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We must not push down a foreign join when the foreign tables involved
should be accessed under different user mappings. Previously we tried
to enforce that rule literally during planning, but that meant that the
resulting plans were dependent on the current contents of the
pg_user_mapping catalog, and we had to blow away all cached plans
containing any remote join when anything at all changed in pg_user_mapping.
This could have been improved somewhat, but the fact that a syscache inval
callback has very limited info about what changed made it hard to do better
within that design. Instead, let's change the planner to not consider user
mappings per se, but to allow a foreign join if both RTEs have the same
checkAsUser value. If they do, then they necessarily will use the same
user mapping at runtime, and we don't need to know specifically which one
that is. Post-plan-time changes in pg_user_mapping no longer require any
plan invalidation.
This rule does give up some optimization ability, to wit where two foreign
table references come from views with different owners or one's from a view
and one's directly in the query, but nonetheless the same user mapping
would have applied. We'll sacrifice the first case, but to not regress
more than we have to in the second case, allow a foreign join involving
both zero and nonzero checkAsUser values if the nonzero one is the same as
the prevailing effective userID. In that case, mark the plan as only
runnable by that userID.
The plancache code already had a notion of plans being userID-specific,
in order to support RLS. It was a little confused though, in particular
lacking clarity of thought as to whether it was the rewritten query or just
the finished plan that's dependent on the userID. Rearrange that code so
that it's clearer what depends on which, and so that the same logic applies
to both RLS-injected role dependency and foreign-join-injected role
dependency.
Note that this patch doesn't remove the other issue mentioned in the
original complaint, which is that while we'll reliably stop using a foreign
join if it's disallowed in a new context, we might fail to start using a
foreign join if it's now allowed, but we previously created a generic
cached plan that didn't use one. It was agreed that the chance of winning
that way was not high enough to justify the much larger number of plan
invalidations that would have to occur if we tried to cause it to happen.
In passing, clean up randomly-varying spelling of EXPLAIN commands in
postgres_fdw.sql, and fix a COSTS ON example that had been allowed to
leak into the committed tests.
This reverts most of commits fbe5a3fb7 and 5d4171d1c, which were the
previous attempt at ensuring we wouldn't push down foreign joins that
span permissions contexts.
Etsuro Fujita and Tom Lane
Discussion: <d49c1e5b-f059-20f4-c132-e9752ee0113e@lab.ntt.co.jp>
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This is fallout from join pushdown; get_relid_attribute_name can't
handle an attribute number of 0, indicating a whole-row reference,
and shouldn't be called in that case.
Etsuro Fujita, reviewed by Ashutosh Bapat
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As pointed out by Ashutosh Bapat, the header comments for this file
say that schema-qualification is needed for all and only those types
outside pg_catalog. pg_catalog.text is not outside pg_catalog.
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something.* IS NOT NULL means that every attribute of the row is not
NULL, not that the row itself is non-NULL (e.g. because it's coming
from below an outer join. Use (somevar.*)::pg_catalog.text IS NOT
NULL instead.
Ashutosh Bapat, per a report by Rushabh Lathia. Reviewed by
Amit Langote and Etsuro Fujita. Schema-qualification added by me.
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Etsuro Fujita
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Per gripe from Thomas Munro, who only complained about a more
localized problem, but I couldn't resist a bit more wordsmithing.
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As discovered by Andreas Seltenreich via sqlsmith, it's possible for a
remote join to need to generate a target list which contains a
PlaceHolderVar which would need to be evaluated on the remote server.
This happens when we try to push down a join tree which contains outer
joins and the nullable side of the join contains a subquery which
evauates some expression which can go to NULL above the level of the
join. Since the deparsing logic can't build a remote query that
involves subqueries, it fails while trying to produce an SQL query
that can be sent to the remote side. Detect such cases and don't try
to push down the join at all.
It's actually fine to push down the join if the PlaceHolderVar needs
to be evaluated at the current join level. This patch makes a small
change to build_tlist_to_deparse so that this case will work.
Amit Langote, Ashutosh Bapat, and me.
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Andreas Seltenreich reports that it is possible for a PlaceHolderVar
to creep into this tlist, and I fear that even after that's fixed we
might have other, similar bugs in this area either now or in the
future. There's a lot of action-at-a-distance here, because the
validity of this assertion depends on core planner behavior; so, let's
use elog() to make sure we catch this even in non-assert builds,
rather than just crashing.
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Commit 3151f16e1874db82ed85a005dac15368903ca9fb was intended to be
a commit of a patch from Ashutosh Bapat, but instead I mistakenly
committed an earlier version from Michael Paquier (because both
patches were submitted with the same filename, and I confused them).
Michael's patch fixes the crash but doesn't actually implement the
correct test.
Repair the incorrect logic, and also expand the comments considerably
so that this is all more clear.
Ashutosh Bapat and Robert Haas
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First, even if we cancel a query, we still have to roll back the
containing transaction; otherwise, the session will be left in a
failed transaction state.
Second, we need to support canceling queries whe aborting a
subtransaction as well as when aborting a toplevel transaction.
Etsuro Fujita, reviewed by Michael Paquier
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This fixes a problem which is not new, but with the advent of direct
foreign table modification in 0bf3ae88af330496517722e391e7c975e6bad219,
it's somewhat more likely to be annoying than previously. So,
arrange for a local query cancelation to propagate to the remote side.
Michael Paquier, reviewed by Etsuro Fujita. Original report by
Thom Brown.
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If there's a filter condition on either side of a full outer join,
it is neither correct to attach it to the join's ON clause nor to
throw it into the toplevel WHERE clause. Just don't push down the
join in that case.
To maximize the number of cases where we can still push down full
joins, push inner join conditions into the ON clause at the first
opportunity rather than postponing them to the top-level WHERE
clause. This produces nicer SQL, anyway.
This bug was introduced in e4106b2528727c4b48639c0e12bf2f70a766b910.
Ashutosh Bapat, per report from Rajkumar Raghuwanshi.
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Previously, querying the xmin column of a single postgres_fdw foreign
table fetched the tuple length, xmax the typmod, and cmin or cmax the
composite type OID of the tuple. However, when you queried several
such tables and the join got shipped to the remote side, these columns
ended up containing the remote values of the corresponding columns.
Both behaviors are rather unprincipled, the former for obvious reasons
and the latter because the remote values of these columns don't have
any local significance; our transaction IDs are in a different space
than those of the remote machine. Clean this up by setting all of
these fields to 0 in both cases. Also fix the handling of tableoid
to be sane.
Robert Haas and Ashutosh Bapat, reviewed by Etsuro Fujita.
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Getting annoyed at the amount of unrelated chatter I get from pgindent'ing
Rowley's unique-joins patch. Re-indent all the files it touches.
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Commit fbe5a3fb73102c2cfec11aaaa4a67943f4474383 accidentally changed
this behavior; put things back the way they were, and add some
regression tests.
Report by Andres Freund; patch by Ashutosh Bapat, with a bit of
kibitzing by me.
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A join clause might mention multiple relations on either side, so it
need not be the case that a given joinrel's constituent relations are
all on one side of the join clause or all on the other.
Report by Rajkumar Raghuwanshi. Analysis and fix by Michael Paquier
and Ashutosh Bapat.
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The two get_tle_by_resno() calls introduced by this commit lacked any
check for a NULL return, unlike any other calls of that function anywhere
in our tree. Coverity quite properly complained about it. Also fix a
misindented line in process_query_params(), which Coverity also complained
about on the grounds that the bad indentation suggested possible programmer
misinterpretation.
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postgres_fdw can now sent an UPDATE or DELETE statement directly to
the foreign server in simple cases, rather than sending a SELECT FOR
UPDATE statement and then updating or deleting rows one-by-one.
Etsuro Fujita, reviewed by Rushabh Lathia, Shigeru Hanada, Kyotaro
Horiguchi, Albe Laurenz, Thom Brown, and me.
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There's no reason for this function to do this for every other
attribute number and omit it for CTID, especially since
conversion_error_callback has code to handle that case. This seems
to be an oversight in commit e690b9515072fd7767fdeca5c54166f6a77733bc.
Etsuro Fujita
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Although the default choice of rel->reltarget should typically be
sufficient for scan or join paths, it's not at all sufficient for the
purposes PathTargets were invented for; in particular not for
upper-relation Paths. So break API compatibility by adding a PathTarget
argument to create_foreignscan_path(). To ease updating of existing
code, accept a NULL value of the argument as selecting rel->reltarget.
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In commit 19a541143a09c067 I did not make PathTarget a subtype of Node,
and embedded a RelOptInfo's reltarget directly into it rather than having
a separately-allocated Node. In hindsight that was misguided
micro-optimization, enabled by the fact that at that point we didn't have
any Paths with custom PathTargets. Now that PathTarget processing has
been fleshed out some more, it's easier to see that it's better to have
PathTarget as an indepedent Node type, even if it does cost us one more
palloc to create a RelOptInfo. So change it while we still can.
This commit just changes the representation, without doing anything more
interesting than that.
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Etsuro Fujita, reviewed (though not completely endorsed) by Ashutosh
Bapat, and slightly expanded by me.
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In commit 1d97c19a0f748e94 and later c1d9579dd8bf3c92, we extended
pull_var_clause's API by adding enum-type arguments. That's sort of a pain
to maintain, though, because it means every time we add a new behavior we
must touch every last one of the call sites, even if there's a reasonable
default behavior that most of them could use. Let's switch over to using a
bitmask of flags, instead; that seems more maintainable and might save a
nanosecond or two as well. This commit changes no behavior in itself,
though I'm going to follow it up with one that does add a new behavior.
In passing, remove flatten_tlist(), which has not been used since 9.1
and would otherwise need the same API changes.
Removing these enums means that optimizer/tlist.h no longer needs to
depend on optimizer/var.h. Changing that caused a number of C files to
need addition of #include "optimizer/var.h" (probably we can thank old
runs of pgrminclude for that); but on balance it seems like a good change
anyway.
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Commit ccd8f97922944566d26c7d90eb67ab7848ee9905 gave us the ability to
request that the remote side sort the data, and, later, commit
e4106b2528727c4b48639c0e12bf2f70a766b910 gave us the ability to
request that the remote side perform the join for us rather than doing
it locally. But we could not do both things at the same time: a
remote SQL query that had an ORDER BY clause would never be a join.
This commit adds that capability.
Ashutosh Bapat, reviewed by me.
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Ashutosh Bapat
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Previously, we included NULLS FIRST when appropriate but relied on the
default behavior to be NULLS LAST. This is, however, not true for a
sort in descending order and seems like a fragile assumption anyway.
Report by Rajkumar Raghuwanshi. Patch by Ashutosh Bapat. Review
comments from Michael Paquier and Tom Lane.
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list_concat(list_concat(a, b), c) destructively changes both a and b;
to avoid such perils, copy lists of remote_conds before incorporating
them into larger lists via list_concat().
Ashutosh Bapat, per a report from Etsuro Fujita
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Up to now, there's been an assumption that all Paths for a given relation
compute the same output column set (targetlist). However, there are good
reasons to remove that assumption. For example, an indexscan on an
expression index might be able to return the value of an expensive function
"for free". While we have the ability to generate such a plan today in
simple cases, we don't have a way to model that it's cheaper than a plan
that computes the function from scratch, nor a way to create such a plan
in join cases (where the function computation would normally happen at
the topmost join node). Also, we need this so that we can have Paths
representing post-scan/join steps, where the targetlist may well change
from one step to the next. Therefore, invent a "struct PathTarget"
representing the columns we expect a plan step to emit. It's convenient
to include the output tuple width and tlist evaluation cost in this struct,
and there will likely be additional fields in future.
While Path nodes that actually do have custom outputs will need their own
PathTargets, it will still be true that most Paths for a given relation
will compute the same tlist. To reduce the overhead added by this patch,
keep a "default PathTarget" in RelOptInfo, and allow Paths that compute
that column set to just point to their parent RelOptInfo's reltarget.
(In the patch as committed, actually every Path is like that, since we
do not yet have any cases of custom PathTargets.)
I took this opportunity to provide some more-honest costing of
PlaceHolderVar evaluation. Up to now, the assumption that "scan/join
reltargetlists have cost zero" was applied not only to Vars, where it's
reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval
cost of a PlaceHolderVar's expression to the first plan level where it can
be computed, by including it in the PathTarget cost field and adding that
to the cost estimates for Paths. This isn't perfect yet but it's much
better than before, and there is a way forward to improve it more. This
costing change affects the join order chosen for a couple of the regression
tests, changing expected row ordering.
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Per buildfarm member pademelon.
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It causes warnings in non-Assert-enabled builds.
Per report from Jeff Janes.
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Per Tom Lane and the buildfarm.
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If we've got a relatively straightforward join between two tables,
this pushes that join down to the remote server instead of fetching
the rows for each table and performing the join locally. Some cases
are not handled yet, such as SEMI and ANTI joins. Also, we don't
yet attempt to create presorted join paths or parameterized join
paths even though these options do get tried for a base relation
scan. Nevertheless, this seems likely to be a very significant win
in many practical cases.
Shigeru Hanada and Ashutosh Bapat, reviewed by Robert Haas, with
additional review at various points by Tom Lane, Etsuro Fujita,
KaiGai Kohei, and Jeevan Chalke.
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Oversight in commit 96198d94c.
Etsuro Fujita
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Per buildfarm member pademelon.
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In preparation for upcoming commits.
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deparseReturningList ended up adding up RETURNING NULL to the code, but
code elsewhere saw an empty list of attributes and concluded that it
should not expect tuples from the remote side.
Etsuro Fujita and Robert Haas, reviewed by Thom Brown
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Remove duplicate assignment. This part by Ashutosh Bapat.
Remove now-obsolete comment. This part by me, although the pending
join pushdown patch does something similar, and for the same reason:
there's no reason to keep two lists of the things in the fdw_private
structure that have to be kept in sync with each other.
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The default fetch size of 100 rows might not be right in every
environment, so allow users to configure it.
Corey Huinker, reviewed by Kyotaro Horiguchi, Andres Freund, and me.
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The code that generates a complete SQL query for a given foreign relation
was repeated in two places, and they didn't quite agree: the EXPLAIN case
left out the locking clause. Centralize the code so we get the same
behavior everywhere, and adjust calling conventions and which functions
are static vs. extern accordingly . Centralize the code so we get the same
behavior everywhere, and adjust calling conventions and which functions
are static vs. extern accordingly.
Ashutosh Bapat, reviewed and slightly adjusted by me.
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listForeignTables' invocation of processSQLNamePattern did not match up
with the other ones that handle potentially-schema-qualified names; it
failed to make use of pg_table_is_visible() and also passed the name
arguments in the wrong order. Bug seems to have been aboriginal in commit
0d692a0dc9f0e532. It accidentally sort of worked as long as you didn't
inquire too closely into the behavior, although the silliness was later
exposed by inconsistencies in the test queries added by 59efda3e50ca4de6
(which I probably should have questioned at the time, but didn't).
Per bug #13899 from Reece Hart. Patch by Reece Hart and Tom Lane.
Back-patch to all affected branches.
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The upcoming patch to allow join pushdown in postgres_fdw needs to use
this code multiple times, which requires moving it to deparse.c. That
seems like a good idea anyway, so do that now both on general principle
and to simplify the future patch.
Inspired by a patch by Shigeru Hanada and Ashutosh Bapat, but I did
it a little differently than what that patch did.
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This fix accidentally got left out of the previous commit.
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Previously, postgres_fdw's connection cache was keyed by user OID and
server OID, but this can lead to multiple connections when it's not
really necessary. In particular, if all relevant users are mapped to
the public user mapping, then their connection options are certainly
the same, so one connection can be used for all of them.
While we're cleaning things up here, drop the "server" argument to
GetConnection(), which isn't really needed. This saves a few cycles
because callers no longer have to look this up; the function itself
does, but only when establishing a new connection, not when reusing
an existing one.
Ashutosh Bapat, with a few small changes by me.
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Backpatch certain files through 9.1
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postgresImportForeignSchema pays attention to IMPORT's EXCEPT and LIMIT TO
options, but only as an efficiency hack, not for correctness' sake. The
FDW documentation does explain that, but someone using postgres_fdw.c
as a coding guide might not remember it, so let's add a comment here.
Per question from Regina Obe.
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When use_remote_estimate is enabled, consider adding ORDER BY to the
query we sending to the remote server so that we can use that ordered
data for a merge join. Commit f18c944b6137329ac4a6b2dce5745c5dc21a8578
arranges to push down the query pathkeys, which seems like the case
mostly likely to be a win, but testing shows this can sometimes win,
too.
For a regular table, we know which indexes are present and therefore
test whether the ordering provided by each such index is useful. Here,
we take the opposite approach: guess what orderings would be useful if
they could be generated cheaply, and then ask the remote side what those
will cost.
Ashutosh Bapat, with very substantial cosmetic revisions by me. Also
reviewed by Rushabh Lathia.
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Commit e7cb7ee14555cc9c5773e2c102efd6371f6f2005 provided basic
infrastructure for allowing a foreign data wrapper or custom scan
provider to replace a join of one or more tables with a scan.
However, this infrastructure failed to take into account the need
for possible EvalPlanQual rechecks, and ExecScanFetch would fail
an assertion (or just overwrite memory) if such a check was attempted
for a plan containing a pushed-down join. To fix, adjust the EPQ
machinery to skip some processing steps when scanrelid == 0, making
those the responsibility of scan's recheck method, which also has
the responsibility in this case of correctly populating the relevant
slot.
To allow foreign scans to gain control in the right place to make
use of this new facility, add a new, optional RecheckForeignScan
method. Also, allow a foreign scan to have a child plan, which can
be used to correctly populate the slot (or perhaps for something
else, but this is the only use currently envisioned).
KaiGai Kohei, reviewed by Robert Haas, Etsuro Fujita, and Kyotaro
Horiguchi.
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Remote expressions now also matter to make_foreignscan()
Noted by Etsuro Fujita.
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Rather than relying on other extensions to be available for installation,
let's just add some test objects to the postgres_fdw extension itself
within the regression script.
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