techniques such as TOAST's LZ
compressor.  That's bad enough, but because the offset array is at the
front, it tended to trigger the give-up-after-1KB heuristic in the TOAST
code, so that the entire JSONB object was stored uncompressed; which was
the root cause of bug #11109 from Larry White.

To fix without losing the ability to extract a random array element in O(1)
time, change this scheme so that most of the JEntry array elements hold
lengths rather than offsets.  With data that's compressible at all, there
tend to be fewer distinct element lengths, so that there is scope for
compression of the JEntry array.  Every N'th entry is still an offset.
To determine the length or offset of any specific element, we might have
to examine up to N preceding JEntrys, but that's still O(1) so far as the
total container size is concerned.  Testing shows that this cost is
negligible compared to other costs of accessing a JSONB field, and that
the method does largely fix the incompressible-data problem.

While at it, rearrange the order of elements in a JSONB object so that
it's "all the keys, then all the values" not alternating keys and values.
This doesn't really make much difference right at the moment, but it will
allow providing a fast path for extracting individual object fields from
large JSONB values stored EXTERNAL (ie, uncompressed), analogously to the
existing optimization for substring extraction from large EXTERNAL text
values.

Bump catversion to denote the incompatibility in on-disk format.
We will need to fix pg_upgrade to disallow upgrading jsonb data stored
with 9.4 betas 1 and 2.

Heikki Linnakangas and Tom Lane
Revert 95d737ff to add 'ignore_nulls'

Per discussion, revert the commit which added 'ignore_nulls' to
row_to_json.  This capability would be better added as an independent
function rather than being bolted on to row_to_json.  Additionally,
the implementation didn't address complex JSON objects, and so was
incomplete anyway.

Pointed out by Tom and discussed with Andrew and Robert.
Also revert e3ec0728, JSON regression tests

Managed to forget to update the other JSON regression test output,
again.  Revert the commit which fixed it before.

Per buildfarm.
doc fix for pg_recvlogical: --create doesn't immediately exit.

Author: Michael Paquier
pg_upgrade:  have pg_upgrade fail for old 9.4 JSONB format

Backpatch through 9.4
Fix pg_dump's --if-exists for large objects

This was born broken in 9067310cc5dd590e36c2c3219dbf3961d7c9f8cb.

Per trouble report from Joachim Wieland.

Pavel Stěhule and Álvaro Herrera
Correct stdin/stdout usage in COPY .. PROGRAM

The COPY documentation incorrectly stated, for the PROGRAM case,
that we read from stdin and wrote to stdout.  Fix that, and improve
consistency by referring to the 'PostgreSQL' user instead of the
'postgres' user, as is done in the rest of the COPY documentation.

Pointed out by Peter van Dijk.

Back-patch to 9.3 where COPY .. PROGRAM was introduced.
Rename CACHE_LINE_SIZE to PG_CACHE_LINE_SIZE.

As noted in http://bugs.debian.org/763098 there is a conflict between
postgres' definition of CACHE_LINE_SIZE and the definition by various
*bsd platforms. It's debatable who has the right to define such a
name, but postgres' use was only introduced in 375d8526f290 (9.4), so
it seems like a good idea to rename it.

Discussion: 20140930195756.GC27407@msg.df7cb.de

Per complaint of Christoph Berg in the above email, although he's not
the original bug reporter.

Backpatch to 9.4 where the define was introduced.
Improve documentation about binary/textual output mode for output plugins.

Also improve related error message as it contributed to the confusion.

Discussion: CAB7nPqQrqFzjqCjxu4GZzTrD9kpj6HMn9G5aOOMwt1WZ8NfqeA@mail.gmail.com,
    CAB7nPqQXc_+g95zWnqaa=mVQ4d3BVRs6T41frcEYi2ocUrR3+A@mail.gmail.com

Per discussion between Michael Paquier, Robert Haas and Andres Freund

Backpatch to 9.4 where logical decoding was introduced.
Add functions for dealing with PGP armor header lines to pgcrypto.

This add a new pgp_armor_headers function to extract armor headers from an
ASCII-armored blob, and a new overloaded variant of the armor function, for
constructing an ASCII-armor with extra headers.

Marko Tiikkaja and me.
Block signals while computing the sleep time in postmaster's main loop.

DetermineSleepTime() was previously called without blocked
signals. That's not good, because it allows signal handlers to
interrupt its workings.

DetermineSleepTime() was added in 9.3 with the addition of background
workers (da07a1e856511), where it only read from
BackgroundWorkerList.

Since 9.4, where dynamic background workers were added (7f7485a0cde),
the list is also manipulated in DetermineSleepTime(). That's bad
because the list now can be persistently corrupted if modified by both
a signal handler and DetermineSleepTime().

This was discovered during the investigation of hangs on buildfarm
member anole. It's unclear whether this bug is the source of these
hangs or not, but it's worth fixing either way. I have confirmed that
it can cause crashes.

It luckily looks like this only can cause problems when bgworkers are
actively used.

Discussion: 20140929193733.GB14400@awork2.anarazel.de

Backpatch to 9.3 where background workers were introduced.
Remove num_xloginsert_locks GUC, replace with a #define

I left the GUC in place for the beta period, so that people could experiment
with different values. No-one's come up with any data that a different value
would be better under some circumstances, so rather than try to document to
users what the GUC, let's just hard-code the current value, 8.
pg_recvlogical.c code review.

Several comments still referred to 'initiating', 'freeing', 'stopping'
replication slots. These were terms used during different phases of
the development of logical decoding, but are no long accurate.

Also rename StreamLog() to StreamLogicalLog() and add 'void' to the
prototype.

Author: Michael Paquier, with some editing by me.

Backpatch to 9.4 where pg_recvlogical was introduced.
Refactor replication connection code of various pg_basebackup utilities.

Move some more code to manage replication connection command to
streamutil.c. A later patch will introduce replication slot via
pg_receivexlog and this avoid duplicating relevant code between
pg_receivexlog and pg_recvlogical.

Author: Michael Paquier, with some editing by me.