poll() is preferred over select() on platforms where both are available,
because it tends to be a bit faster and it doesn't have an arbitrary limit
on the range of FD numbers that can be accessed. The FD range limit does
not appear to be a risk factor for any 9.1 usages, so this doesn't need to
be back-patched, but we need to have it in place if we keep on expanding
the uses of WaitLatch.
In pursuit of this (and with the expectation that WaitLatch will be needed
in more places), convert the latch field that was already added to PGPROC
for sync rep into a generic latch that is activated for all PGPROC-owning
processes, and change many of the standard backend signal handlers to set
that latch when a signal happens. This will allow WaitLatch callers to be
wakened properly by these signals.
In passing, fix a whole bunch of signal handlers that had been hacked to do
things that might change errno, without adding the necessary save/restore
logic for errno. Also make some minor fixes in unix_latch.c, and clean
up bizarre and unsafe scheme for disowning the process's latch. Much of
this has to be back-patched into 9.1.
Peter Geoghegan, with additional work by Tom
The original definition had the problem that timeouts exceeding about 2100
seconds couldn't be specified on 32-bit machines. Milliseconds seem like
sufficient resolution, and finer grain than that would be fantasy anyway
on many platforms.
Back-patch to 9.1 so that this aspect of the latch API won't change between
9.1 and later releases.
Peter Geoghegan
Improve the documentation around weak-memory-ordering risks, and do a pass
of general editorialization on the comments in the latch code. Make the
Windows latch code more like the Unix latch code where feasible; in
particular provide the same Assert checks in both implementations.
Fix poorly-placed WaitLatch call in syncrep.c.
This patch resolves, for the moment, concerns around weak-memory-ordering
bugs in latch-related code: we have documented the restrictions and checked
that existing calls meet them. In 9.2 I hope that we will install suitable
memory barrier instructions in SetLatch/ResetLatch, so that their callers
don't need to be quite so careful.
detect postmaster death. Postmaster keeps the write-end of the pipe open,
so when it dies, children get EOF in the read-end. That can conveniently
be waited for in select(), which allows eliminating some of the polling
loops that check for postmaster death. This patch doesn't yet change all
the loops to use the new mechanism, expect a follow-on patch to do that.
This changes the interface to WaitLatch, so that it takes as argument a
bitmask of events that it waits for. Possible events are latch set, timeout,
postmaster death, and socket becoming readable or writeable.
The pipe method behaves slightly differently from the kill() method
previously used in PostmasterIsAlive() in the case that postmaster has died,
but its parent has not yet read its exit code with waitpid(). The pipe
returns EOF as soon as the process dies, but kill() continues to return
true until waitpid() has been called (IOW while the process is a zombie).
Because of that, change PostmasterIsAlive() to use the pipe too, otherwise
WaitLatch() would return immediately with WL_POSTMASTER_DEATH, while
PostmasterIsAlive() would claim it's still alive. That could easily lead to
busy-waiting while postmaster is in zombie state.
Peter Geoghegan with further changes by me, reviewed by Fujii Masao and
Florian Pflug.
For consistency, have all non-ASCII characters from contributors'
names in the source be in UTF-8. But remove some other more
gratuitous uses of non-ASCII characters.
Also, we removed the display of the current value of
max_connections/MaxBackends from some messages earlier, because it was
confusing, so do that in the remaining one as well.
Most of these cast DWORD to int or unsigned int for printf type handling.
This is safe even on 64 bit architectures because a DWORD is always 32 bits.
In one case a variable is initialised to keep the compiler happy.
Remove the hard-wired assumption that __mips__ (and only __mips__) lacks
dlopen in FreeBSD and OpenBSD. This assumption is outdated at least for
OpenBSD, as per report from an anonymous 9.1 tester. We can perfectly well
use HAVE_DLOPEN instead to decide which code to use.
Some other cosmetic adjustments to make freebsd.c, netbsd.c, and openbsd.c
exactly alike.
than replication_timeout (a new GUC) milliseconds. The TCP timeout is often
too long, you want the master to notice a dead connection much sooner.
People complained about that in 9.0 too, but with synchronous replication
it's even more important to notice dead connections promptly.
Fujii Masao and Heikki Linnakangas
Fix broken test for pre-existing postmaster, caused by wrong code for
appending lines to the lockfile; don't write a failed listen_address
setting into the lockfile; don't arbitrarily change the location of the
data directory in the lockfile compared to previous releases; provide more
consistent and useful definitions of the socket path and listen_address
entries; avoid assuming that pg_ctl has the same DEFAULT_PGSOCKET_DIR as
the postmaster; assorted code style improvements.
Since we're not multithreaded it only provides marginally useful
information, and it does require a newer version of the Platform SDK
than we target. We may want to reconsider this in the future along
with a fix for MinGW.
Add support for collecting "minidump" style crash dumps on
Windows, by setting up an exception handling filter. Crash
dumps will be generated in PGDATA/crashdumps if the directory
is created (the existance of the directory is used as on/off
switch for the generation of the dumps).
Craig Ringer and Magnus Hagander
dynamic pool of event handles, we can permanently assign one for each
shared latch. Thanks to that, we no longer need a separate shared memory
block for latches, and we don't need to know in advance how many shared
latches there is, so you no longer need to remember to update
NumSharedLatches when you introduce a new latch to the system.
wait until it is set. Latches can be used to reliably wait until a signal
arrives, which is hard otherwise because signals don't interrupt select()
on some platforms, and even when they do, there's race conditions.
On Unix, latches use the so called self-pipe trick under the covers to
implement the sleep until the latch is set, without race conditions. On
Windows, Windows events are used.
Use the new latch abstraction to sleep in walsender, so that as soon as
a transaction finishes, walsender is woken up to immediately send the WAL
to the standby. This reduces the latency between master and standby, which
is good.
Preliminary work by Fujii Masao. The latch implementation is by me, with
helpful comments from many people.
It turns out that some platforms return ENOMEM for a request that violates
SHMALL, whereas we were assuming that ENOSPC would always be used for that.
Apparently the latter is a Linuxism while ENOMEM is the BSD tradition.
Extend the ENOMEM hint to suggest that raising SHMALL might be needed.
Per gripe from A.M.
Backpatch to 9.0, but not further, because this doesn't seem important
enough to warrant creating extra translation work in the stable branches.
(If it were, we'd have figured this out years ago.)
linking both executables and shared libraries, and we add on LDFLAGS_EX when
linking executables or LDFLAGS_SL when linking shared libraries. This
provides a significantly cleaner way of dealing with link-time switches than
the former behavior. Also, make sure that the various platform-specific
%.so: %.o rules incorporate LDFLAGS and LDFLAGS_SL; most of them missed that
before. (I did not add these variables for the platforms that invoke $(LD)
directly, however. It's not clear if we can do that safely, since for the
most part we assume these variables use CC command-line syntax.)
Per gripe from Aaron Swenson and subsequent investigation.
returns EINVAL for an existing shared memory segment. Although it's not
terribly sensible, that behavior does meet the POSIX spec because EINVAL
is the appropriate error code when the existing segment is smaller than the
requested size, and the spec explicitly disclaims any particular ordering of
error checks. Moreover, it does in fact happen on OS X and probably other
BSD-derived kernels. (We were able to talk NetBSD into changing their code,
but purging that behavior from the wild completely seems unlikely to happen.)
We need to distinguish collision with a pre-existing segment from invalid size
request in order to behave sensibly, so it's worth some extra code here to get
it right. Per report from Gavin Kistner and subsequent investigation.
Back-patch to all supported versions, since any of them could get used
with a kernel having the debatable behavior.
and use this in pq_getbyte_if_available.
It's only a limited implementation which swithes the whole emulation layer
no non-blocking mode, but that's enough as long as non-blocking is only
used during a short period of time, and only one socket is accessed during
this time.
There was a race condition where the receiving pipe could be closed by the
child thread if the main thread was pre-empted before it got a chance to
create a new one, and the dispatch thread ran to completion during that time.
One symptom of this is that rows in pg_listener could be dropped under
heavy load.
Analysis and original patch by Radu Ilie, with some small
modifications by Magnus Hagander.
Bruce Momjian
Peter Eisentraut
Tom Lane
Andrew Dunstan
Heikki Linnakangas
Robert Haas
Magnus Hagander
Itagaki Takahiro