PostgreSQL already checked the vast majority of these, missing this
handful that nearly cannot fail. If putenv() failed with ENOMEM in
pg_GSS_recvauth(), authentication would proceed with the wrong keytab
file. If strftime() returned zero in cache_locale_time(), using the
unspecified buffer contents could lead to information exposure or a
crash. Back-patch to 9.0 (all supported versions).
Other unchecked calls to these functions, especially those in frontend
code, pose negligible security concern. This patch does not address
them. Nonetheless, it is always better to check return values whose
specification provides for indicating an error.
In passing, fix an off-by-one error in strftime_win32()'s invocation of
WideCharToMultiByte(). Upon retrieving a value of exactly MAX_L10N_DATA
bytes, strftime_win32() would overrun the caller's buffer by one byte.
MAX_L10N_DATA is chosen to exceed the length of every possible value, so
the vulnerable scenario probably does not arise.
Security: CVE-2015-3166
This SQL standard functionality allows to aggregate data by different
GROUP BY clauses at once. Each grouping set returns rows with columns
grouped by in other sets set to NULL.
This could previously be achieved by doing each grouping as a separate
query, conjoined by UNION ALLs. Besides being considerably more concise,
grouping sets will in many cases be faster, requiring only one scan over
the underlying data.
The current implementation of grouping sets only supports using sorting
for input. Individual sets that share a sort order are computed in one
pass. If there are sets that don't share a sort order, additional sort &
aggregation steps are performed. These additional passes are sourced by
the previous sort step; thus avoiding repeated scans of the source data.
The code is structured in a way that adding support for purely using
hash aggregation or a mix of hashing and sorting is possible. Sorting
was chosen to be supported first, as it is the most generic method of
implementation.
Instead of, as in an earlier versions of the patch, representing the
chain of sort and aggregation steps as full blown planner and executor
nodes, all but the first sort are performed inside the aggregation node
itself. This avoids the need to do some unusual gymnastics to handle
having to return aggregated and non-aggregated tuples from underlying
nodes, as well as having to shut down underlying nodes early to limit
memory usage. The optimizer still builds Sort/Agg node to describe each
phase, but they're not part of the plan tree, but instead additional
data for the aggregation node. They're a convenient and preexisting way
to describe aggregation and sorting. The first (and possibly only) sort
step is still performed as a separate execution step. That retains
similarity with existing group by plans, makes rescans fairly simple,
avoids very deep plans (leading to slow explains) and easily allows to
avoid the sorting step if the underlying data is sorted by other means.
A somewhat ugly side of this patch is having to deal with a grammar
ambiguity between the new CUBE keyword and the cube extension/functions
named cube (and rollup). To avoid breaking existing deployments of the
cube extension it has not been renamed, neither has cube been made a
reserved keyword. Instead precedence hacking is used to make GROUP BY
cube(..) refer to the CUBE grouping sets feature, and not the function
cube(). To actually group by a function cube(), unlikely as that might
be, the function name has to be quoted.
Needs a catversion bump because stored rules may change.
Author: Andrew Gierth and Atri Sharma, with contributions from Andres Freund
Reviewed-By: Andres Freund, Noah Misch, Tom Lane, Svenne Krap, Tomas
Vondra, Erik Rijkers, Marti Raudsepp, Pavel Stehule
Discussion: CAOeZVidmVRe2jU6aMk_5qkxnB7dfmPROzM7Ur8JPW5j8Y5X-Lw@mail.gmail.com
This lets BRIN be used with R-Tree-like indexing strategies.
Also provided are operator classes for range types, box and inet/cidr.
The infrastructure provided here should be sufficient to create operator
classes for similar datatypes; for instance, opclasses for PostGIS
geometries should be doable, though we didn't try to implement one.
(A box/point opclass was also submitted, but we ripped it out before
commit because the handling of floating point comparisons in existing
code is inconsistent and would generate corrupt indexes.)
Author: Emre Hasegeli. Cosmetic changes by me
Review: Andreas Karlsson
For upcoming BRIN opclasses, it's convenient to have strategy numbers
defined in a single place. Since there's nothing appropriate, create
it. The StrategyNumber typedef now lives there, as well as existing
strategy numbers for B-trees (from skey.h) and R-tree-and-friends (from
gist.h). skey.h is forced to include stratnum.h because of the
StrategyNumber typedef, but gist.h is not; extensions that currently
rely on gist.h for rtree strategy numbers might need to add a new
A few .c files can stop including skey.h and/or gist.h, which is a nice
side benefit.
Per discussion:
https://www.postgresql.org/message-id/20150514232132.GZ2523@alvh.no-ip.org
Authored by Emre Hasegeli and Álvaro.
(It's not clear to me why bootscanner.l has any #include lines at all.)
Our previous code for GB18030 <-> UTF8 conversion only covered Unicode code
points up to U+FFFF, but the actual spec defines conversions for all code
points up to U+10FFFF. That would be rather impractical as a lookup table,
but fortunately there is a simple algorithmic conversion between the
additional code points and the equivalent GB18030 byte patterns. Make use
of the just-added callback facility in LocalToUtf/UtfToLocal to perform the
additional conversions.
Having created the infrastructure to do that, we can use the same code to
map certain linearly-related subranges of the Unicode space below U+FFFF,
allowing removal of the corresponding lookup table entries. This more
than halves the lookup table size, which is a substantial savings;
utf8_and_gb18030.so drops from nearly a megabyte to about half that.
In support of doing that, replace ISO10646-GB18030.TXT with the data file
gb-18030-2000.xml (retrieved from
http://source.icu-project.org/repos/icu/data/trunk/charset/data/xml/ )
in which these subranges have been deleted from the simple lookup entries.
Per bug #12845 from Arjen Nienhuis. The conversion code added here is
based on his proposed patch, though I whacked it around rather heavily.
Add a TABLESAMPLE clause to SELECT statements that allows
user to specify random BERNOULLI sampling or block level
SYSTEM sampling. Implementation allows for extensible
sampling functions to be written, using a standard API.
Basic version follows SQLStandard exactly. Usable
concrete use cases for the sampling API follow in later
commits.
Petr Jelinek
Reviewed by Michael Paquier and Simon Riggs
The previous coding effectively only verified that the second byte of a
multibyte character was in the expected range; moreover, it wasn't careful
to make sure that the second byte even exists in the buffer before touching
it. The latter seems unlikely to cause any real problems in the field
(in particular, it could never be a problem with null-terminated input),
but it's still a bug.
Since GB18030 is not a supported backend encoding, the only thing we'd
really be doing with GB18030 text is converting it to UTF8 in LocalToUtf,
which would fail anyway on any invalid character for lack of a match in
its lookup table. So the only user-visible consequence of this change
should be that you'll get "invalid byte sequence for encoding" rather than
"character has no equivalent" for malformed GB18030 input. However,
impending changes to the GB18030 conversion code will require these tighter
up-front checks to avoid producing bogus results.
The distance function can now set *recheck = false, like index quals. The
executor will then re-check the ORDER BY expressions, and use a queue to
reorder the results on the fly.
This makes it possible to do kNN-searches on polygons and circles, which
don't store the exact value in the index, but just a bounding box.
Alexander Korotkov and me
Until now, these functions have only supported encoding conversions using
lookup tables, which is fine as long as there's not too many code points
to convert. However, GB18030 expects all 1.1 million Unicode code points
to be convertible, which would require a ridiculously-sized lookup table.
Fortunately, a large fraction of those conversions can be expressed through
arithmetic, ie the conversions are one-to-one in certain defined ranges.
To support that, provide a callback function that is used after consulting
the lookup tables. (This patch doesn't actually change anything about the
GB18030 conversion behavior, just provide infrastructure for fixing it.)
Since this requires changing the APIs of UtfToLocal/LocalToUtf anyway,
take the opportunity to rearrange their argument lists into what seems
to me a saner order. And beautify the call sites by using lengthof()
instead of error-prone sizeof() arithmetic.
In passing, also mark all the lookup tables used by these calls "const".
This moves an impressive amount of stuff into the text segment, at least
on my machine, and is safer anyhow.
This patch introduces the ability for complex datatypes to have an
in-memory representation that is different from their on-disk format.
On-disk formats are typically optimized for minimal size, and in any case
they can't contain pointers, so they are often not well-suited for
computation. Now a datatype can invent an "expanded" in-memory format
that is better suited for its operations, and then pass that around among
the C functions that operate on the datatype. There are also provisions
(rudimentary as yet) to allow an expanded object to be modified in-place
under suitable conditions, so that operations like assignment to an element
of an array need not involve copying the entire array.
The initial application for this feature is arrays, but it is not hard
to foresee using it for other container types like JSON, XML and hstore.
I have hopes that it will be useful to PostGIS as well.
In this initial implementation, a few heuristics have been hard-wired
into plpgsql to improve performance for arrays that are stored in
plpgsql variables. We would like to generalize those hacks so that
other datatypes can obtain similar improvements, but figuring out some
appropriate APIs is left as a task for future work. (The heuristics
themselves are probably not optimal yet, either, as they sometimes
force expansion of arrays that would be better left alone.)
Preliminary performance testing shows impressive speed gains for plpgsql
functions that do element-by-element access or update of large arrays.
There are other cases that get a little slower, as a result of added array
format conversions; but we can hope to improve anything that's annoyingly
bad. In any case most applications should see a net win.
Tom Lane, reviewed by Andres Freund
These operations now error out if attempted on scalars, and simply
return the input if attempted on empty arrays or objects. Along the way
we remove the unnecessary cloning of the input when it's known to be
unchanged. Regression tests covering these cases are added.
jsonb_pretty(jsonb) produces nicely indented json output.
jsonb || jsonb concatenates two jsonb values.
jsonb - text removes a key and its associated value from the json
jsonb - int removes the designated array element
jsonb - text[] removes a key and associated value or array element at
the designated path
jsonb_replace(jsonb,text[],jsonb) replaces the array element designated
by the path or the value associated with the key designated by the path
with the given value.
Original work by Dmitry Dolgov, adapted and reworked for PostgreSQL core
by Andrew Dunstan, reviewed and tidied up by Petr Jelinek.
This feature lets user code inspect and take action on DDL events.
Whenever a ddl_command_end event trigger is installed, DDL actions
executed are saved to a list which can be inspected during execution of
a function attached to ddl_command_end.
The set-returning function pg_event_trigger_ddl_commands can be used to
list actions so captured; it returns data about the type of command
executed, as well as the affected object. This is sufficient for many
uses of this feature. For the cases where it is not, we also provide a
"command" column of a new pseudo-type pg_ddl_command, which is a
pointer to a C structure that can be accessed by C code. The struct
contains all the info necessary to completely inspect and even
reconstruct the executed command.
There is no actual deparse code here; that's expected to come later.
What we have is enough infrastructure that the deparsing can be done in
an external extension. The intention is that we will add some deparsing
code in a later release, as an in-core extension.
A new test module is included. It's probably insufficient as is, but it
should be sufficient as a starting point for a more complete and
future-proof approach.
Authors: Álvaro Herrera, with some help from Andres Freund, Ian Barwick,
Abhijit Menon-Sen.
Reviews by Andres Freund, Robert Haas, Amit Kapila, Michael Paquier,
Craig Ringer, David Steele.
Additional input from Chris Browne, Dimitri Fontaine, Stephen Frost,
Petr Jelínek, Tom Lane, Jim Nasby, Steven Singer, Pavel Stěhule.
Based on original work by Dimitri Fontaine, though I didn't use his
code.
Discussion:
https://www.postgresql.org/message-id/m2txrsdzxa.fsf@2ndQuadrant.frhttps://www.postgresql.org/message-id/20131108153322.GU5809@eldon.alvh.no-ip.orghttps://www.postgresql.org/message-id/20150215044814.GL3391@alvh.no-ip.org
Commit e7cb7ee145 included some design
decisions that seem pretty questionable to me, and there was quite a lot
of stuff not to like about the documentation and comments. Clean up
as follows:
* Consider foreign joins only between foreign tables on the same server,
rather than between any two foreign tables with the same underlying FDW
handler function. In most if not all cases, the FDW would simply have had
to apply the same-server restriction itself (far more expensively, both for
lack of caching and because it would be repeated for each combination of
input sub-joins), or else risk nasty bugs. Anyone who's really intent on
doing something outside this restriction can always use the
set_join_pathlist_hook.
* Rename fdw_ps_tlist/custom_ps_tlist to fdw_scan_tlist/custom_scan_tlist
to better reflect what they're for, and allow these custom scan tlists
to be used even for base relations.
* Change make_foreignscan() API to include passing the fdw_scan_tlist
value, since the FDW is required to set that. Backwards compatibility
doesn't seem like an adequate reason to expect FDWs to set it in some
ad-hoc extra step, and anyway existing FDWs can just pass NIL.
* Change the API of path-generating subroutines of add_paths_to_joinrel,
and in particular that of GetForeignJoinPaths and set_join_pathlist_hook,
so that various less-used parameters are passed in a struct rather than
as separate parameter-list entries. The objective here is to reduce the
probability that future additions to those parameter lists will result in
source-level API breaks for users of these hooks. It's possible that this
is even a small win for the core code, since most CPU architectures can't
pass more than half a dozen parameters efficiently anyway. I kept root,
joinrel, outerrel, innerrel, and jointype as separate parameters to reduce
code churn in joinpath.c --- in particular, putting jointype into the
struct would have been problematic because of the subroutines' habit of
changing their local copies of that variable.
* Avoid ad-hocery in ExecAssignScanProjectionInfo. It was probably all
right for it to know about IndexOnlyScan, but if the list is to grow
we should refactor the knowledge out to the callers.
* Restore nodeForeignscan.c's previous use of the relcache to avoid
extra GetFdwRoutine lookups for base-relation scans.
* Lots of cleanup of documentation and missed comments. Re-order some
code additions into more logical places.
The new type has the scope of whole the database cluster so it doesn't
behave the same as the existing OID alias types which have database
scope,
concerning object dependency. To avoid confusion constants of the new
type are prohibited from appearing where dependencies are made involving
it.
Also, add a note to the docs about possible MVCC violation and
optimization issues, which are general over the all reg* types.
Kyotaro Horiguchi
The head_p and tail_p pointers passed to ParseConfigFp() are actually
input/output parameters, not strictly output paramaters. This updates
the function comment to reflect that.
Per discussion with Tom.
This updates pg_stat_get_activity() to build a tuplestore for its
results instead of using the old-style multiple-call method. This
simplifies the function, though that wasn't the primary motivation for
the change, which is that we may turn it into a helper function which
can filter the results (or not) much more easily.
The function and view added here provide a way to look at all settings
in postgresql.conf, any #include'd files, and postgresql.auto.conf
(which is what backs the ALTER SYSTEM command).
The information returned includes the configuration file name, line
number in that file, sequence number indicating when the parameter is
loaded (useful to see if it is later masked by another definition of the
same parameter), parameter name, and what it is set to at that point.
This information is updated on reload of the server.
This is unfiltered, privileged, information and therefore access is
restricted to superusers through the GRANT system.
Author: Sawada Masahiko, various improvements by me.
Reviewers: David Steele
The newly added ON CONFLICT clause allows to specify an alternative to
raising a unique or exclusion constraint violation error when inserting.
ON CONFLICT refers to constraints that can either be specified using a
inference clause (by specifying the columns of a unique constraint) or
by naming a unique or exclusion constraint. DO NOTHING avoids the
constraint violation, without touching the pre-existing row. DO UPDATE
SET ... [WHERE ...] updates the pre-existing tuple, and has access to
both the tuple proposed for insertion and the existing tuple; the
optional WHERE clause can be used to prevent an update from being
executed. The UPDATE SET and WHERE clauses have access to the tuple
proposed for insertion using the "magic" EXCLUDED alias, and to the
pre-existing tuple using the table name or its alias.
This feature is often referred to as upsert.
This is implemented using a new infrastructure called "speculative
insertion". It is an optimistic variant of regular insertion that first
does a pre-check for existing tuples and then attempts an insert. If a
violating tuple was inserted concurrently, the speculatively inserted
tuple is deleted and a new attempt is made. If the pre-check finds a
matching tuple the alternative DO NOTHING or DO UPDATE action is taken.
If the insertion succeeds without detecting a conflict, the tuple is
deemed inserted.
To handle the possible ambiguity between the excluded alias and a table
named excluded, and for convenience with long relation names, INSERT
INTO now can alias its target table.
Bumps catversion as stored rules change.
Author: Peter Geoghegan, with significant contributions from Heikki
Linnakangas and Andres Freund. Testing infrastructure by Jeff Janes.
Reviewed-By: Heikki Linnakangas, Andres Freund, Robert Haas, Simon Riggs,
Dean Rasheed, Stephen Frost and many others.
This commit adds the following functions:
box(point) -> box
bound_box(box, box) -> box
inet_same_family(inet, inet) -> bool
inet_merge(inet, inet) -> cidr
range_merge(anyrange, anyrange) -> anyrange
The first of these is also used to implement a new assignment cast from
point to box.
These functions are the first part of a base to implement an "inclusion"
operator class for BRIN, for multidimensional data types.
Author: Emre Hasegeli
Reviewed by: Andreas Karlsson
The first bug is not releasing a tupdesc when doing an early return out
of the function. The second bug is a logic error in choosing when to do
an early return if given an empty jsonb object.
Bug reports from Pavel Stehule and Tom Lane respectively.
Backpatch to 9.4 where these were introduced.
Commit ef3f9e642d suppressed one cause of warnings here, but
recent clang on OS X is still unhappy because we're passing a "long"
to abs(). The fact that tm_gmtoff is declared as long is no doubt a
hangover from days when int might be only 16 bits; but Postgres has
never been able to run on such machines, so we can just cast it to int
with no worries. For consistency, also cast to int in the other
uses of tm_gmtoff in this stanza.
Note: this code is still broken on machines that don't follow C99
integer-division-truncates-towards-zero rules. Given the lack of
complaints about it, I don't feel a large desire to complicate things
enough to cope with the pre-C99 rules.
Tom Lane pointed out that this wasn't done, and asked whether that was
intentional. Subsequent discussion was in favor of making the change,
so here we go.
Foreign data wrappers can use this capability for so-called "join
pushdown"; that is, instead of executing two separate foreign scans
and then joining the results locally, they can generate a path which
performs the join on the remote server and then is scanned locally.
This commit does not extend postgres_fdw to take advantage of this
capability; it just provides the infrastructure.
Custom scan providers can use this in a similar way. Previously,
it was only possible for a custom scan provider to scan a single
relation. Now, it can scan an entire join tree, provided of course
that it knows how to produce the same results that the join would
have produced if executed normally.
KaiGai Kohei, reviewed by Shigeru Hanada, Ashutosh Bapat, and me.
This does four basic things. First, it provides convenience routines
to coordinate the startup and shutdown of parallel workers. Second,
it synchronizes various pieces of state (e.g. GUCs, combo CID
mappings, transaction snapshot) from the parallel group leader to the
worker processes. Third, it prohibits various operations that would
result in unsafe changes to that state while parallelism is active.
Finally, it propagates events that would result in an ErrorResponse,
NoticeResponse, or NotifyResponse message being sent to the client
from the parallel workers back to the master, from which they can then
be sent on to the client.
Robert Haas, Amit Kapila, Noah Misch, Rushabh Lathia, Jeevan Chalke.
Suggestions and review from Andres Freund, Heikki Linnakangas, Noah
Misch, Simon Riggs, Euler Taveira, and Jim Nasby.
When this code was written, catalog scans were normally performed using
SnapshotNow, making special handling necessary here. Now, however, all
catalog scans use MVCC snapshots, so we can change these cases to look
more like what we do for catalog scans elsewhere in the code.
Per discussion with Tom Lane and a reminder from Bruce Momjian.
When implementing a replication solution ontop of logical decoding, two
related problems exist:
* How to safely keep track of replication progress
* How to change replication behavior, based on the origin of a row;
e.g. to avoid loops in bi-directional replication setups
The solution to these problems, as implemented here, consist out of
three parts:
1) 'replication origins', which identify nodes in a replication setup.
2) 'replication progress tracking', which remembers, for each
replication origin, how far replay has progressed in a efficient and
crash safe manner.
3) The ability to filter out changes performed on the behest of a
replication origin during logical decoding; this allows complex
replication topologies. E.g. by filtering all replayed changes out.
Most of this could also be implemented in "userspace", e.g. by inserting
additional rows contain origin information, but that ends up being much
less efficient and more complicated. We don't want to require various
replication solutions to reimplement logic for this independently. The
infrastructure is intended to be generic enough to be reusable.
This infrastructure also replaces the 'nodeid' infrastructure of commit
timestamps. It is intended to provide all the former capabilities,
except that there's only 2^16 different origins; but now they integrate
with logical decoding. Additionally more functionality is accessible via
SQL. Since the commit timestamp infrastructure has also been introduced
in 9.5 (commit 73c986add) changing the API is not a problem.
For now the number of origins for which the replication progress can be
tracked simultaneously is determined by the max_replication_slots
GUC. That GUC is not a perfect match to configure this, but there
doesn't seem to be sufficient reason to introduce a separate new one.
Bumps both catversion and wal page magic.
Author: Andres Freund, with contributions from Petr Jelinek and Craig Ringer
Reviewed-By: Heikki Linnakangas, Petr Jelinek, Robert Haas, Steve Singer
Discussion: 20150216002155.GI15326@awork2.anarazel.de,
20140923182422.GA15776@alap3.anarazel.de,
20131114172632.GE7522@alap2.anarazel.de
This provides a mechanism for specifying conversions between SQL data
types and procedural languages. As examples, there are transforms
for hstore and ltree for PL/Perl and PL/Python.
reviews by Pavel Stěhule and Andres Freund
The USING policies were not being checked for differences as the same
policy was being passed in to both sides of the equal(). This could
result in backends not realizing that a policy had been changed, if
none of the other attributes had been changed.
Fix by passing to equal() the policy1 and policy2 using quals for
comparison.
No need to back-patch as this is not yet released. Noticed while
testing changes to RLS proposed by Dean Rasheed.
Previously, these functions were created in a schema "binary_upgrade",
which was deleted after pg_upgrade was finished. Because we don't want
to keep that schema around permanently, move them to pg_catalog but
rename them with a binary_upgrade_... prefix.
The provided functions are only small wrappers around global variables
that were added specifically for pg_upgrade use, so keeping the module
separate does not create any modularity.
The functions still check that they are only called in binary upgrade
mode, so it is not possible to call these during normal operation.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Now that we use CRC-32C in WAL and the control file, the "traditional" and
"legacy" CRC-32 variants are not used in any frontend programs anymore.
Move the code for those back from src/common to src/backend/utils/hash.
Also move the slicing-by-8 implementation (back) to src/port. This is in
preparation for next patch that will add another implementation that uses
Intel SSE 4.2 instructions to calculate CRC-32C, where available.
This view shows information about all connections, such as if the
connection is using SSL, which cipher is used, and which client
certificate (if any) is used.
Reviews by Alex Shulgin, Heikki Linnakangas, Andres Freund & Michael Paquier
Locking and updating the same tuple repeatedly led to some strange
multixacts being created which had several subtransactions of the same
parent transaction holding locks of the same strength. However,
once a subxact of the current transaction holds a lock of a given
strength, it's not necessary to acquire the same lock again. This made
some coding patterns much slower than required.
The fix is twofold. First we change HeapTupleSatisfiesUpdate to return
HeapTupleBeingUpdated for the case where the current transaction is
already a single-xid locker for the given tuple; it used to return
HeapTupleMayBeUpdated for that case. The new logic is simpler, and the
change to pgrowlocks is a testament to that: previously we needed to
check for the single-xid locker separately in a very ugly way. That
test is simpler now.
As fallout from the HTSU change, some of its callers need to be amended
so that tuple-locked-by-own-transaction is taken into account in the
BeingUpdated case rather than the MayBeUpdated case. For many of them
there is no difference; but heap_delete() and heap_update now check
explicitely and do not grab tuple lock in that case.
The HTSU change also means that routine MultiXactHasRunningRemoteMembers
introduced in commit 11ac4c73cb is no longer necessary and can be
removed; the case that used to require it is now handled naturally as
result of the changes to heap_delete and heap_update.
The second part of the fix to the performance issue is to adjust
heap_lock_tuple to avoid the slowness:
1. Previously we checked for the case that our own transaction already
held a strong enough lock and returned MayBeUpdated, but only in the
multixact case. Now we do it for the plain Xid case as well, which
saves having to LockTuple.
2. If the current transaction is the only locker of the tuple (but with
a lock not as strong as what we need; otherwise it would have been
caught in the check mentioned above), we can skip sleeping on the
multixact, and instead go straight to create an updated multixact with
the additional lock strength.
3. Most importantly, make sure that both the single-xid-locker case and
the multixact-locker case optimization are applied always. We do this
by checking both in a single place, rather than them appearing in two
separate portions of the routine -- something that is made possible by
the HeapTupleSatisfiesUpdate API change. Previously we would only check
for the single-xid case when HTSU returned MayBeUpdated, and only
checked for the multixact case when HTSU returned BeingUpdated. This
was at odds with what HTSU actually returned in one case: if our own
transaction was locker in a multixact, it returned MayBeUpdated, so the
optimization never applied. This is what led to the large multixacts in
the first place.
Per bug report #8470 by Oskari Saarenmaa.
When certain event-trigger-only functions are called when not in the
wrong context, they were reporting the "feature not supported" SQLSTATE,
which is somewhat misleading. Create a new custom error code for such
uses instead.
Not backpatched since it may be seen as an undesirable behavioral
change.
Author: Michael Paquier
Discussion: https://www.postgresql.org/message-id/CAB7nPqQ-5NAkHQHh_NOm7FPep37NCiLKwPoJ2Yxb8TDoGgbYYA@mail.gmail.com
This is consistent with what the new numeric suppor for abbreviated keys
now does, and seems much more convenient than having a separate compiler
define to control this debug output.
Peter Geoghegan
It now also reports temporary objects dropped that are local to the
backend. Previously we weren't reporting any temp objects because it
was deemed unnecessary; but as it turns out, it is necessary if we want
to keep close track of DDL command execution inside one session. Temp
objects are reported as living in schema pg_temp, which works because
such a schema-qualification always refers to the temp objects of the
current session.
When committing abd94bcac4, I tried to make
it decide what kind of abbreviation to use based only on SIZEOF_DATUM,
without regard to USE_FLOAT8_BYVAL. That attempt was a few bricks short
of a load, so try to fix it, and add a comment explaining what we're
about.
Patch by me; review (but not a full endorsement) by Andrew Gierth.
Be more aggressive about aborting early on if it looks like it's not
helping, but be less aggressive about aborting later on, since it's
more expensive at that point, and also since we're currently aborting
in some cases where abbreviation can still deliver a substantial win.
Peter Geoghegan. Extensive testing by Tomas Vondra.
This commit also adds pg_malloc_extended for frontend. These interfaces
can be used to control at a lower level memory allocation using an interface
similar to MemoryContextAllocExtended. For example, the callers can specify
MCXT_ALLOC_NO_OOM if they want to suppress the "out of memory" error while
allocating the memory and handle a NULL return value.
Michael Paquier, reviewed by me.
While a new backend nominally participates in sinval signaling starting
from the SharedInvalBackendInit call near the top of InitPostgres, it
cannot recognize sinval messages for unshared catalogs of its database
until it has set up MyDatabaseId. This is not problematic for the catcache
or relcache, which by definition won't have loaded any data from or about
such catalogs before that point. However, commit 568d4138c6
introduced a mechanism for re-using MVCC snapshots for catalog scans, and
made invalidation of those depend on recognizing relevant sinval messages.
So it's possible to establish a catalog snapshot to read pg_authid and
pg_database, then before we set MyDatabaseId, receive sinval messages that
should result in invalidating that snapshot --- but do not, because we
don't realize they are for our database. This mechanism explains the
intermittent buildfarm failures we've seen since commit 31eae6028e.
That commit was not itself at fault, but it introduced a new regression
test that does reconnections concurrently with the "vacuum full pg_am"
command in vacuum.sql. This allowed the pre-existing error to be exposed,
given just the right timing, because we'd fail to update our information
about how to access pg_am. In principle any VACUUM FULL on a system
catalog could have created a similar hazard for concurrent incoming
connections. Perhaps there are more subtle failure cases as well.
To fix, force invalidation of the catalog snapshot as soon as we've
set MyDatabaseId.
Back-patch to 9.4 where the error was introduced.
In 83ff1618 we defined integer limits iff they're not provided by the
system. That turns out not to be the greatest idea because there's
different ways some datatypes can be represented. E.g. on OSX PG's 64bit
datatype will be a 'long int', but OSX unconditionally uses 'long
long'. That disparity then can lead to warnings, e.g. around printf
formats.
One way to fix that would be to back int64 using stdint.h's
int64_t. While a good idea it's not that easy to implement. We would
e.g. need to include stdint.h in our external headers, which we don't
today. Also computing the correct int64 printf formats in that case is
nontrivial.
Instead simply prefix the integer limits with PG_ and define them
unconditionally. I've adjusted all the references to them in code, but
not the ones in comments; the latter seems unnecessary to me.
Discussion: 20150331141423.GK4878@alap3.anarazel.de
This patch fills in the formerly-stub networksel() and networkjoinsel()
estimation functions. Those are used for << <<= >> >>= and && operators
on inet/cidr types. The estimation is not perfect, certainly, because
we rely on the existing statistics collected for the inet btree operators.
But it's a long way better than nothing, and it's not clear that asking
ANALYZE to collect separate stats for these operators would be a win.
Emre Hasegeli, with reviews from Dilip Kumar and Heikki Linnakangas,
and some further hacking by me
... and rename it and its sibling array_offsets to array_position and
array_positions, to account for the changed behavior.
Having the functions return subscripts better matches existing practice,
and is better suited to using the result value as a subscript into the
array directly. For one-based arrays, the new definition is identical
to what was originally committed.
(We use the term "subscript" in the documentation, which is what we use
whenever we talk about arrays; but the functions themselves are named
using the word "position" to match the standard-defined POSITION()
functions.)
Author: Pavel Stěhule
Behavioral problem noted by Dean Rasheed.
The previous coding in get_const_expr() tried to avoid quoting integer,
float, and numeric literals if at all possible. While that looks nice,
it means that dumped expressions might re-parse to something that's
semantically equivalent but not the exact same parsetree; for example
a FLOAT8 constant would re-parse as a NUMERIC constant with a cast to
FLOAT8. Though the result would be the same after constant-folding,
this is problematic in certain contexts. In particular, Jeff Davis
pointed out that this could cause unexpected failures in ALTER INHERIT
operations because of child tables having not-exactly-equivalent CHECK
expressions. Therefore, favor correctness over legibility and dump
such constants in quotes except in the limited cases where they'll
be interpreted as the same type even without any casting.
This results in assorted small changes in the regression test outputs,
and will affect display of user-defined views and rules similarly.
The odds of that causing problems in the field seem non-negligible;
given the lack of previous complaints, it seems best not to change
this in the back branches.
This improves on commit bbfd7edae5 by
making two simple changes:
* pg_attribute_noreturn now takes parentheses, ie pg_attribute_noreturn().
Likewise pg_attribute_unused(), pg_attribute_packed(). This reduces
pgindent's tendency to misformat declarations involving them.
* attributes are now always attached to function declarations, not
definitions. Previously some places were taking creative shortcuts,
which were not merely candidates for bad misformatting by pgindent
but often were outright wrong anyway. (It does little good to put a
noreturn annotation where callers can't see it.) In any case, if
we would like to believe that these macros can be used with non-gcc
compilers, we should avoid gratuitous variance in usage patterns.
I also went through and manually improved the formatting of a lot of
declarations, and got rid of excessively repetitive (and now obsolete
anyway) comments informing the reader what pg_attribute_printf is for.
Several submitted and even committed patches have run into the problem
that C89, our baseline, does not provide minimum/maximum values for
various integer datatypes. C99's stdint.h does, but we can't rely on
it.
Several parts of the code defined limits locally, so instead centralize
the definitions to c.h.
This patch also changes the more obvious usages of literal limit values;
there's more places that could be changed, but it's less clear whether
it's beneficial to change those.
Author: Andrew Gierth
Discussion: 87619tc5wc.fsf@news-spur.riddles.org.uk
Previously, CHECK constraints of the same scope were checked in whatever
order they happened to be read from pg_constraint. (Usually, but not
reliably, this would be creation order for domain constraints and reverse
creation order for table constraints, because of differing implementation
details.) Nondeterministic results of this sort are problematic at least
for testing purposes, and in discussion it was agreed to be a violation of
the principle of least astonishment. Therefore, borrow the principle
already established for triggers, and apply such checks in name order
(using strcmp() sort rules). This lets users control the check order
if they have a mind to.
Domain CHECK constraints still follow the rule of checking lower nested
domains' constraints first; the name sort only applies to multiple
constraints attached to the same domain.
In passing, I failed to resist the temptation to wordsmith a bit in
create_domain.sgml.
Apply to HEAD only, since this could result in a behavioral change in
existing applications, and the potential regression test failures have
not actually been observed in our buildfarm.
Revert "to_char(float4/8): zero pad to specified length". There are
too many platform-specific problems, and the proper rounding is missing.
Also revert companion patch 9d61b9953c.
Previously, zero padding was limited to the internal length, rather than
the specified length. This allows it to match to_char(int/numeric), which
always padded to the specified length.
Regression tests added.
BACKWARD INCOMPATIBILITY
On platforms where we support 128bit integers, use them to implement
faster transition functions for sum(int8), avg(int8),
var_*(int2/int4),stdev_*(int2/int4). Where not supported continue to use
numeric as a transition type.
In some synthetic benchmarks this has been shown to provide significant
speedups.
Bumps catversion.
Discussion: 544BB5F1.50709@proxel.se
Author: Andreas Karlsson
Reviewed-By: Peter Geoghegan, Petr Jelinek, Andres Freund,
Oskari Saarenmaa, David Rowley
The pg_stat and pg_signal-related functions have been using GetUserId()
instead of has_privs_of_role() for checking if the current user should
be able to see details in pg_stat_activity or signal other processes,
requiring a user to do 'SET ROLE' for inheirited roles for a permissions
check, unlike other permissions checks.
This patch changes that behavior to, instead, act like most other
permission checks and use has_privs_of_role(), removing the 'SET ROLE'
need. Documentation and error messages updated accordingly.
Per discussion with Alvaro, Peter, Adam (though not using Adam's patch),
and Robert.
Reviewed by Jeevan Chalke.
This patch fixes two inadequacies of the PlanRowMark representation.
First, that the original LockingClauseStrength isn't stored (and cannot be
inferred for foreign tables, which always get ROW_MARK_COPY). Since some
PlanRowMarks are created out of whole cloth and don't actually have an
ancestral RowMarkClause, this requires adding a dummy LCS_NONE value to
enum LockingClauseStrength, which is fairly annoying but the alternatives
seem worse. This fix allows getting rid of the use of get_parse_rowmark()
in FDWs (as per the discussion around commits 462bd95705 and
8ec8760fc8), and it simplifies some things elsewhere.
Second, that the representation assumed that all child tables in an
inheritance hierarchy would use the same RowMarkType. That's true today
but will soon not be true. We add an "allMarkTypes" field that identifies
the union of mark types used in all a parent table's children, and use
that where appropriate (currently, only in preprocess_targetlist()).
In passing fix a couple of minor infelicities left over from the SKIP
LOCKED patch, notably that _outPlanRowMark still thought waitPolicy
is a bool.
Catversion bump is required because the numeric values of enum
LockingClauseStrength can appear in on-disk rules.
Extracted from a much larger patch to support foreign table inheritance;
it seemed worth breaking this out, since it's a separable concern.
Shigeru Hanada and Etsuro Fujita, somewhat modified by me
The introduction of min_wal_size & max_wal_size in 88e9823026 makes it
feasible to increase the default upper bound in checkpoint
size. Previously raising the default would lead to a increased disk
footprint, even if more segments weren't beneficial. The low default of
checkpoint size is one of common performance problem users have thus
increasing the default makes sense. Setups where the increase in
maximum disk usage is a problem will very likely have to run with a
modified configuration anyway.
Discussion: 54F4EFB8.40202@agliodbs.com,
CA+TgmoZEAgX5oMGJOHVj8L7XOkAe05Gnf45rP40m-K3FhZRVKg@mail.gmail.com
Author: Josh Berkus, after a discussion involving lots of people.
While the SQL standard is pretty vague on the overall topic of operator
precedence (because it never presents a unified BNF for all expressions),
it does seem reasonable to conclude from the spec for <boolean value
expression> that OR has the lowest precedence, then AND, then NOT, then IS
tests, then the six standard comparison operators, then everything else
(since any non-boolean operator in a WHERE clause would need to be an
argument of one of these).
We were only sort of on board with that: most notably, while "<" ">" and
"=" had properly low precedence, "<=" ">=" and "<>" were treated as generic
operators and so had significantly higher precedence. And "IS" tests were
even higher precedence than those, which is very clearly wrong per spec.
Another problem was that "foo NOT SOMETHING bar" constructs, such as
"x NOT LIKE y", were treated inconsistently because of a bison
implementation artifact: they had the documented precedence with respect
to operators to their right, but behaved like NOT (i.e., very low priority)
with respect to operators to their left.
Fixing the precedence issues is just a small matter of rearranging the
precedence declarations in gram.y, except for the NOT problem, which
requires adding an additional lookahead case in base_yylex() so that we
can attach a different token precedence to NOT LIKE and allied two-word
operators.
The bulk of this patch is not the bug fix per se, but adding logic to
parse_expr.c to allow giving warnings if an expression has changed meaning
because of these precedence changes. These warnings are off by default
and are enabled by the new GUC operator_precedence_warning. It's believed
that very few applications will be affected by these changes, but it was
agreed that a warning mechanism is essential to help debug any that are.
Error messages informing the user that no such column exists can
sometimes provoke a perplexed response. This often happens due to
a subtle typo in the column name or, perhaps less likely, in the
alias name. To speed discovery of what the real issue is in such
cases, we'll now search the range table for approximate matches.
If there are one or two such matches that are good enough to think
that they might be what the user intended to type, and better than
all other approximate matches, we'll issue a hint suggesting that
the user might have intended to reference those columns.
Peter Geoghegan and Robert Haas
Until now __attribute__() was defined to be empty for all compilers but
gcc. That's problematic because it prevents using it in other compilers;
which is necessary e.g. for atomics portability. It's also just
generally dubious to do so in a header as widely included as c.h.
Instead add pg_attribute_format_arg, pg_attribute_printf,
pg_attribute_noreturn macros which are implemented in the compilers that
understand them. Also add pg_attribute_noreturn and pg_attribute_packed,
but don't provide fallbacks, since they can affect functionality.
This means that external code that, possibly unwittingly, relied on
__attribute__ defined to be empty on !gcc compilers may now run into
warnings or errors on those compilers. But there shouldn't be many
occurances of that and it's hard to work around...
Discussion: 54B58BA3.8040302@ohmu.fi
Author: Oskari Saarenmaa, with some minor changes by me.
When newly-added GUC parameter, wal_compression, is on, the PostgreSQL server
compresses a full page image written to WAL when full_page_writes is on or
during a base backup. A compressed page image will be decompressed during WAL
replay. Turning this parameter on can reduce the WAL volume without increasing
the risk of unrecoverable data corruption, but at the cost of some extra CPU
spent on the compression during WAL logging and on the decompression during
WAL replay.
This commit changes the WAL format (so bumping WAL version number) so that
the one-byte flag indicating whether a full page image is compressed or not is
included in its header information. This means that the commit increases the
WAL volume one-byte per a full page image even if WAL compression is not used
at all. We can save that one-byte by borrowing one-bit from the existing field
like hole_offset in the header and using it as the flag, for example. But which
would reduce the code readability and the extensibility of the feature.
Per discussion, it's not worth paying those prices to save only one-byte, so we
decided to add the one-byte flag to the header.
This commit doesn't introduce any new compression algorithm like lz4.
Currently a full page image is compressed using the existing PGLZ algorithm.
Per discussion, we decided to use it at least in the first version of the
feature because there were no performance reports showing that its compression
ratio is unacceptably lower than that of other algorithm. Of course,
in the future, it's worth considering the support of other compression
algorithm for the better compression.
Rahila Syed and Michael Paquier, reviewed in various versions by myself,
Andres Freund, Robert Haas, Abhijit Menon-Sen and many others.
Commands such as ALTER USER, ALTER GROUP, ALTER ROLE, GRANT, and the
various ALTER OBJECT / OWNER TO, as well as ad-hoc clauses related to
roles such as the AUTHORIZATION clause of CREATE SCHEMA, the FOR clause
of CREATE USER MAPPING, and the FOR ROLE clause of ALTER DEFAULT
PRIVILEGES can now take the keywords CURRENT_USER and SESSION_USER as
user specifiers in place of an explicit user name.
This commit also fixes some quite ugly handling of special standards-
mandated syntax in CREATE USER MAPPING, which in particular would fail
to work in presence of a role named "current_user".
The special role specifiers PUBLIC and NONE also have more consistent
handling now.
Also take the opportunity to add location tracking to user specifiers.
Authors: Kyotaro Horiguchi. Heavily reworked by Álvaro Herrera.
Reviewed by: Rushabh Lathia, Adam Brightwell, Marti Raudsepp.
Commit 5cefbf5a6c introduced an
assumption that this field would always be non-NULL when doing a merge
pass, but that's not true. Without this fix, you can crash the server
by building a hash index that is sufficiently large relative to
maintenance_work_mem, or by triggering a large datum sort.
Commit 5ea86e6e65 changed the comments
for that field to say that it would be set in all cases except for the
hash index case, but that wasn't (and still isn't) true.
The datum-sort failure was spotted by Tomas Vondra; initial analysis
of that failure was by Peter Geoghegan. The remaining issues were
spotted by me during review of the surrounding code, and the patch is
all my fault.
genericcostestimate() and friends used the cost of the entire indexqual
expressions as the charge for initial evaluation of indexscan arguments.
But of course the index column is not evaluated, only the other side
of the qual expression, so this was a bad overestimate if the index
column was an expensive expression.
To fix, refactor the logic in this area so that there's a single routine
charged with deconstructing index quals and figuring out what is the index
column and what is the comparison expression. This is more or less free in
the case of btree indexes, since btcostestimate() was doing equivalent
deconstruction already. It probably adds a bit of new overhead in the cases
of other index types, but not a lot. (In the case of GIN I think I saved
something by getting rid of code that wasn't aware that the index column
associations were already available "for free".)
Per recent gripe from Jeff Janes.
Arguably this is a bug fix, but I'm hesitant to back-patch because of the
possibility of destabilizing plan choices that people may be happy with.
Previously, we cached domain constraints for the life of a query, or
really for the life of the FmgrInfo struct that was used to invoke
domain_in() or domain_check(). But plpgsql (and probably other places)
are set up to cache such FmgrInfos for the whole lifespan of a session,
which meant they could be enforcing really stale sets of constraints.
On the other hand, searching pg_constraint once per query gets kind of
expensive too: testing says that as much as half the runtime of a
trivial query such as "SELECT 0::domaintype" went into that.
To fix this, delegate the responsibility for tracking a domain's
constraints to the typcache, which has the infrastructure needed to
detect syscache invalidation events that signal possible changes.
This not only removes unnecessary repeat reads of pg_constraint,
but ensures that we never apply stale constraint data: whatever we
use is the current data according to syscache rules.
Unfortunately, the current configuration of the system catalogs means
we have to flush cached domain-constraint data whenever either pg_type
or pg_constraint changes, which happens rather a lot (eg, creation or
deletion of a temp table will do it). It might be worth rearranging
things to split pg_constraint into two catalogs, of which the domain
constraint one would probably be very low-traffic. That's a job for
another patch though, and in any case this patch should improve matters
materially even with that handicap.
This patch makes use of the recently-added memory context reset callback
feature to manage the lifespan of domain constraint caches, so that we
don't risk deleting a cache that might be in the midst of evaluation.
Although this is a bug fix as well as a performance improvement, no
back-patch. There haven't been many if any field complaints about
stale domain constraint checks, so it doesn't seem worth taking the
risk of modifying data structures as basic as MemoryContexts in back
branches.
This makes "ALTER TABLE tabname ALTER tscol TYPE ... USING tscol AT TIME
ZONE 'UTC'" skip rewriting the table when altering from "timestamp" to
"timestamptz" or vice versa. While it would be nicer still to optimize
this in the absence of the USING clause given timezone==UTC, transform
functions must consult IMMUTABLE facts only.
Add documentation about the new reset callback mechanism.
Also, at long last, recast the existing text so that it describes the
current context mechanisms as established fact rather than something
we're going to implement. Shoulda done that in 2001 or so ...
The type variable must get set on first iteration of the while loop,
but there are reasonably modern gcc versions that don't realize that.
Initialize it with a dummy value. This undoes a removal of initialization
in commit 654809e770.
That is, MemoryContextReset() now means what was formerly meant by
MemoryContextResetAndDeleteChildren(), and the latter is now just a macro
alias for the former. If you really want the functionality that was
formerly provided by MemoryContextReset(), what you have to do is
MemoryContextResetChildren() plus MemoryContextResetOnly() (which is a
new API to reset *only* the named context and not touch its children).
The reason for this change is that near fifteen years of experience has
proven that there is noplace where old-style MemoryContextReset() is
actually what you want. Making that the default behavior has led to lots
of context-leakage bugs, while we've not found anyplace where it's actually
necessary to keep the child contexts; at least the standard regression
tests do not reveal anyplace where this change breaks anything. And there
are upcoming patches that will introduce additional reasons why child
contexts need to be removed.
We could change existing calls of MemoryContextResetAndDeleteChildren to be
just MemoryContextReset, but for the moment I'll leave them alone; they're
not costing anything.
This allows cleanup actions to be registered to be called just before a
particular memory context's contents are flushed (either by deletion or
MemoryContextReset). The patch in itself has no use-cases for this, but
several likely reasons for wanting this exist.
In passing, per discussion, rearrange some boolean fields in struct
MemoryContextData so as to avoid wasted padding space. For safety,
this requires making allowInCritSection's existence unconditional;
but I think that's a better approach than what was there anyway.
Typo "aggreagate" appeared three times, and the return value of function
JsonbIteratorNext() was being assigned to an int variable in a bunch of
places.
Commit ab14a73a6c raised an error in these cases and later the
behaviour was copied to jsonb. This is what the XML code, which we
then adopted, does, as the XSD types don't accept infinite values.
However, json dates and timestamps are just strings as far as json is
concerned, so there is no reason not to render these values as
'infinity'.
The json portion of this is backpatched to 9.4 where the behaviour was
introduced. The jsonb portion only affects the development branch.
Per gripe on pgsql-general.
When I rewrote this in commit 56a79a869b,
I forgot that it's possible for the input array type to change from one
call to the next (this can happen when applying the function to
pg_statistic columns, for instance). Fix that.
The "simple" path for printing VALUES clauses doesn't work if we need
to attach nondefault column aliases, because there's noplace to do that
in the minimal VALUES() syntax. So modify get_simple_values_rte() to
detect nondefault aliases and treat that as a non-simple case. This
further exposes that the "non-simple" path never actually worked;
it didn't produce valid syntax. Fix that too. Per bug #12789 from
Curtis McEnroe, and analysis by Andrew Gierth.
Back-patch to all supported branches. Before 9.3, this also requires
back-patching the part of commit 092d7ded29
that created get_simple_values_rte() to begin with; inserting the extra
test into the old factorization of that logic would've been too messy.
Instead of having a single knob (checkpoint_segments) that both triggers
checkpoints, and determines how many checkpoints to recycle, they are now
separate concerns. There is still an internal variable called
CheckpointSegments, which triggers checkpoints. But it no longer determines
how many segments to recycle at a checkpoint. That is now auto-tuned by
keeping a moving average of the distance between checkpoints (in bytes),
and trying to keep that many segments in reserve. The advantage of this is
that you can set max_wal_size very high, but the system won't actually
consume that much space if there isn't any need for it. The min_wal_size
sets a floor for that; you can effectively disable the auto-tuning behavior
by setting min_wal_size equal to max_wal_size.
The max_wal_size setting is now the actual target size of WAL at which a
new checkpoint is triggered, instead of the distance between checkpoints.
Previously, you could calculate the actual WAL usage with the formula
"(2 + checkpoint_completion_target) * checkpoint_segments + 1". With this
patch, you set the desired WAL usage with max_wal_size, and the system
calculates the appropriate CheckpointSegments with the reverse of that
formula. That's a lot more intuitive for administrators to set.
Reviewed by Amit Kapila and Venkata Balaji N.
Replace the if-switch-case constructs with two conversion tables,
containing all the supported conversions between human-readable unit
strings and the base units used in GUC variables. This makes the code
easier to read, and makes adding new units simpler.
Previously when the standby server failed to retrieve WAL files from any sources
(i.e., streaming replication, local pg_xlog directory or WAL archive), it always
waited for five seconds (hard-coded) before the next attempt. For example,
this is problematic in warm-standby because restore_command can fail
every five seconds even while new WAL file is expected to be unavailable for
a long time and flood the log files with its error messages.
This commit adds new parameter, wal_retrieve_retry_interval, to control that
wait time.
Alexey Vasiliev and Michael Paquier, reviewed by Andres Freund and me.
Everywhere else in the file, "context" is of type MemoryContext and
"set" is of type AllocSet. AllocSetContextCreate uses a variable of
type AllocSet, so rename it from "context" to "set".
Previously, each new array created a new memory context that started
out at 8kB. This is incredibly wasteful when there are lots of small
groups of just a few elements each.
Change initArrayResult() and friends to accept a "subcontext" argument
to indicate whether the caller wants the ArrayBuildState allocated in
a new subcontext or not. If not, it can no longer be released
separately from the rest of the memory context.
Fixes bug report by Frank van Vugt on 2013-10-19.
Tomas Vondra. Reviewed by Ali Akbar, Tom Lane, and me.
