Bhis commit introduces enhancements to the pg_stat_checkpointer view by adding
three new columns: restartpoints_timed, restartpoints_req, and
restartpoints_done. These additions aim to improve the visibility and
monitoring of restartpoint processes on replicas.
Previously, it was challenging to differentiate between successful and failed
restartpoint requests. This limitation arises because restartpoints on replicas
are dependent on checkpoint records from the primary, and cannot occur more
frequently than these checkpoints.
The new columns allow for clear distinction and tracking of restartpoint
requests, their triggers, and successful completions. This enhancement aids
database administrators and developers in better understanding and diagnosing
issues related to restartpoint behavior, particularly in scenarios where
restartpoint requests may fail.
System catalog is changed. Catversion is bumped.
Discussion: https://postgr.es/m/99b2ccd1-a77a-962a-0837-191cdf56c2b9%40inbox.ru
Author: Anton A. Melnikov
Reviewed-by: Kyotaro Horiguchi, Alexander Korotkov
The "fsync" level already flushes drive write caches on Windows (as does
"fdatasync"), so it only confuses matters to have an apparently higher
level that isn't actually different at all.
That leaves "fsync_writethrough" only for macOS, where it actually does
something different.
Reviewed-by: Magnus Hagander <magnus@hagander.net>
Discussion: https://postgr.es/m/CA%2BhUKGJ2CG2SouPv2mca2WCTOJxYumvBARRcKPraFMB6GSEMcA%40mail.gmail.com
This also adds references to this new chapter at relevant sections of
our documentation. Previously much of these internal details were
exposed to users, but not explained. This also updates RELEASE
SAVEPOINT.
Discussion: https://postgr.es/m/CANbhV-E_iy9fmrErxrCh8TZTyenpfo72Hf_XD2HLDppva4dUNA@mail.gmail.com
Author: Simon Riggs, Laurenz Albe
Reviewed-by: Bruce Momjian
Backpatch-through: 11
Commit 5ef1eefd76, which added
archive_library, purged most mentions of archive_command from the
documentation. This is inappropriate, since archive_command is still
a feature in use and users will want to see information about it.
This restores all the removed mentions and rephrases things so that
archive_command and archive_library are presented as alternatives of
each other.
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://www.postgresql.org/message-id/9366d634-a917-85a9-4991-b2a4859edaf9@enterprisedb.com
Referring to the WAL as just "log" invites confusion with the
postmaster log, so avoid doing that in docs and error messages.
Also shorten "WAL segment file" to just "WAL file" in various
places.
Bharath Rupireddy, reviewed by Nathan Bossart and Kyotaro Horiguchi
Discussion: https://postgr.es/m/CALj2ACUeXa8tDPaiTLexBDMZ7hgvaN+RTb957-cn5qwv9zf-MQ@mail.gmail.com
Windows 10 gained support for flushing NTFS files with fdatasync()
semantics. The main advantage over open_datasync (in Windows API terms
FILE_FLAG_WRITE_THROUGH) is that the latter does not flush SATA drive
caches. The default setting is not changed, so users have to opt in to
this.
Discussion: https://postgr.es/m/CA%2BhUKGJZJVO%3DiX%2Beb-PXi2_XS9ZRqnn_4URh0NUQOwt6-_51xQ%40mail.gmail.com
Introduce a new GUC recovery_prefetch. When enabled, look ahead in the
WAL and try to initiate asynchronous reading of referenced data blocks
that are not yet cached in our buffer pool. For now, this is done with
posix_fadvise(), which has several caveats. Since not all OSes have
that system call, "try" is provided so that it can be enabled where
available. Better mechanisms for asynchronous I/O are possible in later
work.
Set to "try" for now for test coverage. Default setting to be finalized
before release.
The GUC wal_decode_buffer_size limits the distance we can look ahead in
bytes of decoded data.
The existing GUC maintenance_io_concurrency is used to limit the number
of concurrent I/Os allowed, based on pessimistic heuristics used to
infer that I/Os have begun and completed. We'll also not look more than
maintenance_io_concurrency * 4 block references ahead.
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com> (earlier version)
Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version)
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com> (earlier version)
Tested-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> (earlier version)
Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com> (earlier version)
Tested-by: Dmitry Dolgov <9erthalion6@gmail.com> (earlier version)
Tested-by: Sait Talha Nisanci <Sait.Nisanci@microsoft.com> (earlier version)
Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com
Running a shell command for each file to be archived has a lot of
overhead and may not offer as much error checking as you want, or the
exact semantics that you want. So, offer the option to call a loadable
module for each file to be archived, rather than running a shell command.
Also, add a 'basic_archive' contrib module as an example implementation
that archives to a local directory.
Nathan Bossart, with a little bit of kibitzing by me.
Discussion: http://postgr.es/m/20220202224433.GA1036711@nathanxps13
This set of commits has some bugs with known fixes, but at this late
stage in the release cycle it seems best to revert and resubmit next
time, along with some new automated test coverage for this whole area.
Commits reverted:
dc88460c: Doc: Review for "Optionally prefetch referenced data in recovery."
1d257577: Optionally prefetch referenced data in recovery.
f003d9f8: Add circular WAL decoding buffer.
323cbe7c: Remove read_page callback from XLogReader.
Remove the new GUC group WAL_RECOVERY recently added by a55a9847, as the
corresponding section of config.sgml is now reverted.
Discussion: https://postgr.es/m/CAOuzzgrn7iKnFRsB4MHp3UisEQAGgZMbk_ViTN4HV4-Ksq8zCg%40mail.gmail.com
Comment fixes are applied on HEAD, and documentation improvements are
applied on back-branches where needed.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20210408164008.GJ6592@telsasoft.com
Backpatch-through: 9.6
Introduce a new GUC recovery_prefetch, disabled by default. When
enabled, look ahead in the WAL and try to initiate asynchronous reading
of referenced data blocks that are not yet cached in our buffer pool.
For now, this is done with posix_fadvise(), which has several caveats.
Better mechanisms will follow in later work on the I/O subsystem.
The GUC maintenance_io_concurrency is used to limit the number of
concurrent I/Os we allow ourselves to initiate, based on pessimistic
heuristics used to infer that I/Os have begun and completed.
The GUC wal_decode_buffer_size is used to limit the maximum distance we
are prepared to read ahead in the WAL to find uncached blocks.
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com> (parts)
Reviewed-by: Andres Freund <andres@anarazel.de> (parts)
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> (parts)
Tested-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com>
Tested-by: Dmitry Dolgov <9erthalion6@gmail.com>
Tested-by: Sait Talha Nisanci <Sait.Nisanci@microsoft.com>
Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com
Common recommendations are that the checkpoint should be spread out as
much as possible, provided we avoid having it take too long. This
change updates the default to 0.9 (from 0.5) to match that
recommendation.
There was some debate about possibly removing the option entirely but it
seems there may be some corner-cases where having it set much lower to
try to force the checkpoint to be as fast as possible could result in
fewer periods of time of reduced performance due to kernel flushing.
General agreement is that the "spread more" is the preferred approach
though and those who need to tune away from that value are much less
common.
Reviewed-By: Michael Paquier, Peter Eisentraut, Tom Lane, David Steele,
Nathan Bossart
Discussion: https://postgr.es/m/20201207175329.GM16415%40tamriel.snowman.net
This commit adds new GUC track_wal_io_timing. When this is enabled,
the total amounts of time XLogWrite writes and issue_xlog_fsync syncs
WAL data to disk are counted in pg_stat_wal. This information would be
useful to check how much WAL write and sync affect the performance.
Enabling track_wal_io_timing will make the server query the operating
system for the current time every time WAL is written or synced,
which may cause significant overhead on some platforms. To avoid such
additional overhead in the server with track_io_timing enabled,
this commit introduces track_wal_io_timing as a separate parameter from
track_io_timing.
Note that WAL write and sync activity by walreceiver has not been tracked yet.
This commit makes the server also track the numbers of times XLogWrite
writes and issue_xlog_fsync syncs WAL data to disk, in pg_stat_wal,
regardless of the setting of track_wal_io_timing. This counters can be
used to calculate the WAL write and sync time per request, for example.
Bump PGSTAT_FILE_FORMAT_ID.
Bump catalog version.
Author: Masahiro Ikeda
Reviewed-By: Japin Li, Hayato Kuroda, Masahiko Sawada, David Johnston, Fujii Masao
Discussion: https://postgr.es/m/0509ad67b585a5b86a83d445dfa75392@oss.nttdata.com
Data checksums did not have a longer discussion in the docs,
this adds a short section with an overview.
Extracted from the larger patch for on-line enabling of checksums, which
has many more authors and reviewers.
Author: Daniel Gustafsson
Reviewed-By: Magnus Hagander, Michael Banck (and others through the big patch)
Discussion: https://postgr.es/m/5ff49fa4.1c69fb81.658f3.04ac@mx.google.com
max_slot_wal_keep_size that was added in v13 and wal_keep_segments are
the GUC parameters to specify how much WAL files to retain for
the standby servers. While max_slot_wal_keep_size accepts the number of
bytes of WAL files, wal_keep_segments accepts the number of WAL files.
This difference of setting units between those similar parameters could
be confusing to users.
To alleviate this situation, this commit renames wal_keep_segments to
wal_keep_size, and make users specify the WAL size in it instead of
the number of WAL files.
There was also the idea to rename max_slot_wal_keep_size to
max_slot_wal_keep_segments, in the discussion. But we have been moving
away from measuring in segments, for example, checkpoint_segments was
replaced by max_wal_size. So we concluded to rename wal_keep_segments
to wal_keep_size.
Back-patch to v13 where max_slot_wal_keep_size was added.
Author: Fujii Masao
Reviewed-by: Álvaro Herrera, Kyotaro Horiguchi, David Steele
Discussion: https://postgr.es/m/574b4ea3-e0f9-b175-ead2-ebea7faea855@oss.nttdata.com
Previously the documentation explains that WAL segment files
start at 000000010000000000000000. But the first WAL segment file
that initdb creates is 000000010000000000000001 not
000000010000000000000000. This change was caused by old
commit 8c843fff2d, but the documentation had not been updated
a long time.
Back-patch to all supported branches.
Author: Fujii Masao
Reviewed-by: David Zhang
Discussion: https://postgr.es/m/CAHGQGwHOmGe2OqGOmp8cOfNVDivq7dbV74L5nUGr+3eVd2CU2Q@mail.gmail.com
Update links that resulted in redirects. Most are changes from http to
https, but there are also some other minor edits. (There are still some
redirects where the target URL looks less elegant than the one we
currently have. I have left those as is.)
This reverts the backend sides of commit 1fde38beaa.
I have, at least for now, left the pg_verify_checksums tool in place, as
this tool can be very valuable without the rest of the patch as well,
and since it's a read-only tool that only runs when the cluster is down
it should be a lot safer.
This makes it possible to turn checksums on in a live cluster, without
the previous need for dump/reload or logical replication (and to turn it
off).
Enabling checkusm starts a background process in the form of a
launcher/worker combination that goes through the entire database and
recalculates checksums on each and every page. Only when all pages have
been checksummed are they fully enabled in the cluster. Any failure of
the process will revert to checksums off and the process has to be
started.
This adds a new WAL record that indicates the state of checksums, so
the process works across replicated clusters.
Authors: Magnus Hagander and Daniel Gustafsson
Review: Tomas Vondra, Michael Banck, Heikki Linnakangas, Andrey Borodin
Since some preparation work had already been done, the only source
changes left were changing empty-element tags like <xref linkend="foo">
to <xref linkend="foo"/>, and changing the DOCTYPE.
The source files are still named *.sgml, but they are actually XML files
now. Renaming could be considered later.
In the build system, the intermediate step to convert from SGML to XML
is removed. Everything is build straight from the source files again.
The OpenSP (or the old SP) package is no longer needed.
The documentation toolchain instructions are updated and are much
simpler now.
Peter Eisentraut, Alexander Lakhin, Jürgen Purtz
For DocBook XML compatibility, don't use SGML empty tags (</>) anymore,
replace by the full tag name. Add a warning option to catch future
occurrences.
Alexander Lakhin, Jürgen Purtz
For performance reasons a larger segment size than the default 16MB
can be useful. A larger segment size has two main benefits: Firstly,
in setups using archiving, it makes it easier to write scripts that
can keep up with higher amounts of WAL, secondly, the WAL has to be
written and synced to disk less frequently.
But at the same time large segment size are disadvantageous for
smaller databases. So far the segment size had to be configured at
compile time, often making it unrealistic to choose one fitting to a
particularly load. Therefore change it to a initdb time setting.
This includes a breaking changes to the xlogreader.h API, which now
requires the current segment size to be configured. For that and
similar reasons a number of binaries had to be taught how to recognize
the current segment size.
Author: Beena Emerson, editorialized by Andres Freund
Reviewed-By: Andres Freund, David Steele, Kuntal Ghosh, Michael
Paquier, Peter Eisentraut, Robert Hass, Tushar Ahuja
Discussion: https://postgr.es/m/CAOG9ApEAcQ--1ieKbhFzXSQPw_YLmepaa4hNdnY5+ZULpt81Mw@mail.gmail.com
"xlog" is not a particularly clear abbreviation for "write-ahead log",
and it sometimes confuses users into believe that the contents of the
"pg_xlog" directory are not critical data, leading to unpleasant
consequences. So, rename the directory to "pg_wal".
This patch modifies pg_upgrade and pg_basebackup to understand both
the old and new directory layouts; the former is necessary given the
purpose of the tool, while the latter merely avoids an unnecessary
backward-compatibility break.
We may wish to consider renaming other programs, switches, and
functions which still use the old "xlog" naming to also refer to
"wal". However, that's still under discussion, so let's do just this
much for now.
Discussion: CAB7nPqTeC-8+zux8_-4ZD46V7YPwooeFxgndfsq5Rg8ibLVm1A@mail.gmail.com
Michael Paquier
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?
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
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.
The introduction of min_wal_size & max_wal_size in 88e9823026 makes it
feasible to increase the default upper bound in checkpoint
size. Previously raising the default would lead to a increased disk
footprint, even if more segments weren't beneficial. The low default of
checkpoint size is one of common performance problem users have thus
increasing the default makes sense. Setups where the increase in
maximum disk usage is a problem will very likely have to run with a
modified configuration anyway.
Discussion: 54F4EFB8.40202@agliodbs.com,
CA+TgmoZEAgX5oMGJOHVj8L7XOkAe05Gnf45rP40m-K3FhZRVKg@mail.gmail.com
Author: Josh Berkus, after a discussion involving lots of people.
Instead of having a single knob (checkpoint_segments) that both triggers
checkpoints, and determines how many checkpoints to recycle, they are now
separate concerns. There is still an internal variable called
CheckpointSegments, which triggers checkpoints. But it no longer determines
how many segments to recycle at a checkpoint. That is now auto-tuned by
keeping a moving average of the distance between checkpoints (in bytes),
and trying to keep that many segments in reserve. The advantage of this is
that you can set max_wal_size very high, but the system won't actually
consume that much space if there isn't any need for it. The min_wal_size
sets a floor for that; you can effectively disable the auto-tuning behavior
by setting min_wal_size equal to max_wal_size.
The max_wal_size setting is now the actual target size of WAL at which a
new checkpoint is triggered, instead of the distance between checkpoints.
Previously, you could calculate the actual WAL usage with the formula
"(2 + checkpoint_completion_target) * checkpoint_segments + 1". With this
patch, you set the desired WAL usage with max_wal_size, and the system
calculates the appropriate CheckpointSegments with the reverse of that
formula. That's a lot more intuitive for administrators to set.
Reviewed by Amit Kapila and Venkata Balaji N.
xlog.c is huge, this makes it a little bit smaller, which is nice. Functions
related to putting together the WAL record are in xloginsert.c, and the
lower level stuff for managing WAL buffers and such are in xlog.c.
Also move the definition of XLogRecord to a separate header file. This
causes churn in the #includes of all the files that write WAL records, and
redo routines, but it avoids pulling in xlog.h into most places.
Reviewed by Michael Paquier, Alvaro Herrera, Andres Freund and Amit Kapila.
Alexander Korotkov
Bruce Momjian
Thomas Munro
Peter Eisentraut
Tom Lane
Robert Haas
Michael Paquier
Stephen Frost
Fujii Masao
Magnus Hagander
Andres Freund
Peter Eisentraut
Simon Riggs
Heikki Linnakangas