1349d2790 added support so that aggregate functions with an ORDER BY or
DISTINCT clause could make use of presorted inputs to avoid an implicit
sort within nodeAgg.c. That commit failed to consider that a FILTER
clause may exist that filters rows before the aggregate function
arguments are evaluated. That can be problematic if an aggregate
argument contains an expression which could error out during evaluation.
It's perfectly valid to want to have a FILTER clause which eliminates
such values, and with the pre-sorted path added in 1349d2790, it was
possible that the planner would produce a plan with a Sort node above
the Aggregate to perform the sort on the aggregate's arguments long before
the Aggregate node would filter out the non-matching values.
Here we fix this by inspecting ORDER BY / DISTINCT aggregate functions
which have a FILTER clause to see if the aggregate's arguments are
anything more complex than a Var or a Const. Evaluating these isn't
going to cause an error. If we find any non-Var, non-Const parameters
then the planner will now opt to perform the sort in the Aggregate node
for these aggregates, i.e. disable the presorted aggregate optimization.
An alternative fix would have been to completely disallow the presorted
optimization for Aggrefs with any FILTER clause, but that wasn't done as
that could cause large performance regressions for queries that see
significant gains from 1349d2790 due to presorted results coming in from
an Index Scan.
Backpatch to 16, where 1349d2790 was introduced
Author: David Rowley <dgrowleyml@gmail.com>
Reported-by: Kaimeh <kkaimeh@gmail.com>
Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAK-%2BJz9J%3DQ06-M7cDJoPNeYbz5EZDqkjQbJnmRyQyzkbRGsYkA%40mail.gmail.com
Backpatch-through: 16
Compared to v17 with only \bind able to do extended query protocol work,
v18 has now a total of 11 meta-commands related to the extended query
protocol. These were all listed under the "General" section of the
--help=commands output and are specialized, bloating the output
generated.
All these meta-commands are moved into a new section called "Extended
Query Protocol", listed at the end of --help=commands.
This split has been suggested by Noah Misch.
Discussion: https://postgr.es/m/20250415213450.1f.nmisch@google.com
Noah has reported that the current wording was confusing compared to the
description of the underlying libpq routine. The new wording is from
me.
Reported-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20250415213450.1f.nmisch@google.com
When an invalid number of results is requested for \getresults, the
status code returned by exec_command_getresults() was PSQL_CMD_SKIP_LINE
and not PSQL_CMD_ERROR.
This led to incorrect behaviors, with ON_ERROR_STOP for example.
Reported-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20250415213450.1f.nmisch@google.com
The original intent in heap_page_items() was to return nulls, not
throw an error or crash, if an item was sufficiently corrupt that
we couldn't safely extract data from it. However, commit d6061f83a
utterly missed that memo, and not only put in an un-length-checked
copy of the tuple's data section, but also managed to break the check
on sane nulls-bitmap length. Either mistake could possibly lead to
a SIGSEGV crash if the tuple is corrupt.
Bug: #18896
Reported-by: Dmitry Kovalenko <d.kovalenko@postgrespro.ru>
Author: Dmitry Kovalenko <d.kovalenko@postgrespro.ru>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/18896-add267b8e06663e3@postgresql.org
Backpatch-through: 13
The format of the injection point names used by the AIO code does not
match the existing naming convention used everywhere else in the code,
so let's be consistent. These points are used in test_aio.
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/Z_yTB80bdu1sYDqJ@paquier.xyz
Commit 173c97812f replaced the hardcoded "global/pg_control" in pg_upgrade
log message with a string literal concatenation of XLOG_CONTROL_FILE macro.
However, this change made the message untranslatable.
This commit fixes the issue by using %s with XLOG_CONTROL_FILE instead of
that literal concatenation, allowing the message to be translated properly.
It also wraps the file path in double quotes for consistency with similar
log messages.
Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Masao Fujii <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/20250407.155546.2129693791769531891.horikyota.ntt@gmail.com
Backpatch to 17, where the line was added.
Reported by Noboru Saito while he was working on translating the file
into Japanese.
Discussion: https://postgr.es/m/20250417.203047.1321297410457834775.ishii%40postgresql.org
Reported-by: Noboru Saito <noborusai@gmail.com>
Reviewed-by: Daniel Gustafs <daniel@yesql.se>
Backpatch-through: 17
Use appendPQExpBufferStr when there are no parameters and
appendPQExpBufferChar when the string length is 1.
Unlike 3fae25cbb, which fixed this issue for code that was new to v18,
this one fixes up instances which exist in the backbranches. We've
historically tried to maintain this standard and if we're going to
continue doing that, then we won't be doing that selectively based on
when the code was introduced. Now seems like a good time to flush out the
existing misuses. Waiting until v19 just prolongs their existence in
terms of released versions that the misuses exist in.
Author: David Rowley <drowleyml@gmail.com>
Discussion: https://postgr.es/m/CAApHDvoARMvPeXTTC0HnpARBHn-WgVstc8XFCyMGOzvgu_1HvQ@mail.gmail.com
Both pg_get_process_memory_contexts() and pg_backend_memory_contexts
have 1-based levels, whereas pg_log_backend_memory_contexts() was using
0-based levels. Align these.
This results in slightly saner behavior from MemoryContextStatsDetail()
in regards to the max_level. Previously it would stop at 1 level before
the maximum requested level rather than at that level.
Reported-by: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Author: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Author: David Rowley <drowleyml@gmail.com
Reviewed-by: Melih Mutlu <m.melihmutlu@gmail.com>
Reviewed-by: Rahila Syed <rahilasyed90@gmail.com>
Discussion: https://postgr.es/m/395ea5d4fe190480efa95bf533485c70@oss.nttdata.com
The "children" list won't be used until "got_children" has been set
true, but older compilers don't get that; about half a dozen
buildfarm animals are warning about this. Issue added by 11ff192b5.
While here, improve slightly-shaky grammar in comment.
Discussion: https://postgr.es/m/2057835.1744833309@sss.pgh.pa.us
This gets rid of repetitive get_typlen calls in postquel_sub_params,
which show up as costing a few percent of the runtime in simple test
cases (more with more parameters).
In combination with the preceding patches, this gets us most of the
way back down to the amount of per-call overhead that functions.c
had before commit 0dca5d68d. There are some more things that could
be done, but this seems like an okay place to stop for v18.
At this point, the only data structures we allocate directly in
fcontext are the SQLFunctionCache struct itself, the ParamListInfo
struct, and the execution_state array, all of which are small and
perfectly capable of being re-used across executions of the same
FmgrInfo. Hence, let's give them the same lifespan as the FmgrInfo.
This step gets rid of the separate SQLFunctionLink struct and makes
fn_extra point to SQLFunctionCache again. We also get rid of the
separate fcontext memory context and allocate these items directly
in fn_mcxt.
For notational simplicity, SQLFunctionCache still has an fcontext
field, but it's just a copy of fn_mcxt.
The motivation for this is to allow these structures to live as
long as the FmgrInfo and be re-used across calls, restoring the
original design without its propensity for memory leaks. This
gets rid of some per-call overhead that we added in 0dca5d68d.
We also make an effort to re-use the JunkFilter and result slot.
Those might need to change if the function definition changes,
so we compromise by rebuilding them if the cached plan changes.
This also moves the tuplestore into fn_mcxt so that it can be
re-used across calls, again undoing a change made in 0dca5d68d.
Put the JunkFilter and its result slot (and thence also
some subsidiary data such as the result tupledesc) into a
separate subcontext "jfcontext". This doesn't accomplish
a lot at this point, because we make a new JunkFilter each
time through the SQL function. However, the plan is to make
the fcontext long-lived, and that raises the possibility
that we'll need a new JunkFilter because the plan for the
result-generating query changes. A separate context makes
it easy to free the obsoleted data when that happens.
Also, instead of always running the sub-executor in fcontext,
make a separate context for it if we're doing lazy eval of
a SRF, and otherwise just run it inside CurrentMemoryContext.
Previously, much of this code ran with CurrentMemoryContext set
to be the function's fcontext, so that we tended to leak a lot of
stuff there. Commit 0dca5d68d dealt with that by releasing the
fcontext at the completion of each SQL function call, but we'd
like to go back to the previous approach of allowing the fcontext
to be query-lifespan. To control the leakage problem, rearrange
the code so that we mostly run in the memory context that fmgr_sql
is called in (which we expect to be short-lived). Notably, this
means that parsing/planning is all done in the short-lived context
and doesn't leak cruft into fcontext.
This patch also fixes the allocation of execution_state records
so that we don't leak them across executions. I set that up
with a re-usable array that contains at least as many
execution_state structs as we need for the current querytree.
The chain structure is still there, but it's not really doing
much for us, and maybe somebody will be motivated to get rid
of it. I'm not though.
This incidentally also moves the call of BlessTupleDesc to be
with the code that creates the JunkFilter. That doesn't make
much difference now, but a later patch will reduce the number
of times the JunkFilter gets made, and we needn't bless the
results any more often than that.
We still leak a fair amount in fcontext, particularly when
executing utility statements, but that's material for a
separate patch step; the point here is only to get rid of
unintentional allocations in fcontext.
Late in the development of commit 0dca5d68d, I added a step to copy
the result tlist we extract from the cached final query, because
I was afraid that that might not last as long as the JunkFilter that
we're passing it off to. However, that turns out to cost a noticeable
number of cycles, and it's really quite unnecessary because the
JunkFilter will not examine that tlist after it's been created.
(ExecFindJunkAttribute would use it, but we don't use that function
on this JunkFilter.) Hence, remove the copy step. For safety,
reset the might-become-dangling jf_targetList pointer to NIL.
In passing, remove DR_sqlfunction.cxt, which we don't use anymore;
it's confusing because it's not entirely clear which context it
ought to point at.
Commit 0bada39c83 fixed a bug of this kind,
which existed in all branches for six days before detection. While the
probability of reaching the trouble was low, the disruption was extreme. No
new backends could start, and service restoration needed an immediate
shutdown. Hence, add this to catch the next bug like it.
The new check in RelationIdGetRelation() suffices to make autovacuum detect
the bug in commit 243e9b40f1 that led to commit
0bada39. This also checks in a number of similar places. It replaces each
Assert(IsTransactionState()) that pertained to a conditional catalog read.
No back-patch for now, but a back-patch of commit 243e9b4 should back-patch
this, too. A back-patch could omit the src/test/regress changes, since back
branches won't gain new index columns.
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/20250410191830.0e.nmisch@google.com
Discussion: https://postgr.es/m/10ec0bc3-5933-1189-6bb8-5dec4114558e@gmail.com
The end callback for ZStandard compression frees the private_data
but didn't set the pointer to NULL after freeing. This is not a
bug as the code is right now, since nothing is dereferencing the
pointer upon returning from the callback but it is good practice
to do.
Author: Alexander Kuznetsov <kuznetsovam@altlinux.org>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/efaee52b-9550-44ca-8633-ea86076b3283@altlinux.org
In pg_dump and pg_restore, _allocAH() calls _discoverArchiveFormat() to
determine the archive format when the input format is unknown one.
If the input or discovered format is unrecognized, it reports an error
including the archive format number.
If discovered format is unrecognized, its number should be shown in
the error message. But previously the error message mistakenly showed
the originally requested format number (i.e., unknown one) instead of
the discovered one, due to referencing the wrong variable in the error
message.
This commit corrects the issue by using the appropriate variable in
the error message.
This fix has no practical impact since _discoverArchiveFormat() never
returns an unrecognized format and that error mesasge is actually
never output. Therefore, while the issue exists in back branches,
it's not worth the trouble and buildfarm cycles to back-patch.
So this fix is applied only to the master branch.
Author: Mahendra Singh Thalor <mahi6run@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CAKYtNAqu+N-Ab2Fq6wzNSOm_-0N-BMneanYNV1+6kFDXjva1Eg@mail.gmail.com
estimate_multivariate_ndistinct() is coded to assume the caller handles
passing it a list of GroupVarInfos with unique 'var' fields over the
entire list. 6bb6a62f3 added code which didn't ensure this and that
could result in estimate_multivariate_ndistinct() erroring out with:
ERROR: corrupt MVNDistinct entry
This occurred because estimate_multivariate_ndistinct() first searches
for a set of stats that match to at least two of the given GroupVarInfos
and then later assumes that the MVNDistinctItem.items array of the
best matching stats will have an entry for those two columns. If the
GroupVarInfos List contained a duplicate entry then the same column could
be matched to twice and that could trick the code into thinking we have
>= 2 columns matched in cases where only a single distinct column has been
matched. This could result in a failure to find the correct
MVNDistinctItem in the stats as the array containing those never
contains an item for single columns.
Here we make it more clear that the function needs a distinct set of
GroupVarInfos and also tidy up a few other comments to make things a bit
easier to follow.
Author: David Rowley <drowleyml@gmail.com>
Discussion: https://postgr.es/m/CAApHDvocZCUhM9W9mJ39d6oQz7ePKoqFnao_347mvC-A7QatcQ@mail.gmail.com
Buildfarm member drongo complained because the definitions of these
functions used "const Oid foo" where the forward declarations just
had "Oid foo". (I'm a bit surprised that drongo seems to be the only
complainant.) I chose to fix this by removing the "consts" because
(a) I'm generally not a fan of using const that way, and (b) it was
a minority usage even within these two functions, let alone compared
to the rest of our code base.
Oversight in commit eec0040c4, so no need for back-patch.
We were unnecessarily acquiring AccessExclusiveLock on all child tables
when "ALTER TABLE ONLY sometab ADD PRIMARY KEY" was run on their parent
table, an oversight in commit 14e87ffa5c. This caused deadlocks
during pg_restore of partitioned tables.
The reason to acquire the AEL was that we need to verify that child
tables have the involved columns already marked as not-null; but if the
parent table has an inheritable not-null constraint, then all children
must necessarily be in the correct state already, so we can skip the
check, which avoids acquiring the lock. Reorder the code so that it
works that way. This doesn't change things in the case where the
constraint doesn't exist, but that case is of lesser importance because
it doesn't occur during parallel pg_restore.
While at it, reword some errmsg() and add errhint() to similar cases in
related but not adjacent code.
Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/67469c1c-38bc-7d94-918a-67033f5dd731@gmx.net
Discussion: https://postgr.es/m/2045026.1743801143@sss.pgh.pa.us
Discussion: https://postgr.es/m/1280408.1744650810@sss.pgh.pa.us
Add macros from autoheader which were accidentally omitted in
commit 65c298f61f. There is no function change by this as no
code is currently using the missing macro.
Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://postgr.es/m/CF6D7D7F-E1C4-45BE-9019-0F4B4BC7C135@yesql.se
We'd try to drop the partitions of a partitioned index separately,
which is disallowed by the backend, leading to an error during
restore. While the error is harmless, it causes problems if you
try to use --single-transaction mode.
Fortunately, there seems no need to do a DROP at all, since the
partition will go away silently when we drop either the parent index
or the partition's table. So just make the DROP conditional on not
being a partition.
Reported-by: jian he <jian.universality@gmail.com>
Author: jian he <jian.universality@gmail.com>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxF0QSdkjFKF4di-JGWN6CSdQYEAhGPmQJJCdkSZtd=oLg@mail.gmail.com
Backpatch-through: 13
. remove unnecessary oid_string list stuff
. use pg_get_line_buf() instead of open-coding it
. cleaner parsing of map.dat lines
Reverts 2b69afbe50 add new list type simple_oid_string_list to fe-utils/simple_list
Author: Álvaro Herrera <alvherre@kurilemu.de>
Author: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/202504141220.343fmoxfsbj4@alvherre.pgsql
Memoize typically marks cache entries as complete after fully scanning
the inner side of a join. However, in the case of unique joins, we
skip to the next outer tuple as soon as the first matching inner tuple
is found, leaving no opportunity to scan the inner side to completion.
To work around that, we mark cache entries as complete after fetching
the first matching inner tuple in unique joins.
This approach is only safe when all of the join's restriction clauses
are parameterized; otherwise, there is no guarantee that reading just
one tuple from the inner side is sufficient.
Currently, we check for this by verifying that the number of clauses
in ppi_clauses is no less than the number of the join's restriction
clauses. However, this check isn't entirely reliable, as ppi_clauses
includes join clauses available from all outer rels, not just the
current outer rel. This means the check could pass even if a
restriction clause isn't parameterized, as long as another join
clause, which doesn't belong to the current join, is included in
ppi_clauses.
To fix this, we explicitly check whether each restriction clause of
the current join is present in ppi_clauses.
While we're here, remove the XXX comment from the modified code, as
it's not justified; in certain cases, it's not possible to move a join
clause to the inner side.
This is arguably a bugfix, but no backpatch given the lack of field
reports.
Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: wenhui qiu <qiuwenhuifx@gmail.com>
Reviewed-by: Andrei Lepikhov <lepihov@gmail.com>
Discussion: https://postgr.es/m/CAMbWs4-8JPouj=wBDj4DhK-WO4+Xdx=A2jbjvvyyTBQneJ1=BQ@mail.gmail.com
If a GENERATED column is declared to have a domain data type where
the domain's constraints disallow null values, INSERT commands failed
because we built a targetlist that included coercing a null constant
to the domain's type. The failure occurred even when the generated
value would have been perfectly OK. This is adjacent to the issues
fixed in 0da39aa76, but we didn't notice for lack of testing a domain
with such a constraint.
We aren't going to use the result of the targetlist entry for the
generated column --- ExecComputeStoredGenerated will overwrite it.
So it's not really necessary that it have the exact datatype of
the generated column. This patch fixes the problem by changing
the targetlist entry to be a null Const of the domain's base type,
which should be sufficiently legal. (We do have to tweak
ExecCheckPlanOutput to accept the situation, though.)
This has been broken since we implemented generated columns.
However, this patch only applies easily as far back as v14, partly
because I (tgl) only carried 0da39aa76 back that far, but mostly
because v14 significantly refactored the handling of INSERT/UPDATE
targetlists. Given the lack of field complaints and the short
remaining support lifetime of v13, I judge the cost-benefit ratio
not good for devising a version that would work in v13.
Reported-by: jian he <jian.universality@gmail.com>
Author: jian he <jian.universality@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxG59tip2+9h=rEv-ykOFjt0cbsPVchhi0RTij8bABBA0Q@mail.gmail.com
Backpatch-through: 14
Previously, a space was missing between "<option>--exclude-schema</option>"
and "for" in the pg_restore documentation. This commit fixes the typo by
adding the missing whitespace.
Back-patch to v17 where the typo was added.
Author: Lele Gaifax <lele@metapensiero.it>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/87lds3ysm0.fsf@metapensiero.it
Backpatch-through: 17
The code comment for parse_oid accidentally used the wrong parameter
when referring to the location of the last backup. Also, while there,
improve sentence wording by removing a superfluous word.
Backpatch to v17 where pg_combinebackup was addedd
Author: Amul Sul <sulamul@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/CAAJ_b95ecWgzcS4K3Dx0E_Yp-SLwK5JBasFgioKMSjhQLw9xvg@mail.gmail.com
Backpatch-through: 17
Per the precedent set by 04539e73f, adjust article prefixes for "SQL" to
use "an" consistently rather than "a", i.e., "an es-que-ell" rather than
"a sequel".
Both of these are new to v18. Also see b1b13d2b5, d866f0374 and
7bdd489d3.
Mark the sslkeylogile option as "D" debug as this truly is a debug
option, and it will allow postgres_fdw et.al to filter it out as
well. Also update the display length to match that for an ssl key
as they are both filename based inputs.
Author: Daniel Gustafsson <daniel@yesql.se>
Reported-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://postgr.es/m/CAOYmi+=5GyBKpu7bU4D_xkAnYJTj=rMzGaUvHO99-DpNG_YKcw@mail.gmail.com
Add a paragraph break per suggestion from David G. Johnston.
Use a consistent voice for all the different parameter
descriptions, and fix a couple of grammatical issues.
Reported-by: Igor Korot <ikorot01@gmail.com>
Co-authored-by: "David G. Johnston" <david.g.johnston@gmail.com>
Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA+FnnTz=EW1VQRpWB9J+G-NSchrPFcw4nR7d0JqzEK9jWKB35A@mail.gmail.com
Commit 0f21db36d made an assumption that GIN triConsistentFns
would not modify their input entryRes[] arrays. But in fact,
the "shim" triConsistentFn that we use for opclasses that don't
supply their own did exactly that, potentially leading to wrong
answers from a GIN index search. Through bad luck, none of the
test cases that we have for such opclasses exposed the bug.
One response to this could be that the assumption of consistency check
functions not modifying entryRes[] arrays is a bad one, but it still
seems reasonable to me. Notably, shimTriConsistentFn is itself
assuming that with respect to the underlying boolean consistentFn,
so it's sure being self-centered in supposing that it gets to do so.
Fortunately, it's quite simple to fix shimTriConsistentFn to restore
the entry-time state of entryRes[], so let's do that instead.
This issue doesn't affect any core GIN opclasses, since they all
supply their own triConsistentFns. It does affect contrib modules
btree_gin, hstore, and intarray.
Along the way, I (tgl) noticed that shimTriConsistentFn failed to
pick up on a "recheck" flag returned by its first call to the boolean
consistentFn. This may be only a latent problem, since it would be
unlikely for a consistentFn to set recheck for the all-false case
and not any other cases. (Indeed, none of our contrib modules do
that.) Nonetheless, it's formally wrong.
Reported-by: Vinod Sridharan <vsridh90@gmail.com>
Author: Vinod Sridharan <vsridh90@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAFMdLD7XzsXfi1+DpTqTgrD8XU0i2C99KuF=5VHLWjx4C1pkcg@mail.gmail.com
Backpatch-through: 13
Make sure that function declarations use names that exactly match the
corresponding names from function definitions in a few places. These
inconsistencies were all introduced during Postgres 18 development.
This commit was written with help from clang-tidy, by mechanically
applying the same rules as similar clean-up commits (the earliest such
commit was commit 035ce1fe).
A backend using wal_sync_method set to "open_sync" or "open_datasync"
would fail the test checking the WAL sync data in pg_stat_io. These
modes guarantee that a sync is done when WAL is written to disk, and the
data checked by the test is not incremented in this case,
issue_xlog_fsync() doing nothing.
Oversight in commit a051e71e28.
Author: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CAA5RZ0uxwg3xAi4nvdBMJ-zJQEeyg+RotuU+ebM2F6CKmnvaYA@mail.gmail.com
David Rowley