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subqueries into the same thing you'd have gotten from IN (except always with
unknownEqFalse = true, so as to get the proper semantics for an EXISTS).
I believe this fixes the last case within CVS HEAD in which an EXISTS could
give worse performance than an equivalent IN subquery.
The tricky part of this is that if the upper query probes the EXISTS for only
a few rows, the hashing implementation can actually be worse than the default,
and therefore we need to make a cost-based decision about which way to use.
But at the time when the planner generates plans for subqueries, it doesn't
really know how many times the subquery will be executed. The least invasive
solution seems to be to generate both plans and postpone the choice until
execution. Therefore, in a query that has been optimized this way, EXPLAIN
will show two subplans for the EXISTS, of which only one will actually get
executed.
There is a lot more that could be done based on this infrastructure: in
particular it's interesting to consider switching to the hash plan if we start
out using the non-hashed plan but find a lot more upper rows going by than we
expected. I have therefore left some minor inefficiencies in place, such as
initializing both subplans even though we will currently only use one.
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to be used for SubLinks that are underneath a top-level OR clause. Just as at
the very top level of WHERE, it's not necessary to be accurate about whether
the sublink returns FALSE or NULL, because either result has the same impact
on whether the WHERE will succeed.
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carry typmod.
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Per Microsoft knowledge base article Q201213, early versions of
Windows fail when we do this. Later versions of Windows appear
to have a higher limit than 64Kb, but do still fail on large
sends, so we unconditionally limit it for all versions.
Patch from Tom Lane.
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debug_print_plan to appear at LOG message level, not DEBUG1 as historically.
Make debug_pretty_print default to on. Also, cause plans generated via
EXPLAIN to be subject to debug_print_plan. This is all to make
debug_print_plan a reasonably comfortable substitute for the former behavior
of EXPLAIN VERBOSE.
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eval_const_expressions will generally throw away anything that's ANDed with
constant FALSE, what we're left with given an example like
select * from tenk1 a where (unique1,0) in (select unique2,1 from tenk1 b);
is a cartesian product computation, which is really not acceptable.
This is a regression in CVS HEAD compared to previous releases, which were
able to notice the impossible join condition in this case --- though not in
some related cases that are also improved by this patch, such as
select * from tenk1 a left join tenk1 b on (a.unique1=b.unique2 and 0=1);
Fix by skipping evaluation of the appropriate side of the outer join in
cases where it's demonstrably unnecessary.
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that we're considering pulling up. I hadn't wanted to think through whether
that could work during the first pass at this stuff. However, on closer
inspection it seems to be safe enough.
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level of a JOIN/ON clause, not only at top level of WHERE. (However, we
can't do this in an outer join's ON clause, unless the ANY/EXISTS refers
only to the nullable side of the outer join, so that it can effectively
be pushed down into the nullable side.) Per request from Kevin Grittner.
In passing, fix a bug in the initial implementation of EXISTS pullup:
it would Assert if the EXIST's WHERE clause used a join alias variable.
Since we haven't yet flattened join aliases when this transformation
happens, it's necessary to include join relids in the computed set of
RHS relids.
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returns NULL instead of a PGresult. The former coding would fail, which
is OK, but it neglected to give you the PQerrorMessage that might tell
you why. In the oldest branches, there was another problem: it'd sometimes
report PQerrorMessage from the wrong connection.
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if PQexec returns NULL. These don't seem significant enough to be worth
back-patching, but they ought to get fixed ...
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Gregory Stark
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and anti joins. To do this, pass the SpecialJoinInfo struct for the current
join as an additional optional argument to operator join selectivity
estimation functions. This allows the estimator to tell not only what kind
of join is being formed, but which variable is on which side of the join;
a requirement long recognized but not dealt with till now. This also leaves
the door open for future improvements in the estimators, such as accounting
for the null-insertion effects of lower outer joins. I didn't do anything
about that in the current patch but the information is in principle deducible
from what's passed.
The patch also clarifies the definition of join selectivity for semi/anti
joins: it's the fraction of the left input that has (at least one) match
in the right input. This allows getting rid of some very fuzzy thinking
that I had committed in the original 7.4-era IN-optimization patch.
There's probably room to estimate this better than the present patch does,
but at least we know what to estimate.
Since I had to touch CREATE OPERATOR anyway to allow a variant signature
for join estimator functions, I took the opportunity to add a couple of
additional checks that were missing, per my recent message to -hackers:
* Check that estimator functions return float8;
* Require execute permission at the time of CREATE OPERATOR on the
operator's function as well as the estimator functions;
* Require ownership of any pre-existing operator that's modified by
the command.
I also moved the lookup of the functions out of OperatorCreate() and
into operatorcmds.c, since that seemed more consistent with most of
the other catalog object creation processes, eg CREATE TYPE.
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match in antijoin mode, we should advance to next outer tuple not next inner.
We know we don't want to return this outer tuple, and there is no point in
advancing over matching inner tuples now, because we'd just have to do it
again if the next outer tuple has the same merge key. This makes a noticeable
difference if there are lots of duplicate keys in both inputs.
Similarly, after finding a match in semijoin mode, arrange to advance to
the next outer tuple after returning the current match; or immediately,
if it fails the extra quals. The rationale is the same. (This is a
performance bug in existing releases; perhaps worth back-patching? The
planner tries to avoid using mergejoin with lots of duplicates, so it may
not be a big issue in practice.)
Nestloop and hash got this right to start with, but I made some cosmetic
adjustments there to make the corresponding bits of logic look more similar.
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variable stats_temp_directory, instead of requiring the admin to
mount/symlink the pg_stat_tmp directory manually.
For now the config variable is PGC_POSTMASTER. Room for further improvment
that would allow it to be changed on-the-fly.
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parent, not only those with RangeTblRefs. We need them in ExecCheckRTPerms.
Report by Brendan O'Shea. Back-patch to 8.2, where pull_up_simple_union_all
was introduced.
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the old JOIN_IN code, but antijoins are new functionality.) Teach the planner
to convert appropriate EXISTS and NOT EXISTS subqueries into semi and anti
joins respectively. Also, LEFT JOINs with suitable upper-level IS NULL
filters are recognized as being anti joins. Unify the InClauseInfo and
OuterJoinInfo infrastructure into "SpecialJoinInfo". With that change,
it becomes possible to associate a SpecialJoinInfo with every join attempt,
which permits some cleanup of join selectivity estimation. That needs to be
taken much further than this patch does, but the next step is to change the
API for oprjoin selectivity functions, which seems like material for a
separate patch. So for the moment the output size estimates for semi and
especially anti joins are quite bogus.
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main tables.
This requires vacuum() to accept processing a toast table standalone, so
there's a user-visible change in that it's now possible (for a superuser) to
execute "VACUUM pg_toast.pg_toast_XXX".
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of some WAL records, and two-phase state files, which I forgot.
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of multiple forks, and each fork can be created and grown separately.
The bulk of this patch is about changing the smgr API to include an extra
ForkNumber argument in every smgr function. Also, smgrscheduleunlink and
smgrdounlink no longer implicitly call smgrclose, because other forks might
still exist after unlinking one. The callers of those functions have been
modified to call smgrclose instead.
This patch in itself doesn't have any user-visible effect, but provides the
infrastructure needed for upcoming patches. The additional forks envisioned
are a rewritten FSM implementation that doesn't rely on a fixed-size shared
memory block, and a visibility map to allow skipping portions of a table in
VACUUM that have no dead tuples.
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REINDEX DATABASE including same) is done before a session has done any other
update on pg_class, the pg_class relcache entry was left with an incorrect
setting of rd_indexattr, because the indexed-attributes set would be first
demanded at a time when we'd forced a partial list of indexes into the
pg_class entry, and it would remain cached after that. This could result
in incorrect decisions about HOT-update safety later in the same session.
In practice, since only pg_class_relname_nsp_index would be missed out,
only ALTER TABLE RENAME and ALTER TABLE SET SCHEMA could trigger a problem.
Per report and test case from Ondrej Jirman.
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INSERT or UPDATE will match the target table's current rowtype. In pre-8.3
releases inconsistency can arise with stale cached plans, as reported by
Merlin Moncure. (We patched the equivalent hazard on the SELECT side in Feb
2007; I'm not sure why we thought there was no risk on the insertion side.)
In 8.3 and HEAD this problem should be impossible due to plan cache
invalidation management, but it seems prudent to make the check anyway.
Back-patch as far as 8.0. 7.x versions lack ALTER COLUMN TYPE, so there
seems no way to abuse a stale plan comparably.
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hashtable entries for tuples that are found only in the second input: they
can never contribute to the output. Furthermore, this implies that the
planner should endeavor to put first the smaller (in number of groups) input
relation for an INTERSECT. Implement that, and upgrade prepunion's estimation
of the number of rows returned by setops so that there's some amount of sanity
in the estimate of which one is smaller.
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This completes my project of improving usage of hashing for duplicate
elimination (aggregate functions with DISTINCT remain undone, but that's
for some other day).
As with the previous patches, this means we can INTERSECT/EXCEPT on datatypes
that can hash but not sort, and it means that INTERSECT/EXCEPT without ORDER
BY are no longer certain to produce sorted output.
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but seem like a separate patch since most of the remaining work is on the
executor side.) I took the opportunity to push selection of the grouping
operators for set operations into the parser where it belongs. Otherwise this
is just a small exercise in making prepunion.c consider both alternatives.
As with the recent DISTINCT patch, this means we can UNION on datatypes that
can hash but not sort, and it means that UNION without ORDER BY is no longer
certain to produce sorted output.
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would work, but in fact it didn't return the same rows when moving backwards
as when moving forwards. This would have no visible effect in a DISTINCT
query (at least assuming the column datatypes use a strong definition of
equality), but it gave entirely wrong answers for DISTINCT ON queries.
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sure that DISTINCT ON does what it's supposed to, ie, sort by the full ORDER
BY list before unique-ifying. The error seems masked in simple cases by the
fact that query_planner won't return query pathkeys that only partially match
the requested sort order, but I wouldn't want to bet that it couldn't be
exposed in some way or other.
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PageHeaderIsValid when we zero the buffer instead of reading the page in.
The actual performance improvement is probably marginal since this function
isn't very heavily used, but a cycle saved is a cycle earned.
Zdenek Kotala
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This allows the use of a ramdrive (either through mount or symlink) for
the temporary file that's written every half second, which should
reduce I/O.
On server shutdown/startup, the file is written to the old location in
the global directory, to preserve data across restarts.
Bump catversion since the $PGDATA directory layout changed.
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some failures to expose messages for translation.
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as methods for implementing the DISTINCT step. This eliminates the former
performance gap between DISTINCT and GROUP BY, and also makes it possible
to do SELECT DISTINCT on datatypes that only support hashing not sorting.
SELECT DISTINCT ON is still always implemented by sorting; it would take
executor changes to support hashing that, and it's not clear it's worth
the trouble.
This is a release-note-worthy incompatibility from previous PG versions,
since SELECT DISTINCT can no longer be counted on to deliver sorted output
without explicitly saying ORDER BY. (Anyone who can't cope with that
can consider turning off enable_hashagg.)
Several regression test queries needed to have ORDER BY added to preserve
stable output order. I fixed the ones that manifested here, but there
might be some other cases that show up on other platforms.
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or target database is being accessed by other users, it tells you whether
the "other users" are live sessions or uncommitted prepared transactions.
(Indeed, it tells you exactly how many of each, but that's mostly just
because it was easy to do so.) This should help forestall the gotcha of
not realizing that a prepared transaction is what's blocking the command.
Per discussion.
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sorting. The infrastructure for this was all in place already; it's only
necessary to fix the planner to not assume that sorting is always an available
option.
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a size that is one of the supported values, not just anything <= sizeof(Datum).
Cross-check the alignment specification against size as well.
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read when the --temp-config argument is bad. Noted while wondering why
buildfarm member dungbeetle is failing ... this isn't why, but it is why
the error report isn't very helpful ...
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as per my recent proposal:
1. Fold SortClause and GroupClause into a single node type SortGroupClause.
We were already relying on them to be struct-equivalent, so using two node
tags wasn't accomplishing much except to get in the way of comparing items
with equal().
2. Add an "eqop" field to SortGroupClause to carry the associated equality
operator. This is cheap for the parser to get at the same time it's looking
up the sort operator, and storing it eliminates the need for repeated
not-so-cheap lookups during planning. In future this will also let us
represent GROUP/DISTINCT operations on datatypes that have hash opclasses
but no btree opclasses (ie, they have equality but no natural sort order).
The previous representation simply didn't work for that, since its only
indicator of comparison semantics was a sort operator.
3. Add a hasDistinctOn boolean to struct Query to explicitly record whether
the distinctClause came from DISTINCT or DISTINCT ON. This allows removing
some complicated and not 100% bulletproof code that attempted to figure
that out from the distinctClause alone.
This patch doesn't in itself create any new capability, but it's necessary
infrastructure for future attempts to use hash-based grouping for DISTINCT
and UNION/INTERSECT/EXCEPT.
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Robert Lor
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method is grouped together in a reasonably similar way, keeping the "global
shared functions" together in their own section as well. Makes it a lot easier
to find your way around the code.
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routines, leaving hba.c to deal only with processing the HBA specific files.
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to represent DISTINCT or DISTINCT ON. This gets rid of a longstanding
annoyance that a view or rule using SELECT DISTINCT will be dumped out
with an overspecified ORDER BY list, and is one small step along the way
to decoupling DISTINCT and ORDER BY enough so that hash-based implementation
of DISTINCT will be possible. In passing, improve transformDistinctClause
so that it doesn't reject duplicate DISTINCT ON items, as was reported by
Steve Midgley a couple weeks ago.
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or domains). This was already effectively required because you had to own
the I/O functions, and the I/O functions pretty much have to be written in
C since we don't let PL functions take or return cstring. But given the
possible security consequences of a malicious type definition, it seems
prudent to enforce superuser requirement directly. Per recent discussion.
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of the STRING type category, thereby opening up the mechanism for user-defined
types. This is mainly for the benefit of citext, though; there aren't likely
to be a lot of types that are all general-purpose character strings.
Per discussion with David Wheeler.
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only type categories in which the previous coding made *every* type
preferred; so there is no change in effective behavior, because the function
resolution rules only do something different when faced with a choice
between preferred and non-preferred types in the same category. It just
seems safer and less surprising to have CREATE TYPE default to non-preferred
status ...
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with system catalog lookups, as was foreseen to be necessary almost since
their creation. Instead put the information into two new pg_type columns,
typcategory and typispreferred. Add support for setting these when
creating a user-defined base type.
The category column is just a "char" (i.e. a poor man's enum), allowing
a crude form of user extensibility of the category list: just use an
otherwise-unused character. This seems sufficient for foreseen uses,
but we could upgrade to having an actual category catalog someday, if
there proves to be a huge demand for custom type categories.
In this patch I have attempted to hew exactly to the behavior of the
previous hardwired logic, except for introducing new type categories for
arrays, composites, and enums. In particular the default preferred state
for user-defined types remains TRUE. That seems worth revisiting, but it
should be done as a separate patch from introducing the infrastructure.
Likewise, any adjustment of the standard set of categories should be done
separately.
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