lazy_scan_prune() previously had two separate cases that called
visibilitymap_set() after pruning and freezing. These branches were
nearly identical except that one attempted to avoid dirtying the heap
buffer. However, that situation can never occur — the heap buffer cannot
be clean at that point (and we would hit an assertion if it were).
In lazy_scan_prune(), when we change a previously all-visible page to
all-frozen and the page was recorded as all-visible in the visibility
map by find_next_unskippable_block(), the heap buffer will always be
dirty. Either we have just frozen a tuple and already dirtied the
buffer, or the buffer was modified between find_next_unskippable_block()
and heap_page_prune_and_freeze() and then pruned in
heap_page_prune_and_freeze().
Additionally, XLogRegisterBuffer() asserts that the buffer is dirty, so
attempting to add a clean heap buffer to the WAL chain would assert out
anyway.
Since the “clean heap buffer with already set VM” case is impossible,
the two visibilitymap_set() branches in lazy_scan_prune() can be merged.
Doing so makes the intent clearer and emphasizes that the heap buffer
must always be marked dirty before being added to the WAL chain.
This commit also adds a test case for vacuuming when no heap
modifications are required. Currently this ensures that the heap buffer
is marked dirty before it is added to the WAL chain, but if we later
remove the heap buffer from the VM-set WAL chain or pass it with the
REGBUF_NO_CHANGES flag, this test would guard that behavior.
Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Discussion: https://postgr.es/m/5CEAA162-67B1-44DA-B60D-8B65717E8B05%40gmail.com
Discussion: https://postgr.es/m/flat/CAAKRu_ZWx5gCbeCf7PWCv8p5%3D%3Db7EEws0VD2wksDxpXCvCyHvQ%40mail.gmail.com
Currently, pg_visibility computes its xid horizon using the
GetOldestNonRemovableTransactionId(). The problem is that this horizon can
sometimes go backward. That can lead to reporting false errors.
In order to fix that, this commit implements a new function
GetStrictOldestNonRemovableTransactionId(). This function computes the xid
horizon, which would be guaranteed to be newer or equal to any xid horizon
computed before.
We have to do the following to achieve this.
1. Ignore processes xmin's, because they consider connection to other databases
that were ignored before.
2. Ignore KnownAssignedXids, because they are not database-aware. At the same
time, the primary could compute its horizons database-aware.
3. Ignore walsender xmin, because it could go backward if some replication
connections don't use replication slots.
As a result, we're using only currently running xids to compute the horizon.
Surely these would significantly sacrifice accuracy. But we have to do so to
avoid reporting false errors.
Inspired by earlier patch by Daniel Shelepanov and the following discussion
with Robert Haas and Tom Lane.
Discussion: https://postgr.es/m/1649062270.289865713%40f403.i.mail.ru
Reviewed-by: Alexander Lakhin, Dmitry Koval
When maintaining or merging patches, one of the most common sources
for conflicts are the list of objects in makefiles. Especially when
the split across lines has been changed on both sides, which is
somewhat common due to attempting to stay below 80 columns, those
conflicts are unnecessarily laborious to resolve.
By splitting, and alphabetically sorting, OBJS style lines into one
object per line, conflicts should be less frequent, and easier to
resolve when they still occur.
Author: Andres Freund
Discussion: https://postgr.es/m/20191029200901.vww4idgcxv74cwes@alap3.anarazel.de
Three nologin roles with non-overlapping privs are created by default
* pg_read_all_settings - read all GUCs.
* pg_read_all_stats - pg_stat_*, pg_database_size(), pg_tablespace_size()
* pg_stat_scan_tables - may lock/scan tables
Top level role - pg_monitor includes all of the above by default, plus others
Author: Dave Page
Reviewed-by: Stephen Frost, Robert Haas, Peter Eisentraut, Simon Riggs
The contrib extensions pageinspect, pg_visibility and pgstattuple only
work against regular relations which have storage. They don't work
against foreign tables, partitioned (parent) tables, views, et al.
Add checks to the user-callable functions to return a useful error
message to the user if they mistakenly pass an invalid relation to a
function which doesn't accept that kind of relation.
In passing, improve some of the existing checks to use ereport() instead
of elog(), add a function to consolidate common checks where
appropriate, and add some regression tests.
Author: Amit Langote, with various changes by me
Reviewed by: Michael Paquier and Corey Huinker
Discussion: https://postgr.es/m/ab91fd9d-4751-ee77-c87b-4dd704c1e59c@lab.ntt.co.jp
The new pg_check_visible() and pg_check_frozen() functions can be used to
verify that the visibility map bits for a relation's data pages match the
actual state of the tuples on those pages.
Amit Kapila and Robert Haas, reviewed (in earlier versions) by Andres
Freund. Additional testing help by Thomas Munro.
This lets you examine the visibility map as well as page-level
visibility information. I initially wrote it as a debugging aid,
but was encouraged to polish it for commit.
Patch by me, reviewed by Masahiko Sawada.
Discussion: 56D77803.6080503@BlueTreble.com
