A new thing also called a "barrier" is proposed, but whether we decide
to take that patch or not, this file seems to have outlived its
usefulness.

Thomas Munro

Create a section specifically for the syntactic rules around whole-row
variable usage, such as expansion of "foo.*".  This was previously
documented only haphazardly, with some critical info buried in
unexpected places like xfunc-sql-composite-functions.  Per repeated
questions in different mailing lists.

Discussion: <16288.1479610770@sss.pgh.pa.us>

Avoid memory leak in conninfo_uri_parse_options.  Use the current host
rather than the comma-separated list of host names when the host name
is needed for GSS, SSPI, or SSL authentication.  Document the way
connect_timeout interacts with multiple host specifications.

Takayuki Tsunakawa

Previously, the right-hand side of a multiple-column assignment, if it
wasn't a sub-SELECT, had to be a simple parenthesized expression list,
because gram.y was responsible for "bursting" the construct into
independent column assignments.  This had the minor defect that you
couldn't write ROW (though you should be able to, since the standard says
this is a row constructor), and the rather larger defect that unlike other
uses of row constructors, we would not expand a "foo.*" item into multiple
columns.

Fix that by changing the RHS to be just "a_expr" in the grammar, leaving
it to transformMultiAssignRef to separate the elements of a RowExpr;
which it will do only after performing standard transformation of the
RowExpr, so that "foo.*" behaves as expected.

The key reason we didn't do that before was the hard-wired handling of
DEFAULT tokens (SetToDefault nodes).  This patch deals with that issue by
allowing DEFAULT in any a_expr and having parse analysis throw an error
if SetToDefault is found in an unexpected place.  That's an improvement
anyway since the error can be more specific than just "syntax error".

The SQL standard suggests that the RHS could be any a_expr yielding a
suitable row value.  This patch doesn't really move the goal posts in that
respect --- you're still limited to RowExpr or a sub-SELECT --- but it does
fix the grammar restriction, so it provides some tangible progress towards
a full implementation.  And the limitation is now documented by an explicit
error message rather than an unhelpful "syntax error".

Discussion: <8542.1479742008@sss.pgh.pa.us>

Condition variables provide a flexible way to sleep until a
cooperating process causes an arbitrary condition to become true.  In
simple cases, this can be accomplished with a WaitLatch/ResetLatch
loop; the cooperating process can call SetLatch after performing work
that might cause the condition to be satisfied, and the waiting
process can recheck the condition each time.  However, if the process
performing the work doesn't have an easy way to identify which
processes might be waiting, this doesn't work, because it can't
identify which latches to set.  Condition variables solve that problem
by internally maintaining a list of waiters; a process that may have
caused some waiter's condition to be satisfied must "signal" or
"broadcast" on the condition variable.

Robert Haas and Thomas Munro

There are assorted references to RETURNING in Part II, but nothing
that would qualify as an explanation of the feature, which seems
like an oversight considering how useful it is.  Add something.

Noted while looking for a place to point a cross-reference to ...

A little COLLATE "C" goes a long way.

Pavel Stehule, per suggestion from Craig Ringer

Discussion: <CAFj8pRA8nJZcozgxN=RMSqMmKuHVOkcGAAKPKdFeiMWGDSUDLA@mail.gmail.com>

Oversight in a734fd5d.

Michael Paquier

The code was intentionally not very careful about leaking strdup'd
strings in case of an error.  That was forgivable probably, but it
also failed to notice strdup() failures, which could lead to subsequent
null-pointer-dereference crashes, since many callers unsurprisingly
didn't check for null pointers in the struct lconv fields.  An even
worse problem is that it could throw error while we were setlocale'd
to a non-C locale, causing unwanted behavior in subsequent libc calls.

Rewrite to ensure that we cannot throw elog(ERROR) until after we've
restored the previous locale settings, or at least attempted to.
(I'm sorely tempted to make restore failure be a FATAL error, but
will refrain for the moment.)  Having done that, it's not much more
work to ensure that we clean up strdup'd storage on the way out, too.

This code is substantially the same in all supported branches, so
back-patch all the way.

Michael Paquier and Tom Lane

Discussion: <CAB7nPqRMbGqa_mesopcn4MPyTs34eqtVEK7ELYxvvV=oqS00YA@mail.gmail.com>

Fix thinko in commit da1c9163: even if the original query was free of
parallel hazards, we might introduce such a hazard by adding PARAM_EXEC
Param nodes.  Adjust is_parallel_safe() so that it will scan the given
expression whenever any such nodes have been created.  Per report from
Andreas Seltenreich.

Discussion: <878tse6yvf.fsf@credativ.de>

Previously, we only dropped an orphan temp table when it became old
enough to threaten wraparound; instead, doing it immediately.  The
only value of waiting is that someone might be able to examine the
contents of the orphan temp table for forensic purposes, but it's
pretty difficult to actually do that and few users will wish to do so.
On the flip side, not performing the drop immediately generates log
spam and bloats pg_class.

In addition, per a report from Grigory Smolkin, if a temporary schema
contains a very large number of temporary tables, a backend attempting
to clear the temporary schema might fail due to lock table exhaustion.
It's helpful for autovacuum to clean up after such cases, and we don't
want it to wait for wraparound to threaten before doing so.  To
prevent autovacuum from failing in the same manner as a backend trying
to drop an entire temp schema, remove orphan temp tables in batches of
50, committing after each batch, so that we don't accumulate an
unbounded number of locks.  If a drop fails, retry other orphan tables
that need to be dropped up to 10 times before giving up.  With this
system, if a backend does fail to clean a temporary schema due to
lock table exhaustion, autovacuum should hopefully put things right
the next time it processes the database.

Discussion: CAB7nPqSbYT6dRwsXVgiKmBdL_ARemfDZMPA+RPeC_ge0GK70hA@mail.gmail.com

Michael Paquier, with a bunch of comment changes by me.

We mustn't force parallel mode if the query has any subplans, since
ExecSerializePlan doesn't transmit them to workers.  Testing
top_plan->initPlan is inadequate because (1) there might be initPlans
attached to lower plan nodes, and (2) non-initPlan subplans don't
work either.  There's certainly room for improvement in those
restrictions, but for the moment that's what we've got.

Amit Kapila, per report from Andreas Seltenreich

Discussion: <8737im6pmh.fsf@credativ.de>

Because we use transformTargetList() for UPDATE as well as SELECT
tlists, the code accidentally tried to expand a "*" reference into
several columns.  This is nonsensical, because the UPDATE syntax
provides exactly one target column to put the value into.  The
immediate result was that transformUpdateTargetList() got confused
and reported "UPDATE target count mismatch --- internal error".
It seems better to treat such a reference as a plain whole-row
variable, as it would be in other contexts.  (This could produce
useful results when the target column is of composite type.)

Fix by tweaking transformTargetList() to perform *-expansion only
conditionally, depending on its exprKind parameter.

Back-patch to 9.3.  The problem exists further back, but a fix would be
much more invasive before that, because transformTargetList() wasn't
told what kind of list it was working on.  Doesn't seem worth the
trouble given the lack of field reports.  (I only noticed it because
I was checking the code while trying to improve the documentation about
how we handle "foo.*".)

Discussion: <4308.1479595330@sss.pgh.pa.us>

create_merge_append_path should use the path rowcount it just computed,
not rel->tuples, for costing purposes.  Those numbers should always be
the same at present, but if we ever support parameterized MergeAppend
paths (a case this function is otherwise prepared for), the former would
be right and the latter wrong.

No need for back-patch since the problem is only latent.

Ashutosh Bapat

Discussion: <CAFjFpRek+cLCnTo24youuGtsq4zRphEB8EUUPjDxZjnL4n4HYQ@mail.gmail.com>

The serialization code dumped core for a string-valued GUC whose value
is NULL, which is a legal state.  The infrastructure isn't capable of
transmitting that state exactly, but fortunately, transmitting an empty
string instead should be close enough (compare, eg, commit e45e990e).

The code potentially underestimated the space required to format a
real-valued variable, both because it made an unwarranted assumption that
%g output would never be longer than %e output, and because it didn't count
right even for %e format.  In practice this would pretty much always be
masked by overestimates for other variables, but it's still wrong.

Also fix boundary-case error in read_gucstate, incorrect handling of the
case where guc_sourcefile is non-NULL but zero length (not clear that can
happen, but if it did, this code would get totally confused), and
confusingly useless check for a NULL result from read_gucstate.

Andreas Seltenreich discovered the core dump; other issues noted while
reading nearby code.  Back-patch to 9.5 where this code was introduced.

Michael Paquier and Tom Lane

Discussion: <871sy78wno.fsf@credativ.de>

Like pg_tables, pg_views, and others, this view contains information
about sequences in a way that is independent of the system catalog
layout but more comprehensive than the information schema.

To help implement the view, add a new internal function
pg_sequence_last_value() to return the last value of a sequence.  This
is kept separate from pg_sequence_parameters() to separate querying
run-time state from catalog-like information.
Reviewed-by: Andreas Karlsson <andreas@proxel.se>

Add a loop to check that each test covers all of the pg_dump runs.  We
(I) had been a bit sloppy when adding new runs and not making sure to
mark if they should be under like or unlike for each test, this loop
makes sure that the test system will complain if any are forgotten in
the future.

The loop also correctly handles the 'catch all' cases, which are used to
avoid running unnecessary specific checks when a single catch-all can be
done (eg: a no-acl run should not have any GRANT commands).

Also, re-enable the testing of blobs, but use lo_from_bytea() instead of
trying to be cute and writing out to a file and then reading it back in
with psql, which proved to be difficult for some buildfarm members.
This allows us to add support for testing the --no-blobs option which
will be getting added shortly, provided the buildfarm doesn't blow up on
this.

The debug messages that merely print StartTransactionCommand,
CommitTransactionCommand, ProcessUtilty, or ProcessQuery with no
additional details seem to be useless.  Get rid of them.

The transaction status messages produced by ShowTransactionState are
occasionally useful, but they are extremely verbose, producing
multiple lines of log output every time they fire, which can happens
multiple times per transaction.  So, reduce the level to DEBUG5; avoid
emitting an extra line just to explain which debug point is at issue;
and tighten up the rest of the message so it doesn't use quite so much
horizontal space.

With these changes, it's possible to run a somewhat busy system with a
log level even as high as DEBUG4, whereas previously anything above
DEBUG2 would flood the log with output that probably wasn't really all
that useful.

pg_dump's traditional solution for breaking a circular dependency involving
a view was to create the view with CREATE TABLE and then later issue CREATE
RULE "_RETURN" ... to convert the table to a view, relying on the backend's
very very ancient code that supports making views that way.  We've wanted
to get rid of that kluge for a long time, but the thing that finally
motivates doing something about it is the recognition that this method
fails with the --clean option, because it leads to issuing DROP RULE
"_RETURN" followed by DROP TABLE --- and the backend won't let you drop a
view's _RETURN rule.

Instead, let's break circular dependencies by initially creating the view
using CREATE VIEW AS SELECT NULL::columntype AS columnname, ... (so that
it has the right column names and types to support external references,
but no dependencies beyond the column data types), and then later dumping
the ON SELECT rule using the spelling CREATE OR REPLACE VIEW.  This method
wasn't available when this code was originally written, but it's been
possible since PG 7.3, so it seems fine to start relying on it now.

To solve the --clean problem, make the dropStmt for an ON SELECT rule
be CREATE OR REPLACE VIEW with the same dummy target list as above.
In this way, during the DROP phase, we first reduce the view to have
no extra dependencies, and then we can drop it entirely when we've
gotten rid of whatever had a circular dependency on it.

(Note: this should work adequately well with the --if-exists option, since
the CREATE OR REPLACE VIEW will go through whether the view exists or not.
It could fail if the view exists with a conflicting column set, but we
don't really support --clean against a non-matching database anyway.)

This allows cleaning up some other kluges inside pg_dump, notably that
we don't need a notion of reloptions attached to a rule anymore.

Although this is a bug fix, commit to HEAD only for now.  The problem's
existed for a long time and we've had relatively few complaints, so it
doesn't really seem worth taking risks to fix it in the back branches.
We might revisit that choice if no problems emerge.

Discussion: <19092.1479325184@sss.pgh.pa.us>

Teach it not to complain if the dropStmt attached to an archive entry
is actually spelled CREATE OR REPLACE VIEW, since that will happen due to
an upcoming bug fix.  Also, if it doesn't recognize a dropStmt, have it
print a WARNING and then emit the dropStmt unmodified.  That seems like a
much saner behavior than Assert'ing or dumping core due to a null-pointer
dereference, which is what would happen before :-(.

Back-patch to 9.4 where this option was introduced.

Discussion: <19092.1479325184@sss.pgh.pa.us>

Cleanup for recent patches --- it's not much change, but I got annoyed
while re-indenting the view-rule fix I'm working on.

Replay of XLOG_BTREE_VACUUM during Hot Standby was previously thought to
require complex interlocking that matched the requirements on the
master. This required an O(N) operation that became a significant
problem with large indexes, causing replication delays of seconds or in
some cases minutes while the XLOG_BTREE_VACUUM was replayed.

This commit skips the “pin scan” that was previously required, by
observing in detail when and how it is safe to do so, with full
documentation. The pin scan is skipped only in replay; the VACUUM code
path on master is not touched here.

No tests included. Manual tests using an additional patch to view WAL records
and their timing have shown the change in WAL records and their handling has
successfully reduced replication delay.

This is a back-patch of commits 687f2cd7, 3e4b7d87, b6028426
by Simon Riggs, to branches 9.4 and 9.5.  No further backpatch is
possible because this depends on catalog scans being MVCC.  I (Álvaro)
additionally updated a slight problem in the README, which explains why
this touches the 9.6 and master branches.

Cut out some expensive stuff from the HTML head element that we don't
really need.

This was previously discussed as part of
e8306745, but ended up separate because
it changes the output contents slightly.

The old DSSSL build is still available for a while using the make target
"oldhtml".

This should always be true, but since we're relying on a tuple descriptor
passed from outside pltcl itself, let's check.  Per a gripe from Coverity.

Previously, the handle for the control segment could not be zero, but
some other DSM segment could potentially have a handle value of zero.
However, that means that if someone wanted to store a dsm_handle that
might or might not be valid, they would need a separate boolean to
keep track of whether the associated value is legal.  That's annoying,
so change things so that no DSM segment can ever have a handle of 0 -
or as we call it here, DSM_HANDLE_INVALID.

Thomas Munro.  This was submitted as part of a much larger patch to
add an malloc-like allocator for dynamic shared memory, but this part
seems like a good idea independently of the rest of the patch.

On Windows, libc will mask \r\n line endings for us, since we read the
password file in text mode.  But that doesn't happen on Unix.  People
who share password files across both systems might have \r\n line endings
in a file they use on Unix, so as a convenience, ignore trailing \r.
Per gripe from Josh Berkus.

In passing, put the existing check for empty line somewhere where it's
actually useful, ie after stripping the newline not before.

Vik Fearing, adjusted a bit by me

Discussion: <0de37763-5843-b2cc-855e-5d0e5df25807@agliodbs.com>

The CatalogSnapshot was not plugged into SnapshotResetXmin()'s accounting
for whether MyPgXact->xmin could be cleared or advanced.  In normal
transactions this was masked by the fact that the transaction snapshot
would be older, but during backend startup and certain utility commands
it was possible to re-use the CatalogSnapshot after MyPgXact->xmin had
been cleared, meaning that recently-deleted rows could be pruned even
though this snapshot could still see them, causing unexpected catalog
lookup failures.  This effect appears to be the explanation for a recent
failure on buildfarm member piculet.

To fix, add the CatalogSnapshot to the RegisteredSnapshots heap whenever
it is valid.

In the previous logic, it was possible for the CatalogSnapshot to remain
valid across waits for client input, but with this change that would mean
it delays advance of global xmin in cases where it did not before.  To
avoid possibly causing new table-bloat problems with clients that sit idle
for long intervals, add code to invalidate the CatalogSnapshot before
waiting for client input.  (When the backend is busy, it's unlikely that
the CatalogSnapshot would be the oldest snap for very long, so we don't
worry about forcing early invalidation of it otherwise.)

In passing, remove the CatalogSnapshotStale flag in favor of using
"CatalogSnapshot != NULL" to represent validity, as we do for the other
special snapshots in snapmgr.c.  And improve some obsolete comments.

No regression test because I don't know a deterministic way to cause this
failure.  But the stress test shown in the original discussion provokes
"cache lookup failed for relation 1255" within a few dozen seconds for me.

Back-patch to 9.4 where MVCC catalog scans were introduced.  (Note: it's
quite easy to produce similar failures with the same test case in branches
before 9.4.  But MVCC catalog scans were supposed to fix that.)

Discussion: <16447.1478818294@sss.pgh.pa.us>

Gigantic numbers of tapes don't work out well.

Original patch by Peter Geoghegan; comments entirely rewritten by me.

This has been wrong for a very long time, and it's puzzling to me how
it ever worked for anyone.

Kyotaro Horiguchi

Commit 41124a91 allowed the
transaction log file prefix to be changed but left in place the
existing 64-character limit on the total length of a log file name.
It's possible that could be inconvenient for somebody, so increase the
limit to MAXPGPATH, which ought to be enough for anybody.

Per a suggestion from Tom Lane.

This allows us to avoid running the regression tests in contrib modules
like pg_stat_statement in a less ugly manner.

Discussion: <22432.1478968242@sss.pgh.pa.us>

The function was renamed in 908e2347, but the comment never learned
about it.

Add a new optional Makefile variable PROVE_TESTS that, if passed as a
space-separated list of paths relative to the Makefile invoking
$(prove_check) or $(prove_installcheck), runs just those tests instead
of t/*.pl .

From: Craig Ringer <craig@2ndquadrant.com>
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>

Commit 3c4cf080 should have removed SET TABLESPACE from the synopsis
of ALTER MATERIALIZE VIEW as a possible "action" when it added a
separate line for it in the main command listing, but failed to.
Repair.

Backpatch to 9.4, like the aforementioned commit.

Previously, pg_upgrade migrated sequence data like tables by copying the
on-disk file.  This does not allow any changes in the on-disk format for
sequences.  It's simpler to just have pg_dump set the new sequence
values as it normally does.  To do that, create a hidden submode in
pg_dump that dumps sequence data even when a schema-only dump is
requested, and trigger that submode in binary upgrade mode.  (This new
submode could easily be exposed as a command-line option, but it has
limited use outside of pg_dump and would probably cause some confusion,
so we don't do that at this time.)
Reviewed-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>

Instead of handling both sequence data and table data internally as
"table data", handle sequences separately under a "sequence set" type.
We already handled materialized view data differently, so it makes the
code somewhat cleaner to handle each relation kind separately at the top
level.

This does not change the output format, since there already was a
separate "SEQUENCE SET" archive entry type.  A noticeable difference is
that SEQUENCE SET entries now always appear after TABLE DATA entries.
And in parallel mode there is less sorting to do, because the sequence
data entries are no longer considered table data.
Reviewed-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>

The documentation for ts_headline() recommends using a sub-select to
avoid extra evaluations of ts_headline() in a query with ORDER BY+LIMIT.
Since commit 9118d03a this contortionism is unnecessary, so remove the
recommendation.  Noted by Oleg Bartunov.

Discussion: <CAF4Au4w6rrH_j1bvVhzpOsRiHCog7sGJ3LSX0tY8ZdwhHT88LQ@mail.gmail.com>

While the set of covered functionality is fairly small, the added tests
still are useful to get some basic buildfarm testing of
pg_stat_statements itself, but also to exercise the lwlock tranch code
on the buildfarm.

Author: Amit Kapila, slightly editorialized by me
Reviewed-By: Ashutosh Sharma, Andres Freund
Discussion: <CAA4eK1JOjkdXYtHxh=2aDK4VgDtN-LNGKY_YqX0N=YEvuzQVWg@mail.gmail.com>