This reverts commit 18fb9d8d21. Per
discussion, it does not seem like a good idea to allow committed changes to
go un-checkpointed indefinitely, as could happen in a low-traffic server;
that makes us entirely reliant on the WAL stream with no redundancy that
might aid data recovery in case of disk failure.
This re-introduces the original problem of hot-standby setups generating a
small continuing stream of WAL traffic even when idle, but there are other
ways to address that without compromising crash recovery, so we'll revisit
that issue in a future release cycle.
Aside from adjusting the documentation to say that these are deprecated,
we now report a warning (not an error) for use of GLOBAL, since it seems
fairly likely that we might change that to request SQL-spec-compliant temp
table behavior in the foreseeable future. Although our handling of LOCAL
is equally nonstandard, there is no evident interest in ever implementing
SQL modules, and furthermore some other products interpret LOCAL as
behaving the same way we do. So no expectation of change and no warning
for LOCAL; but it still seems a good idea to deprecate writing it.
Noah Misch
The simplest way to handle this is just to copy-and-paste the relevant
code block in fork_process.c, so that's what I did. (It's possible that
something more complicated would be useful to packagers who want to work
with either the old or the new API; but at this point the number of such
people is rapidly approaching zero, so let's just get the minimal thing
done.) Update relevant documentation as well.
Remove a couple of items that were actually back-patched bug fixes.
Add additional details to a couple of items which lacked a description.
Improve attributions for a couple of items I was involved with.
A few other miscellaneous corrections.
Commit aaa6e1def2 introduced multiple hazards
in the case where pg_ctl is executed with neither a -D switch nor any
PGDATA environment variable. It would dump core on machines which are
unforgiving about printf("%s", NULL), or failing that possibly give a
rather unhelpful complaint about being unable to execute "postgres -C",
rather than the logically prior complaint about not being told where the
data directory is.
Edmund Horner's report suggests that there is another, Windows-specific
hazard here, but I'm not the person to fix that; it would in any case only
be significant when trying to use a config-only PGDATA pointer.
"pg_dump -Ft -f filename ..." got broken by my recent commit
4317e0246c, which I fear I only tested
in the output-to-stdout variant.
Report and fix by Muhammad Asif Naeem.
getopt_long() allows abbreviating long options, so we might as well
give the option the full name, and users can abbreviate it how they
like.
Do some general polishing of the --help output at the same time.
This prevents a pg_basebackup backup session that just does a base
backup (no xlog involved at all) from becoming the synchronous slave
and thus blocking all access while it runs.
Also fixes the problem when a higher priority slave shows up it would
become the sync standby before it has reached the STREAMING state, by
making sure we can only switch to a walsender that's actually STREAMING.
Fujii Masao
To replace it, add -X/--xlog-method that allows the specification
of fetch or stream.
Do this to avoid unnecessary backwards-incompatiblity. Spotted and
suggested by Peter Eisentraut.
Since the replication protocol deals with TimestampTz, we need to
care for the floating point case as well in the frontend tools.
Fujii Masao, with changes from Magnus Hagander
When HS startup is deferred because of overflowed subtransactions, ensure
that we re-initialize KnownAssignedXids for when both existing and incoming
snapshots have non-zero qualifying xids.
Fixes bug #6661 reported by Valentine Gogichashvili.
Analysis and fix by Andres Freund
This provides a speedup of about 4X when NBuffers is large enough.
There is also a useful reduction in sinval traffic, since we
only do CacheInvalidateSmgr() once not once per fork.
Simon Riggs, reviewed and somewhat revised by Tom Lane
DropRelFileNodeBuffers, DropDatabaseBuffers, FlushRelationBuffers, and
FlushDatabaseBuffers have to scan the whole shared_buffers pool because
we have no index structure that would find the target buffers any more
efficiently than that. This gets expensive with large NBuffers. We can
shave some cycles from these loops by prechecking to see if the current
buffer is interesting before we acquire the buffer header lock.
Ordinarily such a test would be unsafe, but in these cases it should be
safe because we are already assuming that the caller holds a lock that
prevents any new target pages from being loaded into the buffer pool
concurrently. Therefore, no buffer tag should be changing to a value of
interest, only away from a value of interest. So a false negative match
is impossible, while a false positive is safe because we'll recheck after
acquiring the buffer lock. Initial testing says that this speeds these
loops by a factor of 2X to 3X on common Intel hardware.
Patch for DropRelFileNodeBuffers by Jeff Janes (based on an idea of
Heikki's); extended to the remaining sequential scans by Tom Lane
WALSender now woken up after each background flush by WALwriter, avoiding
multi-second replication delay for an all-async commit workload.
Replication delay reduced from 7s with default settings to 200ms and often
much less, allowing significantly reduced data loss at failover.
Andres Freund and Simon Riggs
In lazy_scan_heap, we could issue bogus warnings about incorrect
information in the visibility map, because we checked the visibility
map bit before locking the heap page, creating a race condition. Fix
by rechecking the visibility map bit before we complain. Rejigger
some related logic so that we rely on the possibly-outdated
all_visible_according_to_vm value as little as possible.
In heap_multi_insert, it's not safe to clear the visibility map bit
before beginning the critical section. The visibility map is not
crash-safe unless we treat clearing the bit as a critical operation.
Specifically, if the transaction were to error out after we set the
bit and before entering the critical section, we could end up writing
the heap page to disk (with the bit cleared) and crashing before the
visibility map page made it to disk. That would be bad. heap_insert
has this correct, but somehow the order of operations got rearranged
when heap_multi_insert was added.
Also, add some more comments to visibilitymap_test, lazy_scan_heap,
and IndexOnlyNext, expounding on concurrency issues.
Per extensive code review by Andres Freund, and further review by Tom
Lane, who also made the original report about the bogus warnings.
The original coding misbehaved if "char" is signed, and also made the
extremely poor decision to print control characters literally when trying
to complain about them. Report and patch by Shigeru Hanada.
In passing, also fix core dump risk in report_parse_error() should the
parse state be something other than what it expects.
It failed to check for error return from xsltApplyStylesheet(), as reported
by Peter Gagarinov. (So far as I can tell, libxslt provides no convenient
way to get a useful error message in failure cases. There might be some
inconvenient way, but considering that this code is deprecated it's hard to
get enthusiastic about putting lots of work into it. So I just made it say
"failed to apply stylesheet", in line with the existing error checks.)
While looking at the code I also noticed that the string returned by
xsltSaveResultToString was never freed, resulting in a session-lifespan
memory leak.
Back-patch to all supported versions.
This is currently only cosmetic, since all the call sites just curl up
and die in event of a failure return. It might be important for some
future use-case, though, and in any case it quiets warnings from the
clang static analyzer (as reported by Anna Zaks).
Josh Kupershmidt
When we allowed read-only transactions to skip assigning XIDs
we introduced the possibility that a fully deleted btree page
could be reused. This broke the index link sequence which could
then lead to indexscans silently returning fewer rows than would
have been correct. The actual incidence of silent errors from
this is thought to be very low because of the exact workload
required and locking pre-conditions. Fix is to remove pages only
if index page opaque->btpo.xact precedes RecentGlobalXmin.
Noah Misch, reviewed by Simon Riggs
Re-implements similar functionality in 9.1 and previously which
was removed during split of checkpointer and bgwriter.
Requested/spotted by Magnus Hagander
