This is in preparation for splitting WaitEventSet related functions to
a separate source file. That will hide the details of WaitEventSet
from WaitLatch, so it must use an exposed function instead of
modifying WaitEventSet->exit_on_postmaster_death directly.
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/8a507fb6-df28-49d3-81a5-ede180d7f0fb@iki.fi
9d9b9d46f3 has added spinlocks to protect the fields in ProcSignal
flags, introducing a code path in ProcSignalInit() where a spinlock
could be released twice if the pss_pid field of a ProcSignalSlot is
found as already set. Multiple spinlock releases have no effect with
most spinlock implementations, but this could cause the code to run into
issues when the spinlock is acquired concurrently by a different
process.
This sanity check on pss_pid generates a LOG that can be delayed until
after the spinlock is released as, like older versions up to v17, the
code expects the initialization of the ProcSignalSlot to happen even if
pss_pid is found incorrect. The code is changed so as the old pss_pid
is read while holding the slot's spinlock, with the LOG from the sanity
check generated after releasing the spinlock, preventing the double
release.
Author: Maksim Melnikov <m.melnikov@postgrespro.ru>
Co-authored-by: Maxim Orlov <orlovmg@gmail.com>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Discussion: https://postgr.es/m/dca47527-2d8b-4e3b-b5a0-e2deb73371a4@postgrespro.ru
If a WaitEventSetWait() caller asks for multiple events, an already set
latch would previously prevent other events from being reported at the
same time. Now, we'll also poll the kernel for other events that would
fit in the caller's output buffer with a zero wait time. This policy
change doesn't affect callers that ask for only one event.
The main caller affected is the postmaster. If its latch is set
extremely frequently by backends launching workers and workers exiting,
we don't want it to handle only those jobs and ignore incoming client
connections.
Back-patch to 16 where the postmaster began using the API. The
fast-return policy changed here is older than that, but doesn't cause
any known problems in earlier releases.
Reported-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://postgr.es/m/Z1n5UpAiGDmFcMmd%40nathan
Commit 34486b609 effectively redefined isBackgroundWorker as meaning
"not a regular backend", whereas before it had the narrower
meaning of AmBackgroundWorkerProcess(). For clarity, rename the
field to isRegularBackend and invert its sense.
Discussion: https://postgr.es/m/1808397.1735156190@sss.pgh.pa.us
Cause parallel workers to not check datallowconn, rolcanlogin, and
ACL_CONNECT privileges. The leader already checked these things
(except for rolcanlogin which might have been checked for a different
role). Re-checking can accomplish little except to induce unexpected
failures in applications that might not even be aware that their query
has been parallelized. We already had the principle that parallel
workers rely on their leader to pass a valid set of authorization
information, so this change just extends that a bit further.
Also, modify the ReservedConnections, datconnlimit and rolconnlimit
logic so that these limits are only enforced against regular backends,
and only regular backends are counted while checking if the limits
were already reached. Previously, background processes that had an
assigned database or role were subject to these limits (with rather
random exclusions for autovac workers and walsenders), and the set of
existing processes that counted against each limit was quite haphazard
as well. The point of these limits, AFAICS, is to ensure the
availability of PGPROC slots for regular backends. Since all other
types of processes have their own separate pools of PGPROC slots, it
makes no sense either to enforce these limits against them or to count
them while enforcing the limit.
While edge-case failures of these sorts have been possible for a
long time, the problem got a good deal worse with commit 5a2fed911
(CVE-2024-10978), which caused parallel workers to make some of these
checks using the leader's current role where before we had used its
AuthenticatedUserId, thus allowing parallel queries to fail after
SET ROLE. The previous behavior was fairly accidental and I have
no desire to return to it.
This patch includes reverting 73c9f91a1, which was an emergency hack
to suppress these same checks in some cases. It wasn't complete,
as shown by a recent bug report from Laurenz Albe. We can also revert
fd4d93d26 and 492217301, which hacked around the same problems in one
regression test.
In passing, remove the special case for autovac workers in
CheckMyDatabase; it seems cleaner to have AutoVacWorkerMain pass
the INIT_PG_OVERRIDE_ALLOW_CONNS flag, now that that does what's
needed.
Like 5a2fed911, back-patch to supported branches (which sadly no
longer includes v12).
Discussion: https://postgr.es/m/1808397.1735156190@sss.pgh.pa.us
Remove the 'whenTaken' and 'lsn' fields from SnapshotData. After the
removal of the "snapshot too old" feature, they were never set to a
non-zero value.
This largely reverts commit 3e2f3c2e42, which added the
OldestActiveSnapshot tracking, and the init_toast_snapshot()
function. That was only required for setting the 'whenTaken' and 'lsn'
fields. SnapshotToast is now a constant again, like SnapshotSelf and
SnapshotAny. I kept a thin get_toast_snapshot() wrapper around
SnapshotToast though, to check that you have a registered or active
snapshot. That's still a useful sanity check.
Reviewed-by: Nathan Bossart, Andres Freund, Tom Lane
Discussion: https://www.postgresql.org/message-id/cd4b4f8c-e63a-41c0-95f6-6e6cd9b83f6d@iki.fi
Commit ccd38024bc, which introduced the pg_signal_autovacuum_worker
role, added a call to pgstat_get_beentry_by_proc_number() for the
purpose of determining whether the process is an autovacuum worker.
This function calls pgstat_read_current_status(), which can be
fairly expensive and may return cached, out-of-date information.
Since we just need to look up the target backend's BackendType, and
we already know its ProcNumber, we can instead inspect the
BackendStatusArray directly, which is much less expensive and
possibly more up-to-date. There are some caveats with this
approach (which are documented in the code), but it's still
substantially better than before.
Reported-by: Andres Freund
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/ujenaa2uabzfkwxwmfifawzdozh3ljr7geozlhftsuosgm7n7q%40g3utqqyyosb6
The error messages in CreateWaitEventSet() made it hard to know whether the
syscall or AcquireExternalFD() failed. This is particularly relevant because
AcquireExternalFD() imposes a lower limit than what would cause syscalls fail
with EMFILE.
I did not change the message in libpqsrv_connect_prepare(), which is the one
other use of AcquireExternalFD() in our codebase, as the error message already
is less ambiguous.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/xjjx7r4xa7beixuu4qtkdhnwdbchrrpo3gaeb3jsbinvvdiat5@cwjw55mna5of
Previously, only backends, autovacuum workers, and background workers
had an entry in the PMChildFlags array. With this commit, all
postmaster child processes, including all the aux processes, have an
entry. Dead-end backends still don't get an entry, though, and other
processes that don't touch shared memory will never mark their
PMChildFlags entry as active.
We now maintain separate freelists for different kinds of child
processes. That ensures that there are always slots available for
autovacuum and background workers. Previously, pre-authentication
backends could prevent autovacuum or background workers from starting
up, by using up all the slots.
The code to manage the slots in the postmaster process is in a new
pmchild.c source file. Because postmaster.c is just so large.
Assigning pmsignal slot numbers is now pmchild.c's responsibility.
This replaces the PMChildInUse array in pmsignal.c.
Some of the comments in postmaster.c still talked about the "stats
process", but that was removed in commit 5891c7a8ed. Fix those while
we're at it.
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/a102f15f-eac4-4ff2-af02-f9ff209ec66f@iki.fi
3c5db1d6b implemented the pg_wal_replay_wait() stored procedure. Due to
the patch development history, the implementation resided in
src/backend/commands/waitlsn.c (src/include/commands/waitlsn.h for headers).
014f9f34d moved pg_wal_replay_wait() itself to
src/backend/access/transam/xlogfuncs.c near to the WAL-manipulation functions.
But most of the implementation stayed in place.
The code in src/backend/commands/waitlsn.c has nothing to do with commands,
but is related to WAL. So, this commit moves this code into
src/backend/access/transam/xlogwait.c (src/include/access/xlogwait.h for
headers).
Reported-by: Peter Eisentraut
Discussion: https://postgr.es/m/18c0fa64-0475-415e-a1bd-665d922c5201%40eisentraut.org
Reviewed-by: Pavel Borisov
This seems nicer than having to duplicate the logic between
InitProcess() and ProcKill() for which child processes have a
PMChildFlags slot.
Move the MarkPostmasterChildActive() call earlier in InitProcess(),
out of the section protected by the spinlock.
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/a102f15f-eac4-4ff2-af02-f9ff209ec66f@iki.fi
Replace the fixed-size array of fast-path locks with arrays, sized on
startup based on max_locks_per_transaction. This allows using fast-path
locking for workloads that need more locks.
The fast-path locking introduced in 9.2 allowed each backend to acquire
a small number (16) of weak relation locks cheaply. If a backend needs
to hold more locks, it has to insert them into the shared lock table.
This is considerably more expensive, and may be subject to contention
(especially on many-core systems).
The limit of 16 fast-path locks was always rather low, because we have
to lock all relations - not just tables, but also indexes, views, etc.
For planning we need to lock all relations that might be used in the
plan, not just those that actually get used in the final plan. So even
with rather simple queries and schemas, we often need significantly more
than 16 locks.
As partitioning gets used more widely, and the number of partitions
increases, this limit is trivial to hit. Complex queries may easily use
hundreds or even thousands of locks. For workloads doing a lot of I/O
this is not noticeable, but for workloads accessing only data in RAM,
the access to the shared lock table may be a serious issue.
This commit removes the hard-coded limit of the number of fast-path
locks. Instead, the size of the fast-path arrays is calculated at
startup, and can be set much higher than the original 16-lock limit.
The overall fast-path locking protocol remains unchanged.
The variable-sized fast-path arrays can no longer be part of PGPROC, but
are allocated as a separate chunk of shared memory and then references
from the PGPROC entries.
The fast-path slots are organized as a 16-way set associative cache. You
can imagine it as a hash table of 16-slot "groups". Each relation is
mapped to exactly one group using hash(relid), and the group is then
processed using linear search, just like the original fast-path cache.
With only 16 entries this is cheap, with good locality.
Treating this as a simple hash table with open addressing would not be
efficient, especially once the hash table gets almost full. The usual
remedy is to grow the table, but we can't do that here easily. The
access would also be more random, with worse locality.
The fast-path arrays are sized using the max_locks_per_transaction GUC.
We try to have enough capacity for the number of locks specified in the
GUC, using the traditional 2^n formula, with an upper limit of 1024 lock
groups (i.e. 16k locks). The default value of max_locks_per_transaction
is 64, which means those instances will have 64 fast-path slots.
The main purpose of the max_locks_per_transaction GUC is to size the
shared lock table. It is often set to the "average" number of locks
needed by backends, with some backends using significantly more locks.
This should not be a major issue, however. Some backens may have to
insert locks into the shared lock table, but there can't be too many of
them, limiting the contention.
The only solution is to increase the GUC, even if the shared lock table
already has sufficient capacity. That is not free, especially in terms
of memory usage (the shared lock table entries are fairly large). It
should only happen on machines with plenty of memory, though.
In the future we may consider a separate GUC for the number of fast-path
slots, but let's try without one first.
Reviewed-by: Robert Haas, Jakub Wartak
Discussion: https://postgr.es/m/510b887e-c0ce-4a0c-a17a-2c6abb8d9a5c@enterprisedb.com
To make them follow the usual naming convention where
FoobarShmemSize() calculates the amount of shared memory needed by
Foobar subsystem, and FoobarShmemInit() performs the initialization.
I didn't rename CreateLWLocks() and InitShmmeIndex(), because they are
a little special. They need to be called before any of the other
ShmemInit() functions, because they set up the shared memory
bookkeeping itself. I also didn't rename InitProcGlobal(), because
unlike other Shmeminit functions, it's not called by individual
backends.
Reviewed-by: Andreas Karlsson
Discussion: https://www.postgresql.org/message-id/c09694ff-2453-47e5-b26c-32a16cd75ce6@iki.fi
Split the shared and local initialization to separate functions, and
follow the common naming conventions. With this, we no longer create
the LockMethodLocalHash hash table in the postmaster process, which
was always pointless.
Reviewed-by: Andreas Karlsson
Discussion: https://www.postgresql.org/message-id/c09694ff-2453-47e5-b26c-32a16cd75ce6@iki.fi
pg_wal_replay_wait() is to be used on standby and specifies waiting for
the specific WAL location to be replayed. This option is useful when
the user makes some data changes on primary and needs a guarantee to see
these changes are on standby.
The queue of waiters is stored in the shared memory as an LSN-ordered pairing
heap, where the waiter with the nearest LSN stays on the top. During
the replay of WAL, waiters whose LSNs have already been replayed are deleted
from the shared memory pairing heap and woken up by setting their latches.
pg_wal_replay_wait() needs to wait without any snapshot held. Otherwise,
the snapshot could prevent the replay of WAL records, implying a kind of
self-deadlock. This is why it is only possible to implement
pg_wal_replay_wait() as a procedure working without an active snapshot,
not a function.
Catversion is bumped.
Discussion: https://postgr.es/m/eb12f9b03851bb2583adab5df9579b4b%40postgrespro.ru
Author: Kartyshov Ivan, Alexander Korotkov
Reviewed-by: Michael Paquier, Peter Eisentraut, Dilip Kumar, Amit Kapila
Reviewed-by: Alexander Lakhin, Bharath Rupireddy, Euler Taveira
Reviewed-by: Heikki Linnakangas, Kyotaro Horiguchi
Commit 9d9b9d46f3 added spinlocks to protect the fields in ProcSignal
flags, but in EmitProcSignalBarrier(), the spinlock was released
twice. With most spinlock implementations, releasing a lock that's not
held is not easy to notice, because most of the time it does nothing,
but if the spinlock was concurrently acquired by another process, it
could lead to more serious issues. Fortunately, with the
--disable-spinlocks emulation implementation, it caused more visible
failures.
In the passing, fix a type in comment and add an assertion that the
procNumber passed to SendProcSignal looks valid.
Discussion: https://www.postgresql.org/message-id/b8ce284c-18a2-4a79-afd3-1991a2e7d246@iki.fi
Move responsibility of generating the cancel key to the backend
process. The cancel key is now generated after forking, and the
backend advertises it in the ProcSignal array. When a cancel request
arrives, the backend handling it scans the ProcSignal array to find
the target pid and cancel key. This is similar to how this previously
worked in the EXEC_BACKEND case with the ShmemBackendArray, just
reusing the ProcSignal array.
One notable change is that we no longer generate cancellation keys for
non-backend processes. We generated them before just to prevent a
malicious user from canceling them; the keys for non-backend processes
were never actually given to anyone. There is now an explicit flag
indicating whether a process has a valid key or not.
I wrote this originally in preparation for supporting longer cancel
keys, but it's a nice cleanup on its own.
Reviewed-by: Jelte Fennema-Nio
Discussion: https://www.postgresql.org/message-id/508d0505-8b7a-4864-a681-e7e5edfe32aa@iki.fi
The documentation for System V IPC parameters provides complicated
formulas to determine the appropriate values for SEMMNI and SEMMNS.
Furthermore, these formulas have often been wrong because folks
forget to update them (e.g., when adding a new auxiliary process).
This commit introduces a new runtime-computed GUC named
num_os_semaphores that reports the number of semaphores needed for
the configured number of allowed connections, worker processes,
etc. This new GUC allows us to simplify the formulas in the
documentation, and it should help prevent future inaccuracies.
Like the other runtime-computed GUCs, users can view it with
"postgres -C" before starting the server, which is useful for
preconfiguring the necessary operating system resources.
Reviewed-by: Tom Lane, Sami Imseih, Andres Freund, Robert Haas
Discussion: https://postgr.es/m/20240517164452.GA1914161%40nathanxps13
Winsock only signals an FD_CLOSE event once if the other end of the
socket shuts down gracefully. Because each WaitLatchOrSocket() call
constructs and destroys a new event handle every time, with unlucky
timing we can lose it and hang. We get away with this only if the other
end disconnects non-gracefully, because FD_CLOSE is repeatedly signaled
in that case.
To fix this design flaw in our Windows socket support fundamentally,
we'd probably need to rearchitect it so that a single event handle
exists for the lifetime of a socket, or switch to completely different
multiplexing or async I/O APIs. That's going to be a bigger job
and probably wouldn't be back-patchable.
This brute force kludge closes the race by explicitly polling with
MSG_PEEK before sleeping.
Back-patch to all supported releases. This should hopefully clear up
some random build farm and CI hang failures reported over the years. It
might also allow us to try using graceful shutdown in more places again
(reverted in commit 29992a6) to fix instability in the transmission of
FATAL error messages, but that isn't done by this commit.
Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Tested-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/176008.1715492071%40sss.pgh.pa.us
Since commit 3a9b18b309, roles with privileges of pg_signal_backend
cannot signal autovacuum workers. Many users treated the ability
to signal autovacuum workers as a feature instead of a bug, so we
are reintroducing it via a new predefined role. Having privileges
of this new role, named pg_signal_autovacuum_worker, only permits
signaling autovacuum workers. It does not permit signaling other
types of superuser backends.
Bumps catversion.
Author: Kirill Reshke
Reviewed-by: Anthony Leung, Michael Paquier, Andrey Borodin
Discussion: https://postgr.es/m/CALdSSPhC4GGmbnugHfB9G0%3DfAxjCSug_-rmL9oUh0LTxsyBfsg%40mail.gmail.com
e85662df44 made GetRunningTransactionData() calculate the oldest running
transaction id within the current database. This commit optimized this
calculation by performing a cheap transaction id comparison before fetching
the process database id, while the latter could cause extra cache misses.
Reported-by: Noah Misch
Discussion: https://postgr.es/m/20240630231816.bf.nmisch%40google.com
e85662df44 made GetRunningTransactionData() calculate the oldest running
transaction id within the current database. However, because of the typo,
the new code uses oldestRunningXid instead of oldestDatabaseRunningXid
in comparison before updating oldestDatabaseRunningXid. This commit fixes
that issue.
Reported-by: Noah Misch
Discussion: https://postgr.es/m/20240630231816.bf.nmisch%40google.com
Backpatch-through: 17
We did not recover the subtransaction IDs of prepared transactions
when starting a hot standby from a shutdown checkpoint. As a result,
such subtransactions were considered as aborted, rather than
in-progress. That would lead to hint bits being set incorrectly, and
the subtransactions suddenly becoming visible to old snapshots when
the prepared transaction was committed.
To fix, update pg_subtrans with prepared transactions's subxids when
starting hot standby from a shutdown checkpoint. The snapshots taken
from that state need to be marked as "suboverflowed", so that we also
check the pg_subtrans.
Backport to all supported versions.
Discussion: https://www.postgresql.org/message-id/6b852e98-2d49-4ca1-9e95-db419a2696e0@iki.fi
Specifically, it terminates a background worker even if the caller
couldn't terminate the background worker with pg_terminate_backend().
Commit 3a9b18b309 neglected to update
this. Back-patch to v13, which introduced DROP DATABASE FORCE.
Reviewed by Amit Kapila. Reported by Kirill Reshke.
Discussion: https://postgr.es/m/20240429212756.60.nmisch@google.com
GlobalVisTestNonRemovableHorizon() was only used for the implementation of
snapshot_too_old, which was removed in f691f5b80a. As using
GlobalVisTestNonRemovableHorizon() is not particularly efficient, no new uses
for it should be added. Therefore remove.
Discussion: https://postgr.es/m/20240415185720.q4dg4dlcyvvrabz4@awork3.anarazel.de
Execute both freezing and pruning of tuples in the same
heap_page_prune() function, now called heap_page_prune_and_freeze(),
and emit a single WAL record containing all changes. That reduces the
overall amount of WAL generated.
This moves the freezing logic from vacuumlazy.c to the
heap_page_prune_and_freeze() function. The main difference in the
coding is that in vacuumlazy.c, we looked at the tuples after the
pruning had already happened, but in heap_page_prune_and_freeze() we
operate on the tuples before pruning. The heap_prepare_freeze_tuple()
function is now invoked after we have determined that a tuple is not
going to be pruned away.
VACUUM no longer needs to loop through the items on the page after
pruning. heap_page_prune_and_freeze() does all the work. It now
returns the list of dead offsets, including existing LP_DEAD items, to
the caller. Similarly it's now responsible for tracking 'all_visible',
'all_frozen', and 'hastup' on the caller's behalf.
Author: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://www.postgresql.org/message-id/20240330055710.kqg6ii2cdojsxgje@liskov
pg_wal_replay_wait() is to be used on standby and specifies waiting for
the specific WAL location to be replayed before starting the transaction.
This option is useful when the user makes some data changes on primary and
needs a guarantee to see these changes on standby.
The queue of waiters is stored in the shared memory array sorted by LSN.
During replay of WAL waiters whose LSNs are already replayed are deleted from
the shared memory array and woken up by setting of their latches.
pg_wal_replay_wait() needs to wait without any snapshot held. Otherwise,
the snapshot could prevent the replay of WAL records implying a kind of
self-deadlock. This is why it is only possible to implement
pg_wal_replay_wait() as a procedure working in a non-atomic context,
not a function.
Catversion is bumped.
Discussion: https://postgr.es/m/eb12f9b03851bb2583adab5df9579b4b%40postgrespro.ru
Author: Kartyshov Ivan, Alexander Korotkov
Reviewed-by: Michael Paquier, Peter Eisentraut, Dilip Kumar, Amit Kapila
Reviewed-by: Alexander Lakhin, Bharath Rupireddy, Euler Taveira
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
as determined by include-what-you-use (IWYU)
While IWYU also suggests to *add* a bunch of #include's (which is its
main purpose), this patch does not do that. In some cases, a more
specific #include replaces another less specific one.
Some manual adjustments of the automatic result:
- IWYU currently doesn't know about includes that provide global
variable declarations (like -Wmissing-variable-declarations), so
those includes are being kept manually.
- All includes for port(ability) headers are being kept for now, to
play it safe.
- No changes of catalog/pg_foo.h to catalog/pg_foo_d.h, to keep the
patch from exploding in size.
Note that this patch touches just *.c files, so nothing declared in
header files changes in hidden ways.
As a small example, in src/backend/access/transam/rmgr.c, some IWYU
pragma annotations are added to handle a special case there.
Discussion: https://www.postgresql.org/message-id/flat/af837490-6b2f-46df-ba05-37ea6a6653fc%40eisentraut.org
Remove IsBackgroundWorker, IsAutoVacuumLauncherProcess(),
IsAutoVacuumWorkerProcess(), and IsLogicalSlotSyncWorker() in favor of
new Am*Process() macros that use MyBackendType. For consistency with
the existing Am*Process() macros.
Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/f3ecd4cb-85ee-4e54-8278-5fabfb3a4ed0@iki.fi
Now that BackendId was just another index into the proc array, it was
redundant with the 0-based proc numbers used in other places. Replace
all usage of backend IDs with proc numbers.
The only place where the term "backend id" remains is in a few pgstat
functions that expose backend IDs at the SQL level. Those IDs are now
in fact 0-based ProcNumbers too, but the documentation still calls
them "backend ids". That term still seems appropriate to describe what
the numbers are, so I let it be.
One user-visible effect is that pg_temp_0 is now a valid temp schema
name, for backend with ProcNumber 0.
Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/8171f1aa-496f-46a6-afc3-c46fe7a9b407@iki.fi
Previously, backend ID was an index into the ProcState array, in the
shared cache invalidation manager (sinvaladt.c). The entry in the
ProcState array was reserved at backend startup by scanning the array
for a free entry, and that was also when the backend got its backend
ID. Things become slightly simpler if we redefine backend ID to be the
index into the PGPROC array, and directly use it also as an index to
the ProcState array. This uses a little more memory, as we reserve a
few extra slots in the ProcState array for aux processes that don't
need them, but the simplicity is worth it.
Aux processes now also have a backend ID. This simplifies the
reservation of BackendStatusArray and ProcSignal slots.
You can now convert a backend ID into an index into the PGPROC array
simply by subtracting 1. We still use 0-based "pgprocnos" in various
places, for indexes into the PGPROC array, but the only difference now
is that backend IDs start at 1 while pgprocnos start at 0. (The next
commmit will get rid of the term "backend ID" altogether and make
everything 0-based.)
There is still a 'backendId' field in PGPROC, now part of 'vxid' which
encapsulates the backend ID and local transaction ID together. It's
needed for prepared xacts. For regular backends, the backendId is
always equal to pgprocno + 1, but for prepared xact PGPROC entries,
it's the ID of the original backend that processed the transaction.
Reviewed-by: Andres Freund, Reid Thompson
Discussion: https://www.postgresql.org/message-id/8171f1aa-496f-46a6-afc3-c46fe7a9b407@iki.fi
Presently, string keys are not well-supported for dshash tables.
The dshash code always copies key_size bytes into new entries'
keys, and dshash.h only provides compare and hash functions that
forward to memcmp() and tag_hash(), both of which do not stop at
the first NUL. This means that callers must pad string keys so
that the data beyond the first NUL does not adversely affect the
results of copying, comparing, and hashing the keys.
To better support string keys in dshash tables, this commit does
a couple things:
* A new copy_function field is added to the dshash_parameters
struct. This function pointer specifies how the key should be
copied into new table entries. For example, we only want to copy
up to the first NUL byte for string keys. A dshash_memcpy()
helper function is provided and used for all existing in-tree
dshash tables without string keys.
* A set of helper functions for string keys are provided. These
helper functions forward to strcmp(), strcpy(), and
string_hash(), all of which ignore data beyond the first NUL.
This commit also adjusts the DSM registry's dshash table to use the
new helper functions for string keys.
Reviewed-by: Andy Fan
Discussion: https://postgr.es/m/20240119215941.GA1322079%40nathanxps13
