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Commit 0563a3a8b changed how partition constraints were generated such
that this function no longer computes the mapping of parent attnos to
child attnos.
This is an external function that extensions could use, so this is
potentially a breaking change. No external callers are known, however,
and this will make it simpler to write such callers in the future.
Author: Hou Zhijie
Reviewed-by: David Rowley, Michael Paquier, Soumyadeep Chakraborty
Discussion: https://www.postgresql.org/message-id/flat/OS0PR01MB5716A75A45BE46101A1B489894379@OS0PR01MB5716.jpnprd01.prod.outlook.com
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Allow a partition be detached from its partitioned table without
blocking concurrent queries, by running in two transactions and only
requiring ShareUpdateExclusive in the partitioned table.
Because it runs in two transactions, it cannot be used in a transaction
block. This is the main reason to use dedicated syntax: so that users
can choose to use the original mode if they need it. But also, it
doesn't work when a default partition exists (because an exclusive lock
would still need to be obtained on it, in order to change its partition
constraint.)
In case the second transaction is cancelled or a crash occurs, there's
ALTER TABLE .. DETACH PARTITION .. FINALIZE, which executes the final
steps.
The main trick to make this work is the addition of column
pg_inherits.inhdetachpending, initially false; can only be set true in
the first part of this command. Once that is committed, concurrent
transactions that use a PartitionDirectory will include or ignore
partitions so marked: in optimizer they are ignored if the row is marked
committed for the snapshot; in executor they are always included. As a
result, and because of the way PartitionDirectory caches partition
descriptors, queries that were planned before the detach will see the
rows in the detached partition and queries that are planned after the
detach, won't.
A CHECK constraint is created that duplicates the partition constraint.
This is probably not strictly necessary, and some users will prefer to
remove it afterwards, but if the partition is re-attached to a
partitioned table, the constraint needn't be rechecked.
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/20200803234854.GA24158@alvherre.pgsql
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Backpatch-through: 9.5
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Backpatch-through: update all files in master, backpatch legal files through 9.4
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In the wake of commit 5b9312378, there's no particular reason
for this restriction (previously, it was problematic because of
the implied rowtype reference). A simple constraint on a whole-row
Var probably isn't that useful, but conceivably somebody would want
to pass one to a function that extracts a partitioning key. Besides
which, we're expending much more code to enforce the restriction than
we save by having it, since the latter quantity is now zero.
So drop the restriction.
Amit Langote
Discussion: https://postgr.es/m/CA+HiwqFUzjfj9HEsJtYWcr1SgQ_=iCAvQ=O2Sx6aQxoDu4OiHw@mail.gmail.com
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Formerly the rd_partkey and rd_partdesc data structures were always
populated immediately when a relcache entry was built or rebuilt.
This patch changes things so that they are populated only when they
are first requested. (Hence, callers *must* now always use
RelationGetPartitionKey or RelationGetPartitionDesc; just fetching
the pointer directly is no longer acceptable.)
This seems to have some performance benefits, but the main reason to do
it is that it eliminates a recursive-reload failure that occurs if the
partkey or partdesc expressions contain any references to the relation's
rowtype (as discovered by Amit Langote). In retrospect, since loading
these data structures might result in execution of nearly-arbitrary code
via eval_const_expressions, it was a dumb idea to require that to happen
during relcache entry rebuild.
Also, fix things so that old copies of a relcache partition descriptor
will be dropped when the cache entry's refcount goes to zero. In the
previous coding it was possible for such copies to survive for the
lifetime of the session, as I'd complained of in a previous discussion.
(This management technique still isn't perfect, but it's better than
before.) Improve the commentary explaining how that works and why
it's safe to hand out direct pointers to these relcache substructures.
In passing, improve RelationBuildPartitionDesc by using the same
memory-context-parent-swap approach used by RelationBuildPartitionKey,
thereby making it less dependent on strong assumptions about what
partition_bounds_copy does. Avoid doing get_rel_relkind in the
critical section, too.
Patch by Amit Langote and Tom Lane; Robert Haas deserves some credit
for prior work in the area, too. Although this is a pre-existing
problem, no back-patch: the patch seems too invasive to be safe to
back-patch, and the bug it fixes is a corner case that seems
relatively unlikely to cause problems in the field.
Discussion: https://postgr.es/m/CA+HiwqFUzjfj9HEsJtYWcr1SgQ_=iCAvQ=O2Sx6aQxoDu4OiHw@mail.gmail.com
Discussion: https://postgr.es/m/CA+TgmoY3bRmGB6-DUnoVy5fJoreiBJ43rwMrQRCdPXuKt4Ykaw@mail.gmail.com
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Originally, Postgres Lists were a more or less exact reimplementation of
Lisp lists, which consist of chains of separately-allocated cons cells,
each having a value and a next-cell link. We'd hacked that once before
(commit d0b4399d8) to add a separate List header, but the data was still
in cons cells. That makes some operations -- notably list_nth() -- O(N),
and it's bulky because of the next-cell pointers and per-cell palloc
overhead, and it's very cache-unfriendly if the cons cells end up
scattered around rather than being adjacent.
In this rewrite, we still have List headers, but the data is in a
resizable array of values, with no next-cell links. Now we need at
most two palloc's per List, and often only one, since we can allocate
some values in the same palloc call as the List header. (Of course,
extending an existing List may require repalloc's to enlarge the array.
But this involves just O(log N) allocations not O(N).)
Of course this is not without downsides. The key difficulty is that
addition or deletion of a list entry may now cause other entries to
move, which it did not before.
For example, that breaks foreach() and sister macros, which historically
used a pointer to the current cons-cell as loop state. We can repair
those macros transparently by making their actual loop state be an
integer list index; the exposed "ListCell *" pointer is no longer state
carried across loop iterations, but is just a derived value. (In
practice, modern compilers can optimize things back to having just one
loop state value, at least for simple cases with inline loop bodies.)
In principle, this is a semantics change for cases where the loop body
inserts or deletes list entries ahead of the current loop index; but
I found no such cases in the Postgres code.
The change is not at all transparent for code that doesn't use foreach()
but chases lists "by hand" using lnext(). The largest share of such
code in the backend is in loops that were maintaining "prev" and "next"
variables in addition to the current-cell pointer, in order to delete
list cells efficiently using list_delete_cell(). However, we no longer
need a previous-cell pointer to delete a list cell efficiently. Keeping
a next-cell pointer doesn't work, as explained above, but we can improve
matters by changing such code to use a regular foreach() loop and then
using the new macro foreach_delete_current() to delete the current cell.
(This macro knows how to update the associated foreach loop's state so
that no cells will be missed in the traversal.)
There remains a nontrivial risk of code assuming that a ListCell *
pointer will remain good over an operation that could now move the list
contents. To help catch such errors, list.c can be compiled with a new
define symbol DEBUG_LIST_MEMORY_USAGE that forcibly moves list contents
whenever that could possibly happen. This makes list operations
significantly more expensive so it's not normally turned on (though it
is on by default if USE_VALGRIND is on).
There are two notable API differences from the previous code:
* lnext() now requires the List's header pointer in addition to the
current cell's address.
* list_delete_cell() no longer requires a previous-cell argument.
These changes are somewhat unfortunate, but on the other hand code using
either function needs inspection to see if it is assuming anything
it shouldn't, so it's not all bad.
Programmers should be aware of these significant performance changes:
* list_nth() and related functions are now O(1); so there's no
major access-speed difference between a list and an array.
* Inserting or deleting a list element now takes time proportional to
the distance to the end of the list, due to moving the array elements.
(However, it typically *doesn't* require palloc or pfree, so except in
long lists it's probably still faster than before.) Notably, lcons()
used to be about the same cost as lappend(), but that's no longer true
if the list is long. Code that uses lcons() and list_delete_first()
to maintain a stack might usefully be rewritten to push and pop at the
end of the list rather than the beginning.
* There are now list_insert_nth...() and list_delete_nth...() functions
that add or remove a list cell identified by index. These have the
data-movement penalty explained above, but there's no search penalty.
* list_concat() and variants now copy the second list's data into
storage belonging to the first list, so there is no longer any
sharing of cells between the input lists. The second argument is
now declared "const List *" to reflect that it isn't changed.
This patch just does the minimum needed to get the new implementation
in place and fix bugs exposed by the regression tests. As suggested
by the foregoing, there's a fair amount of followup work remaining to
do.
Also, the ENABLE_LIST_COMPAT macros are finally removed in this
commit. Code using those should have been gone a dozen years ago.
Patch by me; thanks to David Rowley, Jesper Pedersen, and others
for review.
Discussion: https://postgr.es/m/11587.1550975080@sss.pgh.pa.us
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The original coding of generate_partition_qual() just copied the list
of predicate expressions into the global CacheMemoryContext, making it
effectively impossible to clean up when the owning relcache entry is
destroyed --- the relevant code in RelationDestroyRelation() only managed
to free the topmost List header :-(. This resulted in a session-lifespan
memory leak whenever a table partition's relcache entry is rebuilt.
Fortunately, that's not normally a large data structure, and rebuilds
shouldn't occur all that often in production situations; but this is
still a bug worth fixing back to v10 where the code was introduced.
To fix, put the cached expression tree into its own small memory context,
as we do with other complicated substructures of relcache entries.
Also, deal more honestly with the case that a partition has an empty
partcheck list; while that probably isn't a case that's very interesting
for production use, it's legal.
In passing, clarify comments about how partitioning-related relcache
data structures are managed, and add some Asserts that we're not leaking
old copies when we overwrite these data fields.
Amit Langote and Tom Lane
Discussion: https://postgr.es/m/7961.1552498252@sss.pgh.pa.us
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This is an SQL-standard feature that allows creating columns that are
computed from expressions rather than assigned, similar to a view or
materialized view but on a column basis.
This implements one kind of generated column: stored (computed on
write). Another kind, virtual (computed on read), is planned for the
future, and some room is left for it.
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com
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This is similar in spirit to the existing partbounds.c file in the
same directory, except that there's a lot less code in the new file
created by this commit. Pending work in this area proposes to add a
bunch more code related to PartitionDescs, though, and this will give
us a good place to put it.
Discussion: http://postgr.es/m/CA+TgmoZUwPf_uanjF==gTGBMJrn8uCq52XYvAEorNkLrUdoawg@mail.gmail.com
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Create a new header optimizer/optimizer.h, which exposes just the
planner functions that can be used "at arm's length", without need
to access Paths or the other planner-internal data structures defined
in nodes/relation.h. This is intended to provide the whole planner
API seen by most of the rest of the system; although FDWs still need
to use additional stuff, and more thought is also needed about just
what selfuncs.c should rely on.
The main point of doing this now is to limit the amount of new
#include baggage that will be needed by "planner support functions",
which I expect to introduce later, and which will be in relevant
datatype modules rather than anywhere near the planner.
This commit just moves relevant declarations into optimizer.h from
other header files (a couple of which go away because everything
got moved), and adjusts #include lists to match. There's further
cleanup that could be done if we want to decide that some stuff
being exposed by optimizer.h doesn't belong in the planner at all,
but I'll leave that for another day.
Discussion: https://postgr.es/m/11460.1548706639@sss.pgh.pa.us
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A lot of files only included heapam.h for relation_open, heap_open etc
- replace the heapam.h include in those files with the narrower
header.
Author: Andres Freund
Discussion: https://postgr.es/m/20190111000539.xbv7s6w7ilcvm7dp@alap3.anarazel.de
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Backpatch-through: certain files through 9.4
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The 'partoids' list which was constructed by the previous version
of this code was necessarily identical to 'inhoids'. There's no
point to duplicating the list, so avoid that. Instead, construct
the array representation directly from the original 'inhoids' list.
Also, use an array rather than a list for 'boundspecs'. We know
exactly how many items we need to store, so there's really no
reason to use a list. Using an array instead reduces the number
of memory allocations we perform.
Patch by me, reviewed by Michael Paquier and Amit Langote, the
latter of whom also helped with rebasing.
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This speeds up write operations (INSERT, UPDATE, DELETE, COPY, as well
as the future MERGE) on partitioned tables.
This changes the setup for tuple routing so that it does far less work
during the initial setup and pushes more work out to when partitions
receive tuples. PartitionDispatchData structs for sub-partitioned
tables are only created when a tuple gets routed through it. The
possibly large arrays in the PartitionTupleRouting struct have largely
been removed. The partitions[] array remains but now never contains any
NULL gaps. Previously the NULLs had to be skipped during
ExecCleanupTupleRouting(), which could add a large overhead to the
cleanup when the number of partitions was large. The partitions[] array
is allocated small to start with and only enlarged when we route tuples
to enough partitions that it runs out of space. This allows us to keep
simple single-row partition INSERTs running quickly. Redesign
The arrays in PartitionTupleRouting which stored the tuple translation maps
have now been removed. These have been moved out into a
PartitionRoutingInfo struct which is an additional field in ResultRelInfo.
The find_all_inheritors() call still remains by far the slowest part of
ExecSetupPartitionTupleRouting(). This commit just removes the other slow
parts.
In passing also rename the tuple translation maps from being ParentToChild
and ChildToParent to being RootToPartition and PartitionToRoot. The old
names mislead you into thinking that a partition of some sub-partitioned
table would translate to the rowtype of the sub-partitioned table rather
than the root partitioned table.
Authors: David Rowley and Amit Langote, heavily revised by Álvaro Herrera
Testing help from Jesper Pedersen and Kato Sho.
Discussion: https://postgr.es/m/CAKJS1f_1RJyFquuCKRFHTdcXqoPX-PYqAd7nz=GVBwvGh4a6xA@mail.gmail.com
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The code building PartitionBoundInfo based on the constituent partition
data read from catalogs has been located in partcache.c, with a specific
set of routines dedicated to bound types, like sorting or bound data
creation. All this logic is moved to partbounds.c and relocates all the
bound-specific logistic into it, with partition_bounds_create() as
principal entry point.
Author: Amit Langote
Reviewed-by: Michael Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/3f289da8-6d10-75fe-814a-635e8b191d43@lab.ntt.co.jp
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It failed if passed a nonexistent relation OID, or one that was a non-heap
relation, because of blindly applying heap_open to a user-supplied OID.
This is not OK behavior for a SQL-exposed function; we have a project
policy that we should return NULL in such cases. Moreover, since
pg_get_partition_constraintdef ought now to work on indexes, restricting
it to heaps is flat wrong anyway.
The underlying function generate_partition_qual() wasn't on board with
indexes having partition quals either, nor for that matter with rels
having relispartition set but yet null relpartbound. (One wonders
whether the person who wrote the function comment blocks claiming that
these functions allow a missing relpartbound had ever tested it.)
Fix by testing relispartition before opening the rel, and by using
relation_open not heap_open. (If any other relkinds ever grow the
ability to have relispartition set, the code will work with them
automatically.) Also, don't reject null relpartbound in
generate_partition_qual.
Back-patch to v11, and all but the null-relpartbound change to v10.
(It's not really necessary to change generate_partition_qual at all
in v10, but I thought s/heap_open/relation_open/ would be a good
idea anyway just to keep the code in sync with later branches.)
Per report from Justin Pryzby.
Discussion: https://postgr.es/m/20180927200020.GJ776@telsasoft.com
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In the original code, we were storing the pg_inherits row for a
partitioned table too early: enough that we had a hack for relcache to
avoid falling flat on its face while reading such a partial entry. If
we finish the pg_class creation first and *then* store the pg_inherits
entry, we don't need that hack.
Also recognize that pg_class.relpartbound is not marked NOT NULL and
therefore it's entirely possible to read null values, so having only
Assert() protection isn't enough. Change those to if/elog tests
instead. This qualifies as a robustness fix, so backpatch to pg11.
In passing, remove one access that wasn't actually needed, and reword
one message to be like all the others that check for the same thing.
Reviewed-by: Amit Langote
Discussion: https://postgr.es/m/20180903213916.hh6wasnrdg6xv2ud@alvherre.pgsql
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"compute_hash_value" is particularly gratuitously generic, but IMO
all of these ought to have names clearly related to partitioning.
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There's been a massive addition of partitioning code in PostgreSQL 11,
with little oversight on its placement, resulting in a
catalog/partition.c with poorly defined boundaries and responsibilities.
This commit tries to set a couple of distinct modules to separate things
a little bit. There are no code changes here, only code movement.
There are three new files:
src/backend/utils/cache/partcache.c
src/include/partitioning/partdefs.h
src/include/utils/partcache.h
The previous arrangement of #including catalog/partition.h almost
everywhere is no more.
Authors: Amit Langote and Álvaro Herrera
Discussion: https://postgr.es/m/98e8d509-790a-128c-be7f-e48a5b2d8d97@lab.ntt.co.jp
https://postgr.es/m/11aa0c50-316b-18bb-722d-c23814f39059@lab.ntt.co.jp
https://postgr.es/m/143ed9a4-6038-76d4-9a55-502035815e68@lab.ntt.co.jp
https://postgr.es/m/20180413193503.nynq7bnmgh6vs5vm@alvherre.pgsql
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