This uses the progress reporting infrastructure added by c16dc1aca5,
adding support for CREATE INDEX and CREATE INDEX CONCURRENTLY.
There are two pieces to this: one is index-AM-agnostic, and the other is
AM-specific. The latter is fairly elaborate for btrees, including
reportage for parallel index builds and the separate phases that btree
index creation uses; other index AMs, which are much simpler in their
building procedures, have simplistic reporting only, but that seems
sufficient, at least for non-concurrent builds.
The index-AM-agnostic part is fairly complete, providing insight into
the CONCURRENTLY wait phases as well as block-based progress during the
index validation table scan. (The index validation index scan requires
patching each AM, which has not been included here.)
Reviewers: Rahila Syed, Pavan Deolasee, Tatsuro Yamada
Discussion: https://postgr.es/m/20181220220022.mg63bhk26zdpvmcj@alvherre.pgsql
Opening a relation with no lock at all is unsafe; there's no guarantee
that we'll see a consistent state of the relevant catalog entries.
While use of MVCC scans to read the catalogs partially addresses that
complaint, it's still possible to switch to a new catalog snapshot
partway through loading the relcache entry. Moreover, whether or not
you trust the reasoning behind sometimes using less than
AccessExclusiveLock for ALTER TABLE, that reasoning is certainly not
valid if concurrent users of the table don't hold a lock corresponding
to the operation they want to perform.
Hence, add some assertion-build-only checks that require any caller
of relation_open(x, NoLock) to hold at least AccessShareLock. This
isn't a full solution, since we can't verify that the lock level is
semantically appropriate for the action --- but it's definitely of
some use, because it's already caught two bugs.
We can also assert that callers of addRangeTableEntryForRelation()
hold at least the lock level specified for the new RTE.
Amit Langote and Tom Lane
Discussion: https://postgr.es/m/16565.1538327894@sss.pgh.pa.us
LockRelationOid and sibling routines supposed that, if our session already
holds the lock they were asked to acquire, they could skip calling
AcceptInvalidationMessages on the grounds that we must have already read
any remote sinval messages issued against the relation being locked.
This is normally true, but there's a critical special case where it's not:
processing inside AcceptInvalidationMessages might attempt to access system
relations, resulting in a recursive call to acquire a relation lock.
Hence, if the outer call had acquired that same system catalog lock, we'd
fall through, despite the possibility that there's an as-yet-unread sinval
message for that system catalog. This could, for example, result in
failure to access a system catalog or index that had just been processed
by VACUUM FULL. This is the explanation for buildfarm failures we've been
seeing intermittently for the past three months. The bug is far older
than that, but commits a54e1f158 et al added a new recursion case within
AcceptInvalidationMessages that is apparently easier to hit than any
previous case.
To fix this, we must not skip calling AcceptInvalidationMessages until
we have *finished* a call to it since acquiring a relation lock, not
merely acquired the lock. (There's already adequate logic inside
AcceptInvalidationMessages to deal with being called recursively.)
Fortunately, we can implement that at trivial cost, by adding a flag
to LOCALLOCK hashtable entries that tracks whether we know we have
completed such a call.
There is an API hazard added by this patch for external callers of
LockAcquire: if anything is testing for LOCKACQUIRE_ALREADY_HELD,
it might be fooled by the new return code LOCKACQUIRE_ALREADY_CLEAR
into thinking the lock wasn't already held. This should be a fail-soft
condition, though, unless something very bizarre is being done in
response to the test.
Also, I added an additional output argument to LockAcquireExtended,
assuming that that probably isn't called by any outside code given
the very limited usefulness of its additional functionality.
Back-patch to all supported branches.
Discussion: https://postgr.es/m/12259.1532117714@sss.pgh.pa.us
XactLockTableWait assumed that its xid argument has already added itself
to the lock table. That assumption led to another assumption that if
locking the xid has succeeded but the xid is reported as still in
progress, then the input xid must have been a subtransaction.
These assumptions hold true for the original uses of this code in
locking related to on-disk tuples, but they break down in logical
replication slot snapshot building -- in particular, when a standby
snapshot logged contains an xid that's already in ProcArray but not yet
in the lock table. This leads to assertion failures that can be
reproduced all the way back to 9.4, when logical decoding was
introduced.
To fix, change SubTransGetParent to SubTransGetTopmostTransaction which
has a slightly different API: it returns the argument Xid if there is no
parent, and it goes all the way to the top instead of moving up the
levels one by one. Also, to avoid busy-waiting, add a 1ms sleep to give
the other process time to register itself in the lock table.
For consistency, change ConditionalXactLockTableWait the same way.
Author: Petr Jelínek
Discussion: https://postgr.es/m/1B3E32D8-FCF4-40B4-AEF9-5C0E3AC57969@postgrespro.ru
Reported-by: Konstantin Knizhnik
Diagnosed-by: Stas Kelvich, Petr Jelínek
Reviewed-by: Andres Freund, Robert Haas
The lower case spellings are C and C++ standard and are used in most
parts of the PostgreSQL sources. The upper case spellings are only used
in some files/modules. So standardize on the standard spellings.
The APIs for ICU, Perl, and Windows define their own TRUE and FALSE, so
those are left as is when using those APIs.
In code comments, we use the lower-case spelling for the C concepts and
keep the upper-case spelling for the SQL concepts.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Contention on the relation extension lock can become quite fierce when
multiple processes are inserting data into the same relation at the same
time at a high rate. Experimentation shows the extending the relation
multiple blocks at a time improves scalability.
Dilip Kumar, reviewed by Petr Jelinek, Amit Kapila, and me.
The old code is wrong, because it returns a pointer to an automatic
variable. And it's also more clever than we really need to be
considering that the case it's worrying about should never happen.
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.
The newly added ON CONFLICT clause allows to specify an alternative to
raising a unique or exclusion constraint violation error when inserting.
ON CONFLICT refers to constraints that can either be specified using a
inference clause (by specifying the columns of a unique constraint) or
by naming a unique or exclusion constraint. DO NOTHING avoids the
constraint violation, without touching the pre-existing row. DO UPDATE
SET ... [WHERE ...] updates the pre-existing tuple, and has access to
both the tuple proposed for insertion and the existing tuple; the
optional WHERE clause can be used to prevent an update from being
executed. The UPDATE SET and WHERE clauses have access to the tuple
proposed for insertion using the "magic" EXCLUDED alias, and to the
pre-existing tuple using the table name or its alias.
This feature is often referred to as upsert.
This is implemented using a new infrastructure called "speculative
insertion". It is an optimistic variant of regular insertion that first
does a pre-check for existing tuples and then attempts an insert. If a
violating tuple was inserted concurrently, the speculatively inserted
tuple is deleted and a new attempt is made. If the pre-check finds a
matching tuple the alternative DO NOTHING or DO UPDATE action is taken.
If the insertion succeeds without detecting a conflict, the tuple is
deemed inserted.
To handle the possible ambiguity between the excluded alias and a table
named excluded, and for convenience with long relation names, INSERT
INTO now can alias its target table.
Bumps catversion as stored rules change.
Author: Peter Geoghegan, with significant contributions from Heikki
Linnakangas and Andres Freund. Testing infrastructure by Jeff Janes.
Reviewed-By: Heikki Linnakangas, Andres Freund, Robert Haas, Simon Riggs,
Dean Rasheed, Stephen Frost and many others.
With this in place, a session blocking behind another one because of
tuple locks will get a context line mentioning the relation name, tuple
TID, and operation being done on tuple. For example:
LOG: process 11367 still waiting for ShareLock on transaction 717 after 1000.108 ms
DETAIL: Process holding the lock: 11366. Wait queue: 11367.
CONTEXT: while updating tuple (0,2) in relation "foo"
STATEMENT: UPDATE foo SET value = 3;
Most usefully, the new line is displayed by log entries due to
log_lock_waits, although of course it will be printed by any other log
message as well.
Author: Christian Kruse, some tweaks by Álvaro Herrera
Reviewed-by: Amit Kapila, Andres Freund, Tom Lane, Robert Haas
In situations where there are over 8MB of empty pages at the end of
a table, the truncation work for trailing empty pages takes longer
than deadlock_timeout, and there is frequent access to the table by
processes other than autovacuum, there was a problem with the
autovacuum worker process being canceled by the deadlock checking
code. The truncation work done by autovacuum up that point was
lost, and the attempt tried again by a later autovacuum worker. The
attempts could continue indefinitely without making progress,
consuming resources and blocking other processes for up to
deadlock_timeout each time.
This patch has the autovacuum worker checking whether it is
blocking any other thread at 20ms intervals. If such a condition
develops, the autovacuum worker will persist the work it has done
so far, release its lock on the table, and sleep in 50ms intervals
for up to 5 seconds, hoping to be able to re-acquire the lock and
try again. If it is unable to get the lock in that time, it moves
on and a worker will try to continue later from the point this one
left off.
While this patch doesn't change the rules about when and what to
truncate, it does cause the truncation to occur sooner, with less
blocking, and with the consumption of fewer resources when there is
contention for the table's lock.
The only user-visible change other than improved performance is
that the table size during truncation may change incrementally
instead of just once.
This problem exists in all supported versions but is infrequently
reported, although some reports of performance problems when
autovacuum runs might be caused by this. Initial commit is just the
master branch, but this should probably be backpatched once the
build farm and general developer usage confirm that there are no
surprising effects.
Jan Wieck
Instead of entering them on transaction startup, we materialize them
only when someone wants to wait, which will occur only during CREATE
INDEX CONCURRENTLY. In Hot Standby mode, the startup process must also
be able to probe for conflicting VXID locks, but the lock need never be
fully materialized, because the startup process does not use the normal
lock wait mechanism. Since most VXID locks never need to touch the
lock manager partition locks, this can significantly reduce blocking
contention on read-heavy workloads.
Patch by me. Review by Jeff Davis.
In the previous coding, we would look up a relation in RangeVarGetRelid,
lock the resulting OID, and then AcceptInvalidationMessages(). While
this was sufficient to ensure that we noticed any changes to the
relation definition before building the relcache entry, it didn't
handle the possibility that the name we looked up no longer referenced
the same OID. This was particularly problematic in the case where a
table had been dropped and recreated: we'd latch on to the entry for
the old relation and fail later on. Now, we acquire the relation lock
inside RangeVarGetRelid, and retry the name lookup if we notice that
invalidation messages have been processed meanwhile. Many operations
that would previously have failed with an error in the presence of
concurrent DDL will now succeed.
There is a good deal of work remaining to be done here: many callers
of RangeVarGetRelid still pass NoLock for one reason or another. In
addition, nothing in this patch guards against the possibility that
the meaning of an unqualified name might change due to the creation
of a relation in a schema earlier in the user's search path than the
one where it was previously found. Furthermore, there's nothing at
all here to guard against similar race conditions for non-relations.
For all that, it's a start.
Noah Misch and Robert Haas
This is appropriate for the same reasons we already do it in
LockSharedObject(): things might have changed while we were waiting
for the lock. There doesn't seem to be a live bug here at the moment,
but that's mostly because it isn't currently used for very much.
temporary table; we can't support that because there's no way to clean up the
source backend's internal state if the eventual COMMIT PREPARED is done by
another backend. This was checked correctly in 8.1 but I broke it in 8.2 :-(.
Patch by Heikki Linnakangas, original trouble report by John Smith.
rows will normally never obtain an XID at all. We already did things this way
for subtransactions, but this patch extends the concept to top-level
transactions. In applications where there are lots of short read-only
transactions, this should improve performance noticeably; not so much from
removal of the actual XID-assignments, as from reduction of overhead that's
driven by the rate of XID consumption. We add a concept of a "virtual
transaction ID" so that active transactions can be uniquely identified even
if they don't have a regular XID. This is a much lighter-weight concept:
uniqueness of VXIDs is only guaranteed over the short term, and no on-disk
record is made about them.
Florian Pflug, with some editorialization by Tom.
named pg_toast_temp_nnn, alongside the pg_temp_nnn schemas used for the temp
tables themselves. This allows low-level code such as the relcache to
recognize that these tables are indeed temporary, which enables various
optimizations such as not WAL-logging changes and using local rather than
shared buffers for access. Aside from obvious performance benefits, this
provides a solution to bug #3483, in which other backends unexpectedly held
open file references to temporary tables. The scheme preserves the property
that TOAST tables are not in any schema that's normally in the search path,
so they don't conflict with user table names.
initdb forced because of changes in system view definitions.
within a signal handler (this might be safe given the relatively narrow code
range in which the interrupt is enabled, but it seems awfully risky); do issue
more informative log messages that tell what is being waited for and the exact
length of the wait; minor other code cleanup. Greg Stark and Tom Lane
the rel, it's easy to get rid of the narrow race-condition window that
used to exist in VACUUM and CLUSTER. Did some minor code-beautification
work in the same area, too.
(table or index) before trying to open its relcache entry. This fixes
race conditions in which someone else commits a change to the relation's
catalog entries while we are in process of doing relcache load. Problems
of that ilk have been reported sporadically for years, but it was not
really practical to fix until recently --- for instance, the recent
addition of WAL-log support for in-place updates helped.
Along the way, remove pg_am.amconcurrent: all AMs are now expected to support
concurrent update.
The former approach used ExclusiveLock on pg_database, which being a
cluster-wide lock meant only one of these operations could proceed at
a time; worse, it also blocked all incoming connections in ReverifyMyDatabase.
Now that we have LockSharedObject(), we can use locks of different types
applied to databases considered as objects. This allows much more
flexible management of the interlocking: two CREATE DATABASEs need not
block each other, and need not block connections except to the template
database being used. Similarly DROP DATABASE doesn't block unrelated
operations. The locking used in flatfiles.c is also much narrower in
scope than before. Per recent proposal.
transaction as aborted. Since we only call XactLockTableWait on XIDs
that we believe to be currently running, the odds of this code ever
actually firing are minimal. It's certainly unnecessary, since a
transaction that's not either running or committed will be presumed
aborted anyway. What's more, it's not hard to imagine scenarios where
this could result in corrupting pg_clog: for instance, if a bogus XID
somehow got passed to XactLockTableWait. I think the code probably
dates from the ancient era when we didn't have TransactionIdIsInProgress;
back then it may have been necessary, but now I think it's a waste of
cycles and potentially dangerous. Per discussion with Qingqing Zhou
and Karsten Hilbert.
the data defining the semantics of a lock method (ie, conflict resolution
table and ancillary data, which is all constant) and the hash tables
storing the current state. The only thing we give up by this is the
ability to use separate hashtables for different lock methods, but there
is no need for that anyway. Put some extra fields into the LockMethod
definition structs to clean up some other uglinesses, like hard-wired
tests for DEFAULT_LOCKMETHOD and USER_LOCKMETHOD. This commit doesn't
do anything about the performance issues we were discussing, but it clears
away some of the underbrush that's in the way of fixing that.
