The original coding in ri_triggers.c had partial support for the concept of
zero-column foreign key constraints.  But this is not defined in the SQL
standard, nor was it ever allowed by any other part of Postgres, nor was it
very fully implemented even here (eg there was no support for preventing
PK-table deletions that would violate the constraint).  Doesn't seem very
useful to carry 100-plus lines of code for a corner case that no one is
interested in making work.  Instead, just add a check that the column list
read from pg_constraint is non-empty.

By my count there are 18 callers of CacheRegisterSyscacheCallback in the
core code in HEAD, so we are potentially leaving as few as 2 slots for any
add-on code to use (though possibly not all these callers would actually
activate in any particular session).  That doesn't seem like a lot of
headroom, so let's pump it up a little.

Extracting data from pg_constraint turned out to take as much as 10% of the
runtime in a bulk-update case where the foreign key column wasn't changing,
because we did it over again for each tuple.  Fix that by maintaining a
backend-local cache of the results.  This is really a pretty small patch,
but converting the trigger functions to work with pointers rather than
local struct variables requires a lot of mechanical changes.

During an update of a PK row, we can skip firing the RI trigger if any old
key value is NULL, because then the row could not have had any matching
rows in the FK table.  Conversely, during an update of an FK row, the
outcome is determined if any new key value is NULL.  In either case it
becomes unnecessary to compare individual key values.

This patch was inspired by discussion of Vik Reykja's patch to use IS NOT
DISTINCT semantics for the key comparisons.  In the event there is no need
for that and so this patch looks nothing like his, but he should still get
credit for having re-opened consideration of the trigger skip logic.

The option --foreign-keys, used at initialization time, will create foreign
key constraints for the columns that represent references to other tables'
primary keys.  This can help in benchmarking FK performance.

Jeff Janes

In passing, reword another instance of the same message that was
gratuitously different.

Author: Josh Kupershmidt
after a bug report by Bosco Rama

pointed out by Stefan Kaltenbrunner

These triggers are identical except for whether ri_Check_Pk_Match is to be
called, so factor out the common code to save a couple hundred lines.

Also, eliminate null-column checks in ri_Check_Pk_Match, since they're
duplicate with the calling functions and require unnecessary complication
in its API statement.

Simplify the way code is shared between RI_FKey_check_ins and
RI_FKey_check_upd, too.

I was confused about this, so try to make it clearer for the next person.

(This seems like a fairly inefficient way of dealing with a corner case,
but I don't have a better idea offhand.  Maybe if there were a way to turn
off the RI_FKey_keyequal_upd_fk event filter temporarily?)

Once upon a time, somebody was worried that cached RI plans wouldn't get
remade with new default values after ALTER TABLE ... SET DEFAULT, so they
didn't allow caching of plans for ON UPDATE/DELETE SET DEFAULT actions.
That time is long gone, though (and even at the time I doubt this was the
greatest hazard posed by ALTER TABLE...).  So allow these triggers to cache
their plans just like the others.

The cache_plan argument to ri_PlanCheck is now vestigial, since there
are no callers that don't pass "true"; but I left it alone in case there
is any future need for it.

We really only need the foreign key constraint's OID and the query type
code to uniquely identify each plan we are caching for FK checks.  The
other stuff that was in the struct had no business being used as part of
a hash key, and was all just being copied from struct RI_ConstraintInfo
anyway.  Get rid of the unnecessary fields, and readjust various function
APIs to make them use RI_ConstraintInfo not RI_QueryKey as info source.

I'd be surprised if this makes any measurable performance difference,
but it certainly feels cleaner.

Now that what we're implementing isn't SQL92, we probably shouldn't cite
chapter and verse in that spec anymore.  Also fix some comments that
talked about MATCH FULL but in fact were in code that's also used for
MATCH SIMPLE.

No code changes in this commit, just comments.

Previously, when executing an ON UPDATE SET NULL or SET DEFAULT action for
a multicolumn MATCH SIMPLE foreign key constraint, we would set only those
referencing columns corresponding to referenced columns that were changed.
This is what the SQL92 standard said to do --- but more recent versions
of the standard say that all referencing columns should be set to null or
their default values, no matter exactly which referenced columns changed.
At least for SET DEFAULT, that is clearly saner behavior.  It's somewhat
debatable whether it's an improvement for SET NULL, but it appears that
other RDBMS systems read the spec this way.  So let's do it like that.

This is a release-notable behavioral change, although considering that
our documentation already implied it was done this way, the lack of
complaints suggests few people use such cases.

Previously we followed the SQL92 wording, "MATCH <unspecified>", but since
SQL99 there's been a less awkward way to refer to the default style.

In addition to the code changes, pg_constraint.confmatchtype now stores
this match style as 's' (SIMPLE) rather than 'u' (UNSPECIFIED).  This
doesn't affect pg_dump or psql because they use pg_get_constraintdef()
to reconstruct foreign key definitions.  But other client-side code might
examine that column directly, so this change will have to be marked as
an incompatibility in the 9.3 release notes.

Before, some places didn't document the short options (-? and -V),
some documented both, some documented nothing, and they were listed in
various orders.  Now this is hopefully more consistent and complete.

Formerly, if the system clock went backwards, the stats collector would
fail to update the stats file any more until the clock reading again
exceeds whatever timestamp was last written into the stats file.  Such
glitches in the clock's behavior are not terribly unlikely on machines
not using NTP.  Such a scenario has been observed to cause regression test
failures in the buildfarm, and it could have bad effects on the behavior
of autovacuum, so it seems prudent to install some defenses.

We could directly detect the clock going backwards by adding
GetCurrentTimestamp calls in the stats collector's main loop, but that
would hurt performance on platforms where GetCurrentTimestamp is expensive.
To minimize the performance hit in normal cases, adopt a more complicated
scheme wherein backends check for clock skew when reading the stats file,
and if they see it, signal the stats collector by sending an extra stats
inquiry message.  The stats collector does an extra GetCurrentTimestamp
only when it receives an inquiry with an apparently out-of-order
timestamp.

To avoid unnecessary GetCurrentTimestamp calls, expand the inquiry messages
to carry the backend's current clock reading as well as its stats cutoff
time.  The latter, being intentionally slightly in-the-past, would trigger
more clock rechecks than we need if it were used for this purpose.

We might want to backpatch this change at some point, but let's let it
shake out in the buildfarm for awhile first.

Since this is the easy way of doing it, it should be listed first. All
the old information is retained for those who want the more advanced way.

Also adds a subheading for compressing logs, that seems to have been missing

Backpatch to 9.2.

Per suggestion from Noah Misch

Àlvaro and Noah Misch.

Backpatch to 9.2.

connection failure.

Backpatch to 9.2.

Per report from Evan D. Hoffman

Because permissions are assigned to element types, not array types,
complaining about permission denied on an array type would be
misleading to users.  So adjust the reporting to refer to the element
type instead.

In order not to duplicate the required logic in two dozen places,
refactor the permission denied reporting for types a bit.

pointed out by Yeb Havinga during the review of the type privilege
feature

Even though we can't do much about the case with multiple plurals in
one sentence, we can fix the other cases.

Gurjeet Singh, with corrections by me.

Fujii Masao

Darold Gilles, reviewed by Gabriele Bartolini and others, rebased by
Marco Nenciarini.  Stylistic cleanup and OID fixes by me.

There's no need to hold onto the locks until the files are needed,
and by doing it this way, we reduce the impact on other backends who
may be awaiting locks we hold.

Noah Misch

When I implemented the ginbuildempty() function as part of
implementing unlogged tables, I falsified the note in the header
comment for log_newpage.  Although we could fix that up by changing
the comment, it seems cleaner to add a new function which is
specifically intended to handle this case.  So do that.

Even when allow_system_table_mods is not set, we allow creation of any
type of SQL object in pg_catalog, except for relations.  And you can
get relations into pg_catalog, too, by initially creating them in some
other schema and then moving them with ALTER .. SET SCHEMA.  So this
restriction, which prevents relations (only) from being created in
pg_catalog directly, is fairly pointless.  If we need a safety mechanism
for this, it should be placed further upstream, so that it affects all
SQL objects uniformly, and picks up both CREATE and SET SCHEMA.

For now, just rip it out, per discussion with Tom Lane.

This may have been important at some point in the past, but it no
longer does anything useful.

Review by Tom Lane.

Alastair Turner, per suggestion from Bruce Momjian.

We have this info in the wiki, but it should be here too.

This includes fixing the MSVC copy of ecpg/preproc's version info, which
seems to have been overlooked repeatedly.  Can't we fix that so there are
not two copies??

Let the hacking begin ...

Instead of identifying error locations only by line number (which could
be entirely unhelpful with long input lines), provide a fragment of the
input text too, placing this info in a new CONTEXT entry.  Make the
error detail messages conform more closely to style guidelines, fix
failure to expose some of them for translation, ensure compiler can
check formats against supplied parameters.

This reverts commit 18fb9d8d.  Per
discussion, it does not seem like a good idea to allow committed changes to
go un-checkpointed indefinitely, as could happen in a low-traffic server;
that makes us entirely reliant on the WAL stream with no redundancy that
might aid data recovery in case of disk failure.

This re-introduces the original problem of hot-standby setups generating a
small continuing stream of WAL traffic even when idle, but there are other
ways to address that without compromising crash recovery, so we'll revisit
that issue in a future release cycle.

I had this slightly wrong, as noted by Noah Misch.