The standard way to check for list emptiness is to compare the
List pointer to NIL; our list code goes out of its way to ensure
that that is the only representation of an empty list. (An
acceptable alternative is a plain boolean test for non-null
pointer, but explicit mention of NIL is usually preferable.)
Various places didn't get that memo and expressed the condition
with list_length(), which might not be so bad except that there
were such a variety of ways to check it exactly: equal to zero,
less than or equal to zero, less than one, yadda yadda. In the
name of code readability, let's standardize all those spellings
as "list == NIL" or "list != NIL". (There's probably some
microscopic efficiency gain too, though few of these look to be
at all performance-critical.)
A very small number of cases were left as-is because they seemed
more consistent with other adjacent list_length tests that way.
Peter Smith, with bikeshedding from a number of us
Discussion: https://postgr.es/m/CAHut+PtQYe+ENX5KrONMfugf0q6NHg4hR5dAhqEXEc2eefFeig@mail.gmail.com
On closer inspection, mcv.c isn't as broken for ScalarArrayOpExpr
as I thought. The Var-on-right issue is real enough, but actually
it does cope fine with a NULL array constant --- I was misled by
an XXX comment suggesting it didn't. Undo that part of the code
change, and replace the XXX comment with something less misleading.
Since v14, the extended stats machinery will try to estimate for
otherwise-unsupported boolean expressions if they match an expression
available from an extended stats object. mcv.c did not get the memo
about this, and would spit up with "unknown clause type". Fortunately
the case is easy to handle, since we can expect the expression yields
boolean.
While here, replace some not-terribly-on-point assertions with
simpler runtime tests for lookup failure. That seems appropriate
so that we get an elog not a crash if we somehow get to the new
it-should-be-a-bool-expression code with a subexpression that
doesn't match any stats column.
Per report from Danny Shemesh. Thanks to Justin Pryzby for
preliminary investigation.
Discussion: https://postgr.es/m/CAFZC=QqD6=27wQPOW1pbRa98KPyuyn+7cL_Ay_Ck-roZV84vHg@mail.gmail.com
statext_is_compatible_clause_internal() checked that the arguments
of a ScalarArrayOpExpr are one Var and one Const, but it would allow
cases where the Const was on the left. Subsequent uses of the clause
are not expecting that and would suffer assertion failures or core
dumps. mcv.c also had not bothered to cope with the case of a NULL
array constant, which seems really unacceptably sloppy of somebody.
(Although our tools failed us there too, since AFAIK neither Coverity
nor any compiler warned of the obvious use-of-uninitialized-variable
condition.) It seems best to handle that by having
statext_is_compatible_clause_internal() reject it.
Noted while fixing bug #17570. Back-patch to v13 where the
extended stats code grew some awareness of ScalarArrayOpExpr.
Commit a4d75c86b improved the extended-stats logic to allow extended
stats to be collected on expressions not just bare Vars. To apply
such stats, we first verify that the user has permissions to read all
columns used in the stats. (If not, the query will likely fail at
runtime, but the planner ought not do so.) That had to get extended
to check permissions of columns appearing within such expressions,
but the code for that was completely wrong: it applied pull_varattnos
to the wrong pointer, leading to "unrecognized node type" failures.
Furthermore, although you couldn't get to this because of that bug,
it failed to account for the attnum offset applied by pull_varattnos.
This escaped recognition so far because the code in question is not
reached when the user has whole-table SELECT privilege (which is the
common case), and because only subexpressions not specially handled
by statext_is_compatible_clause_internal() are at risk.
I think a large part of the reason for this bug is under-documentation
of what statext_is_compatible_clause() is doing and what its arguments
are, so do some work on the comments to try to improve that.
Per bug #17570 from Alexander Kozhemyakin. Patch by Richard Guo;
comments and other cosmetic improvements by me. (Thanks also to
Japin Li for diagnosis.) Back-patch to v14 where the bug came in.
Discussion: https://postgr.es/m/17570-f2f2e0f4bccf0965@postgresql.org
Justin Pryzby reported that some scenarios could cause gathering
of extended statistics to spend many seconds in an un-cancelable
qsort() operation. To fix, invent qsort_interruptible(), which is
just like qsort_arg() except that it will also do CHECK_FOR_INTERRUPTS
every so often. This bloats the backend by a couple of kB, which
seems like a good investment. (We considered just enabling
CHECK_FOR_INTERRUPTS in the existing qsort and qsort_arg functions,
but there are some callers for which that'd demonstrably be unsafe.
Opt-in seems like a better way.)
For now, just apply qsort_interruptible() in statistics collection.
There's probably more places where it could be useful, but we can
always change other call sites as we find problems.
Back-patch to v14. Before that we didn't have extended stats on
expressions, so that the problem was less severe. Also, this patch
depends on the sort_template infrastructure introduced in v14.
Tom Lane and Justin Pryzby
Discussion: https://postgr.es/m/20220509000108.GQ28830@telsasoft.com
There were many calls to construct_array() and deconstruct_array() for
built-in types, for example, when dealing with system catalog columns.
These all hardcoded the type attributes necessary to pass to these
functions.
To simplify this a bit, add construct_array_builtin(),
deconstruct_array_builtin() as wrappers that centralize this hardcoded
knowledge. This simplifies many call sites and reduces the amount of
hardcoded stuff that is spread around.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/2914356f-9e5f-8c59-2995-5997fc48bcba%40enterprisedb.com
This fixes a set of issues that have accumulated over the past months
(or years) in various code areas. Most fixes are related to some recent
additions, as of the development of v15.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20220124030001.GQ23027@telsasoft.com
Add pg_statistic_ext_data.stxdinherit flag, so that for each extended
statistics definition we can store two versions of data - one for the
relation alone, one for the whole inheritance tree. This is analogous to
pg_statistic.stainherit, but we failed to include such flag in catalogs
for extended statistics, and we had to work around it (see commits
859b3003de, 36c4bc6e72 and 20b9fa308e).
This changes the relationship between the two catalogs storing extended
statistics objects (pg_statistic_ext and pg_statistic_ext_data). Until
now, there was a simple 1:1 mapping - for each definition there was one
pg_statistic_ext_data row, and this row was inserted while creating the
statistics (and then updated during ANALYZE). With the stxdinherit flag,
we don't know how many rows there will be (child relations may be added
after the statistics object is defined), so there may be up to two rows.
We could make CREATE STATISTICS to always create both rows, but that
seems wasteful - without partitioning we only need stxdinherit=false
rows, and declaratively partitioned tables need only stxdinherit=true.
So we no longer initialize pg_statistic_ext_data in CREATE STATISTICS,
and instead make that a responsibility of ANALYZE. Which is what we do
for regular statistics too.
Patch by me, with extensive improvements and fixes by Justin Pryzby.
Author: Tomas Vondra, Justin Pryzby
Reviewed-by: Tomas Vondra, Justin Pryzby
Discussion: https://postgr.es/m/20210923212624.GI831%40telsasoft.com
Commit 859b3003de disabled building of extended stats for inheritance
trees, to prevent updating the same catalog row twice. While that
resolved the issue, it also means there are no extended stats for
declaratively partitioned tables, because there are no data in the
non-leaf relations.
That also means declaratively partitioned tables were not affected by
the issue 859b3003de addressed, which means this is a regression
affecting queries that calculate estimates for the whole inheritance
tree as a whole (which includes e.g. GROUP BY queries).
But because partitioned tables are empty, we can invert the condition
and build statistics only for the case with inheritance, without losing
anything. And we can consider them when calculating estimates.
It may be necessary to run ANALYZE on partitioned tables, to collect
proper statistics. For declarative partitioning there should no prior
statistics, and it might take time before autoanalyze is triggered. For
tables partitioned by inheritance the statistics may include data from
child relations (if built 859b3003de), contradicting the current code.
Report and patch by Justin Pryzby, minor fixes and cleanup by me.
Backpatch all the way back to PostgreSQL 10, where extended statistics
were introduced (same as 859b3003de).
Author: Justin Pryzby
Reported-by: Justin Pryzby
Backpatch-through: 10
Discussion: https://postgr.es/m/20210923212624.GI831%40telsasoft.com
Since commit 859b3003de we only build extended statistics for individual
relations, ignoring the child relations. This resolved the issue with
updating catalog tuple twice, but we still tried to use the statistics
when calculating estimates for the whole inheritance tree. When the
relations contain very distinct data, it may produce bogus estimates.
This is roughly the same issue 427c6b5b9 addressed ~15 years ago, and we
fix it the same way - by ignoring extended statistics when calculating
estimates for the inheritance tree as a whole. We still consider
extended statistics when calculating estimates for individual child
relations, of course.
This may result in plan changes due to different estimates, but if the
old statistics were not describing the inheritance tree particularly
well it's quite likely the new plans is actually better.
Report and patch by Justin Pryzby, minor fixes and cleanup by me.
Backpatch all the way back to PostgreSQL 10, where extended statistics
were introduced (same as 859b3003de).
Author: Justin Pryzby
Reported-by: Justin Pryzby
Backpatch-through: 10
Discussion: https://postgr.es/m/20210923212624.GI831%40telsasoft.com
The code inconsistently used "statistic object" or "statistics" where
the correct term, as discussed, is actually "statistics object". This
improves the state of the code to be more consistent.
While on it, fix an incorrect error message introduced in a4d75c8. This
error should never happen, as the code states, but it would be
misleading.
Author: Justin Pryzby
Reviewed-by: Álvaro Herrera, Michael Paquier
Discussion: https://postgr.es/m/20210924215827.GS831@telsasoft.com
Backpatch-through: 14
Several mistakes have piled in the code comments over the time,
including incorrect grammar, function names and simple typos. This
commit takes care of a portion of these.
No backpatch is done as this is only cosmetic.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20210924215827.GS831@telsasoft.com
Calculating degree of a functional dependency may allocate a lot of
memory - we have released mot of the explicitly allocated memory, but
e.g. detoasted varlena values were left behind. That may be an issue,
because we consider a lot of dependencies (all combinations), and the
detoasting may happen for each one again.
Fixed by calling dependency_degree() in a dedicated context, and
resetting it after each call. We only need the calculated dependency
degree, so we don't need to copy anything.
Backpatch to PostgreSQL 10, where extended statistics were introduced.
Backpatch-through: 10
Discussion: https://www.postgresql.org/message-id/20210915200928.GP831%40telsasoft.com
Until now, all extended statistics on a given relation were built in the
same memory context, without resetting. Some of the memory was released
explicitly, but not all of it - for example memory allocated while
detoasting values is hard to free. This is how it worked since extended
statistics were introduced in PostgreSQL 10, but adding support for
extended stats on expressions made the issue somewhat worse as it
increases the number of statistics to build.
Fixed by adding a memory context which gets reset after building each
statistics object (all the statistics kinds included in it). Resetting
it after building each statistics kind would be even better, but it
would require more invasive changes and copying of results, making it
harder to backpatch.
Backpatch to PostgreSQL 10, where extended statistics were introduced.
Author: Justin Pryzby
Reported-by: Justin Pryzby
Reviewed-by: Tomas Vondra
Backpatch-through: 10
Discussion: https://www.postgresql.org/message-id/20210915200928.GP831%40telsasoft.com
All the code paths simplified here were already using a boolean or used
an expression that led to zero or one, making the extra bits
unnecessary.
Author: Justin Pryzby
Reviewed-by: Tom Lane, Michael Paquier, Peter Smith
Discussion: https://postgr.es/m/20210428182936.GE27406@telsasoft.com
Also "make reformat-dat-files".
The only change worthy of note is that pgindent messed up the formatting
of launcher.c's struct LogicalRepWorkerId, which led me to notice that
that struct wasn't used at all anymore, so I just took it out.
The path for *exprs != NIL would misbehave, and likely crash,
since pull_varattnos expects its last argument to be valid
at call.
Found by Coverity --- we have no coverage of this path in
the regression tests.
Comment fixes are applied on HEAD, and documentation improvements are
applied on back-branches where needed.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20210408164008.GJ6592@telsasoft.com
Backpatch-through: 9.6
Handling of incompatible clauses while applying extended statistics was
a bit confused - while handling a mix of compatible and incompatible
clauses it sometimes incorrectly treated the incompatible clauses as
compatible, resulting in a crash.
Fixed by reworking the code applying the selected statistics object to
make it easier to understand, and adding a proper compatibility check.
Reported-by: David Rowley
Discussion: https://postgr.es/m/CAApHDvpYT10-nkSp8xXe-nbO3jmoaRyRFHbzh-RWMfAJynqgpQ%40mail.gmail.com
Since a4d75c86b, some buildfarm members have been warning that
Assert(attnum <= MaxAttrNumber);
is useless if attnum is an AttrNumber. I'm not certain how plausible
it is that the value coming out of the bitmap could actually exceed
MaxAttrNumber, but we seem to have thought that that was possible back
in 7300a6995. Revert the intermediate variable to int so that we have
the same overflow protection as before.
Allow defining extended statistics on expressions, not just just on
simple column references. With this commit, expressions are supported
by all existing extended statistics kinds, improving the same types of
estimates. A simple example may look like this:
CREATE TABLE t (a int);
CREATE STATISTICS s ON mod(a,10), mod(a,20) FROM t;
ANALYZE t;
The collected statistics are useful e.g. to estimate queries with those
expressions in WHERE or GROUP BY clauses:
SELECT * FROM t WHERE mod(a,10) = 0 AND mod(a,20) = 0;
SELECT 1 FROM t GROUP BY mod(a,10), mod(a,20);
This introduces new internal statistics kind 'e' (expressions) which is
built automatically when the statistics object definition includes any
expressions. This represents single-expression statistics, as if there
was an expression index (but without the index maintenance overhead).
The statistics is stored in pg_statistics_ext_data as an array of
composite types, which is possible thanks to 79f6a942bd.
CREATE STATISTICS allows building statistics on a single expression, in
which case in which case it's not possible to specify statistics kinds.
A new system view pg_stats_ext_exprs can be used to display expression
statistics, similarly to pg_stats and pg_stats_ext views.
ALTER TABLE ... ALTER COLUMN ... TYPE now treats indexes the same way it
treats indexes, i.e. it drops and recreates the statistics. This means
all statistics are reset, and we no longer try to preserve at least the
functional dependencies. This should not be a major issue in practice,
as the functional dependencies actually rely on per-column statistics,
which were always reset anyway.
Author: Tomas Vondra
Reviewed-by: Justin Pryzby, Dean Rasheed, Zhihong Yu
Discussion: https://postgr.es/m/ad7891d2-e90c-b446-9fe2-7419143847d7%40enterprisedb.com
A couple error messages and comments used 'statistic kind', not the
correct 'statistics kind'. Fix and backpatch all the way back to 10,
where extended statistics were introduced.
Backpatch-through: 10
Until now the bsearch_arg function was used only in extended statistics
code, so it was defined in that code. But we already have qsort_arg in
src/port, so let's move it next to it.
Formerly, extended statistics only handled clauses that were
RestrictInfos. However, the restrictinfo machinery doesn't create
sub-AND RestrictInfos for AND clauses underneath OR clauses.
Therefore teach extended statistics to handle bare AND clauses,
looking for compatible RestrictInfo clauses underneath them.
Dean Rasheed, reviewed by Tomas Vondra.
Discussion: https://postgr.es/m/CAEZATCW=J65GUFm50RcPv-iASnS2mTXQbr=CfBvWRVhFLJ_fWA@mail.gmail.com
When estimating an OR clause using multiple extended statistics
objects, treat the estimates for each set of clauses for each
statistics object as independent of one another. The overlap estimates
produced for each statistics object do not apply to clauses covered by
other statistics objects.
Dean Rasheed, reviewed by Tomas Vondra.
Discussion: https://postgr.es/m/CAEZATCW=J65GUFm50RcPv-iASnS2mTXQbr=CfBvWRVhFLJ_fWA@mail.gmail.com
Formerly we only applied extended statistics to an OR clause as part
of the clauselist_selectivity() code path for an OR clause appearing
in an implicitly-ANDed list of clauses. This meant that it could only
use extended statistics if all sub-clauses of the OR clause were
covered by a single extended statistics object.
Instead, teach clause_selectivity() how to apply extended statistics
to an OR clause by handling its ORed list of sub-clauses in a similar
manner to an implicitly-ANDed list of sub-clauses, but with different
combination rules. This allows one or more extended statistics objects
to be used to estimate all or part of the list of sub-clauses. Any
remaining sub-clauses are then treated as if they are independent.
Additionally, to avoid double-application of extended statistics, this
introduces "extended" versions of clause_selectivity() and
clauselist_selectivity(), which include an option to ignore extended
statistics. This replaces the old clauselist_selectivity_simple()
function which failed to completely ignore extended statistics when
called from the extended statistics code.
A known limitation of the current infrastructure is that an AND clause
under an OR clause is not treated as compatible with extended
statistics (because we don't build RestrictInfos for such sub-AND
clauses). Thus, for example, "(a=1 AND b=1) OR (a=2 AND b=2)" will
currently be treated as two independent AND clauses (each of which may
be estimated using extended statistics), but extended statistics will
not currently be used to account for any possible overlap between
those clauses. Improving that is left as a task for the future.
Original patch by Tomas Vondra, with additional improvements by me.
Discussion: https://postgr.es/m/20200113230008.g67iyk4cs3xbnjju@development
It's a bit inefficient to test if a Bitmapset is empty by counting all the
members and seeing if that number is zero. It's much better just to use
bms_is_empty(). Likewise for checking if there are at least two members,
just use bms_membership(), which does not need to do anything more after
finding two members.
Discussion: https://postgr.es/m/CAApHDvpvwm_QjbDOb5xga%2BKmX9XkN9xQavNGm3SvDbVnCYOerQ%40mail.gmail.com
Reviewed-by: Tomas Vondra
Thomas Munro fixed a longstanding annoyance in pg_bsd_indent, that
it would misformat lines containing IsA() macros on the assumption
that the IsA() call should be treated like a cast. This improves
some other cases involving field/variable names that match typedefs,
too. The only places that get worse are a couple of uses of the
OpenSSL macro STACK_OF(); we'll gladly take that trade-off.
Discussion: https://postgr.es/m/20200114221814.GA19630@alvherre.pgsql
Includes some manual cleanup of places that pgindent messed up,
most of which weren't per project style anyway.
Notably, it seems some people didn't absorb the style rules of
commit c9d297751, because there were a bunch of new occurrences
of function calls with a newline just after the left paren, all
with faulty expectations about how the rest of the call would get
indented.
2nd pass of modifying various places which obtain the next power
of 2 of a number and make them use the new functions added in
f0705bb62.
In passing, also modify num_combinations(). This can be implemented
using simple bitshifting rather than looping.
Reviewed-by: John Naylor
Discussion: https://postgr.es/m/20200114173553.GE32763%40fetter.org
Must hold some lock on the pg_statistic_ext_data catalog *before*
we look up the tuple we aim to replace. Otherwise a concurrent
VACUUM FULL or similar operation could move it to a different TID,
leaving us trying to replace the wrong tuple.
Back-patch to v12 where this got broken.
Credit goes to Dean Rasheed; I'm just doing the clerical work.
Discussion: https://postgr.es/m/CAEZATCU0zHMDiQV0g8P2U+YSP9C1idUPrn79DajsbonwkN0xvQ@mail.gmail.com
Formerly we applied a functional dependency "a => b with dependency
degree f" using the formula
P(a,b) = P(a) * [f + (1-f)*P(b)]
This leads to the possibility that the combined selectivity P(a,b)
could exceed P(b), which is not ideal. The addition of support for IN
and OR clauses (commits 8f321bd16c and ccaa3569f5) would seem to make
this more likely, since the user-supplied values in such clauses are
not necessarily compatible with the functional dependency.
Mitigate this by using the formula
P(a,b) = f * Min(P(a), P(b)) + (1-f) * P(a) * P(b)
instead, which guarantees that the combined selectivity is less than
each column's individual selectivity. Logically, this is modifies the
part of the formula that accounts for dependent rows to handle cases
where P(a) > P(b), whilst not changing the second term which accounts
for independent rows.
Additionally, this refactors the way that functional dependencies are
applied, so now dependencies_clauselist_selectivity() estimates both
the implying clauses and the implied clauses for each functional
dependency (formerly only the implied clauses were estimated), and now
all clauses for each attribute are taken into account (formerly only
one clause for each implied attribute was estimated). This removes the
previously built-in assumption that only equality clauses will be
seen, which is no longer true, and opens up the possibility of
applying functional dependencies to more general clauses.
Patch by me, reviewed by Tomas Vondra.
Discussion: https://postgr.es/m/CAEZATCXaNFZyOhR4XXAfkvj1tibRBEjje6ZbXwqWUB_tqbH%3Drw%40mail.gmail.com
Discussion: https://postgr.es/m/20200318002946.6dvblukm3cfmgir2%40development
Since commit 8f321bd16c functional dependencies can handle IN clauses,
which however introduced a possible (and surprising) inconsistency,
because IN clauses may be expressed as an OR clause, which are still
considered incompatible. For example
a IN (1, 2, 3)
may be rewritten as
(a = 1 OR a = 2 OR a = 3)
The IN clause will work fine with functional dependencies, but the OR
clause will force the estimation to fall back to plain per-column
estimates, possibly introducing significant estimation errors.
This commit recognizes OR clauses equivalent to an IN clause (when all
arugments are compatible and reference the same attribute) as a special
case, compatible with functional dependencies. This allows applying
functional dependencies, just like for IN clauses.
This does not eliminate the difference in estimating the clause itself,
i.e. IN clause and OR clause still use different formulas. It would be
possible to change that (for these special OR clauses), but that's not
really about extended statistics - it was always like this. Moreover the
errors are usually much smaller compared to ignoring dependencies.
Author: Tomas Vondra
Reviewed-by: Dean Rasheed
Discussion: https://www.postgresql.org/message-id/flat/13902317.Eha0YfKkKy%40pierred-pdoc
Commit 8f321bd16c added support for estimating ScalarArrayOpExpr clauses
(IN/ANY) clauses using functional dependencies. There's no good reason
not to support estimation of these clauses using multi-variate MCV lists
too, so this commits implements that. That makes the behavior consistent
and MCV lists can estimate all variants (ANY/ALL, inequalities, ...).
Author: Tomas Vondra
Review: Dean Rasheed
Discussion: https://www.postgresql.org/message-id/flat/13902317.Eha0YfKkKy%40pierred-pdoc
Until now functional dependencies supported only simple equality clauses
and clauses that can be trivially translated to equalities. This commit
allows estimation of some ScalarArrayOpExpr (IN/ANY) clauses.
For IN clauses we can do this thanks to using operator with equality
semantics, which means an IN clause
WHERE c IN (1, 2, ..., N)
can be translated to
WHERE (c = 1 OR c = 2 OR ... OR c = N)
IN clauses are now considered compatible with functional dependencies,
and rely on the same assumption of consistency of queries with data
(which is an assumption we already used for simple equality clauses).
This applies also to ALL clauses with an equality operator, which can be
considered equivalent to IN clause.
ALL clauses are still considered incompatible, although there's some
discussion about maybe relaxing this in the future.
Author: Pierre Ducroquet
Reviewed-by: Tomas Vondra, Dean Rasheed
Discussion: https://www.postgresql.org/message-id/flat/13902317.Eha0YfKkKy%40pierred-pdoc
The need for this was removed by
8b9e9644dc.
A number of files now need to include utils/acl.h or
parser/parse_node.h explicitly where they previously got it indirectly
somehow.
Since parser/parse_node.h already includes nodes/parsenodes.h, the
latter is then removed where the former was added. Also, remove
nodes/pg_list.h from objectaddress.h, since that's included via
nodes/parsenodes.h.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/7601e258-26b2-8481-36d0-dc9dca6f28f1%402ndquadrant.com
Tom Lane