When VACUUM determines that an existing MultiXact should use a freeze
plan that sets xmax to InvalidTransactionId, the original Multi may or
may not be before OldestMxact. Remove an incorrect assertion that
expected it to always be from before OldestMxact.
Oversight in commit 4ce3af.
Author: Peter Geoghegan <pg@bowt.ie>
Reported-By: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/TYAPR01MB5866B24104FD80B5D7E65C3EF5ED9@TYAPR01MB5866.jpnprd01.prod.outlook.com
Perform a failsafe check every time VACUUM's first heap scan scans a
further FAILSAFE_EVERY_PAGES pages, rather than using an approach based
on the number of physical blocks that our current blkno is from the
blkno at the time of the previous failsafe check. That way VACUUM will
perform a failsafe check every time it has scanned a uniform number of
pages, without it mattering when or how VACUUM skipped pages using the
visibility map.
Sami Imseih, with changes to FAILSAFE_EVERY_PAGES comments added by me.
Author: Sami Imseih <simseih@amazon.com>
Reviewed-By: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/401CE010-4049-4B94-9961-0B610A5D254D%40amazon.com
Use a dedicated struct for the XID/MXID cutoffs used by VACUUM, such as
FreezeLimit and OldestXmin. This state is initialized in vacuum.c, and
then passed around by code from vacuumlazy.c to heapam.c freezing
related routines. The new convention is that everybody works off of the
same cutoff state, which is passed around via pointers to const.
Also simplify some of the logic for dealing with frozen xmin in
heap_prepare_freeze_tuple: add dedicated "xmin_already_frozen" state to
clearly distinguish xmin XIDs that we're going to freeze from those that
were already frozen from before. That way the routine's xmin handling
code is symmetrical with the existing xmax handling code. This is
preparation for an upcoming commit that will add page level freezing.
Also refactor the control flow within FreezeMultiXactId(), while adding
stricter sanity checks. We now test OldestXmin directly, instead of
using FreezeLimit as an inexact proxy for OldestXmin. This is further
preparation for the page level freezing work, which will make the
function's caller cede control of page level freezing to the function
where appropriate (where heap_prepare_freeze_tuple sees a tuple that
happens to contain a MultiXactId in its xmax).
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Jeff Davis <pgsql@j-davis.com>
Discussion: https://postgr.es/m/CAH2-WznS9TxXmz2_=SY+SyJyDFbiOftKofM9=aDo68BbXNBUMA@mail.gmail.com
Because we added StaticAssertStmt() first before StaticAssertDecl(),
some uses as well as the instructions in c.h are now a bit backwards
from the "native" way static assertions are meant to be used in C.
This updates the guidance and moves some static assertions to better
places.
Specifically, since the addition of StaticAssertDecl(), we can put
static assertions at the file level. This moves a number of static
assertions out of function bodies, where they might have been stuck
out of necessity, to perhaps better places at the file level or in
header files.
Also, when the static assertion appears in a position where a
declaration is allowed, then using StaticAssertDecl() is more native
than StaticAssertStmt().
Reviewed-by: John Naylor <john.naylor@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/941a04e7-dd6f-c0e4-8cdf-a33b3338cbda%40enterprisedb.com
The same code pattern is repeated 17 times for int64 counters (0 for
missing entry) and 5 times for timestamps (NULL for missing entry) on
table entries. This code is switched to use a macro for the basic code
instead, shaving a few hundred lines of originally-duplicated code. The
function names remain the same, but some fields of PgStat_StatTabEntry
have to be renamed to cope with the new style.
Author: Bertrand Drouvot
Reviewed-by: Nathan Bossart
Discussion: https:/postgr.es/m/20221204173207.GA2669116@nathanxps13
Pass VACUUM parameters (VacuumParams state) to vacuum_set_xid_limits()
directly, rather than passing most individual VacuumParams fields as
separate arguments.
Also make vacuum_set_xid_limits() output parameter symbol names match
those used by its vacuumlazy.c caller.
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-Wz=TE7gW5DgSahDkf0UEZigFGAoHNNN6EvSrdzC=Kn+hrA@mail.gmail.com
We shouldn't ever need to rely on whether HEAP_XMAX_INVALID is set in
t_infomask when considering whether or not an xmax should be deemed
already frozen, since that status flag is just a hint. The only
acceptable representation for an "xmax_already_frozen" raw xmax field is
the transaction ID value zero (also known as InvalidTransactionId).
Adjust code that superficially appeared to rely on HEAP_XMAX_INVALID to
make the rule about xmax_already_frozen clear. Also avoid needlessly
rereading the tuple's raw xmax.
Oversight in bugfix commit d2599ecf. There is no evidence that this
ever led to incorrect behavior, so no backpatch. The worst consequence
of this bug was that VACUUM could hypothetically fail to notice and
report on certain kinds of corruption, which seems fairly benign.
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-Wzkh3DMCDRPfhZxj9xCq9v3WmzvmbiCpf1dNKUBPadhCbQ@mail.gmail.com
Standardize on the name snapshotConflictHorizon for all XID fields from
WAL records that generate recovery conflicts when in hot standby mode.
This supersedes the previous latestRemovedXid naming convention.
The new naming convention places emphasis on how the values are actually
used by REDO routines. How the values are generated during original
execution (details of which vary by record type) is deemphasized. Users
of tools like pg_waldump can now grep for snapshotConflictHorizon to see
all potential sources of recovery conflicts in a standardized way,
without necessarily having to consider which specific record types might
be involved.
Also bring a couple of WAL record types that didn't follow any kind of
naming convention into line. These are heapam's VISIBLE record type and
SP-GiST's VACUUM_REDIRECT record type. Now every WAL record whose REDO
routine calls ResolveRecoveryConflictWithSnapshot() passes through the
snapshotConflictHorizon field from its WAL record. This is follow-up
work to the refactoring from commit 9e540599 that made FREEZE_PAGE WAL
records use a standard snapshotConflictHorizon style XID cutoff.
No bump in XLOG_PAGE_MAGIC, since the underlying format of affected WAL
records doesn't change.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CAH2-Wzm2CQUmViUq7Opgk=McVREHSOorYaAjR1ZpLYkRN7_dPw@mail.gmail.com
Make heapam WAL records that describe freezing performed by VACUUM more
space efficient by storing each distinct "freeze plan" once, alongside
an array of associated page offset numbers (one per freeze plan). The
freeze plans required for most heap pages tend to naturally have a great
deal of redundancy, so this technique is very effective in practice. It
often leads to freeze WAL records that are less than 20% of the size of
equivalent WAL records generated using the previous approach.
The freeze plan concept was introduced by commit 3b97e6823b, which fixed
bugs in VACUUM's handling of MultiXacts. We retain the concept of
freeze plans, but go back to using page offset number arrays. There is
no loss of generality here because deduplication is an additive process
that gets applied mechanically when FREEZE_PAGE WAL records are built.
More than anything else, freeze plan deduplication is an optimization
that reduces the marginal cost of freezing additional tuples on pages
that will need to have at least one or two tuples frozen in any case.
Ongoing work that adds page-level freezing to VACUUM will take full
advantage of the improved cost profile through batching.
Also refactor some of the details surrounding recovery conflicts needed
to REDO freeze records in passing: make original execution responsible
for generating a standard latestRemovedXid cutoff, rather than working
backwards to get the same cutoff in the REDO routine. Bugfix commit
66fbcb0d2e did it the other way around, which is equivalent but obscures
what's going on.
Also rename the cutoff field from the WAL record/struct (rename the
field cutoff_xid to latestRemovedXid to match similar WAL records).
Processing of conflicts by REDO routines is already completely uniform,
so tools like pg_waldump should present the information driving the
process uniformly. There are two remaining WAL record types that still
don't quite follow this convention (heapam's VISIBLE record type and
SP-GiST's VACUUM_REDIRECT record type). They can be brought into line
by later work that totally standardizes how the cutoffs are presented.
Bump XLOG_PAGE_MAGIC.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-By: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-By: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/CAH2-Wz=XytErMnb8FAyFd+OQEbiipB0Q2FmFdXrggPL4VBnRYQ@mail.gmail.com
The original report was concerned with a possible inconsistency
between the heap and the visibility map, which I was unable to
confirm. The concern has been retracted.
However, there did seem to be a torn page hazard when using
checksums. By not setting the heap page LSN during redo, the
protections of minRecoveryPoint were bypassed. Fixed, along with a
misleading comment.
It may have been impossible to hit this problem in practice, because
it would require a page tear between the checksum and the flags, so I
am marking this as a theoretical risk. But, as discussed, it did
violate expectations about the page LSN, so it may have other
consequences.
Backpatch to all supported versions.
Reported-by: Konstantin Knizhnik
Reviewed-by: Konstantin Knizhnik
Discussion: https://postgr.es/m/fed17dac-8cb8-4f5b-d462-1bb4908c029e@garret.ru
Backpatch-through: 11
We have various requirements when using a dlist_head to keep track of the
number of items in the list. This, traditionally, has been done by
maintaining a counter variable in the calling code. Here we tidy this up
by adding "dclist", which is very similar to dlist but also keeps track of
the number of items stored in the list.
Callers may use the new dclist_count() function when they need to know how
many items are stored. Obtaining the count is an O(1) operation.
For simplicity reasons, dclist and dlist both use dlist_node as their node
type and dlist_iter/dlist_mutable_iter as their iterator type. dclists
have all of the same functionality as dlists except there is no function
named dclist_delete(). To remove an item from a list dclist_delete_from()
must be used. This requires knowing which dclist the given item is stored
in.
Additionally, here we also convert some dlists where additional code
exists to keep track of the number of items stored and to make these use
dclists instead.
Author: David Rowley
Reviewed-by: Bharath Rupireddy, Aleksander Alekseev
Discussion: https://postgr.es/m/CAApHDvrtVxr+FXEX0VbViCFKDGxA3tWDgw9oFewNXCJMmwLjLg@mail.gmail.com
Here we add a new 'copy' parameter to tuplesort_getdatum so that we can
instruct the function not to datumCopy() byref Datums before returning.
Similar to 91e9e89dc, this can provide significant performance
improvements in nodeSort when sorting by a single byref column and the
sort's targetlist contains only that column.
This allows us to re-enable Datum sorts for byref types which was disabled
in 3a5817695 due to a reported memory leak.
Additionally, here we slightly optimize DISTINCT aggregates so that we no
longer perform any datumCopy() when we find the current value not to be
distinct from the previous value. Previously the code would always take a
copy of the most recent Datum and pfree the previous value, even when the
values were the same. Testing shows a small but noticeable performance
increase when aggregate transitions are skipped due to the current
transition value being the same as the prior one.
Author: David Rowley
Discussion: https://postgr.es/m/CAApHDvqS6wC5U==k9Hd26E4EQXH3QR67-T4=Q1rQ36NGvjfVSg@mail.gmail.com
Discussion: https://postgr.es/m/CAApHDvqHonfe9G1cVaKeHbDx70R_zCrM3qP2AGXpGrieSKGnhA@mail.gmail.com
In a similar effort to f01592f91, here we mostly rename shadowed local
variables to remove the warnings produced when compiling with
-Wshadow=compatible-local.
This fixes 63 warnings and leaves just 5.
Author: Justin Pryzby, David Rowley
Reviewed-by: Justin Pryzby
Discussion https://postgr.es/m/20220817145434.GC26426%40telsasoft.com
Commit 34f581c39 intended to ensure that RelationGetBufferForTuple
would acquire a visibility-map page pin in case the otherBuffer's
all-visible bit had become set since we last had lock on that page.
But I missed a case: when we're extending the relation, VM concerns
were dealt with only in the relatively-less-likely case that we
fail to conditionally lock the otherBuffer. I think I'd believed
that we couldn't need to worry about it if the conditional lock
succeeds, which is true for the target buffer; but the otherBuffer
was unlocked for awhile so its bit might be set anyway. So we need
to do the GetVisibilityMapPins dance, and then also recheck the
page's free space, in both cases.
Per report from Jaime Casanova. Back-patch to v12 as the previous
patch was (although there's still no evidence that the bug is
reachable pre-v14).
Discussion: https://postgr.es/m/E1lWLjP-00006Y-Ml@gemulon.postgresql.org
Commits cf112c12 and a0dc8271 were a little too hasty in getting rid of
the pg_ prefixes where we use pread(), pwrite() and vectored variants.
We dropped support for ancient Unixes where we needed to use lseek() to
implement replacements for those, but it turns out that Windows also
changes the current position even when you pass in an offset to
ReadFile() and WriteFile() if the file handle is synchronous, despite
its documentation saying otherwise.
Switching to asynchronous file handles would fix that, but have other
complications. For now let's just put back the pg_ prefix and add some
comments to highlight the non-standard side-effect, which we can now
describe as Windows-only.
Reported-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/20220923202439.GA1156054%40nathanxps13
Autoconf is showing its age, fewer and fewer contributors know how to wrangle
it. Recursive make has a lot of hard to resolve dependency issues and slow
incremental rebuilds. Our home-grown MSVC build system is hard to maintain for
developers not using Windows and runs tests serially. While these and other
issues could individually be addressed with incremental improvements, together
they seem best addressed by moving to a more modern build system.
After evaluating different build system choices, we chose to use meson, to a
good degree based on the adoption by other open source projects.
We decided that it's more realistic to commit a relatively early version of
the new build system and mature it in tree.
This commit adds an initial version of a meson based build system. It supports
building postgres on at least AIX, FreeBSD, Linux, macOS, NetBSD, OpenBSD,
Solaris and Windows (however only gcc is supported on aix, solaris). For
Windows/MSVC postgres can now be built with ninja (faster, particularly for
incremental builds) and msbuild (supporting the visual studio GUI, but
building slower).
Several aspects (e.g. Windows rc file generation, PGXS compatibility, LLVM
bitcode generation, documentation adjustments) are done in subsequent commits
requiring further review. Other aspects (e.g. not installing test-only
extensions) are not yet addressed.
When building on Windows with msbuild, builds are slower when using a visual
studio version older than 2019, because those versions do not support
MultiToolTask, required by meson for intra-target parallelism.
The plan is to remove the MSVC specific build system in src/tools/msvc soon
after reaching feature parity. However, we're not planning to remove the
autoconf/make build system in the near future. Likely we're going to keep at
least the parts required for PGXS to keep working around until all supported
versions build with meson.
Some initial help for postgres developers is at
https://wiki.postgresql.org/wiki/Meson
With contributions from Thomas Munro, John Naylor, Stone Tickle and others.
Author: Andres Freund <andres@anarazel.de>
Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Author: Peter Eisentraut <peter@eisentraut.org>
Reviewed-By: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/20211012083721.hvixq4pnh2pixr3j@alap3.anarazel.de
Make sure that function declarations use names that exactly match the
corresponding names from function definitions. Having parameter names
that are reliably consistent in this way will make it easier to reason
about groups of related C functions from the same translation unit as a
module. It will also make certain refactoring tasks easier.
Like other recent commits that cleaned up function parameter names, this
commit was written with help from clang-tidy. Later commits will do the
same for other parts of the codebase.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAH2-WznJt9CMM9KJTMjJh_zbL5hD9oX44qdJ4aqZtjFi-zA3Tg@mail.gmail.com
Add a new line to log reports from autovacuum (as well as VACUUM VERBOSE
output) that shows information about freezing. Emphasis is placed on
the total number of heap pages that had one or more tuples frozen by
VACUUM. The total number of tuples frozen is also shown.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Jeff Janes <jeff.janes@gmail.com>
Discussion: https://postgr.es/m/CAH2-WznTY6D0zyE8VLrC6Gd4kh_HGAXxnTPtcOQOOsxzLx9zog@mail.gmail.com
Several backend-side loops scanning one or more directories with
ReadDir() (WAL segment recycle/removal in xlog.c, backend-side directory
copy, temporary file removal, configuration file parsing, some logical
decoding logic and some pgtz stuff) already know the type of the entry
being scanned thanks to the dirent structure associated to the entry, on
platforms where we know about DT_REG, DT_DIR and DT_LNK to make the
difference between a regular file, a directory and a symbolic link.
Relying on the direct structure of an entry saves a few system calls to
stat() and lstat() in the loops updated here, shaving some code while on
it. The logic of the code remains the same, calling stat() or lstat()
depending on if it is necessary to look through symlinks.
Authors: Nathan Bossart, Bharath Rupireddy
Reviewed-by: Andres Freund, Thomas Munro, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACV8n-J-f=yiLUOx2=HrQGPSOZM3nWzyQQvLPcccPXxEdg@mail.gmail.com
Before now, the cutoffs that VACUUM used to determine which XIDs/MXIDs
to freeze were determined at the start of each VACUUM by taking related
cutoffs that represent which XIDs/MXIDs VACUUM should treat as still
running, and subtracting an XID/MXID age based value controlled by GUCs
like vacuum_freeze_min_age. The FreezeLimit cutoff (XID freeze cutoff)
was derived by subtracting an XID age value from OldestXmin, while the
MultiXactCutoff cutoff (MXID freeze cutoff) was derived by subtracting
an MXID age value from OldestMxact. This approach didn't match the
approach used nearby to determine whether this VACUUM operation should
be an aggressive VACUUM or not.
VACUUM now uses the standard approach instead: it subtracts the same
age-based values from next XID/next MXID (rather than subtracting from
OldestXmin/OldestMxact). This approach is simpler and more uniform.
Most of the time it will have only a negligible impact on how and when
VACUUM freezes. It will occasionally make VACUUM more robust in the
event of problems caused by long running transaction. These are cases
where OldestXmin and OldestMxact are held back by so much that they
attain an age that is a significant fraction of the value of age-based
settings like vacuum_freeze_min_age.
There is no principled reason why freezing should be affected in any way
by the presence of a long-running transaction -- at least not before the
point that the OldestXmin and OldestMxact limits used by each VACUUM
operation attain an age that makes it unsafe to freeze some of the
XIDs/MXIDs whose age exceeds the value of the relevant age-based
settings. The new approach should at least make freezing degrade more
gracefully than before, even in the most extreme cases.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-By: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://postgr.es/m/CAH2-WzkOv5CEeyOO=c91XnT5WBR_0gii0Wn5UbZhJ=4TTykDYg@mail.gmail.com
pread() and pwrite() are in SUSv2, and all targeted Unix systems have
them.
Previously, we defined pg_pread and pg_pwrite to emulate these function
with lseek() on old Unixen. The names with a pg_ prefix were a reminder
of a portability hazard: they might change the current file position.
That hazard is gone, so we can drop the prefixes.
Since the remaining replacement code is Windows-only, move it into
src/port/win32p{read,write}.c, and move the declarations into
src/include/port/win32_port.h.
No need for vestigial HAVE_PREAD, HAVE_PWRITE macros as they were only
used for declarations in port.h which have now moved into win32_port.h.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Greg Stark <stark@mit.edu>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA+hUKGJ3LHeP9w5Fgzdr4G8AnEtJ=z=p6hGDEm4qYGEUX5B6fQ@mail.gmail.com
We have been using the term RelFileNode to refer to either (1) the
integer that is used to name the sequence of files for a certain relation
within the directory set aside for that tablespace/database combination;
or (2) that value plus the OIDs of the tablespace and database; or
occasionally (3) the whole series of files created for a relation
based on those values. Using the same name for more than one thing is
confusing.
Replace RelFileNode with RelFileNumber when we're talking about just the
single number, i.e. (1) from above, and with RelFileLocator when we're
talking about all the things that are needed to locate a relation's files
on disk, i.e. (2) from above. In the places where we refer to (3) as
a relfilenode, instead refer to "relation storage".
Since there is a ton of SQL code in the world that knows about
pg_class.relfilenode, don't change the name of that column, or of other
SQL-facing things that derive their name from it.
On the other hand, do adjust closely-related internal terminology. For
example, the structure member names dbNode and spcNode appear to be
derived from the fact that the structure itself was called RelFileNode,
so change those to dbOid and spcOid. Likewise, various variables with
names like rnode and relnode get renamed appropriately, according to
how they're being used in context.
Hopefully, this is clearer than before. It is also preparation for
future patches that intend to widen the relfilenumber fields from its
current width of 32 bits. Variables that store a relfilenumber are now
declared as type RelFileNumber rather than type Oid; right now, these
are the same, but that can now more easily be changed.
Dilip Kumar, per an idea from me. Reviewed also by Andres Freund.
I fixed some whitespace issues, changed a couple of words in a
comment, and made one other minor correction.
Discussion: http://postgr.es/m/CA+TgmoamOtXbVAQf9hWFzonUo6bhhjS6toZQd7HZ-pmojtAmag@mail.gmail.com
Discussion: http://postgr.es/m/CA+Tgmobp7+7kmi4gkq7Y+4AM9fTvL+O1oQ4-5gFTT+6Ng-dQ=g@mail.gmail.com
Discussion: http://postgr.es/m/CAFiTN-vTe79M8uDH1yprOU64MNFE+R3ODRuA+JWf27JbhY4hJw@mail.gmail.com
This reverts commits 5753d4ee32 and fe60b67250 that modified HOT to
ignore BRIN indexes. The commit message for 5753d4ee32 claims that:
When determining whether an index update may be skipped by using
HOT, we can ignore attributes indexed only by BRIN indexes. There
are no index pointers to individual tuples in BRIN, and the page
range summary will be updated anyway as it relies on visibility
info.
This is partially incorrect - it's true BRIN indexes don't point to
individual tuples, so HOT chains are not an issue, but the visibitlity
info is not sufficient to keep the index up to date. This can easily
result in corrupted indexes, as demonstrated in the hackers thread.
This does not mean relaxing the HOT restrictions for BRIN is a lost
cause, but it needs to handle the two aspects (allowing HOT chains and
updating the page range summaries) as separate. But that requires a
major changes, and it's too late for that in the current dev cycle.
Reported-by: Tomas Vondra
Discussion: https://postgr.es/m/05ebcb44-f383-86e3-4f31-0a97a55634cf@enterprisedb.com
Per-backend global variables like VacuumPageHit are initialized once per
VACUUM command. This was missed by commit 49c9d9fc, which unified
VACUUM VERBOSE and autovacuum logging. As a result of that oversight,
incorrect values were shown when multiple relations were processed by a
single VACUUM VERBOSE command.
Relations that happened to be processed later on would show "buffer
usage:" values that incorrectly included buffer accesses made while
processing earlier unrelated relations. The same accesses were counted
multiple times.
To fix, take initial values for the tracker variables at the start of
heap_vacuum_rel(), and report delta values later on.
Be consistent about the lines that VACUUM VERBOSE outputs by including
an "index scan not needed: " line for completely empty tables. This
makes the output more readable, especially with multiple distinct VACUUM
operations processed by the same VACUUM command. It's also more
consistent; even empty tables can use the failsafe, which wasn't
reported in the standard way until now.
Follow-up to commit 6e20f460, which taught VACUUM VERBOSE to be more
consistent about reporting on scanned pages with empty tables.
The age of OldestXmin (a.k.a. "removable cutoff") when VACUUM ends often
indicates the approximate number of XIDs consumed while VACUUM ran.
However, there is at least one important exception: the cutoff could be
held back by a snapshot that was acquired before our VACUUM even began.
Successive VACUUM operations may even use exactly the same old cutoff in
extreme cases involving long held snapshots.
The log messages that described how removable cutoff aged (which were
added by commit 872770fd) created the impression that we were reporting
on how VACUUM's usable cutoff advanced while VACUUM ran, which was
misleading in these extreme cases. Fix by using a more general wording.
Per gripe from Tom Lane.
In passing, relocate related instrumentation code for clarity.
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/1643035.1650035653@sss.pgh.pa.us
heap_fetch() used to have a "keep_buf" parameter that told it to return
ownership of the buffer pin to the caller after finding that the
requested tuple TID exists but is invisible to the specified snapshot.
This was thoughtlessly removed in commit 5db6df0c0, which broke
heapam_tuple_lock() (formerly EvalPlanQualFetch) because that function
needs to do more accesses to the tuple even if it's invisible. The net
effect is that we would continue to touch the page for a microsecond or
two after releasing pin on the buffer. Usually no harm would result;
but if a different session decided to defragment the page concurrently,
we could see garbage data and mistakenly conclude that there's no newer
tuple version to chain up to. (It's hard to say whether this has
happened in the field. The bug was actually found thanks to a later
change that allowed valgrind to detect accesses to non-pinned buffers.)
The most reasonable way to fix this is to reintroduce keep_buf,
although I made it behave slightly differently: buffer ownership
is passed back only if there is a valid tuple at the requested TID.
In HEAD, we can just add the parameter back to heap_fetch().
To avoid an API break in the back branches, introduce an additional
function heap_fetch_extended() in those branches.
In HEAD there is an additional, less obvious API change: tuple->t_data
will be set to NULL in all cases where buffer ownership is not returned,
in particular when the tuple exists but fails the time qual (and
!keep_buf). This is to defend against any other callers attempting to
access non-pinned buffers. We concluded that making that change in back
branches would be more likely to introduce problems than cure any.
In passing, remove a comment about heap_fetch that was obsoleted by
9a8ee1dc6.
Per bug #17462 from Daniil Anisimov. Back-patch to v12 where the bug
was introduced.
Discussion: https://postgr.es/m/17462-9c98a0f00df9bd36@postgresql.org
All but a few existing callers assume without checking that this
function succeeds. While it probably will, that's a poor excuse for
not checking. Let's make it return void and instead throw an error
if it doesn't find the block reference. Callers that actually need
to handle the no-such-block case must now use the underlying function
XLogRecGetBlockTagExtended.
In addition to being a bit less error-prone, this should also serve
to suppress some Coverity complaints about XLogRecGetBlockRefInfo.
While at it, clean up some inconsistency about use of the
XLogRecHasBlockRef macro: make XLogRecGetBlockTagExtended use
that instead of open-coding the same condition, and avoid calling
XLogRecHasBlockRef twice in relevant code paths. (That is,
calling XLogRecHasBlockRef followed by XLogRecGetBlockTag is now
deprecated: use XLogRecGetBlockTagExtended instead.)
Patch HEAD only; this doesn't seem to have enough value to consider
a back-branch API break.
Discussion: https://postgr.es/m/425039.1649701221@sss.pgh.pa.us
Remove comment block about how heap page vacuuming used to set tuples
with storage to LP_UNUSED in a rare edge case that can no longer happen
following commit 8523492d4e. The comments seem unnecessary now, since
it's now generally clear that heap vacuuming only applies to LP_DEAD
items from VACUUM's first heap pass following more recent work from
commits 12b5ade902 and 4f8d9d1217.
Reclaim space from the line pointer array when heap pruning leaves
behind a contiguous group of LP_UNUSED items at the end of the array.
This happens during subsequent page defragmentation. Certain kinds of
heap line pointer bloat are ameliorated by this new optimization.
Follow-up work to commit 3c3b8a4b26, which taught VACUUM to truncate the
line pointer array in about the same way during VACUUM's second pass
over the heap. We now apply line pointer array truncation during both
the first and the second pass over the heap made by VACUUM. We can also
perform line pointer array truncation during opportunistic pruning.
Matthias van de Meent, with small tweaks by me.
Author: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://postgr.es/m/CAEze2WjgaQc55Y5f5CQd3L=eS5CZcff2Obxp=O6pto8-f0hC4w@mail.gmail.com
Discussion: https://postgr.es/m/CAEze2Wg36%2B4at2eWJNcYNiW2FJmht34x3YeX54ctUSs7kKoNcA%40mail.gmail.com
Soon the stats collector will be no more, with statistics instead getting
stored in shared memory. There are a lot of references to the stats collector
in comments. This commit replaces most of these references with "cumulative
statistics system", with the remaining ones getting replaced as part of
subsequent commits.
This is done separately from the - quite large - shared memory statistics
patch to make review easier.
Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-By: Thomas Munro <thomas.munro@gmail.com>
Reviewed-By: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20220303021600.hs34ghqcw6zcokdh@alap3.anarazel.de
Discussion: https://postgr.es/m/20220308205351.2xcn6k4x5yivcxyd@alap3.anarazel.de
This replaces the bool flag for randomAccess. An upcoming patch requires
adding another option, so instead of breaking the API for that, then
breaking it again one day if we add more options, let's just break it
once. Any boolean options we add in the future will just make use of an
unused bit in the flags.
Any extensions making use of tuplesorts will need to update their code
to pass TUPLESORT_RANDOMACCESS instead of true for randomAccess.
TUPLESORT_NONE can be used for a set of empty options.
Author: David Rowley
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/CAApHDvoH4ASzsAOyHcxkuY01Qf%2B%2B8JJ0paw%2B03dk%2BW25tQEcNQ%40mail.gmail.com
Non-aggressive VACUUMs were at a gratuitous disadvantage (relative to
aggressive VACUUMs) around advancing relfrozenxid and relminmxid before
now. The issue only came up when concurrent activity unset some heap
page's visibility map bit right as VACUUM was considering if the page
should get counted in frozenskipped_pages. The non-aggressive case
would recheck the all-frozen bit at this point. The aggressive case
reasoned that the page (a skippable page) must have at least been
all-frozen in the recent past, so skipping it won't make relfrozenxid
advancement unsafe (which is never okay for aggressive VACUUMs).
The recheck created a window for some other backend to confuse matters
for VACUUM. If the page's VM bit turned out to be unset, VACUUM would
conclude that the page was _never_ all-frozen. frozenskipped_pages was
not incremented, and yet VACUUM couldn't back out of skipping at this
late stage (it couldn't choose to scan the page instead). This made it
unsafe to advance relfrozenxid later on.
Consistently avoid the issue by generalizing how we skip frozen pages
during aggressive VACUUMs: take the same approach when skipping any
skippable page range during aggressive and non-aggressive VACUUMs alike.
The new approach makes ranges (not individual pages) the fundamental
unit of skipping using the visibility map. frozenskipped_pages is
replaced with a boolean flag that represents whether some skippable
range with one or more all-visible pages was actually skipped.
It is safe for VACUUM to treat a page as all-frozen provided it at least
had its all-frozen bit set after the OldestXmin cutoff was established.
VACUUM is only required to scan pages that might have XIDs < OldestXmin
(unfrozen XIDs) to be able to safely advance relfrozenxid. Tuples
concurrently inserted on "skipped" pages can be thought of as equivalent
to tuples concurrently inserted on a block >= rel_pages.
It's possible that the issue this commit fixes hardly ever came up in
practice. But we only had to be unlucky once to lose out on advancing
relfrozenxid -- a single affected heap page was enough to throw VACUUM
off. That seems like something to avoid on general principle. This is
similar to an issue fixed by commit 44fa8488, which taught vacuumlazy.c
to not give up on non-aggressive relfrozenxid advancement just because a
cleanup lock wasn't immediately available on some heap page.
Skipping an all-visible range is now explicitly structured as a choice
made by non-aggressive VACUUMs, by weighing known costs (scanning extra
skippable pages to freeze their tuples early) against known benefits
(advancing relfrozenxid early). This works in essentially the same way
as it always has (don't skip ranges < SKIP_PAGES_THRESHOLD). We could
do much better here in the future by considering other relevant factors.
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/CAH2-Wzn6bGJGfOy3zSTJicKLw99PHJeSOQBOViKjSCinaxUKDQ@mail.gmail.com
Discussion: https://postgr.es/m/CA%2BTgmoZiSOY6H7aadw5ZZGm7zYmfDzL6nwmL5V7GL4HgJgLF_w%40mail.gmail.com
Peter Geoghegan
Andrew Dunstan
Peter Eisentraut
Michael Paquier
Jeff Davis
Andres Freund
David Rowley
Tom Lane
Thomas Munro
Robert Haas
Tomas Vondra
Alvaro Herrera