Jeff Davis, additional test by me

Remove message when FREEZE not honoured,
clarify reasons in comments and docs.

For some reason lost in the mists of prehistory, RETURN was only coded to
allow a simple reference to a composite variable when the function's return
type is composite.  Allow an expression instead, while preserving the
efficiency of the original code path in the case where the expression is
indeed just a composite variable's name.  Likewise for RETURN NEXT.

As is true in various other places, the supplied expression must yield
exactly the number and data types of the required columns.  There was some
discussion of relaxing that for pl/pgsql, but no consensus yet, so this
patch doesn't address that.

Asif Rehman, reviewed by Pavel Stehule

Background workers are postmaster subprocesses that run arbitrary
user-specified code.  They can request shared memory access as well as
backend database connections; or they can just use plain libpq frontend
database connections.

Modules listed in shared_preload_libraries can register background
workers in their _PG_init() function; this is early enough that it's not
necessary to provide an extra GUC option, because the necessary extra
resources can be allocated early on.  Modules can install more than one
bgworker, if necessary.

Care is taken that these extra processes do not interfere with other
postmaster tasks: only one such process is started on each ServerLoop
iteration.  This means a large number of them could be waiting to be
started up and postmaster is still able to quickly service external
connection requests.  Also, shutdown sequence should not be impacted by
a worker process that's reasonably well behaved (i.e. promptly responds
to termination signals.)

The current implementation lets worker processes specify their start
time, i.e. at what point in the server startup process they are to be
started: right after postmaster start (in which case they mustn't ask
for shared memory access), when consistent state has been reached
(useful during recovery in a HOT standby server), or when recovery has
terminated (i.e. when normal backends are allowed).

In case of a bgworker crash, actions to take depend on registration
data: if shared memory was requested, then all other connections are
taken down (as well as other bgworkers), just like it were a regular
backend crashing.  The bgworker itself is restarted, too, within a
configurable timeframe (which can be configured to be never).

More features to add to this framework can be imagined without much
effort, and have been discussed, but this seems good enough as a useful
unit already.

An elementary sample module is supplied.

Author: Álvaro Herrera

This patch is loosely based on prior patches submitted by KaiGai Kohei,
and unsubmitted code by Simon Riggs.

Reviewed by: KaiGai Kohei, Markus Wanner, Andres Freund,
Heikki Linnakangas, Simon Riggs, Amit Kapila

When deleteOneObject closes and reopens the pg_depend relation,
we must see to it that the relcache pointer held by the calling function
(typically performMultipleDeletions) is updated.  Usually the relcache
entry is retained so that the pointer value doesn't change, which is why
the problem had escaped notice ... but after a cache flush event there's
no guarantee that the same memory will be reassigned.  To fix, change
the recursive functions' APIs so that we pass around a "Relation *"
not just "Relation".

Per investigation of occasional buildfarm failures.  This is trivial
to reproduce with -DCLOBBER_CACHE_ALWAYS, which points up the sad
lack of any buildfarm member running that way on a regular basis.

I neglected to update it in commit f4c4335a.

Michael Paquier

If we're not in hot standby mode, then there's no way for users to connect
to reset the recoveryPause flag, so we shouldn't pause.  The code was aware
of this but the test to see if pausing was safe was seriously inadequate:
it wasn't paying attention to reachedConsistency, and besides what it was
testing was that we could legally enter hot standby, not that we have
done so.  Get rid of that in favor of checking LocalHotStandbyActive,
which because of the coding in CheckRecoveryConsistency is tantamount to
checking that we have told the postmaster to enter hot standby.

Also, move the recoveryPausesHere() call that reacts to asynchronous
recoveryPause requests so that it's not in the middle of application of a
WAL record.  I put it next to the recoveryStopsHere() call --- in future
those are going to need to interact significantly, so this seems like a
good waystation.

Also, don't bother trying to read another WAL record if we've already
decided not to continue recovery.  This was no big deal when the code was
written originally, but now that reading a record might entail actions like
fetching an archive file, it seems a bit silly to do it like that.

Per report from Jeff Janes and subsequent discussion.  The pause feature
needs quite a lot more work, but this gets rid of some indisputable bugs,
and seems safe enough to back-patch.

When waiting for an XLOG_BACKUP_RECORD the minRecoveryPoint
will be incorrect, so we must not declare recovery as consistent
before we have seen the record. Major bug allowing recovery to end
too early in some cases, allowing people to see inconsistent db.
This patch to HEAD and 9.2, other fix required for 9.1 and 9.0

Simon Riggs and Andres Freund, bug report by Jeff Janes

Fujii Masao, reviewed by Kyotaro Horiguchi.

The buildfarm shows this case is entirely broken, and I'm betting the
reason is lack of any include file.

Patch done by Jiang Guiqing <jianggq@cn.fujitsu.com>.

I never intended this to be anything other than a debugging aid, but forgot
to change the level before committing.

This allows us to do some more rigorous sanity checking for various
incorrect point-in-time recovery scenarios, and provides more information
for debugging purposes. It will also come handy in the upcoming patch to
allow timeline switches to be replicated by streaming replication.

report is clearer.

Some code was not ifdef'ed out for non-LDAP builds.

patch from Bruce Momjian

This allows recovery to notice certain incorrect recovery scenarios.
If a server has recovered to point X on timeline 5, and you restart
recovery, it better be on timeline 5 when it reaches point X again, not on
some timeline with a higher ID. This can happen e.g if you a standby server
is shut down, a new timeline appears in the WAL archive, and the standby
server is restarted. It will try to follow the new timeline, which is wrong
because some WAL on the old timeline was already replayed before shutdown.

Requires an initdb (or at least pg_resetxlog), because this adds a field to
the control file.

executed.

Allow specifying LDAP authentication parameters as RFC 4516 LDAP URLs.

creation and xlog symlink creation to separate functions.

Per suggestions from Andrew Dunstan.

storage.

Have pg_upgrade use it, and enable server options fsync=off and
full_page_writes=off.

Document that users turning fsync from off to on should run initdb
--sync-only.

[ Previous commit was incorrectly applied as a git merge. ]

binary-upgrade mode;  instead only skip dumping the current user.

This bug was introduced in during the removal of split_old_dump().  Bug
discovered during local testing.

This reverts commit e2b3c21b.

During VACUUM if we pause to perform a cycle
of index cleanup we drop the vmbuffer pin,
so we should do the same thing when heap
scan completes. This avoids holding vmbuffer
pin across the main index cleanup in VACUUM,
which could be minutes or hours longer than
necessary for correctness.

Bug report and suggested fix from Pavan Deolasee

Obviously, this returns type "path", but somebody made a copy-and-pasteo
long ago.

Dagfinn Ilmari Mannsåker

We can't use type uint, so use uint32.

Rename PGXACT->inCommit flag into delayChkpt flag,
and generalise comments to allow use in other situations,
such as the forthcoming potential use in checksum patch.
Replace wait loop to look for VXIDs with delayChkpt set.
No user visible changes, not behaviour changes at present.

Simon Riggs, reviewed and rebased by Jeff Davis

Update README to explain prerequisites for
correct access to LSN fields of a page.
Independent chunk removed from checksums
patch to reduce size of patch.

It is now easier to see that it's a state machine, making the code easier
to understand overall.

Normally each module is tested in aq database named contrib_regression,
which is dropped and recreated at the beginhning of each pg_regress run.
This mode, enabled by adding USE_MODULE_DB=1 to the make command line,
runs most modules in a database with the module name embedded in it.

This will make testing pg_upgrade on clusters with the contrib modules
a lot easier.

Still to be done: adapt to the MSVC build system.

Backpatch to 9.0, which is the earliest version it is reasonably possible
to test upgrading from.

DST law changes in Cuba, Israel, Jordan, Libya, Palestine, Western Samoa,
and portions of Brazil.

We've generally recommended use of INSTEAD triggers over rules since that
feature was added; but this old text in the CREATE VIEW reference page
didn't get the memo.  Noted by Thomas Kellerer.