Vinayak Pokale provided a patch for a copy-and-paste error in a
comment. I noticed that I'd use the word "automatically" nearby where
I meant to talk about things being "atomic". Rahila Syed spotted a
misplaced counter update. Fix all that stuff.
There's a lot more that could be done here yet - in particular, this
reports only very coarse-grained information about the index vacuuming
phase - but even as it stands, the new pg_stat_progress_vacuum can
tell you quite a bit about what a long-running vacuum is actually
doing.
Amit Langote and Robert Haas, based on earlier work by Vinayak Pokale
and Rahila Syed.
Currently writes to the main data files of postgres all go through the
OS page cache. This means that some operating systems can end up
collecting a large number of dirty buffers in their respective page
caches. When these dirty buffers are flushed to storage rapidly, be it
because of fsync(), timeouts, or dirty ratios, latency for other reads
and writes can increase massively. This is the primary reason for
regular massive stalls observed in real world scenarios and artificial
benchmarks; on rotating disks stalls on the order of hundreds of seconds
have been observed.
On linux it is possible to control this by reducing the global dirty
limits significantly, reducing the above problem. But global
configuration is rather problematic because it'll affect other
applications; also PostgreSQL itself doesn't always generally want this
behavior, e.g. for temporary files it's undesirable.
Several operating systems allow some control over the kernel page
cache. Linux has sync_file_range(2), several posix systems have msync(2)
and posix_fadvise(2). sync_file_range(2) is preferable because it
requires no special setup, whereas msync() requires the to-be-flushed
range to be mmap'ed. For the purpose of flushing dirty data
posix_fadvise(2) is the worst alternative, as flushing dirty data is
just a side-effect of POSIX_FADV_DONTNEED, which also removes the pages
from the page cache. Thus the feature is enabled by default only on
linux, but can be enabled on all systems that have any of the above
APIs.
While desirable and likely possible this patch does not contain an
implementation for windows.
With the infrastructure added, writes made via checkpointer, bgwriter
and normal user backends can be flushed after a configurable number of
writes. Each of these sources of writes controlled by a separate GUC,
checkpointer_flush_after, bgwriter_flush_after and backend_flush_after
respectively; they're separate because the number of flushes that are
good are separate, and because the performance considerations of
controlled flushing for each of these are different.
A later patch will add checkpoint sorting - after that flushes from the
ckeckpoint will almost always be desirable. Bgwriter flushes are most of
the time going to be random, which are slow on lots of storage hardware.
Flushing in backends works well if the storage and bgwriter can keep up,
but if not it can have negative consequences. This patch is likely to
have negative performance consequences without checkpoint sorting, but
unfortunately so has sorting without flush control.
Discussion: alpine.DEB.2.10.1506011320000.28433@sto
Author: Fabien Coelho and Andres Freund
Earlier version committed in 9.0 caused spurious waits in some cases.
New infrastructure for lock waits in 9.3 used to correct and improve this.
Jeff Janes based upon a proposal by Simon Riggs, who also reviewed
Additional review comments from Amit Kapila
When a process is waiting for a heavyweight lock, we will now indicate
the type of heavyweight lock for which it is waiting. Also, you can
now see when a process is waiting for a lightweight lock - in which
case we will indicate the individual lock name or the tranche, as
appropriate - or for a buffer pin.
Amit Kapila, Ildus Kurbangaliev, reviewed by me. Lots of helpful
discussion and suggestions by many others, including Alexander
Korotkov, Vladimir Borodin, and many others.
Renaming a file using rename(2) is not guaranteed to be durable in face
of crashes. Use the previously added durable_rename()/durable_link_or_rename()
in various places where we previously just renamed files.
Most of the changed call sites are arguably not critical, but it seems
better to err on the side of too much durability. The most prominent
known case where the previously missing fsyncs could cause data loss is
crashes at the end of a checkpoint. After the actual checkpoint has been
performed, old WAL files are recycled. When they're filled, their
contents are fdatasynced, but we did not fsync the containing
directory. An OS/hardware crash in an unfortunate moment could then end
up leaving that file with its old name, but new content; WAL replay
would thus not replay it.
Reported-By: Tomas Vondra
Author: Michael Paquier, Tomas Vondra, Andres Freund
Discussion: 56583BDD.9060302@2ndquadrant.com
Backpatch: All supported branches
Using this facility, any utility command can report the target relation
upon which it is operating, if there is one, and up to 10 64-bit
counters; the intent of this is that users should be able to figure out
what a utility command is doing without having to resort to ugly hacks
like attaching strace to a backend.
As a demonstration, this adds very crude reporting to lazy vacuum; we
just report the target relation and nothing else. A forthcoming patch
will make VACUUM report a bunch of additional data that will make this
much more interesting. But this gets the basic framework in place.
Vinayak Pokale, Rahila Syed, Amit Langote, Robert Haas, reviewed by
Kyotaro Horiguchi, Jim Nasby, Thom Brown, Masahiko Sawada, Fujii Masao,
and Masanori Oyama.
Commit 4de82f7d7 increased the WAL flush rate, mainly to increase the
likelihood that hint bits can be set quickly. More quickly set hint bits
can reduce contention around the clog et al. But unfortunately the
increased flush rate can have a significant negative performance impact,
I have measured up to a factor of ~4. The reason for this slowdown is
that if there are independent writes to the underlying devices, for
example because shared buffers is a lot smaller than the hot data set,
or because a checkpoint is ongoing, the fdatasync() calls force cache
flushes to be emitted to the storage.
This is achieved by flushing WAL only if the last flush was longer than
wal_writer_delay ago, or if more than wal_writer_flush_after (new GUC)
unflushed blocks are pending. Based on some tests the default for
wal_writer_delay is 1MB, which seems to work well both on SSD and
rotational media.
To avoid negative performance impact due to 4de82f7d7 an earlier
commit (db76b1e) made SetHintBits() more likely to succeed; preventing
performance regressions in the pgbench tests I performed.
Discussion: 20160118163908.GW10941@awork2.anarazel.de
Further investigation says that there may be some slow operations after
we've finished ShutdownXLOG(), so add some more log messages to try to
isolate that. This is all temporary code too.
This is a quick hack, due to be reverted when its purpose has been served,
to try to gather information about why some of the buildfarm critters
regularly fail with "postmaster does not shut down" complaints. Maybe they
are just really overloaded, but maybe something else is going on. Hence,
instrument pg_ctl to print the current time when it starts waiting for
postmaster shutdown and when it gives up, and add a lot of logging of the
current time in the server's checkpoint and shutdown code paths.
No attempt has been made to make this pretty. I'm not even totally sure
if it will build on Windows, but we'll soon find out.
The previous RequestAddinLWLocks() method had several disadvantages.
First, the locks would be in the main tranche; we've recently decided
that it's useful for LWLocks used for separate purposes to have
separate tranche IDs. Second, there wasn't any correlation between
what code called RequestAddinLWLocks() and what code called
LWLockAssign(); when multiple modules are in use, it could become
quite difficult to troubleshoot problems where LWLockAssign() ran out
of locks. To fix, create a concept of named LWLock tranches which
can be used either by extension or by core code.
Amit Kapila and Robert Haas
Insert sd_notify() calls at server start and stop for integration with
systemd. This allows the use of systemd service units of type "notify",
which greatly simplifies the systemd configuration.
Reviewed-by: Pavel Stěhule <pavel.stehule@gmail.com>
We entirely randomly chose to initialize port->remote_host just after
printing the log_connections message, when we could perfectly well do it
just before, allowing %h and %r to work for that message. Per gripe from
Artem Tomyuk.
This patch reduces pg_am to just two columns, a name and a handler
function. All the data formerly obtained from pg_am is now provided
in a C struct returned by the handler function. This is similar to
the designs we've adopted for FDWs and tablesample methods. There
are multiple advantages. For one, the index AM's support functions
are now simple C functions, making them faster to call and much less
error-prone, since the C compiler can now check function signatures.
For another, this will make it far more practical to define index access
methods in installable extensions.
A disadvantage is that SQL-level code can no longer see attributes
of index AMs; in particular, some of the crosschecks in the opr_sanity
regression test are no longer possible from SQL. We've addressed that
by adding a facility for the index AM to perform such checks instead.
(Much more could be done in that line, but for now we're content if the
amvalidate functions more or less replace what opr_sanity used to do.)
We might also want to expose some sort of reporting functionality, but
this patch doesn't do that.
Alexander Korotkov, reviewed by Petr Jelínek, and rather heavily
editorialized on by me.
Up until now, the total amount of data that could be passed to a
background worker at startup was one datum, which can be a small as
4 bytes on some systems. That's enough to pass a dsm_handle or an
array index, but not much else. Add a bgw_extra flag to the
BackgroundWorker struct, allowing up to 128 bytes to be passed to
a new worker on any platform.
Use this to fix a problem I recently discovered with the parallel
context machinery added in 9.5: the master assigns each worker an
array index, and each worker subsequently assigns itself an array
index, and there's nothing to guarantee that the two sets of indexes
match, leading to chaos.
Normally, I would not back-patch the change to add bgw_extra, since it
is basically a feature addition. However, since 9.5 is still in beta
and there seems to be no other sensible way to repair the broken
parallel context machinery, back-patch to 9.5. Existing background
worker code can ignore the bgw_extra field without a problem, but
might need to be recompiled since the structure size has changed.
Report and patch by me. Review by Amit Kapila.
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
This flag has proven to be a recipe for bugs, and it doesn't seem like
it can really buy anything in terms of performance. So let's just
*always* set the process latch when we receive SIGUSR1 instead of
trying to do it only when needed.
Per my recent proposal on pgsql-hackers.
For some reason, neither of the compilers I usually use noticed the
uninitialized-variable problem I introduced in commit 7e2a18a916.
That's hardly a good enough excuse though. Committing with brown paper bag
on head.
In addition to putting the operations in the right order, move the
declaration of "now" inside the loop; there's no need for it to be
outside, and that does wake up older gcc enough to notice any similar
future problem.
Back-patch to 9.4; earlier versions lack the time-to-SIGKILL stanza
so there's no bug.
The postmaster now checks every minute or so (worst case, at most two
minutes) that postmaster.pid is still there and still contains its own PID.
If not, it performs an immediate shutdown, as though it had received
SIGQUIT.
The original goal behind this change was to ensure that failed buildfarm
runs would get fully cleaned up, even if the test scripts had left a
postmaster running, which is not an infrequent occurrence. When the
buildfarm script removes a test postmaster's $PGDATA directory, its next
check on postmaster.pid will fail and cause it to exit. Previously, manual
intervention was often needed to get rid of such orphaned postmasters,
since they'd block new test postmasters from obtaining the expected socket
address.
However, by checking postmaster.pid and not something else, we can provide
additional robustness: manual removal of postmaster.pid is a frequent DBA
mistake, and now we can at least limit the damage that will ensue if a new
postmaster is started while the old one is still alive.
Back-patch to all supported branches, since we won't get the desired
improvement in buildfarm reliability otherwise.
Prior to commit 0709b7ee72, access to
variables within a spinlock-protected critical section had to be done
through a volatile pointer, but that should no longer be necessary.
This continues work begun in df4077cda2
and 6ba4ecbf47.
Thomas Munro and Michael Paquier
This commit makes postmaster forcibly remove the files signaling
a standby promotion request. Otherwise, the existence of those files
can trigger a promotion too early, whether a user wants that or not.
This removal of files is usually unnecessary because they can exist
only during a few moments during a standby promotion. However
there is a race condition: if pg_ctl promote is executed and creates
the files during a promotion, the files can stay around even after
the server is brought up to new master. Then, if new standby starts
by using the backup taken from that master, the files can exist
at the server startup and should be removed in order to avoid
an unexpected promotion.
Back-patch to 9.1 where promote signal file was introduced.
Problem reported by Feike Steenbergen.
Original patch by Michael Paquier, modified by me.
Discussion: 20150528100705.4686.91426@wrigleys.postgresql.org
Previously, if one background worker registered another background
worker and set bgw_notify_pid while for the second background worker,
it would not receive notifications from the postmaster unless, at the
time the "parent" was registered, BGWORKER_BACKEND_DATABASE_CONNECTION
was set.
To fix, instead instead of including only those background workers that
requested database connections in the postmater's BackendList, include
them all. There doesn't seem to be any reason not do this, and indeed
it removes a significant amount of duplicated code. The other option
is to make PostmasterMarkPIDForWorkerNotify look at BackgroundWorkerList
in addition to BackendList, but that adds more code duplication instead
of getting rid of it.
Patch by me. Review and testing by Ashutosh Bapat.
Commit c9b0cbe98b accidentally broke the
order of operations during postmaster shutdown: it resulted in removing
the per-socket lockfiles after, not before, postmaster.pid. This creates
a race-condition hazard for a new postmaster that's started immediately
after observing that postmaster.pid has disappeared; if it sees the
socket lockfile still present, it will quite properly refuse to start.
This error appears to be the explanation for at least some of the
intermittent buildfarm failures we've seen in the pg_upgrade test.
Another problem, which has been there all along, is that the postmaster
has never bothered to close() its listen sockets, but has just allowed them
to close at process death. This creates a different race condition for an
incoming postmaster: it might be unable to bind to the desired listen
address because the old postmaster is still incumbent. This might explain
some odd failures we've seen in the past, too. (Note: this is not related
to the fact that individual backends don't close their client communication
sockets. That behavior is intentional and is not changed by this patch.)
Fix by adding an on_proc_exit function that closes the postmaster's ports
explicitly, and (in 9.3 and up) reshuffling the responsibility for where
to unlink the Unix socket files. Lock file unlinking can stay where it
is, but teach it to unlink the lock files in reverse order of creation.
Fix additional bogosity in commit 9029f4b374. Include the
BackendSslStatusBuffer in the BackendStatusShmemSize calculation,
avoid ugly and error-prone casts to char* and back, put related
code stanzas into a consistent order (and fix a couple of previous
instances of that sin). All cosmetic except for the size oversight.
Ordinarily, a failure (unexpected exit status) of the startup subprocess
should be considered fatal, so the postmaster should just close up shop
and quit. However, if we sent the startup process a SIGQUIT or SIGKILL
signal, the failure is hardly "unexpected", and we should attempt restart;
this is necessary for recovery from ordinary backend crashes in hot-standby
scenarios. I attempted to implement the latter rule with a two-line patch
in commit 442231d7f7, but it now emerges that
that patch was a few bricks shy of a load: it failed to distinguish the
case of a signaled startup process from the case where the new startup
process crashes before reaching database consistency. That resulted in
infinitely respawning a new startup process only to have it crash again.
To handle this properly, we really must track whether we have sent the
*current* startup process a kill signal. Rather than add yet another
ad-hoc boolean to the postmaster's state, I chose to unify this with the
existing RecoveryError flag into an enum tracking the startup process's
state. That seems more consistent with the postmaster's general state
machine design.
Back-patch to 9.0, like the previous patch.
When archive recovery and restartpoints were initially introduced,
checkpoint_segments was ignored on the grounds that the files restored from
archive don't consume any space in the recovery server. That was changed in
later releases, but even then it was arguably a feature rather than a bug,
as performing restartpoints as often as checkpoints during normal operation
might be excessive, but you might nevertheless not want to waste a lot of
space for pre-allocated WAL by setting checkpoint_segments to a high value.
But now that we have separate min_wal_size and max_wal_size settings, you
can bound WAL usage with max_wal_size, and still avoid consuming excessive
space usage by setting min_wal_size to a lower value, so that argument is
moot.
There are still some issues with actually limiting the space usage to
max_wal_size: restartpoints in recovery can only start after seeing the
checkpoint record, while a checkpoint starts flushing buffers as soon as
the redo-pointer is set. Restartpoint is paced to happen at the same
leisurily speed, determined by checkpoint_completion_target, as checkpoints,
but because they are started later, max_wal_size can be exceeded by upto
one checkpoint cycle's worth of WAL, depending on
checkpoint_completion_target. But that seems better than not trying at all,
and max_wal_size is a soft limit anyway.
The documentation already claimed that max_wal_size is obeyed in recovery,
so this just fixes the behaviour to match the docs. However, add some
weasel-words there to mention that max_wal_size may well be exceeded by
some amount in recovery.
This adjusts commit 82233ce7ea so that the
postmaster does not exit until all its child processes have exited, even
if the 5-second timeout elapses and we have to send SIGKILL. There is no
great value in having the postmaster process quit sooner, and doing so can
mislead onlookers into thinking that the cluster is fully terminated when
actually some child processes still survive.
This effect might explain recent test failures on buildfarm member hamster,
wherein we failed to restart a cluster just after shutting it down with
"pg_ctl stop -m immediate".
I also did a bit of code review/beautification, including fixing a faulty
use of the Max() macro on a volatile expression.
Back-patch to 9.4. In older branches, the postmaster never waited for
children to exit during immediate shutdowns, and changing that would be
too much of a behavioral change.
This avoids the problem that it might go to sleep for an unreasonable
amount of time in unusual conditions like the server clock moving
backwards an unreasonable amount of time.
(Simply moving the server clock forward again doesn't solve the problem
unless you wake up the autovacuum launcher manually, say by sending it
SIGHUP).
Per trouble report from Prakash Itnal in
https://www.postgresql.org/message-id/CAHC5u79-UqbapAABH2t4Rh2eYdyge0Zid-X=Xz-ZWZCBK42S0Q@mail.gmail.com
Analyzed independently by Haribabu Kommi and Tom Lane.
After the archiver dies, postmaster tries to start a new one immediately.
But previously this could happen only while server was running normally
even though archiving was enabled always (i.e., archive_mode was set to
always). So the archiver running during recovery could not restart soon
after it died. This is an oversight in commit ffd3774.
This commit changes reaper(), postmaster's signal handler to cleanup
after a child process dies, so that it tries to a new archiver even during
recovery if necessary.
Patch by me. Review by Alvaro Herrera.
Reentering this function with the right timing caused a double free,
typically crashing the backend. By synchronizing a disconnection with
the authentication timeout, an unauthenticated attacker could achieve
this somewhat consistently. Call be_tls_close() solely from within
proc_exit_prepare(). Back-patch to 9.0 (all supported versions).
Benkocs Norbert Attila
Security: CVE-2015-3165
The logic introduced in commit b69bf30b9b
and repaired in commits 669c7d20e6 and
7be47c56af helps to ensure that we don't
overwrite old multixact member information while it is still needed,
but a user who creates many large multixacts can still exhaust the
member space (and thus start getting errors) while autovacuum stands
idly by.
To fix this, progressively ramp down the effective value (but not the
actual contents) of autovacuum_multixact_freeze_max_age as member space
utilization increases. This makes autovacuum more aggressive and also
reduces the threshold for a manual VACUUM to perform a full-table scan.
This patch leaves unsolved the problem of ensuring that emergency
autovacuums are triggered even when autovacuum=off. We'll need to fix
that via a separate patch.
Thomas Munro and Robert Haas
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.
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
It was previously possible to have the launcher re-execute its main loop
before shutting down if some other signal was received or an error
occurred after getting SIGTERM, as reported by Qingqing Zhou.
While investigating, Tom Lane further noticed that if autovacuum had
been disabled in the config file, it would misbehave by trying to start
a new worker instead of bailing out immediately -- it would consider
itself as invoked in emergency mode.
Fix both problems by checking the shutdown flag in a few more places.
These problems have existed since autovacuum was introduced, so
backpatch all the way back.
This is useful to control autovacuum log volume, for situations where
monitoring only a set of tables is necessary.
Author: Michael Paquier
Reviewed by: A team led by Naoya Anzai (also including Akira Kurosawa,
Taiki Kondo, Huong Dangminh), Fujii Masao.
Robert Haas
Andres Freund
Simon Riggs
Tom Lane
Peter Eisentraut
Magnus Hagander
Bruce Momjian
Fujii Masao
Heikki Linnakangas
Alvaro Herrera
Noah Misch