We have long forbidden fetching backwards from a NO SCROLL cursor,
but the prohibition didn't extend to cases in which we rewind the
query altogether and then re-fetch forwards. I think the reason is
that this logic was mainly meant to protect plan nodes that can't
be run in the reverse direction. However, re-reading the query output
is problematic if the query is volatile (which includes SELECT FOR
UPDATE, not just queries with volatile functions): the re-read can
produce different results, which confuses the cursor navigation logic
completely. Another reason for disliking this approach is that some
code paths will either fetch backwards or rewind-and-fetch-forwards
depending on the distance to the target row; so that seemingly
identical use-cases may or may not draw the "cursor can only scan
forward" error. Hence, let's clean things up by disallowing rewind
as well as fetch-backwards in a NO SCROLL cursor.
Ordinarily we'd only make such a definitional change in HEAD, but
there is a third reason to consider this change now. Commit ba2c6d6ce
created some new user-visible anomalies for non-scrollable cursors
WITH HOLD, in that navigation in the cursor result got confused if the
cursor had been partially read before committing. The only good way
to resolve those anomalies is to forbid rewinding such a cursor, which
allows removal of the incorrect cursor state manipulations that
ba2c6d6ce added to PersistHoldablePortal.
To minimize the behavioral change in the back branches (including
v14), refuse to rewind a NO SCROLL cursor only when it has a holdStore,
ie has been held over from a previous transaction due to WITH HOLD.
This should avoid breaking most applications that have been sloppy
about whether to declare cursors as scrollable. We'll enforce the
prohibition across-the-board beginning in v15.
Back-patch to v11, as ba2c6d6ce was.
Discussion: https://postgr.es/m/3712911.1631207435@sss.pgh.pa.us
This switches the default ACL to what the documentation has recommended
since CVE-2018-1058. Upgrades will carry forward any old ownership and
ACL. Sites that declined the 2018 recommendation should take a fresh
look. Recipes for commissioning a new database cluster from scratch may
need to create a schema, grant more privileges, etc. Out-of-tree test
suites may require such updates.
Reviewed by Peter Eisentraut.
Discussion: https://postgr.es/m/20201031163518.GB4039133@rfd.leadboat.com
Some plan node types don't react well to being called again after
they've already returned NULL. PortalRunSelect() has long dealt
with this by calling the executor with NoMovementScanDirection
if it sees that we've already run the portal to the end. However,
commit ba2c6d6ce overlooked this point, so that persisting an
already-fully-fetched cursor would fail if it had such a plan.
Per report from Tomas Barton. Back-patch to v11, as the faulty
commit was. (I've omitted a test case because the type of plan
that causes a problem isn't all that stable.)
Discussion: https://postgr.es/m/CAPV2KRjd=ErgVGbvO2Ty20tKTEZZr6cYsYLxgN_W3eAo9pf5sw@mail.gmail.com
When throttling is used, transactions that lag behind schedule by
more than the latency limit are counted and reported as skipped.
Previously, there was the case where pgbench counted all skipped
transactions even if the timer specified in -T option was exceeded.
This could take a very long time to do that especially when unrealistically
high rate setting in -R option caused quite a lot of transactions that
lagged behind schedule. This could prevent pgbench from ending
immediately, and so pgbench could look like it got stuck to users.
To fix the issue, this commit changes pgbench so that it stops counting
skipped transactions as soon as the timer is exceeded. The timer can
make pgbench end soon even when there are lots of skipped transactions
that have not been counted yet.
Note that there is no guarantee that all skipped transactions are
counted under -T though there is under -t. This is OK in practice
because it's very unlikely to happen with realistic setting. Also this is
not the issue that this commit newly introdues. There used to be
the case where pgbench ended without counting all skipped
transactions since before.
Back-patch to v14. Per discussion, we decided not to bother
back-patch to the stable branches because it's hard to imagine
the issue happens in practice (with realistic setting).
Author: Yugo Nagata, Fabien COELHO
Reviewed-by: Greg Sabino Mullane, Fujii Masao
Discussion: https://postgr.es/m/20210613040151.265ff59d832f835bbcf8b3ba@sraoss.co.jp
We don't allow relations to exceed 2^32-1 blocks, because block
numbers are 32 bits and the last possible block number is reserved
to mean InvalidBlockNumber. There is a check for this in mdextend,
but that's really way too late, because the smgr API requires us to
create a buffer for the block-to-be-added, and we do not want to
have any buffer with blocknum InvalidBlockNumber. (Such a case
can trigger assertions in bufmgr.c, plus I think it might confuse
ReadBuffer's logic for data-past-EOF later on.) So put the check
into ReadBuffer.
Per report from Christoph Berg. It's been like this forever,
so back-patch to all supported branches.
Discussion: https://postgr.es/m/YTn1iTkUYBZfcODk@msg.credativ.de
Previously, walreceiver always closed the currently-opened WAL segment
and created its archive notification file, after it finished writing
the current segment up and received any WAL data that should be
written into the next segment. If walreceiver exited just before
any WAL data in the next segment arrived at standby, it did not
create the archive notification file of the current segment
even though that's known completed. This behavior could cause
WAL archiving of the segment to be delayed until subsequent
restartpoints or checkpoints created its notification file.
To fix the issue, this commit changes walreceiver so that it creates
an archive notification file of a current WAL segment immediately
if that's known completed before receiving next WAL data.
Back-patch to all supported branches.
Reported-by: Kyotaro Horiguchi
Author: Fujii Masao
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/20200630.165503.1465894182551545886.horikyota.ntt@gmail.com
The Value node struct is a weird construct. It is its own node type,
but most of the time, it actually has a node type of Integer, Float,
String, or BitString. As a consequence, the struct name and the node
type don't match most of the time, and so it has to be treated
specially a lot. There doesn't seem to be any value in the special
construct. There is very little code that wants to accept all Value
variants but nothing else (and even if it did, this doesn't provide
any convenient way to check it), and most code wants either just one
particular node type (usually String), or it accepts a broader set of
node types besides just Value.
This change removes the Value struct and node type and replaces them
by separate Integer, Float, String, and BitString node types that are
proper node types and structs of their own and behave mostly like
normal node types.
Also, this removes the T_Null node tag, which was previously also a
possible variant of Value but wasn't actually used outside of the
Value contained in A_Const. Replace that by an isnull field in
A_Const.
Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/5ba6bc5b-3f95-04f2-2419-f8ddb4c046fb@enterprisedb.com
Casting the argument of strVal() to (Value *) is useless, since
strVal() already does that.
Most code didn't do that anyway; this was apparently just a style that
snuck into certain files.
Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/5ba6bc5b-3f95-04f2-2419-f8ddb4c046fb@enterprisedb.com
Coverity complained that one caller of getFormattedTypeName() failed
to free the returned string. Which is true, but rather than fixing
that one, let's get rid of this tedious and error-prone requirement.
Now that getFormattedTypeName() caches its result, strdup'ing that
result and expecting the caller to free it accomplishes little except
to waste cycles. We do create a leak in the case where getTypes didn't
make a TypeInfo for the type, but that basically shouldn't ever happen.
Back-patch, as commit 6c450a861 was. This isn't a particularly
interesting bug fix, but the API change seems like a hazard for
future back-patching activity if we don't back-patch it.
Various psql backslash commands have both single-letter and long
forms, for example \e and \edit. Previously, tab completion
generally offered the single-letter form but not the long form.
It seems more sensible to offer the long form, because (a) no
useful completion can happen when you've already typed the single
letter, and (b) if you're not so familiar with the command set
as to know that, the long form is likely to be less confusing.
Haiying Tang, reviewed by Dagfinn Ilmari Mannsåker and myself
Discussion: https://postgr.es/m/OS0PR01MB61136018064660F095CB57A8FB129@OS0PR01MB6113.jpnprd01.prod.outlook.com
If we copy data-modifying CTEs from the original query to a replacement
query (from a DO INSTEAD rule), we must set hasModifyingCTE properly
in the replacement query. Failure to do this can cause various
unpleasantness, such as unsafe usage of parallel plans. The code also
neglected to propagate hasRecursive, though that's only cosmetic at
the moment.
A difficulty arises if the rule action is an INSERT...SELECT. We
attach the original query's RTEs and CTEs to the sub-SELECT Query, but
data-modifying CTEs are only allowed to appear in the topmost Query.
For the moment, throw an error in such cases. It would probably be
possible to avoid this error by attaching the CTEs to the top INSERT
Query instead; but that would require a bunch of new code to adjust
ctelevelsup references. Given the narrowness of the use-case, and
the need to back-patch this fix, it does not seem worth the trouble
for now. We can revisit this if we get field complaints.
Per report from Greg Nancarrow. Back-patch to all supported branches.
(The test case added here does not fail before v10, but there are
plenty of places checking top-level hasModifyingCTE in 9.6, so I have
no doubt that this code change is necessary there too.)
Greg Nancarrow and Tom Lane
Discussion: https://postgr.es/m/CAJcOf-f68DT=26YAMz_i0+Au3TcLO5oiHY5=fL6Sfuits6r+_w@mail.gmail.com
Discussion: https://postgr.es/m/CAJcOf-fAdj=nDKMsRhQzndm-O13NY4dL6xGcEvdX5Xvbbi0V7g@mail.gmail.com
The correct nomenclature for the highest privileged user is superuser
and not "super user", this replaces the few instances where that was
used erroneously. No user-visible changes are done as all changes are
in comments, so no back-patching.
Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/CALj2ACW3snGBD8BAQiArMDS1Y43LuX3ymwO+N8aUg1Hrv6hYNw@mail.gmail.com
Commit 01e658fa74 added hash support for row types. This also added
support for hashing anonymous record types, using the same approach
that the type cache uses for comparison support for record types: It
just reports that it works, but it might fail at run time if a
component type doesn't actually support the operation. We get away
with that for comparison because most types support that. But some
types don't support hashing, so the current state can result in
failures at run time where the planner chooses hashing over sorting,
whereas that previously worked if only sorting was an option.
We do, however, want the record hashing support for path tracking in
recursive unions, and the SEARCH and CYCLE clauses built on that. In
that case, hashing is the only plan option. So enable that, this
commit implements the following approach: The type cache does not
report that hashing is available for the record type. This undoes
that part of 01e658fa74. Instead, callers that require hashing no
matter what can override that result themselves. This patch only
touches the callers to make the aforementioned recursive query cases
work, namely the parse analysis of unions, as well as the hash_array()
function.
Reported-by: Sait Talha Nisanci <sait.nisanci@microsoft.com>
Bug: #17158
Discussion: https://www.postgresql.org/message-id/flat/17158-8a2ba823982537a4%40postgresql.org
Commit 449ab63505 added the tests that check that postgres_fdw.application_name
GUC works as expected. But they were unstable and caused some buildfarm
members to report the failure. This commit reverts those unstable tests.
Reported-by: Tom Lane as per buildfarm
Discussion: https://postgr.es/m/3220909.1631054766@sss.pgh.pa.us
Updates/Deletes on a relation were allowed even without replica identity
after we define the publication for all tables. This would later lead to
an error on subscribers. The reason was that for such publications we were
not invalidating the relcache and the publication information for
relations was not getting rebuilt. Similarly, we were not invalidating the
relcache after dropping of such publications which will prohibit
Updates/Deletes without replica identity even without any publication.
Author: Vignesh C and Hou Zhijie
Reviewed-by: Hou Zhijie, Kyotaro Horiguchi, Amit Kapila
Backpatch-through: 10, where it was introduced
Discussion: https://postgr.es/m/CALDaNm0pF6zeWqCA8TCe2sDuwFAy8fCqba=nHampCKag-qLixg@mail.gmail.com
This runtime-computed GUC shows the size of the server's main shared
memory area, taking into account the amount of shared memory allocated
by extensions as this is calculated after processing
shared_preload_libraries.
Author: Nathan Bossart
Discussion: https://postgr.es/m/F2772387-CE0F-46BF-B5F1-CC55516EB885@amazon.com
All the code paths simplified here were already using a boolean or used
an expression that led to zero or one, making the extra bits
unnecessary.
Author: Justin Pryzby
Reviewed-by: Tom Lane, Michael Paquier, Peter Smith
Discussion: https://postgr.es/m/20210428182936.GE27406@telsasoft.com
Previously pgwin32_is_service() would falsely return true when postgres is
started from somewhere within a service, but not as a service. That is
e.g. always the case with windows docker containers, which some CI services
use to run windows tests in.
When postgres falsely thinks its running as a service, no messages are
writting to stdout / stderr. That can be very confusing and causes a few tests
to fail.
To fix additionally check if stderr is invalid in pgwin32_is_service(). For
that to work in backend processes, pg_ctl is changed to pass down handles so
that postgres can do the same check (otherwise "default" handles are created).
While this problem exists in all branches, there have been no reports by
users, the prospective CI usage currently is only for master, and I am not a
windows expert. So doing the change in only master for now seems the sanest
approach.
Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Magnus Hagander <magnus@hagander.net>
Discussion: https://postgr.es/m/20210305185752.3up5eq2eanb7ofmb@alap3.anarazel.de
This commit adds postgres_fdw.application_name GUC which specifies
a value for application_name configuration parameter used
when postgres_fdw establishes a connection to a foreign server.
This GUC setting always overrides application_name option of
the foreign server object. This GUC is useful when we want to
specify our own application_name per remote connection.
Previously application_name of a remote connection could be set
basically only via options of a server object. But which meant that
every session connecting to the same foreign server basically
should use the same application_name. Also if we want to change
the setting, we had to execute "ALTER SERVER ... OPTIONS ..." command.
It was inconvenient.
Author: Hayato Kuroda
Reviewed-by: Masahiro Ikeda, Fujii Masao
Discussion: https://postgr.es/m/TYCPR01MB5870D1E8B949DAF6D3B84E02F5F29@TYCPR01MB5870.jpnprd01.prod.outlook.com
Similar to LogicalIncreaseRestartDecodingForSlot() add a debug message to
LogicalIncreaseXminForSlot() reporting a new catalog_xmin candidate.
This just adds additional diagnostic information during logical decoding that
can aid debugging.
Author: Ashutosh Bapat
Reviewed-by: Masahiko Sawada, Amit Kapila
Discussion: https://postgr.es/m/CAExHW5usQWbiUz0hHOCu5twS1O9DvpcPojf6sor=8q--VUuMbA@mail.gmail.com
We make each AIX shared library export all globals found in .o files
that originate in the library. That doesn't include symbols acquired by
-lpgcommon_shlib. That is good on average, but it became a problem for
libpq when commit e6afa8918c moved five
official libpq API symbols into src/common. Fix this by implementing
the SHLIB_EXPORTS mechanism for AIX, so affected libraries export the
same symbols that they export on Linux. This reintroduces symbols
pg_encoding_to_char, pg_utf_mblen, pg_char_to_encoding,
pg_valid_server_encoding, and pg_valid_server_encoding_id. Back-patch
to v13, where the aforementioned commit first appeared. While a minor
release is usually the wrong time to add or remove symbol exports in
libpq or libecpg, we should expect users to want each documented symbol.
Tony Reix
Discussion: https://postgr.es/m/PR3PR02MB6396742E2FC3E77D37A920BC86C79@PR3PR02MB6396.eurprd02.prod.outlook.com
These encapsulate a relation when referred from replication DDL.
Currently they don't do anything useful (they're just wrappers around
RangeVar and Relation respectively) but in the future they'll be used to
carry column lists.
Extracted from a larger patch by Rahila Syed.
Author: Rahila Syed <rahilasyed90@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CAH2L28vddB_NFdRVpuyRBJEBWjz4BSyTB=_ektNRH8NJ1jf95g@mail.gmail.com
pgtime.h documented the PG interpretation of tm_mon right alongside
the POSIX interpretation of tm_year, with no hint that neither
comment was correct throughout our code.
Perhaps someday we ought to switch to using two separate struct
definitions to provide a clearer indication of which semantics are
in use where. But I fear the tedium-versus-safety-gain tradeoff
would not be very good.
Discussion: https://postgr.es/m/CAJ7c6TOMG8zSNEZtCn5SPe+cCk3Lfxb71ZaQwT2F4T7PJ_t=KA@mail.gmail.com
Historically, timetz_zone() has used time(NULL) as the reference point
for deciding whether DST is active. That means its result can change
intra-statement, requiring it to be marked VOLATILE (cf. 35979e6c3).
But that definition is pretty inconsistent with the way we deal with
timestamps elsewhere. Let's make it use the transaction start time
("now()") as the reference point instead. That lets it be marked
STABLE, and also saves a kernel call per invocation.
While at it, remove the function's use of pg_time_t and pg_localtime.
Those are inconsistent with the other code in this area, which indeed
created a bug: timetz_zone() delivered completely wrong answers if
the zone was specified by a dynamic TZ abbreviation. (We need to do
something about that in the back branches, but the fix will look
different from this.)
Aleksander Alekseev and Tom Lane
Discussion: https://postgr.es/m/CAJ7c6TOMG8zSNEZtCn5SPe+cCk3Lfxb71ZaQwT2F4T7PJ_t=KA@mail.gmail.com
This change refactors the shared memory size calculation in
CreateSharedMemoryAndSemaphores() to its own function. This is intended
for use in a future change related to the setup of huge pages and shared
memory with some GUCs, while useful on its own for extensions.
Author: Nathan Bossart
Discussion: https://postgr.es/m/F2772387-CE0F-46BF-B5F1-CC55516EB885@amazon.com
Attempting to make hashfloat4() look as much as possible like
hashfloat8(), I'd figured I could replace NaNs with get_float4_nan()
before widening to float8. However, results from protosciurus
and topminnow show that on some platforms that produces a different
bit-pattern from get_float8_nan(), breaking the intent of ce773f230.
Rearrange so that we use the result of get_float8_nan() for all NaN
cases. As before, back-patch.
Replace fixed-length command buffers with psprintf() calls. We didn't
have anything as convenient as psprintf() when this code was written,
but now that we do, there's little reason for the limitation to
stand. Removing it eliminates some corner cases where (for example)
starting the postmaster with a whole lot of options fails.
Most individual file names that pg_ctl deals with are still restricted
to MAXPGPATH, but we've seldom had complaints about that limitation
so long as it only applies to one filename.
Back-patch to all supported branches.
Phil Krylov
Discussion: https://postgr.es/m/567e199c6b97ee19deee600311515b86@krylov.eu
Previously this was allowed, but the collation effectively vanished
into the ether because of the way lookup_collation() works: you could
not use the collation, nor even drop it. Seems better to give an
error up front than to leave the user wondering why it doesn't work.
(Because this test is in DefineCollation not CreateCollation, it does
not prevent pg_import_system_collations from creating ICU collations,
regardless of the initially-chosen encoding.)
Per bug #17170 from Andrew Bille. Back-patch to v10 where ICU support
was added.
Discussion: https://postgr.es/m/17170-95845cf3f0a9c36d@postgresql.org
543f36b43d was too hasty in thinking that the volatility of date_bin()
had to match date_trunc(), since only the latter references
session_timezone.
Bump catversion
Per feedback from Aleksander Alekseev
Backpatch to v14, as the former commit was
Modern POSIX seems to require strtod() to accept "-NaN", but there's
nothing about NaN in SUSv2, and some of our oldest buildfarm members
don't like it. Let's try writing it as -'NaN' instead; that seems
to produce the same result, at least on Intel hardware.
Per buildfarm.
Currently the pc files use hard coded paths for "includedir" and
"libdir."
Example:
Cflags: -I/usr/include
Libs: -L/usr/lib -lpq
This is not very fortunate when cross compiling inside a buildroot,
where the includes and libs are inside a staging directory, because
this introduces host paths into the build:
checking for pkg-config... /builder/shared-workdir/build/sdk/staging_dir/host/bin/pkg-config
checking for PostgreSQL libraries via pkg_config... -L/usr/lib <----
This commit addresses this by doing the following two things:
1. Instead of hard coding the paths in "Cflags" and "Libs"
"${includedir}" and "${libdir}" are used. Note: these variables
can be overriden on the pkg-config command line
("--define-variable=libdir=/some/path").
2. Add the variables "prefix" and "exec_prefix". If "includedir"
and/or "libdir" are using these then construct them accordingly.
This is done because buildroots (for instance OpenWrt) tend to
rename the real pkg-config and call it indirectly from a script
that sets "prefix", "exec_prefix" and "bindir", like so:
pkg-config.real --define-variable=prefix=${STAGING_PREFIX} \
--define-variable=exec_prefix=${STAGING_PREFIX} \
--define-variable=bindir=${STAGING_PREFIX}/bin $@
Example #1: user calls ./configure with "--libdir=/some/lib" and
"--includedir=/some/include":
prefix=/usr/local/pgsql
exec_prefix=${prefix}
libdir=/some/lib
includedir=/some/include
Name: libpq
Description: PostgreSQL libpq library
Url: http://www.postgresql.org/
Version: 12.1
Requires:
Requires.private:
Cflags: -I${includedir}
Libs: -L${libdir} -lpq
Libs.private: -lcrypt -lm
Example #2: user calls ./configure with no arguments:
prefix=/usr/local/pgsql
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
Name: libpq
Description: PostgreSQL libpq library
Url: http://www.postgresql.org/
Version: 12.1
Requires:
Requires.private:
Cflags: -I${includedir}
Libs: -L${libdir} -lpq
Libs.private: -lcrypt -lm
Like this the paths can be forced into the staging directory when
using a buildroot setup:
checking for pkg-config... /home/sk/tmp/openwrt/staging_dir/host/bin/pkg-config
checking for PostgreSQL libraries via pkg_config... -L/home/sk/tmp/openwrt/staging_dir/target-mips_24kc_musl/usr/lib
Author: Sebastian Kemper <sebastian_ml@gmx.net>
Co-authored-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/20200305213827.GA25135%40darth.lan
We had a complaint that the postmaster fails to start if the invoking
program closes stdin. That happens because count_usable_fds expects
to be able to dup(0), and if it can't, we conclude there are no free
FDs and go belly-up. So far as I can find, though, there is no other
place in the server that touches stdin, and it's not unreasonable to
expect that a daemon wouldn't use that file.
As a simple improvement, let's dup FD 2 (stderr) instead. Unlike stdin,
it *is* reasonable for us to expect that stderr be open; even if we are
configured not to touch it, common libraries such as libc might try to
write error messages there.
Per gripe from Mario Emmenlauer. Given the lack of previous complaints,
I'm not excited about pushing this into stable branches, but it seems
OK to squeeze it into v14.
Discussion: https://postgr.es/m/48bafc63-c30f-3962-2ded-f2e985d93e86@emmenlauer.de
The IEEE 754 standard allows a wide variety of bit patterns for NaNs,
of which at least two ("NaN" and "-NaN") are pretty easy to produce
from SQL on most machines. This is problematic because our btree
comparison functions deem all NaNs to be equal, but our float hash
functions know nothing about NaNs and will happily produce varying
hash codes for them. That causes unexpected results from queries
that hash a column containing different NaN values. It could also
produce unexpected lookup failures when using a hash index on a
float column, i.e. "WHERE x = 'NaN'" will not find all the rows
it should.
To fix, special-case NaN in the float hash functions, not too much
unlike the existing special case that forces zero and minus zero
to hash the same. I arranged for the most vanilla sort of NaN
(that coming from the C99 NAN constant) to still have the same
hash code as before, to reduce the risk to existing hash indexes.
I dithered about whether to back-patch this into stable branches,
but ultimately decided to do so. It's a clear improvement for
queries that hash internally. If there is anybody who has -NaN
in a hash index, they'd be well advised to re-index after applying
this patch ... but the misbehavior if they don't will not be much
worse than the misbehavior they had before.
Per bug #17172 from Ma Liangzhu.
Discussion: https://postgr.es/m/17172-7505bea9e04e230f@postgresql.org
Tom Lane