EXPLAIN (ANALYZE, SERIALIZE) allows collection of statistics about
the volume of data emitted by a query, as well as the time taken
to convert the data to the on-the-wire format. Previously there
was no way to investigate this without actually sending the data
to the client, in which case network transmission costs might
swamp what you wanted to see. In particular this feature allows
investigating the costs of de-TOASTing compressed or out-of-line
data during formatting.
Stepan Rutz and Matthias van de Meent,
reviewed by Tomas Vondra and myself
Discussion: https://postgr.es/m/ca0adb0e-fa4e-c37e-1cd7-91170b18cae1@gmx.de
There is a hook called ExplainOneQuery_hook that gives modules the
possibility to plug into this code path, but, like utility.c for utility
statement execution, there is no corresponding "standard" routine in
the case of EXPLAIN executed for one Query.
This commit adds a new standard_ExplainOneQuery() in explain.c, which is
able to run explain on a non-utility Query without calling its hook.
Per the feedback received from a couple of hackers, this change gives
the possibility to cut a few hundred lines of code in some of the
popular out-of-core modules as these maintained a copy of
ExplainOneQuery(), adding custom extra information at the beginning or
the end of the EXPLAIN output.
Author: Mats Kindahl
Reviewed-by: Aleksander Alekseev, Jelte Fennema-Nio, Andrei Lepikhov
Discussion: https://postgr.es/m/CA+14427V_B4EAoC_o-iYYucRdMSOTfpuH9k-QbexffY1HYJBiA@mail.gmail.com
This adds a new "Memory:" line under the "Planning:" group (which
currently only has "Buffers:") when the MEMORY option is specified.
In order to make the reporting reasonably accurate, we create a separate
memory context for planner activities, to be used only when this option
is given. The total amount of memory allocated by that context is
reported as "allocated"; we subtract memory in the context's freelists
from that and report that result as "used". We use
MemoryContextStatsInternal() to obtain the quantities.
The code structure to show buffer usage during planning was not in
amazing shape, so I (Álvaro) modified the patch a bit to clean that up
in passing.
Author: Ashutosh Bapat
Reviewed-by: David Rowley, Andrey Lepikhov, Jian He, Andy Fan
Discussion: https://www.postgresql.org/message-id/CAExHW5sZA=5LJ_ZPpRO-w09ck8z9p7eaYAqq3Ks9GDfhrxeWBw@mail.gmail.com
Since C99, there can be a trailing comma after the last value in an
enum definition. A lot of new code has been introducing this style on
the fly. Some new patches are now taking an inconsistent approach to
this. Some add the last comma on the fly if they add a new last
value, some are trying to preserve the existing style in each place,
some are even dropping the last comma if there was one. We could
nudge this all in a consistent direction if we just add the trailing
commas everywhere once.
I omitted a few places where there was a fixed "last" value that will
always stay last. I also skipped the header files of libpq and ecpg,
in case people want to use those with older compilers. There were
also a small number of cases where the enum type wasn't used anywhere
(but the enum values were), which ended up confusing pgindent a bit,
so I left those alone.
Discussion: https://www.postgresql.org/message-id/flat/386f8c45-c8ac-4681-8add-e3b0852c1620%40eisentraut.org
This provides a very simple way to see the generic plan for a
parameterized query. Without this, it's necessary to define
a prepared statement and temporarily change plan_cache_mode,
which is a bit tedious.
One thing that's a bit of a hack perhaps is that we disable
execution-time partition pruning when the GENERIC_PLAN option
is given. That's because the pruning code may attempt to
fetch the value of one of the parameters, which would fail.
Laurenz Albe, reviewed by Julien Rouhaud, Christoph Berg,
Michel Pelletier, Jim Jones, and myself
Discussion: https://postgr.es/m/0a29b954b10b57f0d135fe12aa0909bd41883eb0.camel@cybertec.at
auto_explain.log_parameter_max_length is a new GUC part of the
extension, similar to the corresponding core setting, that controls the
inclusion of query parameters in the logged explain output.
More tests are added to check the behavior of this new parameter: when
parameters logged in full (the default of -1), when disabled (value of
0) and when partially truncated (value different than the two others).
Author: Dagfinn Ilmari Mannsåker
Discussion: https://postgr.es/m/87ee09mohb.fsf@wibble.ilmari.org
This commit adds a new option WAL similar to existing option BUFFERS in the
EXPLAIN command. This option allows to include information on WAL record
generation added by commit df3b181499 in EXPLAIN output.
This also allows the WAL usage information to be displayed via
the auto_explain module. A new parameter auto_explain.log_wal controls
whether WAL usage statistics are printed when an execution plan is logged.
This parameter has no effect unless auto_explain.log_analyze is enabled.
Author: Julien Rouhaud
Reviewed-by: Dilip Kumar and Amit Kapila
Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com
When BUFFERS option is enabled, EXPLAIN command includes the information
on buffer usage during each plan node, in its output. In addition to that,
this commit makes EXPLAIN command include also the information on
buffer usage during planning phase, in its output. This feature makes it
easier to discern the cases where lots of buffer access happen during
planning.
This commit revives the original commit ed7a509571 that was reverted by
commit 19db23bcbd. The original commit had to be reverted because
it caused the regression test failure on the buildfarm members prion and
dory. But since commit c0885c4c30 got rid of the caues of the test failure,
the original commit can be safely introduced again.
Author: Julien Rouhaud, slightly revised by Fujii Masao
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/16109-26a1a88651e90608@postgresql.org
When BUFFERS option is enabled, EXPLAIN command includes the information
on buffer usage during each plan node, in its output. In addition to that,
this commit makes EXPLAIN command include also the information on
buffer usage during planning phase, in its output. This feature makes it
easier to discern the cases where lots of buffer access happen during
planning.
Author: Julien Rouhaud, slightly revised by Fujii Masao
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/16109-26a1a88651e90608@postgresql.org
Previously, it was possible for EXPLAIN ANALYZE of a parallel query
to produce several different "Workers" fields for a single plan node,
because different portions of explain.c independently generated
per-worker data and wrapped that output in separate fields. This
is pretty bogus, especially for the structured output formats: even
if it's not technically illegal, most programs would have a hard time
dealing with such data.
To improve matters, add infrastructure that allows redirecting
per-worker values into a side data structure, and then collect that
data into a single "Workers" field after we've finished running all
the relevant code for a given plan node.
There are a few visible side-effects:
* In text format, instead of something like
Sort Method: external merge Disk: 4920kB
Worker 0: Sort Method: external merge Disk: 5880kB
Worker 1: Sort Method: external merge Disk: 5920kB
Buffers: shared hit=682 read=10188, temp read=1415 written=2101
Worker 0: actual time=130.058..130.324 rows=1324 loops=1
Buffers: shared hit=337 read=3489, temp read=505 written=739
Worker 1: actual time=130.273..130.512 rows=1297 loops=1
Buffers: shared hit=345 read=3507, temp read=505 written=744
you get
Sort Method: external merge Disk: 4920kB
Buffers: shared hit=682 read=10188, temp read=1415 written=2101
Worker 0: actual time=130.058..130.324 rows=1324 loops=1
Sort Method: external merge Disk: 5880kB
Buffers: shared hit=337 read=3489, temp read=505 written=739
Worker 1: actual time=130.273..130.512 rows=1297 loops=1
Sort Method: external merge Disk: 5920kB
Buffers: shared hit=345 read=3507, temp read=505 written=744
* When JIT is enabled, any relevant per-worker JIT stats are attached
to the child node of the Gather or Gather Merge node, which is where
the other per-worker output has always been. Previously, that info
was attached directly to a Gather node, or missed entirely for Gather
Merge.
* A query's summary JIT data no longer includes a bogus
"Worker Number: -1" field.
A notable code-level change is that indenting for lines of text-format
output should now be handled by calling "ExplainIndentText(es)",
instead of hard-wiring how much space to emit. This seems a good deal
cleaner anyway.
This patch also adds a new "explain.sql" regression test script that's
dedicated to testing EXPLAIN. There is more that can be done in that
line, certainly, but for now it just adds some coverage of the XML and
YAML output formats, which had been completely untested.
Although this is surely a bug fix, it's not clear that people would
be happy with rearranging EXPLAIN output in a minor release, so apply
to HEAD only.
Maciek Sakrejda and Tom Lane, based on an idea of Andres Freund's;
reviewed by Georgios Kokolatos
Discussion: https://postgr.es/m/CAOtHd0AvAA8CLB9Xz0wnxu1U=zJCKrr1r4QwwXi_kcQsHDVU=Q@mail.gmail.com
Pass ParseState into the functions called from
standard_ProcessUtility() instead passing the query string and query
environment separately. No functionality change, but it makes the
notation consistent. We had already started moving things into
that direction piece by piece, and this completes it.
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/6e7aa4a1-be6a-1a75-b1f9-83a678e5184a@2ndquadrant.com
force_parallel_mode = regress is supposed to force use of a Gather
node without having any impact on EXPLAIN output. But it failed to
accomplish that if both ANALYZE and VERBOSE are given, because that
enables per-worker output data that you wouldn't see if the Gather
hadn't been inserted. Improve the logic so that we suppress the
per-worker data too.
This allows putting the new test case added by commit 5935917ce
back into the originally intended form (cf. 776a2c887, 22864f6e0).
We can also get rid of a kluge in subselect.sql, which previously
had to clean up after force_parallel_mode's failure to do what it
said on the tin.
Discussion: https://postgr.es/m/18445.1576177309@sss.pgh.pa.us
Query planning is affected by a number of configuration options, and it
may be crucial to know which of those options were set to non-default
values. With this patch you can say EXPLAIN (SETTINGS ON) to include
that information in the query plan. Only options affecting planning,
with values different from the built-in default are printed.
This patch also adds auto_explain.log_settings option, providing the
same capability in auto_explain module.
Author: Tomas Vondra
Reviewed-by: Rafia Sabih, John Naylor
Discussion: https://postgr.es/m/e1791b4c-df9c-be02-edc5-7c8874944be0@2ndquadrant.com
I (Andres) was more than a bit hasty in committing 33001fd7a7
after last minute changes, leading to a number of problems (jit output
was only shown for JIT in parallel workers, and just EXPLAIN without
ANALYZE didn't work). Lukas luckily found these issues quickly.
Instead of combining instrumentation in in standard_ExecutorEnd(), do
so on demand in the new ExplainPrintJITSummary().
Also update a documentation example of the JIT output, changed in
52050ad8eb.
Author: Lukas Fittl, with minor changes by me
Discussion: https://postgr.es/m/CAP53PkxmgJht69pabxBXJBM+0oc6kf3KHMborLP7H2ouJ0CCtQ@mail.gmail.com
Backpatch: 11, where JIT compilation was introduced
Previously, when using parallel query, EXPLAIN (ANALYZE)'s JIT
compilation timings did not include the overhead from doing so on the
workers. Fix that.
We do so by simply aggregating the cost of doing JIT compilation on
workers and the leader together. Arguably that's not quite accurate,
because the total time spend doing so is spent in parallel - but it's
hard to do much better. For additional detail, when VERBOSE is
specified, the stats for workers are displayed separately.
Author: Amit Khandekar and Andres Freund
Discussion: https://postgr.es/m/CAJ3gD9eLrz51RK_gTkod+71iDcjpB_N8eC6vU2AW-VicsAERpQ@mail.gmail.com
Backpatch: 11-
This just shows a few details about JITing, e.g. how many functions
have been JITed, and how long that took. To avoid noise in regression
tests with functions sometimes being JITed in --with-llvm builds,
disable display when COSTS OFF is specified.
Author: Andres Freund
Discussion: https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de
This allows to deduplicate some existing code, but mainly avoids some
duplication in upcoming commits.
In passing, fix variable names indicating wrong unit (seconds instead
of ms).
Author: Andres Freund
Discussion: https://postgr.es/m/20180314002740.cah3mdsonz5mxney@alap3.anarazel.de
'long' is not useful type across platforms, as it's 32bit on 32 bit
platforms, and even on some 64bit platforms (e.g. windows) it's still
only 32bits wide.
As ExplainPropertyInteger should never be performance critical, change
it to accept a 64bit argument and remove ExplainPropertyLong.
Author: Andres Freund
Discussion: https://postgr.es/m/20180314164832.n56wt7zcbpzi6zxe@alap3.anarazel.de
This should have been done in commit 18ce3a4ab, which added that parameter
to ExplainOneQuery, but it was overlooked. This makes it impossible for
a user of the hook to pass the queryEnv down to ExplainOnePlan.
It's too late to change this API in v10, I suppose, but fortunately
passing NULL to ExplainOnePlan will work in nearly all interesting
cases in v10. That might not be true forever, so we'd better fix it.
Tatsuro Yamada, reviewed by Thomas Munro
Discussion: https://postgr.es/m/890e8dd9-c1c7-a422-6892-874f5eaee048@lab.ntt.co.jp
Don't move parenthesized lines to the left, even if that means they
flow past the right margin.
By default, BSD indent lines up statement continuation lines that are
within parentheses so that they start just to the right of the preceding
left parenthesis. However, traditionally, if that resulted in the
continuation line extending to the right of the desired right margin,
then indent would push it left just far enough to not overrun the margin,
if it could do so without making the continuation line start to the left of
the current statement indent. That makes for a weird mix of indentations
unless one has been completely rigid about never violating the 80-column
limit.
This behavior has been pretty universally panned by Postgres developers.
Hence, disable it with indent's new -lpl switch, so that parenthesized
lines are always lined up with the preceding left paren.
This patch is much less interesting than the first round of indent
changes, but also bulkier, so I thought it best to separate the effects.
Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
Change pg_bsd_indent to follow upstream rules for placement of comments
to the right of code, and remove pgindent hack that caused comments
following #endif to not obey the general rule.
Commit e3860ffa4d wasn't actually using
the published version of pg_bsd_indent, but a hacked-up version that
tried to minimize the amount of movement of comments to the right of
code. The situation of interest is where such a comment has to be
moved to the right of its default placement at column 33 because there's
code there. BSD indent has always moved right in units of tab stops
in such cases --- but in the previous incarnation, indent was working
in 8-space tab stops, while now it knows we use 4-space tabs. So the
net result is that in about half the cases, such comments are placed
one tab stop left of before. This is better all around: it leaves
more room on the line for comment text, and it means that in such
cases the comment uniformly starts at the next 4-space tab stop after
the code, rather than sometimes one and sometimes two tabs after.
Also, ensure that comments following #endif are indented the same
as comments following other preprocessor commands such as #else.
That inconsistency turns out to have been self-inflicted damage
from a poorly-thought-through post-indent "fixup" in pgindent.
This patch is much less interesting than the first round of indent
changes, but also bulkier, so I thought it best to separate the effects.
Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
The new indent version includes numerous fixes thanks to Piotr Stefaniak.
The main changes visible in this commit are:
* Nicer formatting of function-pointer declarations.
* No longer unexpectedly removes spaces in expressions using casts,
sizeof, or offsetof.
* No longer wants to add a space in "struct structname *varname", as
well as some similar cases for const- or volatile-qualified pointers.
* Declarations using PG_USED_FOR_ASSERTS_ONLY are formatted more nicely.
* Fixes bug where comments following declarations were sometimes placed
with no space separating them from the code.
* Fixes some odd decisions for comments following case labels.
* Fixes some cases where comments following code were indented to less
than the expected column 33.
On the less good side, it now tends to put more whitespace around typedef
names that are not listed in typedefs.list. This might encourage us to
put more effort into typedef name collection; it's not really a bug in
indent itself.
There are more changes coming after this round, having to do with comment
indentation and alignment of lines appearing within parentheses. I wanted
to limit the size of the diffs to something that could be reviewed without
one's eyes completely glazing over, so it seemed better to split up the
changes as much as practical.
Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
A QueryEnvironment concept is added, which allows new types of
objects to be passed into queries from parsing on through
execution. At this point, the only thing implemented is a
collection of EphemeralNamedRelation objects -- relations which
can be referenced by name in queries, but do not exist in the
catalogs. The only type of ENR implemented is NamedTuplestore, but
provision is made to add more types fairly easily.
An ENR can carry its own TupleDesc or reference a relation in the
catalogs by relid.
Although these features can be used without SPI, convenience
functions are added to SPI so that ENRs can easily be used by code
run through SPI.
The initial use of all this is going to be transition tables in
AFTER triggers, but that will be added to each PL as a separate
commit.
An incidental effect of this patch is to produce a more informative
error message if an attempt is made to modify the contents of a CTE
from a referencing DML statement. No tests previously covered that
possibility, so one is added.
Kevin Grittner and Thomas Munro
Reviewed by Heikki Linnakangas, David Fetter, and Thomas Munro
with valuable comments and suggestions from many others
This patch makes several changes that improve the consistency of
representation of lists of statements. It's always been the case
that the output of parse analysis is a list of Query nodes, whatever
the types of the individual statements in the list. This patch brings
similar consistency to the outputs of raw parsing and planning steps:
* The output of raw parsing is now always a list of RawStmt nodes;
the statement-type-dependent nodes are one level down from that.
* The output of pg_plan_queries() is now always a list of PlannedStmt
nodes, even for utility statements. In the case of a utility statement,
"planning" just consists of wrapping a CMD_UTILITY PlannedStmt around
the utility node. This list representation is now used in Portal and
CachedPlan plan lists, replacing the former convention of intermixing
PlannedStmts with bare utility-statement nodes.
Now, every list of statements has a consistent head-node type depending
on how far along it is in processing. This allows changing many places
that formerly used generic "Node *" pointers to use a more specific
pointer type, thus reducing the number of IsA() tests and casts needed,
as well as improving code clarity.
Also, the post-parse-analysis representation of DECLARE CURSOR is changed
so that it looks more like EXPLAIN, PREPARE, etc. That is, the contained
SELECT remains a child of the DeclareCursorStmt rather than getting flipped
around to be the other way. It's now true for both Query and PlannedStmt
that utilityStmt is non-null if and only if commandType is CMD_UTILITY.
That allows simplifying a lot of places that were testing both fields.
(I think some of those were just defensive programming, but in many places,
it was actually necessary to avoid confusing DECLARE CURSOR with SELECT.)
Because PlannedStmt carries a canSetTag field, we're also able to get rid
of some ad-hoc rules about how to reconstruct canSetTag for a bare utility
statement; specifically, the assumption that a utility is canSetTag if and
only if it's the only one in its list. While I see no near-term need for
relaxing that restriction, it's nice to get rid of the ad-hocery.
The API of ProcessUtility() is changed so that what it's passed is the
wrapper PlannedStmt not just the bare utility statement. This will affect
all users of ProcessUtility_hook, but the changes are pretty trivial; see
the affected contrib modules for examples of the minimum change needed.
(Most compilers should give pointer-type-mismatch warnings for uncorrected
code.)
There's also a change in the API of ExplainOneQuery_hook, to pass through
cursorOptions instead of expecting hook functions to know what to pick.
This is needed because of the DECLARE CURSOR changes, but really should
have been done in 9.6; it's unlikely that any extant hook functions
know about using CURSOR_OPT_PARALLEL_OK.
Finally, teach gram.y to save statement boundary locations in RawStmt
nodes, and pass those through to Query and PlannedStmt nodes. This allows
more intelligent handling of cases where a source query string contains
multiple statements. This patch doesn't actually do anything with the
information, but a follow-on patch will. (Passing this information through
cleanly is the true motivation for these changes; while I think this is all
good cleanup, it's unlikely we'd have bothered without this end goal.)
catversion bump because addition of location fields to struct Query
affects stored rules.
This patch is by me, but it owes a good deal to Fabien Coelho who did
a lot of preliminary work on the problem, and also reviewed the patch.
Discussion: https://postgr.es/m/alpine.DEB.2.20.1612200926310.29821@lancre
Add a location field to the DefElem struct, used to parse many utility
commands. Update various error messages to supply error position
information.
To propogate the error position information in a more systematic way,
create a ParseState in standard_ProcessUtility() and pass that to
interested functions implementing the utility commands. This seems
better than passing the query string and then reassembling a parse state
ad hoc, which violates the encapsulation of the ParseState type.
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
We have, for a very long time, allowed the same subplan (same member of the
PlannedStmt.subplans list) to be referenced by more than one SubPlan node;
this avoids problems for cases such as subplans within an IndexScan's
indxqual and indxqualorig fields. However, EXPLAIN had not gotten the memo
and would print each reference as though it were an independent identical
subplan. To fix, track plan_ids of subplans we've printed and don't print
the same plan_id twice. Per report from Pavel Stehule.
BTW: the particular case of IndexScan didn't cause visible duplication
in a plain EXPLAIN, only EXPLAIN ANALYZE, because in the former case we
short-circuit executor startup before the indxqual field is processed by
ExecInitExpr. That seems like it could easily lead to other EXPLAIN
problems in future, but it's not clear how to avoid it without breaking
the "EXPLAIN a plan using hypothetical indexes" use-case. For now I've
left that issue alone.
Although this is a longstanding bug, it's purely cosmetic (no great harm
is done by the repeat printout) and we haven't had field complaints before.
So I'm hesitant to back-patch it, especially since there is some small risk
of ABI problems due to the need to add a new field to ExplainState.
In passing, rearrange order of fields in ExplainState to be less random,
and update some obsolete comments about when/where to initialize them.
Report: <CAFj8pRAimq+NK-menjt+3J4-LFoodDD8Or6=Lc_stcFD+eD4DA@mail.gmail.com>
In non-text output formats, parallelized aggregates were reporting
"Partial" or "Finalize" as a field named "Operation", which might be all
right in the absence of any context --- but other plan node types use that
field to report SQL-visible semantics, such as Select/Insert/Update/Delete.
So that naming choice didn't seem good to me. I changed it to "Partial
Mode".
Also, the field did not appear at all for a non-parallelized Agg plan node,
which is contrary to expectation in non-text formats. We're notionally
producing objects that conform to a schema, so the set of fields for a
given node type and EXPLAIN mode should be well-defined. I set it up to
fill in "Simple" in such cases.
Other fields that were added for parallel query, namely "Parallel Aware"
and Gather's "Single Copy", had not gotten the word on that point either.
Make them appear always in non-text output.
Also, the latter two fields were nominally producing boolean output, but
were getting it wrong, because bool values shouldn't be quoted in JSON or
YAML. Somehow we'd not needed an ExplainPropertyBool formatting subroutine
before 9.6; but now we do, so invent it.
Discussion: <16002.1466972724@sss.pgh.pa.us>
This SQL standard functionality allows to aggregate data by different
GROUP BY clauses at once. Each grouping set returns rows with columns
grouped by in other sets set to NULL.
This could previously be achieved by doing each grouping as a separate
query, conjoined by UNION ALLs. Besides being considerably more concise,
grouping sets will in many cases be faster, requiring only one scan over
the underlying data.
The current implementation of grouping sets only supports using sorting
for input. Individual sets that share a sort order are computed in one
pass. If there are sets that don't share a sort order, additional sort &
aggregation steps are performed. These additional passes are sourced by
the previous sort step; thus avoiding repeated scans of the source data.
The code is structured in a way that adding support for purely using
hash aggregation or a mix of hashing and sorting is possible. Sorting
was chosen to be supported first, as it is the most generic method of
implementation.
Instead of, as in an earlier versions of the patch, representing the
chain of sort and aggregation steps as full blown planner and executor
nodes, all but the first sort are performed inside the aggregation node
itself. This avoids the need to do some unusual gymnastics to handle
having to return aggregated and non-aggregated tuples from underlying
nodes, as well as having to shut down underlying nodes early to limit
memory usage. The optimizer still builds Sort/Agg node to describe each
phase, but they're not part of the plan tree, but instead additional
data for the aggregation node. They're a convenient and preexisting way
to describe aggregation and sorting. The first (and possibly only) sort
step is still performed as a separate execution step. That retains
similarity with existing group by plans, makes rescans fairly simple,
avoids very deep plans (leading to slow explains) and easily allows to
avoid the sorting step if the underlying data is sorted by other means.
A somewhat ugly side of this patch is having to deal with a grammar
ambiguity between the new CUBE keyword and the cube extension/functions
named cube (and rollup). To avoid breaking existing deployments of the
cube extension it has not been renamed, neither has cube been made a
reserved keyword. Instead precedence hacking is used to make GROUP BY
cube(..) refer to the CUBE grouping sets feature, and not the function
cube(). To actually group by a function cube(), unlikely as that might
be, the function name has to be quoted.
Needs a catversion bump because stored rules may change.
Author: Andrew Gierth and Atri Sharma, with contributions from Andres Freund
Reviewed-By: Andres Freund, Noah Misch, Tom Lane, Svenne Krap, Tomas
Vondra, Erik Rijkers, Marti Raudsepp, Pavel Stehule
Discussion: CAOeZVidmVRe2jU6aMk_5qkxnB7dfmPROzM7Ur8JPW5j8Y5X-Lw@mail.gmail.com
The folly of the previous arrangement was just demonstrated: there's no
convenient way to add fields to ExplainState without breaking ABI, even
if callers have no need to touch those fields. Since we might well need
to do that again someday in back branches, let's change things so that
only explain.c has to have sizeof(ExplainState) compiled into it. This
costs one extra palloc() per EXPLAIN operation, which is surely pretty
negligible.
As of 9.3, ruleutils.c goes to some lengths to ensure that table and column
aliases used in its output are unique. Of course this takes more time than
was required before, which in itself isn't fatal. However, EXPLAIN was set
up so that recalculation of the unique aliases was repeated for each
subexpression printed in a plan. That results in O(N^2) time and memory
consumption for large plan trees, which did not happen in older branches.
Fortunately, the expensive work is the same across a whole plan tree,
so there is no need to repeat it; we can do most of the initialization
just once per query and re-use it for each subexpression. This buys
back most (not all) of the performance loss since 9.2.
We need an extra ExplainState field to hold the precalculated deparse
context. That's no problem in HEAD, but in the back branches, expanding
sizeof(ExplainState) seems risky because third-party extensions might
have local variables of that struct type. So, in 9.4 and 9.3, introduce
an auxiliary struct to keep sizeof(ExplainState) the same. We should
refactor the APIs to avoid such local variables in future, but that's
material for a separate HEAD-only commit.
Per gripe from Alexey Bashtanov. Back-patch to 9.3 where the issue
was introduced.
We've gotten enough push-back on that change to make it clear that it
wasn't an especially good idea to do it like that. Revert plain EXPLAIN
to its previous behavior, but keep the extra output in EXPLAIN ANALYZE.
Per discussion.
Internally, I set this up as a separate flag ExplainState.summary that
controls printing of planning time and execution time. For now it's
just copied from the ANALYZE option, but we could consider exposing it
to users.
This doesn't work for prepared queries, but it's not too easy to get
the information in that case and there's some debate as to exactly
what the right thing to measure is, so just do this for now.
Andreas Karlsson, with slight doc changes by me.
Tom Lane
Michael Paquier
Alvaro Herrera
Bruce Momjian
Peter Eisentraut
Amit Kapila
Fujii Masao
Tomas Vondra
Andres Freund
Kevin Grittner
Peter Eisentraut
Robert Haas