Previously, the "sem" field of PGPROC varied in size depending on which
kernel semaphore API we were using. That was okay as long as there was
only one likely choice per platform, but in the wake of commit ecb0d20a9,
that assumption seems rather shaky. It doesn't seem out of the question
anymore that an extension compiled against one API choice might be loaded
into a postmaster built with another choice. Moreover, this prevents any
possibility of selecting the semaphore API at postmaster startup, which
might be something we want to do in future.
Hence, change PGPROC.sem to be PGSemaphore (i.e. a pointer) for all Unix
semaphore APIs, and turn the pointed-to data into an opaque struct whose
contents are only known within the responsible modules.
For the SysV and unnamed-POSIX APIs, the pointed-to data has to be
allocated elsewhere in shared memory, which takes a little bit of
rejiggering of the InitShmemAllocation code sequence. (I invented a
ShmemAllocUnlocked() function to make that a little cleaner than it used
to be. That function is not meant for any uses other than the ones it
has now, but it beats having InitShmemAllocation() know explicitly about
allocation of space for semaphores and spinlocks.) This change means an
extra indirection to access the semaphore data, but since we only touch
that when blocking or awakening a process, there shouldn't be any
meaningful performance penalty. Moreover, at least for the unnamed-POSIX
case on Linux, the sem_t type is quite a bit wider than a pointer, so this
reduces sizeof(PGPROC) which seems like a good thing.
For the named-POSIX API, there's effectively no change: the PGPROC.sem
field was and still is a pointer to something returned by sem_open() in
the postmaster's memory space. Document and check the pre-existing
limitation that this case can't work in EXEC_BACKEND mode.
It did not seem worth unifying the Windows semaphore ABI with the Unix
cases, since there's no likelihood of needing ABI compatibility much less
runtime switching across those cases. However, we can simplify the Windows
code a bit if we define PGSemaphore as being directly a HANDLE, rather than
pointer to HANDLE, so let's do that while we're here. (This also ends up
being no change in what's physically stored in PGPROC.sem. We're just
moving the HANDLE fetch from callees to callers.)
It would take a bunch of additional code shuffling to get to the point of
actually choosing a semaphore API at postmaster start, but the effects
of that would now be localized in the port/XXX_sema.c files, so it seems
like fit material for a separate patch. The need for it is unproven as
yet, anyhow, whereas the ABI risk to extensions seems real enough.
Discussion: https://postgr.es/m/4029.1481413370@sss.pgh.pa.us
Even if Linux's mmap() is okay with a partial-hugepage request, munmap()
is not, as reported by Chris Richards. Therefore it behooves us to try
a bit harder to find out the actual hugepage size, instead of assuming
that we can skate by with a guess.
For the moment, just look into /proc/meminfo to find out the default
hugepage size, and use that. Later, on kernels that support requests
for nondefault sizes, we might try to consider other alternatives.
But that smells more like a new feature than a bug fix, especially if
we want to provide any way for the DBA to control it, so leave it for
another day.
I set this up to allow easy addition of platform-specific code for
non-Linux platforms, if needed; but right now there are no reports
suggesting that we need to work harder on other platforms.
Back-patch to 9.4 where hugepage support was introduced.
Discussion: <31056.1476303954@sss.pgh.pa.us>
Fix detaching of the mmap'd segment to have its own on_shmem_exit callback,
rather than piggybacking on the one for detaching from the SysV segment.
That was confusing, and given the distance between the two attach calls,
it was trouble waiting to happen.
Make the detaching calls idempotent by clearing AnonymousShmem to show
we've already unmapped. I spent quite a bit of time yesterday trying
to find a path that would allow the munmap()'s to be done twice, and
while I did not succeed, it seems silly that there's even a question.
Make the #ifdef logic less confusing by separating "do we want to use
anonymous shmem" from EXEC_BACKEND. Even though there's no current
scenario where those conditions are different, it is not helpful for
different places in the same file to be testing EXEC_BACKEND for what
are fundamentally different reasons.
Don't do on_exit_reset() in StartBackgroundWorker(). At best that's
useless (InitPostmasterChild would have done it already) and at worst
it could zap some callback that's unrelated to shared memory.
Improve comments, and simplify the huge_pages enablement logic slightly.
Back-patch to 9.4 where hugepage support was introduced.
Arguably this should go into 9.3 as well, but the code looks
significantly different there, and I doubt it's worth the
trouble of adapting the patch given I can't show a live bug.
SCO OpenServer and SCO UnixWare are more or less dead platforms.
We have never had a buildfarm member testing the "sco" port, and
the last "unixware" member was last heard from in 2012, so it's
fair to doubt that the code even compiles anymore on either one.
Remove both ports. We can always undo this if someone shows up
with an interest in maintaining and testing these platforms.
Discussion: <17177.1476136994@sss.pgh.pa.us>
I somehow had assumed that in the spinlock (in turn possibly using
semaphores) based fallback atomics implementation 32 bit writes could be
done without a lock. As far as the write goes that's correct, since
postgres supports only platforms with single-copy atomicity for aligned
32bit writes. But writing without holding the spinlock breaks
read-modify-write operations like pg_atomic_compare_exchange_u32(),
since they'll potentially "miss" a concurrent write, which can't happen
in actual hardware implementations.
In 9.6+ when using the fallback atomics implementation this could lead
to buffer header locks not being properly marked as released, and
potentially some related state corruption. I don't see a related danger
in 9.5 (earliest release with the API), because pg_atomic_write_u32()
wasn't used in a concurrent manner there.
The state variable of local buffers, before this change, were
manipulated using pg_atomic_write_u32(), to avoid unnecessary
synchronization overhead. As that'd not be the case anymore, introduce
and use pg_atomic_unlocked_write_u32(), which does not correctly
interact with RMW operations.
This bug only caused issues when postgres is compiled on platforms
without atomics support (i.e. no common new platform), or when compiled
with --disable-atomics, which explains why this wasn't noticed in
testing.
Reported-By: Tom Lane
Discussion: <14947.1475690465@sss.pgh.pa.us>
Backpatch: 9.5-, where the atomic operations API was introduced.
We weren't terribly consistent about whether to call Apple's OS "OS X"
or "Mac OS X", and the former is probably confusing to people who aren't
Apple users. Now that Apple has rebranded it "macOS", follow their lead
to establish a consistent naming pattern. Also, avoid the use of the
ancient project name "Darwin", except as the port code name which does not
seem desirable to change. (In short, this patch touches documentation and
comments, but no actual code.)
I didn't touch contrib/start-scripts/osx/, either. I suspect those are
obsolete and due for a rewrite, anyway.
I dithered about whether to apply this edit to old release notes, but
those were responsible for quite a lot of the inconsistencies, so I ended
up changing them too. Anyway, Apple's being ahistorical about this,
so why shouldn't we be?
Where possible, use palloc or pg_malloc instead; otherwise, insert
explicit NULL checks.
Generally speaking, these are places where an actual OOM is quite
unlikely, either because they're in client programs that don't
allocate all that much, or they're very early in process startup
so that we'd likely have had a fork() failure instead. Hence,
no back-patch, even though this is nominally a bug fix.
Michael Paquier, with some adjustments by me
Discussion: <CAB7nPqRu07Ot6iht9i9KRfYLpDaF2ZuUv5y_+72uP23ZAGysRg@mail.gmail.com>
Adjust the way we detect the locale. As a result the minumum Windows
version supported by VS2015 and later is Windows Vista. Add some tweaks
to remove new compiler warnings. Remove documentation references to the
now obsolete msysGit.
Michael Paquier, somewhat edited by me, reviewed by Christian Ullrich.
Backpatch to 9.5
The coverage was rather lean for cases that bind() or listen() might
return. Add entries for everything that there's a direct equivalent
for in the set of Unix errnos that elog.c has heard of.
I've seen one too many "could not bind IPv4 socket: No error" log entries
from the Windows buildfarm members. Per previous discussion, this is
likely caused by the fact that we're doing nothing to translate
WSAGetLastError() to errno. Put in a wrapper layer to do that.
If this works as expected, it should get back-patched, but let's see what
happens in the buildfarm first.
Discussion: <4065.1452450340@sss.pgh.pa.us>
The first iteration of the signal-checking loop would compute sigmask(0)
which expands to 1<<(-1) which is undefined behavior according to the
C standard. The lack of field reports of trouble suggest that it
evaluates to 0 on all existing Windows compilers, but that's hardly
something to rely on. Since signal 0 isn't a queueable signal anyway,
we can just make the loop iterate from 1 instead, and save a few cycles
as well as avoiding the undefined behavior.
In passing, avoid evaluating the volatile expression UNBLOCKED_SIGNAL_QUEUE
twice in a row; there's no reason to waste cycles like that.
Noted by Aleksander Alekseev, though this isn't his proposed fix.
Back-patch to all supported branches.
Whenever this function is used with the FORMAT_MESSAGE_FROM_SYSTEM flag,
it's good practice to include FORMAT_MESSAGE_IGNORE_INSERTS as well.
Otherwise, if the message contains any %n insertion markers, the function
will try to fetch argument strings to substitute --- which we are not
passing, possibly leading to a crash. This is exactly analogous to the
rule about not giving printf() a format string you're not in control of.
Noted and patched by Christian Ullrich.
Back-patch to all supported branches.
Previously latches for windows and unix had been implemented in
different files. A later patch introduce an expanded wait
infrastructure, keeping the implementation separate would introduce too
much duplication.
This basically just moves the functions, without too much change. The
reason to keep this separate is that it allows blame to continue working
a little less badly; and to make review a tiny bit easier.
Discussion: 20160114143931.GG10941@awork2.anarazel.de
This avoids a good number of, individually quite fast, system calls in
scenarios with many quick queries. Besides the aesthetic benefit of
seing fewer superflous system calls with strace, it also improves
performance by ~2% measured by pgbench -M prepared -c 96 -j 8 -S (scale
100).
Without having benchmarked it, this patch also adjust the windows code,
as that makes it easier to unify the unix/windows codepaths in a later
patch. There's little reason to diverge in behaviour between the
platforms.
Discussion: CA+TgmoYc1Zm+Szoc_Qbzi92z2c1vRHZmjhfPn5uC=w8bXv6Avg@mail.gmail.com
Reviewed-By: Robert Haas
This allows for easier testing of the different primitives; in
preparation for adding a new primitive.
Discussion: 20160114143931.GG10941@awork2.anarazel.de
Reviewed-By: Robert Haas
pg_ctl is using isatty() to verify whether the process is running in a
terminal, and if not it sends its output to Windows' Event Log ... which
does the wrong thing when the output has been redirected to a pipe, as
reported in bug #13592.
To fix, make pg_ctl use the code we already have to detect service-ness:
in the master branch, move src/backend/port/win32/security.c to src/port
(with suitable tweaks so that it runs properly in backend and frontend
environments); pg_ctl already has access to pgport so it Just Works. In
older branches, that's likely to cause trouble, so instead duplicate the
required code in pg_ctl.c.
Author: Michael Paquier
Bug report and diagnosis: Egon Kocjan
Backpatch: all supported branches
pgwin32_recv() has treated a non-error return of zero bytes from WSARecv()
as being a reason to block ever since the current implementation was
introduced in commit a4c40f140d. However, so far as one can tell
from Microsoft's documentation, that is just wrong: what it means is
graceful connection closure (in stream protocols) or receipt of a
zero-length message (in message protocols), and neither case should result
in blocking here. The only reason the code worked at all was that control
then fell into the retry loop, which did *not* treat zero bytes specially,
so we'd get out after only wasting some cycles. But as of 9.5 we do not
normally reach the retry loop and so the bug is exposed, as reported by
Shay Rojansky and diagnosed by Andres Freund.
Remove the unnecessary test on the byte count, and rearrange the code
in the retry loop so that it looks identical to the initial sequence.
Back-patch to 9.5. The code is wrong all the way back, AFAICS, but
since it's relatively harmless in earlier branches we'll leave it alone.
Postmaster child processes that aren't supposed to be attached to shared
memory were not bothering to close the shared memory mapping handle they
inherit from the postmaster process. That's mostly harmless, since the
handle vanishes anyway when the child process exits -- but the syslogger
process, if used, doesn't get killed and restarted during recovery from a
backend crash. That meant that Windows doesn't see the shared memory
mapping as becoming free, so it doesn't delete it and the postmaster is
unable to create a new one, resulting in failure to recover from crashes
whenever logging_collector is turned on.
Per report from Dmitry Vasilyev. It's a bit astonishing that we'd not
figured this out long ago, since it's been broken from the very beginnings
of out native Windows support; probably some previously-unexplained trouble
reports trace to this.
A secondary problem is that on Cygwin (perhaps only in older versions?),
exec() may not detach from the shared memory segment after all, in which
case these child processes did remain attached to shared memory, posing
the risk of an unexpected shared memory clobber if they went off the rails
somehow. That may be a long-gone bug, but we can deal with it now if it's
still live, by detaching within the infrastructure introduced here to deal
with closing the handle.
Back-patch to all supported branches.
Tom Lane and Amit Kapila
So far we have worked around the fact that some very old compilers do
not support 'inline' functions by only using inline functions
conditionally (or not at all). Since such compilers are very rare by
now, we have decided to rely on inline functions from 9.6 onwards.
To avoid breaking these old compilers inline is defined away when not
supported. That'll cause "function x defined but not used" type of
warnings, but since nobody develops on such compilers anymore that's
ok.
This change in policy will allow us to more easily employ inline
functions.
I chose to remove code previously conditional on PG_USE_INLINE as it
seemed confusing to have code dependent on a define that's always
defined.
Blacklisting of compilers, like in c53f73879f, now has to be done
differently. A platform template can define PG_FORCE_DISABLE_INLINE to
force inline to be defined empty.
Discussion: 20150701161447.GB30708@awork2.anarazel.de
In the previous coding, timeout would be noticed and reported only when
poll() or socket() returned zero (or the equivalent behavior on Windows).
Ordinarily that should work well enough, but it seems conceivable that we
could get into a state where poll() always returns a nonzero value --- for
example, if it is noticing a condition on one of the file descriptors that
we do not think is reason to exit the loop. If that happened, we'd be in a
busy-wait loop that would fail to terminate even when the timeout expires.
We can make this more robust at essentially no cost, by deciding to exit
of our own accord if we compute a zero or negative time-remaining-to-wait.
Previously the code noted this but just clamped the time-remaining to zero,
expecting that we'd detect timeout on the next loop iteration.
Back-patch to 9.2. While 9.1 had a version of WaitLatchOrSocket, it was
primitive compared to later versions, and did not guarantee reliable
detection of timeouts anyway. (Essentially, this is a refinement of
commit 3e7fdcffd6, which was back-patched only as far as 9.2.)
This was essentially "broken" since 0c8eda62; but until more
recently (14e8803f) barriers usage in signal handlers was infrequent.
The failure to be reentrant was noticed because the test_shm_mq, which
uses memory barriers at a high frequency, occasionally got stuck on some
solaris buildfarm animals. Turns out, those machines use sun studio
12.1, which doesn't yet have efficient memory barrier support. A machine
with a newer sun studio did not fail. Forcing the barrier fallback to
be used on x86 allows to reproduce the problem.
The new fallback is to use kill(PostmasterPid, 0) based on the theory
that that'll always imply a barrier due to checking the liveliness of
PostmasterPid on systems old enough to need fallback support. It's hard
to come up with a good and performant fallback.
I'm not backpatching this for now - the problem isn't active in the back
branches, and we haven't backpatched barrier changes for
now. Additionally master looks entirely different than the back branches
due to the new atomics abstraction. It seems better to let this rest in
master, where the non-reentrancy actively causes a problem, and then
consider backpatching.
Found-By: Robert Haas
Discussion: 55626265.3060800@dunslane.net
Use "a" and "an" correctly, mostly in comments. Two error messages were
also fixed (they were just elogs, so no translation work required). Two
function comments in pg_proc.h were also fixed. Etsuro Fujita reported one
of these, but I found a lot more with grep.
Also fix a few other typos spotted while grepping for the a/an typos.
For example, "consists out of ..." -> "consists of ...". Plus a "though"/
"through" mixup reported by Euler Taveira.
Many of these typos were in old code, which would be nice to backpatch to
make future backpatching easier. But much of the code was new, and I didn't
feel like crafting separate patches for each branch. So no backpatching.
The remaining caller (lwlocks) doesn't need that facility, and we plan
to remove ImmedidateInterruptOK entirely. That means that interrupts
can't be serviced race-free and portably anyway, so there's little
reason for keeping the feature.
Reviewed-By: Heikki Linnakangas
Since their introduction latches have required barriers in SetLatch
and ResetLatch - but when they were introduced there wasn't any
barrier abstraction. Instead latches were documented to rely on the
callsites to provide barrier semantics.
Now that the barrier support looks halfway complete, add the necessary
barriers to both latch implementations.
Also remove a now superflous lock acquisition from syncrep.c and a
superflous (and insufficient) barrier from freelist.c. There might be
other cases that can now be simplified, but those are the only ones
I've seen on a quick scan.
We might want to backpatch this at some later point, but right now the
barrier infrastructure in the backbranches isn't totally on par with
master.
Discussion: 20150112154026.GB2092@awork2.anarazel.de
So far WaitLatchOrSocket() required to pass in WL_SOCKET_READABLE as
that solely was used to indicate error conditions, like EOF. Waiting
for WL_SOCKET_WRITEABLE would have meant to busy wait upon socket
errors.
Adjust the API to signal errors by returning the socket as readable,
writable or both, depending on WL_SOCKET_READABLE/WL_SOCKET_WRITEABLE
being specified. It would arguably be nicer to return WL_SOCKET_ERROR
but that's not possible on platforms and would probably also result in
more complex callsites.
This previously had explicitly been forbidden in e42a21b9e6, as
there was no strong use case at that point. We now are looking into
making FE/BE communication use latches, so changing this makes sense.
There also are some portability concerns because there cases of older
platforms where select(2) is known to, in violation of POSIX, not
return a socket as writable after the peer has closed it. So far the
platforms where that's the case provide a working poll(2). If we find
one where that's not the case, we'll need to add a workaround for that
platform.
Discussion: 20140927191243.GD5423@alap3.anarazel.de
Reviewed-By: Heikki Linnakangas, Noah Misch
If the compiler/arch combination does not provide compiler barriers,
provide a fallback. That fallback simply consists out of a function
call into a externally defined function. That should guarantee
compiler barrierer semantics except for compilers that do inter
translation unit/global optimization - those better provide an actual
compiler barrier.
Hopefully this fixes Tom's report of linker failures due to
pg_compiler_barrier_impl not being provided.
I'm not backpatching this commit as it builds on the new atomics
infrastructure. If we decide an equivalent fix needs to be
backpatched, I'll do so in a separate commit.
Discussion: 27746.1420930690@sss.pgh.pa.us
Per report from Tom Lane.
Several upcoming performance/scalability improvements require atomic
operations. This new API avoids the need to splatter compiler and
architecture dependent code over all the locations employing atomic
ops.
For several of the potential usages it'd be problematic to maintain
both, a atomics using implementation and one using spinlocks or
similar. In all likelihood one of the implementations would not get
tested regularly under concurrency. To avoid that scenario the new API
provides a automatic fallback of atomic operations to spinlocks. All
properties of atomic operations are maintained. This fallback -
obviously - isn't as fast as just using atomic ops, but it's not bad
either. For one of the future users the atomics ontop spinlocks
implementation was actually slightly faster than the old purely
spinlock using implementation. That's important because it reduces the
fear of regressing older platforms when improving the scalability for
new ones.
The API, loosely modeled after the C11 atomics support, currently
provides 'atomic flags' and 32 bit unsigned integers. If the platform
efficiently supports atomic 64 bit unsigned integers those are also
provided.
To implement atomics support for a platform/architecture/compiler for
a type of atomics 32bit compare and exchange needs to be
implemented. If available and more efficient native support for flags,
32 bit atomic addition, and corresponding 64 bit operations may also
be provided. Additional useful atomic operations are implemented
generically ontop of these.
The implementation for various versions of gcc, msvc and sun studio have
been tested. Additional existing stub implementations for
* Intel icc
* HUPX acc
* IBM xlc
are included but have never been tested. These will likely require
fixes based on buildfarm and user feedback.
As atomic operations also require barriers for some operations the
existing barrier support has been moved into the atomics code.
Author: Andres Freund with contributions from Oskari Saarenmaa
Reviewed-By: Amit Kapila, Robert Haas, Heikki Linnakangas and Álvaro Herrera
Discussion: CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com,
20131015123303.GH5300@awork2.anarazel.de,
20131028205522.GI20248@awork2.anarazel.de
Some Sparc CPUs can be run in various coherence models, ranging from
RMO (relaxed) over PSO (partial) to TSO (total). Solaris has always
run CPUs in TSO mode while in userland, but linux didn't use to and
the various *BSDs still don't. Unfortunately the sparc TAS/S_UNLOCK
were only correct under TSO. Fix that by adding the necessary memory
barrier instructions. On sparcv8+, which should be all relevant CPUs,
these are treated as NOPs if the current consistency model doesn't
require the barriers.
Discussion: 20140630222854.GW26930@awork2.anarazel.de
Will be backpatched to all released branches once a few buildfarm
cycles haven't shown up problems. As I've no access to sparc, this is
blindly written.
This return code is possible wherever we pass bAlertable = TRUE; it
arises when Windows caused the current thread to run an "I/O completion
routine" or an "asynchronous procedure call". PostgreSQL does not
provoke either of those Windows facilities, hence this bug remaining
largely unnoticed, but other local code might do so. Due to a shortage
of complaints, no back-patch for now.
Per report from Shiv Shivaraju Gowda, this bug can cause
PGSemaphoreLock() to PANIC. The bug can also cause select() to report
timeout expiration too early, which might confuse pgstat_init() and
CheckRADIUSAuth().
Support for running postgres on Alpha hasn't been tested for a long
while. Due to Alpha's uniquely lax cache coherency model it's a hard
to develop for platform (especially blindly!) and thought to be
unlikely to currently work correctly.
As Alpha is the only supported architecture for Tru64 drop support for
it as well. Tru64's support has ended 2012 and it has been in
maintenance-only mode for much longer.
Also remove stray references to __ksr__ and ultrix defines.
Previously, in some places, socket creation errors were checked for
negative values, which is not true for Windows because sockets are
unsigned. This masked socket creation errors on Windows.
Backpatch through 9.0. 8.4 doesn't have the infrastructure to fix this.
Instead of storing the ID of the dynamic shared memory control
segment in a file within the data directory, store it in the main
control segment. This avoids a number of nasty corner cases,
most seriously that doing an online backup and then using it on
the same machine (e.g. to fire up a standby) would result in the
standby clobbering all of the master's dynamic shared memory
segments.
Per complaints from Heikki Linnakangas, Fujii Masao, and Tom
Lane.
This doesn't seem to be useful any more, and it's not really worth the
effort to keep updating it every time relevant dependencies or calling
signatures in the shared memory or semaphore code change.
