This didn't actually work: COPY would fail to flush the right files, and
instead would try to flush a non-existing file, causing the whole
transaction to fail.
Cope by raising an error as soon as the command is sent instead, to
avoid a nasty later surprise. Of course, it would be much better to
make it work, but we don't have a patch for that yet, and we don't know
if we'll want to backpatch one when we do.
Reported-by: Tomas Vondra
Author: David Rowley
Reviewed-by: Amit Langote, Steve Singer, Tomas Vondra
On some operating systems, it doesn't make sense to retry fsync(),
because dirty data cached by the kernel may have been dropped on
write-back failure. In that case the only remaining copy of the
data is in the WAL. A subsequent fsync() could appear to succeed,
but not have flushed the data. That means that a future checkpoint
could apparently complete successfully but have lost data.
Therefore, violently prevent any future checkpoint attempts by
panicking on the first fsync() failure. Note that we already
did the same for WAL data; this change extends that behavior to
non-temporary data files.
Provide a GUC data_sync_retry to control this new behavior, for
users of operating systems that don't eject dirty data, and possibly
forensic/testing uses. If it is set to on and the write-back error
was transient, a later checkpoint might genuinely succeed (on a
system that does not throw away buffers on failure); if the error is
permanent, later checkpoints will continue to fail. The GUC defaults
to off, meaning that we panic.
Back-patch to all supported releases.
There is still a narrow window for error-loss on some operating
systems: if the file is closed and later reopened and a write-back
error occurs in the intervening time, but the inode has the bad
luck to be evicted due to memory pressure before we reopen, we could
miss the error. A later patch will address that with a scheme
for keeping files with dirty data open at all times, but we judge
that to be too complicated to back-patch.
Author: Craig Ringer, with some adjustments by Thomas Munro
Reported-by: Craig Ringer
Reviewed-by: Robert Haas, Thomas Munro, Andres Freund
Discussion: https://postgr.es/m/20180427222842.in2e4mibx45zdth5%40alap3.anarazel.de
If fsync() fails, md.c must keep the request in its bitmap, so that
future attempts will try again.
Back-patch to all supported releases.
Author: Thomas Munro
Reviewed-by: Amit Kapila
Reported-by: Andrew Gierth
Discussion: https://postgr.es/m/87y3i1ia4w.fsf%40news-spur.riddles.org.uk
When reading a WAL record, its contents are copied into an intermediate
buffer. However, doing so is not necessary if the record fits fully
into the current page, saving one memcpy for each such record. The
allocation handling of the intermediate buffer is also now done only
when a record crosses a page boundary, shaving some extra cycles when
reading a WAL record.
Author: Andrey Lepikhov
Reviewed-by: Kyotaro Horiguchi, Heikki Linnakangas
Discussion: https://postgr.es/m/c2ea54dd-a1d3-80eb-ddbf-7e6f258e615e@postgrespro.ru
Any Autoconf macro that uses AC_REQUIRES -- directly or indirectly --
must not be inside a plain shell "if" test; if it is, whatever code
gets pulled in by the AC_REQUIRES will also be inside that "if".
Instead of "if" we can use AS_IF, which knows how to get this right
(cf commit 01051a987).
The only immediate problem from getting this wrong was that AC_PROG_AWK
had to be run twice, once inside the "if llvm" block and once in the
main line. However, it broke a different patch I'm about to submit
more thoroughly.
wcsrtombs (called through wchar2char from common functions like lower,
upper, etc.) uses various optimizations that may look like access to
uninitialized data, triggering valgrind reports.
For example AVX2 instructions load data in 256-bit chunks, and gconv
does something similar with 32-bit chunks. This is faster than accessing
the bytes one by one, and the uninitialized part of the buffer is not
actually used. So suppress the bogus reports.
The exact stack depends on possible optimizations - it might be AVX, SSE
(as in the report by Aleksander Alekseev) or something else. Hence the
last frame is wildcarded, to deal with this.
Backpatch all the way back to 9.4.
Author: Tomas Vondra
Discussion: https://www.postgresql.org/message-id/flat/90ac0452-e907-e7a4-b3c8-15bd33780e62%402ndquadrant.com
Discussion: https://www.postgresql.org/message-id/20180220150838.GD18315@e733.localdomain
Setting them to SIG_IGN seems unlikely to have any beneficial effect
on that platform, and given the signal numbering collision with SIGABRT,
it could easily have bad effects.
Given the lack of field complaints that can be traced to this, I don't
presently feel a need to back-patch.
Discussion: https://postgr.es/m/5627.1542477392@sss.pgh.pa.us
For reasons lost in the mists of time, most postmaster child processes
reset SIGTTIN/SIGTTOU signal handling to SIG_DFL, with the major exception
that backend sessions do not. It seems like a pretty bad idea for any
postmaster children to do that: if stderr is connected to the terminal,
and the user has put the postmaster in background, any log output would
result in the child process freezing up. Hence, switch them all to
doing what backends do, ie, nothing. This allows them to inherit the
postmaster's SIG_IGN setting. On the other hand, manually-launched
processes such as standalone backends will have default processing,
which seems fine.
In passing, also remove useless resets of SIGCONT and SIGWINCH signal
processing. Perhaps the postmaster once changed those to something
besides SIG_DFL, but it doesn't now, so these are just wasted (and
confusing) syscalls.
Basically, this propagates the changes made in commit 8e2998d8a from
backends to other postmaster children. Probably the only reason these
calls now exist elsewhere is that I missed changing pgstat.c along with
postgres.c at the time.
Given the lack of field complaints that can be traced to this, I don't
presently feel a need to back-patch.
Discussion: https://postgr.es/m/5627.1542477392@sss.pgh.pa.us
This commit completes the work prepared in 1a0586de36, splitting the
old TupleTableSlot implementation (which could store buffer, heap,
minimal and virtual slots) into four different slot types. As
described in the aforementioned commit, this is done with the goal of
making tuple table slots extensible, to allow for pluggable table
access methods.
To achieve runtime extensibility for TupleTableSlots, operations on
slots that can differ between types of slots are performed using the
TupleTableSlotOps struct provided at slot creation time. That
includes information from the size of TupleTableSlot struct to be
allocated, initialization, deforming etc. See the struct's definition
for more detailed information about callbacks TupleTableSlotOps.
I decided to rename TTSOpsBufferTuple to TTSOpsBufferHeapTuple and
ExecCopySlotTuple to ExecCopySlotHeapTuple, as that seems more
consistent with other naming introduced in recent patches.
There's plenty optimization potential in the slot implementation, but
according to benchmarking the state after this commit has similar
performance characteristics to before this set of changes, which seems
sufficient.
There's a few changes in execReplication.c that currently need to poke
through the slot abstraction, that'll be repaired once the pluggable
storage patchset provides the necessary infrastructure.
Author: Andres Freund and Ashutosh Bapat, with changes by Amit Khandekar
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
This becomes useful when used to retry a transaction after a
serialization error or deadlock abort. (We don't yet have that feature,
but this is preparation for it.)
While at it, use separate random state for thread administratrivia such
as deciding which script to run, how long to delay for throttling, or
whether to log a message when sampling; this not only makes these tasks
independent of each other, but makes the actual thread run
deterministic.
Author: Marina Polyakova
Reviewed-by: Fabien Coelho
Discussion: https://postgr.es/m/72a0d590d6ba06f242d75c2e641820ec@postgrespro.ru
This speeds up write operations (INSERT, UPDATE, DELETE, COPY, as well
as the future MERGE) on partitioned tables.
This changes the setup for tuple routing so that it does far less work
during the initial setup and pushes more work out to when partitions
receive tuples. PartitionDispatchData structs for sub-partitioned
tables are only created when a tuple gets routed through it. The
possibly large arrays in the PartitionTupleRouting struct have largely
been removed. The partitions[] array remains but now never contains any
NULL gaps. Previously the NULLs had to be skipped during
ExecCleanupTupleRouting(), which could add a large overhead to the
cleanup when the number of partitions was large. The partitions[] array
is allocated small to start with and only enlarged when we route tuples
to enough partitions that it runs out of space. This allows us to keep
simple single-row partition INSERTs running quickly. Redesign
The arrays in PartitionTupleRouting which stored the tuple translation maps
have now been removed. These have been moved out into a
PartitionRoutingInfo struct which is an additional field in ResultRelInfo.
The find_all_inheritors() call still remains by far the slowest part of
ExecSetupPartitionTupleRouting(). This commit just removes the other slow
parts.
In passing also rename the tuple translation maps from being ParentToChild
and ChildToParent to being RootToPartition and PartitionToRoot. The old
names mislead you into thinking that a partition of some sub-partitioned
table would translate to the rowtype of the sub-partitioned table rather
than the root partitioned table.
Authors: David Rowley and Amit Langote, heavily revised by Álvaro Herrera
Testing help from Jesper Pedersen and Kato Sho.
Discussion: https://postgr.es/m/CAKJS1f_1RJyFquuCKRFHTdcXqoPX-PYqAd7nz=GVBwvGh4a6xA@mail.gmail.com
The assumption made in 1a0586de36 was wrong, as evidenced by
buildfarm failure on locust, which runs with
force_parallel_mode=regress. The tuples accessed in either nodes are
in the outer slot, and we can't trivially rely on the slot type being
known because the leader might execute the subsidiary node directly,
or via the tuple queue on a worker. In the latter case the tuple will
always be a heaptuple slot, but in the former, it'll be whatever the
subsidiary node returns.
Virtual tuple table slots never need tuple deforming. Therefore, if we
know at expression compilation time, that a certain slot will always
be virtual, there's no need to create a tuple deforming routine for
it.
Author: Andres Freund
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
This is important so JIT compilation knows what kind of tuple slot the
deforming routine can expect. There's also optimization potential for
expression initialization without JIT compilation. It e.g. seems
plausible to elide EEOP_*_FETCHSOME ops entirely when dealing with
virtual slots.
Author: Andres Freund
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
Previously this information was computed when JIT compiling an
expression. But the information is useful for assertions in the
non-JIT case too (for assertions), therefore it makes sense to move
it.
This will, in a followup commit, allow to treat different slot types
differently. E.g. for virtual slots there's no need to generate a JIT
function to deform the slot.
Author: Andres Freund
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
Upcoming work intends to allow pluggable ways to introduce new ways of
storing table data. Accessing those table access methods from the
executor requires TupleTableSlots to be carry tuples in the native
format of such storage methods; otherwise there'll be a significant
conversion overhead.
Different access methods will require different data to store tuples
efficiently (just like virtual, minimal, heap already require fields
in TupleTableSlot). To allow that without requiring additional pointer
indirections, we want to have different structs (embedding
TupleTableSlot) for different types of slots. Thus different types of
slots are needed, which requires adapting creators of slots.
The slot that most efficiently can represent a type of tuple in an
executor node will often depend on the type of slot a child node
uses. Therefore we need to track the type of slot is returned by
nodes, so parent slots can create slots based on that.
Relatedly, JIT compilation of tuple deforming needs to know which type
of slot a certain expression refers to, so it can create an
appropriate deforming function for the type of tuple in the slot.
But not all nodes will only return one type of slot, e.g. an append
node will potentially return different types of slots for each of its
subplans.
Therefore add function that allows to query the type of a node's
result slot, and whether it'll always be the same type (whether it's
fixed). This can be queried using ExecGetResultSlotOps().
The scan, result, inner, outer type of slots are automatically
inferred from ExecInitScanTupleSlot(), ExecInitResultSlot(),
left/right subtrees respectively. If that's not correct for a node,
that can be overwritten using new fields in PlanState.
This commit does not introduce the actually abstracted implementation
of different kind of TupleTableSlots, that will be left for a followup
commit. The different types of slots introduced will, for now, still
use the same backing implementation.
While this already partially invalidates the big comment in
tuptable.h, it seems to make more sense to update it later, when the
different TupleTableSlot implementations actually exist.
Author: Ashutosh Bapat and Andres Freund, with changes by Amit Khandekar
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
Previously materializing a slot always returned a HeapTuple. As
current work aims to reduce the reliance on HeapTuples (so other
storage systems can work efficiently), that needs to change. Thus
split the tasks of materializing a slot (i.e. making it independent
from the underlying storage / other memory contexts) from fetching a
HeapTuple from the slot. For brevity, allow to fetch a HeapTuple from
a slot and materializing the slot at the same time, controlled by a
parameter.
For now some callers of ExecFetchSlotHeapTuple, with materialize =
true, expect that changes to the heap tuple will be reflected in the
underlying slot. Those places will be adapted in due course, so while
not pretty, that's OK for now.
Also rename ExecFetchSlotTuple to ExecFetchSlotHeapTupleDatum and
ExecFetchSlotTupleDatum to ExecFetchSlotHeapTupleDatum, as it's likely
that future storage methods will need similar methods. There already
is ExecFetchSlotMinimalTuple, so the new names make the naming scheme
more coherent.
Author: Ashutosh Bapat and Andres Freund, with changes by Amit Khandekar
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
It was not really that obvious that there's meant to be exactly 1 item
in the partexprs List for each zero-valued partattrs element. Some
incorrect code using these fields was the cause of CVE-2018-1052, so
it's worthwhile to mention how they should be used in the comments.
Author: David Rowley <david.rowley@2ndquadrant.com>
The comments above the PartitionedRelPruneInfo struct incorrectly
document how subplan_map and subpart_map are indexed. This seems to
have snuck in on 4e23236403.
Author: David Rowley <david.rowley@2ndquadrant.com>
With run-time partition pruning, there is no longer necessarily an
executor node for each corresponding plan node.
Author: David Rowley <david.rowley@2ndquadrant.com>
The current pattern of reseting expressions both in
ExecProcessReturning() and ExecOnConflictUpdate() makes it harder than
necessary to reason about memory lifetimes. It also requires
materializing slots unnecessarily, although this patch doesn't take
advantage of the fact that that's not necessary anymore.
Instead reset the expression context once for each input tuple.
Author: Ashutosh Bapat
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
ExecFindInitialMatchingSubPlans has to update the PartitionPruneState's
subplan mapping data to account for the removal of subplans it prunes.
However, that's only necessary if run-time pruning will also occur,
so we can skip it when that won't happen, which should result in not
needing to do the remapping in many cases. (We now need it only when
some partitions are potentially startup-time prunable and others are
potentially run-time prunable, which seems like an unusual case.)
Also make some marginal performance improvements in the remapping
itself. These will mainly win if most partitions got pruned by
the startup-time pruning, which is perhaps a debatable assumption
in this context.
Also fix some bogus comments, and rearrange code to marginally
reduce space consumption in the executor's query-lifespan context.
David Rowley, reviewed by Yoshikazu Imai
Discussion: https://postgr.es/m/CAKJS1f9+m6-di-zyy4B4AGn0y1B9F8UKDRigtBbNviXOkuyOpw@mail.gmail.com
These functions were not crystal clear about what their respective APIs
are. Make an effort to improve that.
Emre's patch was correct AFAICT, but I (Álvaro) felt the need to improve
a few comments a bit more. Any resulting errors are my own.
Per complaint from Coverity, Ning Yu, and Tom Lane.
Author: Emre Hasegeli, Álvaro Herrera
Reviewed-by: Tomas Vondra, Álvaro Herrera
Discussion: https://postgr.es/m/26769.1533090136@sss.pgh.pa.us
Commit 197e4af9 refactored the initialization of the libc random()
seed, but reduced the number of possible seeds values that could be
chosen in a given time period. This negation of the effects of
commit 98c50656c was unintentional. Replace with code that
shifts the fast moving timestamp bits left, similar to the original
algorithm (though not the previous float-tolerating coding, which
is no longer necessary).
Author: Thomas Munro
Reported-by: Noah Misch
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/20181112083358.GA1073796%40rfd.leadboat.com
BufFileSize() can't use off_t, because it's only 32 bits wide on
some systems. BufFile objects can have many 1GB segments so the
total size can exceed 2^31. The only known client of the function
is parallel CREATE INDEX, which was reported to fail when building
large indexes on Windows.
Though this is technically an ABI break on platforms with a 32 bit
off_t and we might normally avoid back-patching it, the function is
brand new and thus unlikely to have been discovered by extension
authors yet, and it's fairly thoroughly broken on those platforms
anyway, so just fix it.
Defect in 9da0cc35. Bug #15460. Back-patch to 11, where this
function landed.
Author: Thomas Munro
Reported-by: Paul van der Linden, Pavel Oskin
Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/15460-b6db80de822fa0ad%40postgresql.org
Discussion: https://postgr.es/m/CAHDGBJP_GsESbTt4P3FZA8kMUKuYxjg57XHF7NRBoKnR%3DCAR-g%40mail.gmail.com
The previous behavior of preferring the oldest match had the advantage
of not breaking existing scripts when we add a conflicting format name;
but that behavior was undocumented and fragile (it seems just luck that
commit add9182e5 didn't break it). Let's go over to the less mistake-
prone approach of complaining when there are multiple matches.
Since this is a small compatibility break, no back-patch.
Daniel Vérité
Discussion: https://postgr.es/m/cb7e1caf-3ea6-450d-af28-f524903a030c@manitou-mail.org
This hasn't been correct since 9.3 added "latex-longtable".
I left the phraseology "Unique abbreviations are allowed" alone.
It's correct as far as it goes, and we are studiously refraining
from specifying exactly what happens if you give a non-unique
abbreviation. (The answer in the back branches is "you get a
backwards-compatible choice", and the answer in HEAD will shortly
be "you get an error", but there seems no need to mention such
details here.)
Daniel Vérité
Discussion: https://postgr.es/m/cb7e1caf-3ea6-450d-af28-f524903a030c@manitou-mail.org
date_trunc(field, timestamptz, zone_name) performs truncation using
the named time zone as reference, rather than working in the session
time zone as is the default behavior. It's equivalent to
date_trunc(field, timestamptz at time zone zone_name) at time zone zone_name
but it's faster, easier to type, and arguably easier to understand.
Vik Fearing and Tom Lane
Discussion: https://postgr.es/m/6249ffc4-2b22-4c1b-4e7d-7af84fedd7c6@2ndquadrant.com
In commit ecfd55795, I removed sqlda.c's checks for ndigits != 0 on the
grounds that we should duplicate the state of the numeric value's digit
buffer even when all the digits are zeroes. However, that still isn't
quite right, because another possible state of the digit buffer is
buf == digits == NULL (this occurs for a NaN). As the code now stands,
it'll invoke memcpy with a NULL source address and zero bytecount,
which we know a few platforms crash on. Hence, reinstate the no-copy
short-circuit, but make it test specifically for buf != NULL rather than
some other condition. In hindsight, the ndigits test (added by commit
f2ae9f9c3) was almost certainly meant to fix the NaN case not the
all-zeroes case as the associated thread alleged.
As before, back-patch to all supported versions.
Discussion: https://postgr.es/m/1803D792815FC24D871C00D17AE95905C71161@g01jpexmbkw24
Change lock level for renaming index (either ALTER INDEX or implicitly
via some other commands) from AccessExclusiveLock to
ShareUpdateExclusiveLock.
One reason we need a strong lock for relation renaming is that the
name change causes a rebuild of the relcache entry. Concurrent
sessions that have the relation open might not be able to handle the
relcache entry changing underneath them. Therefore, we need to lock
the relation in a way that no one can have the relation open
concurrently. But for indexes, the relcache handles reloads specially
in RelationReloadIndexInfo() in a way that keeps changes in the
relcache entry to a minimum. As long as no one keeps pointers to
rd_amcache and rd_options around across possible relcache flushes,
which is the case, this ought to be safe.
We also want to use a self-exclusive lock for correctness, so that
concurrent DDL doesn't overwrite the rename if they start updating
while still seeing the old version. Therefore, we use
ShareUpdateExclusiveLock, which is already used by other DDL commands
that want to operate in a concurrent manner.
The reason this is interesting at all is that renaming an index is a
typical part of a concurrent reindexing workflow (CREATE INDEX
CONCURRENTLY new + DROP INDEX CONCURRENTLY old + rename back). And
indeed a future built-in REINDEX CONCURRENTLY might rely on the ability
to do concurrent renames as well.
Reviewed-by: Andrey Klychkov <aaklychkov@mail.ru>
Reviewed-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/1531767486.432607658@f357.i.mail.ru
If a failure happens when a transaction is starting between the moment
the transaction status is changed from TRANS_DEFAULT to TRANS_START and
the moment the current user ID and security context flags are fetched
via GetUserIdAndSecContext(), or before initializing its basic fields,
then those may get reset to incorrect values when the transaction
aborts, leaving the session in an inconsistent state.
One problem reported is that failing a starting transaction at the first
query of a session could cause several kinds of system crashes on the
follow-up queries.
In order to solve that, move the initialization of the transaction state
fields and the call of GetUserIdAndSecContext() in charge of fetching
the current user ID close to the point where the transaction status is
switched to TRANS_START, where there cannot be any error triggered
in-between, per an idea of Tom Lane. This properly ensures that the
current user ID, the security context flags and that the basic fields of
TransactionState remain consistent even if the transaction fails while
starting.
Reported-by: Richard Guo
Diagnosed-By: Richard Guo
Author: Michael Paquier
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/CAN_9JTxECSb=pEPcb0a8d+6J+bDcOZ4=DgRo_B7Y5gRHJUM=Rw@mail.gmail.com
Backpatch-through: 9.4
Hexadecimal is consistently used as format to not bloat too much the
output but keep it readable. This information is useful mainly for
debugging purposes with for example pg_waldump.
Author: Michael Paquier
Reviewed-by: Nathan Bossart, Dmitry Dolgov, Andres Freund, Álvaro
Herrera
Discussion: https://postgr.es/m/20180413034734.GE1552@paquier.xyz
The code building PartitionBoundInfo based on the constituent partition
data read from catalogs has been located in partcache.c, with a specific
set of routines dedicated to bound types, like sorting or bound data
creation. All this logic is moved to partbounds.c and relocates all the
bound-specific logistic into it, with partition_bounds_create() as
principal entry point.
Author: Amit Langote
Reviewed-by: Michael Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/3f289da8-6d10-75fe-814a-635e8b191d43@lab.ntt.co.jp
Numeric values with leading zeroes were incorrectly copied into a
SQLDA (SQL Descriptor Area), leading to wrong results in ECPG programs.
Report and patch by Daisuke Higuchi. Back-patch to all supported
versions.
Discussion: https://postgr.es/m/1803D792815FC24D871C00D17AE95905C71161@g01jpexmbkw24
The realfail1 and realfail2 backup-prevention rules always returned
token type FCONST, ignoring the possibility that what we've scanned
is more appropriately described as ICONST. I think that at the
time that code was added, it might actually have been safe to not
distinguish; but since we started allowing AS-less aliases in SELECT
target lists, it's definitely legal to have a number immediately
followed by an identifier.
In the SELECT case, it seems there's no visible consequence because
make_const() will change the type back to integer anyway. But I'm
worried that there are other contexts, or will be in future, where
it's more important to get the constant's type right.
Hence, use process_integer_literal to correctly determine which
token type to return.
Arguably this is a bug fix, but given the lack of evidence of
user-visible problems, I'll refrain from back-patching.
Discussion: https://postgr.es/m/21364.1542136808@sss.pgh.pa.us
Make a bunch of basically-cosmetic changes to reduce the diffs between
the flex rules in scan.l, psqlscan.l, and pgc.l. Reorder some code,
adjust a lot of whitespace, sync some comments, make use of flex start
condition scopes to do that.
There are a few non-cosmetic changes in the ECPG lexer:
* Bring over the decimalfail rule (and support function
process_integer_literal) so that ECPG will lex "1..10" into
the same tokens as the backend would. I'm not sure this makes any
visible difference to users, but I'm not sure it doesn't, either.
* <xdc><<EOF>> gets its own rule so as to produce a more on-point
error message.
* Remove duplicate <SQL>{xdstart} rule.
John Naylor, with a few additional changes by me
Discussion: https://postgr.es/m/CAJVSVGWGqY9YBs2EwtRUkbNv=hXkN8yRPOoD1wxE6COgvvrz5g@mail.gmail.com
Alvaro Herrera