In nearly all cases, the caller already knows the correct collation, and
in a number of places, the value the caller has handy is more correct than
the default for the type would be.  (In particular, this patch makes it
significantly less likely that eval_const_expressions will result in
changing the exposed collation of an expression.)  So an internal lookup
is both expensive and wrong.

Turns out it was this, and not so much plpgsql, that was at fault in Stefan
Huehner's collation-error-in-a-trigger bug report of a couple weeks ago.

This is pretty minimal but covers the bare facts.

Make plpgsql treat the input collation as a polymorphism variable, so
that we cache separate plans for each input collation that's used in a
particular session, as per recent discussion.  Propagate the input
collation to all collatable input parameters.

I chose to also propagate the input collation to all declared variables of
collatable types, which is a bit more debatable but seems to be necessary
for non-astonishing behavior.  (Copying a parameter into a separate local
variable shouldn't result in a change of behavior, for example.)  There is
enough infrastructure here to support declaring a collation for each local
variable to override that default, but I thought we should wait to see what
the field demand is before adding such a feature.

In passing, remove exec_get_rec_fieldtype(), which wasn't used anywhere.

Documentation patch to follow.

Temporarily move some of the alpha release note disclaimers into the regular
release notes, for the sake of alpha5.

It originally worked this way, but was changed by commit
a8a8a3e0, since which time it's been impossible
for walreceiver to ever send a reply with write_location and flush_location
set to different values.

-r no_indicator
-r prepare
-r questionsmarks

Ensure that parameter symbols receive collation from the function's
resolved input collation, and fix inlining to behave properly.

BTW, this commit lays about 90% of the infrastructure needed to support
use of argument names in SQL functions.  Parsing of parameters is now
done via the parser-hook infrastructure ... we'd just need to supply
a column-ref hook ...

KaiGai Kohei

Add some new items and some additional details to existing items, mostly
by cribbing from the 9.1alpha notes.  Some additional clarifications and
corrections elsewhere, and a few typo fixes.

Ensure that COLLATE at the top level of an index expression is treated the
same as a grammatically separate COLLATE.  Fix bogus reverse-parsing logic
in pg_get_indexdef.

On closer inspection, that two-element initcond value seems to have been
a little white lie to avoid explaining the full behavior of float8_accum.
But if people are going to expect the examples to be exactly correct,
I suppose we'd better explain.  Per comment from Thom Brown.

Change location LOG message so it works each time we pause, not
just for final pause.
Ensure that we pause only if we are in Hot Standby and can connect
to allow us to run resume function. This change supercedes the
code to override parameter recoveryPauseAtTarget to false if not
attempting to enter Hot Standby, which is now removed.

The description of the initcond value for the built-in avg(float8)
aggregate has been wrong since it was written.  Noted by Disc Magnet.

This is no longer necessary, and might result in a situation where the
configuration file is reloaded (and everything seems OK) but a subsequent
restart of the database fails.

Per an observation from Fujii Masao.

Startup process waited for cleanup lock but when hot_standby = off
the pid was not registered, so that the bgwriter would not wake
the waiting process as intended.

Bug report from Alvaro Herrera

While putting such entries into pg_collation is harmless (since backends
will ignore entries that don't match the database encoding), it's also
useless.

pg_newlocale_from_collation does not have enough context to give an error
message that's even a little bit useful, so move the responsibility for
complaining up to its callers.  Also, reword ERRCODE_INDETERMINATE_COLLATION
error messages in a less jargony, more message-style-guide-compliant
fashion.

This restores a parse error that was thrown (though only in the ORDER BY
case) by the original collation patch.  I had removed it in my recent
revisions because it was thrown at a place where collations now haven't
been computed yet; but I thought of another way to handle it.

Throwing the error at parse time, rather than leaving it to be done at
runtime, is good because a syntax error pointer is helpful for localizing
the problem.  We can reasonably assume that the comparison function for a
collatable datatype will complain if it doesn't have a collation to use.
Now the planner might choose to implement GROUP or DISTINCT via hashing,
in which case no runtime error would actually occur, but it seems better
to throw error consistently rather than let the error depend on what the
planner chooses to do.  Another possible objection is that the user might
specify a nondefault sort operator that doesn't care about collation
... but that's surely an uncommon usage, and it wouldn't hurt him to throw
in a COLLATE clause anyway.  This change also makes the ORDER BY/GROUP
BY/DISTINCT case more consistent with the UNION/INTERSECT/EXCEPT case,
which was already coded to throw this error even though the same objections
could be raised there.

Opening a catcache's index could require reading from that cache's own
catalog, which of course would acquire AccessShareLock on the catalog.
So the original coding here risks locking index before heap, which could
deadlock against another backend trying to get exclusive locks in the
normal order.  Because InitCatCachePhase2 is only called when a backend
has to start up without a relcache init file, the deadlock was seldom seen
in the field.  (And by the same token, there's no need to worry about any
performance disadvantage; so not much point in trying to distinguish
exactly which catalogs have the risk.)

Bug report, diagnosis, and patch by Nikhil Sontakke.  Additional commentary
by me.  Back-patch to all supported branches.

Instead of playing cute games with pathkeys, just build a direct
representation of the intended sub-select, and feed it through
query_planner to get a Path for the index access.  This is a bit slower
than 9.1's previous method, since we'll duplicate most of the overhead of
query_planner; but since the whole optimization only applies to rather
simple single-table queries, that probably won't be much of a problem in
practice.  The advantage is that we get to do the right thing when there's
a partial index that needs the implicit IS NOT NULL clause to be usable.
Also, although this makes planagg.c be a bit more closely tied to the
ordering of operations in grouping_planner, we can get rid of some coupling
to lower-level parts of the planner.  Per complaint from Marti Raudsepp.

ensure that they use different checkpoints as the starting point. We use
the checkpoint redo location as a unique identifier for the base backup in
the end-of-backup record, and in the backup history file name.

Bug spotted by Fujii Masao.

There's a lot we can't test very well without platform dependencies,
but the C/POSIX collations should now work the same way everywhere.

The local variable "sock" can be unused depending on compilation flags.
But there seems no particular need for it, since the kernel calls can
just as easily say port->sock instead.

Install just one instance of the "C" and "POSIX" collations into
pg_collation, rather than one per encoding.  Make these instances exist
and do something useful even in machines without locale_t support: to wit,
it's now possible to force comparisons and case-folding functions to use C
locale in an otherwise non-C database, whether or not the platform has
support for using any additional collations.

Fix up severely broken upper/lower/initcap functions, too: the C/POSIX
fastpath now does what it is supposed to, and non-default collations are
handled correctly in single-byte database encodings.

Merge the two separate collation hashtables that were being maintained in
pg_locale.c, and be more wary of the possibility that we fail partway
through filling a cache entry.

notes.

Remove excessive linking to pg_ctl manual page.

Reorder incompatibility sections.

Thom Brown

All expression nodes now have an explicit output-collation field, unless
they are known to only return a noncollatable data type (such as boolean
or record).  Also, nodes that can invoke collation-aware functions store
a separate field that is the collation value to pass to the function.
This avoids confusion that arises when a function has collatable inputs
and noncollatable output type, or vice versa.

Also, replace the parser's on-the-fly collation assignment method with
a post-pass over the completed expression tree.  This allows us to use
a more complex (and hopefully more nearly spec-compliant) assignment
rule without paying for it in extra storage in every expression node.

Fix assorted bugs in the planner's handling of collations by making
collation one of the defining properties of an EquivalenceClass and
by converting CollateExprs into discardable RelabelType nodes during
expression preprocessing.