Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Mon, Mar 19, 2018 at 11:57 AM, Robert Haas  wrote:
> On Fri, Mar 16, 2018 at 7:35 AM, Rajkumar Raghuwanshi
>  wrote:
>> On Fri, Mar 9, 2018 at 1:04 AM, Robert Haas  wrote:
>>> Great.  Committed 0001.  Are you planning any further testing of this
>>> patch series?
>>
>> Sorry I missed the mail.
>> Yes, I have further tested patches and find no more issues.
>
> OK, thanks to both you and Ashutosh Bapat.  Committed 0002 and 0003.

And now committed 0004.  This area could use significantly more work,
but I think it's better to have this much than not.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Fri, Mar 16, 2018 at 7:35 AM, Rajkumar Raghuwanshi
 wrote:
> On Fri, Mar 9, 2018 at 1:04 AM, Robert Haas  wrote:
>> Great.  Committed 0001.  Are you planning any further testing of this
>> patch series?
>
> Sorry I missed the mail.
> Yes, I have further tested patches and find no more issues.

OK, thanks to both you and Ashutosh Bapat.  Committed 0002 and 0003.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Re: parallel append vs. simple UNION ALL

[Rajkumar Raghuwanshi]

On Fri, Mar 9, 2018 at 1:04 AM, Robert Haas  wrote:

> Great.  Committed 0001.  Are you planning any further testing of this
> patch series?


Sorry I missed the mail.
Yes, I have further tested patches and find no more issues.

Thanks & Regards,
Rajkumar Raghuwanshi
QMG, EnterpriseDB Corporation

Re: parallel append vs. simple UNION ALL

[Ashutosh Bapat]

On Wed, Mar 14, 2018 at 2:09 AM, Robert Haas  wrote:
> On Tue, Mar 13, 2018 at 12:35 AM, Ashutosh Bapat
>  wrote:
>> It looks like it was not changed in all the places. make falied. I
>> have fixed all the instances of these two functions in the attached
>> patchset (only 0003 changes). Please check.
>
> Oops.  Thanks.
>
> I'm going to go ahead and commit 0001 here.  Any more thoughts on the rest?

Nope. I am good with the patchset.

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Tue, Mar 13, 2018 at 12:35 AM, Ashutosh Bapat
 wrote:
> It looks like it was not changed in all the places. make falied. I
> have fixed all the instances of these two functions in the attached
> patchset (only 0003 changes). Please check.

Oops.  Thanks.

I'm going to go ahead and commit 0001 here.  Any more thoughts on the rest?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Re: parallel append vs. simple UNION ALL

[Ashutosh Bapat]

On Fri, Mar 9, 2018 at 1:28 AM, Robert Haas  wrote:
>
>> 0003
>> Probably we want to rename generate_union_path() as generate_union_rel() or
>> generate_union_paths() since the function doesn't return a path anymore.
>> Similarly for generate_nonunion_path().
>
> Good point.  Changed.

It looks like it was not changed in all the places. make falied. I
have fixed all the instances of these two functions in the attached
patchset (only 0003 changes). Please check.

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
From 7e654c0ae30d867edea5a1a2ca8f7a17b05ed7c5 Mon Sep 17 00:00:00 2001
From: Robert Haas 
Date: Fri, 23 Feb 2018 11:53:07 -0500
Subject: [PATCH 1/4] Let Parallel Append over simple UNION ALL have partial
 subpaths.

A simple UNION ALL gets flattened into an appendrel of subquery
RTEs, but up until now it's been impossible for the appendrel to use
the partial paths for the subqueries, so we can implement the
appendrel as a Parallel Append but only one with non-partial paths
as children.

There are three separate obstacles to removing that limitation.
First, when planning a subquery, propagate any partial paths to the
final_rel so that they are potentially visible to outer query levels
(but not if they have initPlans attached, because that wouldn't be
safe).  Second, after planning a subquery, propagate any partial paths
for the final_rel to the subquery RTE in the outer query level in the
same way we do for non-partial paths.  Third, teach finalize_plan() to
account for the possibility that the fake parameter we use for rescan
signalling when the plan contains a Gather (Merge) node may be
propagated from an outer query level.

Patch by me, reviewed and tested by Amit Khandekar and Rajkumar
Raghuwanshi.  Test cases based on examples by Rajkumar Raghuwanshi.

Discussion: http://postgr.es/m/ca+tgmoa6l9a1nnck3atdvzlz4kkhdn1+tm7mfyfvp+uqps7...@mail.gmail.com
---
 src/backend/optimizer/path/allpaths.c |   22 +
 src/backend/optimizer/plan/planner.c  |   16 ++
 src/backend/optimizer/plan/subselect.c|   17 ++-
 src/test/regress/expected/select_parallel.out |   65 +
 src/test/regress/sql/select_parallel.sql  |   25 ++
 5 files changed, 143 insertions(+), 2 deletions(-)

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 1c792a0..ea4e683 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2179,6 +2179,28 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
  create_subqueryscan_path(root, rel, subpath,
 		  pathkeys, required_outer));
 	}
+
+	/* If consider_parallel is false, there should be no partial paths. */
+	Assert(sub_final_rel->consider_parallel ||
+		   sub_final_rel->partial_pathlist == NIL);
+
+	/* Same for partial paths. */
+	foreach(lc, sub_final_rel->partial_pathlist)
+	{
+		Path	   *subpath = (Path *) lfirst(lc);
+		List	   *pathkeys;
+
+		/* Convert subpath's pathkeys to outer representation */
+		pathkeys = convert_subquery_pathkeys(root,
+			 rel,
+			 subpath->pathkeys,
+			 make_tlist_from_pathtarget(subpath->pathtarget));
+
+		/* Generate outer path using this subpath */
+		add_partial_path(rel, (Path *)
+		 create_subqueryscan_path(root, rel, subpath,
+  pathkeys, required_outer));
+	}
 }
 
 /*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 24e6c46..66e7e7b 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -2195,6 +2195,22 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 	}
 
 	/*
+	 * Generate partial paths for final_rel, too, if outer query levels might
+	 * be able to make use of them.
+	 */
+	if (final_rel->consider_parallel && root->query_level > 1 &&
+		!limit_needed(parse))
+	{
+		Assert(!parse->rowMarks && parse->commandType == CMD_SELECT);
+		foreach(lc, current_rel->partial_pathlist)
+		{
+			Path	   *partial_path = (Path *) lfirst(lc);
+
+			add_partial_path(final_rel, partial_path);
+		}
+	}
+
+	/*
 	 * If there is an FDW that's responsible for all baserels of the query,
 	 * let it consider adding ForeignPaths.
 	 */
diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index dc86dd5..83008d7 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -2202,6 +2202,13 @@ SS_charge_for_initplans(PlannerInfo *root, RelOptInfo *final_rel)
 		path->parallel_safe = false;
 	}
 
+	/*
+	 * Forget about any partial paths and clear consider_parallel, too;
+	 * they're not usable if we attached an initPlan.
+	 */
+	final_rel->partial_pathlist = NIL;
+	final_rel->consider_parallel = false;
+
 	/* We needn't do set_cheapest() here, caller will do it */
 }
 
@@ -2407,10 +2414,16 @@ 

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Thu, Mar 1, 2018 at 8:30 AM, Ashutosh Bapat
 wrote:
> The patches look clean. I particularly looked at 0003.
>
> patch 0001
> +/*
> + * Generate partial paths for final_rel, too, if outer query levels might
> + * be able to make use of them.
> + */
> I am not able to understand the construct esp. the if clause. Did you want to
> say "... if there are outer query levels. Those might ..." or something like
> that?

Well, that's what I meant, but I didn't think it was necessary to
spell it out in quite that much detail.

> 0002
> (op->all == top_union->all || op->all) &&
> This isn't really your change.  Checking
> op->all is cheaper than checking equality, so may be we should check that 
> first
> and take advantage of short-circuit condition evaluation. If we do that above
> condition reduces to (op->all || !top_union->all) which is two boolean
> conditions, even cheaper. But may be the second optimization is not worth the
> loss of readability.

I doubt this makes any difference.  The compiler should be smart
enough to do this the same way regardless of exactly how we write it,
and if it's not, it can't make more than a few instructions worth of
difference.  This code is not nearly performance-critical enough for
that to matter.  Also, it's not the job of this patch to whack this
around.

> "identically-propertied UNIONs" may be "UNIONs with identical properties".

Likewise, I didn't write those words, so I don't plan to change them
just because I might have written them differently.

> 0003
> Probably we want to rename generate_union_path() as generate_union_rel() or
> generate_union_paths() since the function doesn't return a path anymore.
> Similarly for generate_nonunion_path().

Good point.  Changed.

> In recurse_set_operations()
> -return NULL;/* keep compiler quiet */
> This line is deleted and instead rel is initialized to NULL. That way we loose
> any chance to detect a future bug because of a block leaving rel uninitialized
> through compiler warning. May be we should replace "return NULL" with "rel =
> NULL", which will not be executed because of the error.

I don't think this is really a problem.  If some code path fails to
initialize rel, it's going to crash when postprocess_setop_rel() calls
set_cheapest().  Any warning the compiler gives is more likely to be a
false-positive than an actual problem.

> +/* Build path list and relid set. */
> +foreach(lc, rellist)
> +{
> With the changes in this patch, we could actually use 
> add_paths_to_append_rel()
> to create an append path. That function builds paths with different pathkeys,
> parameterization (doesn't matter here) and also handles parallel append. So we
> can avoid code duplication and also leverage more optimizations like using
> MergeAppend instead of overall sort etc. But that function doesn't have 
> ability
> to add a final node like make_union_unique(). A similar requirement has arisen
> in partition-wise join where we need to add a final node for finalising
> aggregate on top of paths created by add_paths_to_append_rel().  May be we can
> change that function to return a list of paths, which are then finalized by 
> the
> caller and added to "append" rel. But I don't think doing all that is in the
> scope of this patch set.

Yeah, I thought about all of that and came to similar conclusions.

> 0004
> +if (!op->all)
> +ppath = make_union_unique(op, ppath, tlist, root);
> We could probably push the grouping/sorting down to the parallel workers. But
> again not part of this patchset.

Yep.  There's a lot more work that could be done to improve setop
planning, but I think getting even this much done for v11 would be a
significant step forward.

Updated patches attached.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL CompanyOn Thu, Mar 1, 2018 at 8:30 AM, Ashutosh Bapat
mailto:ashutosh.ba...@enterprisedb.com;
target="_blank">ashutosh.ba...@enterprisedb.com
wrote:On
Sat, Feb 24, 2018 at 2:55 AM, Robert Haas mailto:robertmh...@gmail.com;>robertmh...@gmail.com
wrote:


 Here's an extended series of patches that
now handles both the simple
 UNION ALL case (where we flatten it) and the unflattened case:


The patches look clean. I particularly looked at 0003.

patch 0001
+  /*
+  * Generate partial paths for final_rel, too, if
outer query levels might
+  * be able to make use of them.
+  */
I am not able to understand the construct esp. the if clause. Did you
want to
say "... if there are outer query levels. Those might ..." or something like
that?

0002
(op-all ==
top_union-all || op-all) 
This isn't really your change. Checking
op-all is cheaper than checking equality, so may be we should
check that first
and take advantage of short-circuit condition evaluation. If we do
that above
condition reduces to (op-all || !top_union-all) which is two boolean
conditions, even 

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Thu, Mar 8, 2018 at 2:46 AM, Rajkumar Raghuwanshi
 wrote:
> On Thu, Mar 8, 2018 at 12:27 AM, Robert Haas  wrote:
>>
>> New patches attached, fixing all 3 of the issues you reported:
>
> Thanks. new patches applied cleanly on head and fixing all reported issue.

Great.  Committed 0001.  Are you planning any further testing of this
patch series?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Wed, Mar 7, 2018 at 5:36 AM, Rajkumar Raghuwanshi
 wrote:
> With 0001 applied on PG-head, I got reference leak warning and later a
> server crash.
> this crash is reproducible with enable_parallel_append=off also.
> below is the test case to reproduce this.

New patches attached, fixing all 3 of the issues you reported:

0001 is a new patch to fix the incorrect parallel safety marks on
upper relations.  I don't know of a visible effect of this patch by
itself, but there might be one.

0002 is the same as the old 0001, but I made a fix in
SS_charge_for_initplans() which fixed your most recent crash report.
Either this or the previous change also fixed the crash you saw when
using tab-completion.  Also, I added some test cases based on your
failing examples.

0003-0005 are the same as the old 0002-0004.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


0005-Consider-Parallel-Append-as-a-way-to-implement-a-uni.patch
Description: Binary data


0004-Generate-a-separate-upper-relation-for-each-stage-of.patch
Description: Binary data


0003-Rewrite-recurse_union_children-to-iterate-rather-tha.patch
Description: Binary data


0002-Let-Parallel-Append-over-simple-UNION-ALL-have-parti.patch
Description: Binary data


0001-Correctly-assess-parallel-safety-of-tlists-when-SRFs.patch
Description: Binary data

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Tue, Feb 27, 2018 at 6:21 AM, Rajkumar Raghuwanshi
 wrote:
> I have applied 0001 on pg-head, and while playing with regression tests, it
> crashed with below test case.
>
> postgres=# SET min_parallel_table_scan_size=0;
> SET
> postgres=# SELECT * FROM information_schema.foreign_data_wrapper_options
> ORDER BY 1, 2, 3;
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> The connection to the server was lost. Attempting reset: Failed.

Hmm, nice catch.  I think part of the problem here is that commit
69f4b9c85f168ae006929eec44fc44d569e846b9, wherein Andres introduced
the ProjectSet node, didn't really do the right thing in terms of
testing parallel-safety.  Before that commit, is_parallel_safe(root,
(Node *) scanjoin_target->exprs)) was really testing whether the tlist
produced during the scan/join phase was parallel-safe.  However, after
that commit, scanjoin_target->exprs wasn't really the final target for
the scan/join phase any more; instead, it was the first of possibly
several targets computed by split_pathtarget_at_srfs().  Really, the
right thing to do is to test the *last* element in that list for
parallel-safety, but as the code stands we end up testing the *first*
element.  So, if there's a parallel-restricted item in the target list
(this query ends up putting a CoerceToDomain in the target list, which
we currently consider parallel-restricted), it looks we can
nevertheless end up trying to project it in what is supposed to be a
partial path.

There are a large number of cases where this doesn't end up mattering
because the next upper_rel created will not get marked
consider_parallel because its target list will also contain the same
parallel-restricted construct, and therefore the partial paths
generated for the scan/join rel will never get used -- except to
generate Gather/Gather Merge paths, which has already happened; but
that step didn't know about the rest of the scan/join targets either,
so it won't have used them.  However, both create_distinct_paths() and
the code in grouping_planner that populates final_rel assume that they
don't need to retest the target for parallel-safety because no
projection is done at those levels; they just inherit the
parallel-safety marking of the input rel, so in those cases if the
input rel's marking is wrong the result is populated upward.

There's another way final_rel->consider_parallel can be wrong, too: if
the FROM-list is empty, then we create a join rel and set its
consider_parallel flag without regard to the parallel-safety of the
target list.  There are comments in query_planner() says that this
will be dealt with "later", but this seems not to be true. (Before
Tom's commit da1c91631e3577ea5818f855ebb5bd206d559006, the comments
simply ignored the question of whether a check was needed here, but
Tom seems to have inserted an incorrect justification for the
already-wrong code.)

I'm not sure to what degree, if at all, any of these problems are
visible given that we don't use final_rel->consider_parallel for much
of anything.  Certainly, it gets much easier to trigger a problem with
0001 applied, as the test case shows.  But I'm not entirely convinced
that there's no problem even without that.  It seems like every upper
rel that is setting its consider_parallel flag based on the first
element of some list of targets rather than the last is potentially
vulnerable to ending up with the wrong answer, and I'm afraid that
might have some adverse consequence that I haven't quite pinned down
yet.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Re: parallel append vs. simple UNION ALL

[Ashutosh Bapat]

On Sat, Feb 24, 2018 at 2:55 AM, Robert Haas  wrote:

>
> Here's an extended series of patches that now handles both the simple
> UNION ALL case (where we flatten it) and the unflattened case:
>

The patches look clean. I particularly looked at 0003.

patch 0001
+/*
+ * Generate partial paths for final_rel, too, if outer query levels might
+ * be able to make use of them.
+ */
I am not able to understand the construct esp. the if clause. Did you want to
say "... if there are outer query levels. Those might ..." or something like
that?

0002
(op->all == top_union->all || op->all) &&
This isn't really your change.  Checking
op->all is cheaper than checking equality, so may be we should check that first
and take advantage of short-circuit condition evaluation. If we do that above
condition reduces to (op->all || !top_union->all) which is two boolean
conditions, even cheaper. But may be the second optimization is not worth the
loss of readability.

"identically-propertied UNIONs" may be "UNIONs with identical properties".

0003
Probably we want to rename generate_union_path() as generate_union_rel() or
generate_union_paths() since the function doesn't return a path anymore.
Similarly for generate_nonunion_path().

In recurse_set_operations()
-return NULL;/* keep compiler quiet */
This line is deleted and instead rel is initialized to NULL. That way we loose
any chance to detect a future bug because of a block leaving rel uninitialized
through compiler warning. May be we should replace "return NULL" with "rel =
NULL", which will not be executed because of the error.

+/* Build path list and relid set. */
+foreach(lc, rellist)
+{
With the changes in this patch, we could actually use add_paths_to_append_rel()
to create an append path. That function builds paths with different pathkeys,
parameterization (doesn't matter here) and also handles parallel append. So we
can avoid code duplication and also leverage more optimizations like using
MergeAppend instead of overall sort etc. But that function doesn't have ability
to add a final node like make_union_unique(). A similar requirement has arisen
in partition-wise join where we need to add a final node for finalising
aggregate on top of paths created by add_paths_to_append_rel().  May be we can
change that function to return a list of paths, which are then finalized by the
caller and added to "append" rel. But I don't think doing all that is in the
scope of this patch set.

0004
+if (!op->all)
+ppath = make_union_unique(op, ppath, tlist, root);
We could probably push the grouping/sorting down to the parallel workers. But
again not part of this patchset.

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

Re: parallel append vs. simple UNION ALL

[Rajkumar Raghuwanshi]

On Sat, Feb 24, 2018 at 2:55 AM, Robert Haas  wrote:

> 0004 causes generate_union_path() to consider both the traditional
> method and also Gather -> Parallel Append -> [partial path for each
> subquery].  This is still a bit rough around the edges and there's a
> lot more that could be done here, but I'm posting what I have for now
> in the (perhaps vain) hope of getting some feedback.  With this, you
> can use Parallel Append for the UNION ALL step of a query like SELECT
> .. UNION ALL .. SELECT ... EXCEPT SELECT ...
>

Hi,

With all 0001,0002,0003 and 0004 patch applied on head, I am getting a
strange crash, while trying to change table name
in a query by using "TAB" key.

Same test case working fine with only 0001 applied and also on PG-head.

below are steps to reproduce.

--run below sqls

SET parallel_setup_cost=0;
SET parallel_tuple_cost=0;
SET min_parallel_table_scan_size=0;
CREATE TABLE tbl_union_t1 (c1 INTEGER PRIMARY KEY,c2 INTEGER,c3 CHAR(10));
INSERT INTO tbl_union_t1 SELECT i, i % 125, to_char(i % 4, 'FM') FROM
generate_series(0, 499,2) i;
CREATE TABLE tbl_union_t2 (c1 INTEGER PRIMARY KEY,c2 INTEGER,c3 CHAR(10));
INSERT INTO tbl_union_t2 SELECT i, i % 125, to_char(i % 4, 'FM') FROM
generate_series(0, 499,3) i;
ANALYSE tbl_union_t1;
ANALYSE tbl_union_t2;

EXPLAIN SELECT AVG(c1),SUM(c2) FROM (SELECT c1,c2 FROM tbl_union_t1 EXCEPT
SELECT c1,c2 FROM tbl_union_t2 WHERE c1 % 25 =0 )UA;


--now try modifying tbl_union_t1 in the above query
--remove "_union_t1" and press TAB key, It crashed for me.

EXPLAIN SELECT AVG(c1),SUM(c2) FROM (SELECT c1,c2 FROM tbl**EXCEPT SELECT c1,c2 FROM tbl_union_t2 WHERE c1 % 25 =0 )UA;

postgres=# EXPLAIN SELECT AVG(c1),SUM(c2) FROM (SELECT c1,c2 FROM
tblWARNING:  terminating connection because of crash of another server
process
DETAIL:  The postmaster has commanded this server process to roll back the
current transaction and exit, because another server process exited
abnormally and possibly corrupted shared memory.
HINT:  In a moment you should be able to reconnect to the database and
repeat your command.

--logfile says something like this
2018-03-01 18:37:36.456 IST [50071] LOG:  database system is ready to
accept connections
2018-03-01 18:38:38.668 IST [50071] LOG:  background worker "parallel
worker" (PID 51703) was terminated by signal 11: Segmentation fault
2018-03-01 18:38:38.668 IST [50071] DETAIL:  Failed process was running:
SELECT pg_catalog.quote_ident(c.relname) FROM pg_catalog.pg_class c WHERE
c.relkind IN ('r', 'S', 'v', 'm', 'f', 'p') AND
substring(pg_catalog.quote_ident(c.relname),1,3)='tbl' AND
pg_catalog.pg_table_is_visible(c.oid) AND c.relnamespace <> (SELECT oid
FROM pg_catalog.pg_namespace WHERE nspname = 'pg_catalog')
UNION
SELECT pg_catalog.quote_ident(n.nspname) || '.' FROM
pg_catalog.pg_namespace n WHERE substring(pg_catalog.quote_ident(n.nspname)
|| '.',1,3)='tbl' AND (SELECT pg_catalog.count(*) FROM
pg_catalog.pg_namespace WHERE substring(pg_catalog.quote_ident(nspname) ||
'.',1,3) =
substring('tbl',1,pg_catalog.length(pg_catalog.quote_ident(nspname))+1)) > 1
UNION
SELECT pg_catalog.quote_ident(n.nspname) || '.' ||
pg_catalog.quote_ident(c.relname) FROM pg_catalog.pg_class c,
pg_catalog.pg_namespace n WHERE c.relnamespace = n.oid AND c.relkind IN
('r', 'S', 'v', 'm', 'f', 'p') AND
substring(pg_catalog.quote_ident(n.nspname) || '.' ||
pg_catalog.quote_ident(c.relname),1,3)='tbl' AND
substring(pg_catalog.quote_id
2018-03-01 18:38:38.668 IST [50071] LOG:  terminating any other active
server processes
2018-03-01 18:38:38.668 IST [50082] WARNING:  terminating connection
because of crash of another server process
2018-03-01 18:38:38.668 IST [50082] DETAIL:  The postmaster has commanded
this server process to roll back the current transaction and exit, because
another server process exited abnormally and possibly corrupted shared
memory.
2018-03-01 18:38:38.668 IST [50082] HINT:  In a moment you should be able
to reconnect to the database and repeat your command.
2018-03-01 18:38:38.670 IST [50076] WARNING:  terminating connection
because of crash of another server process
2018-03-01 18:38:38.670 IST [50076] DETAIL:  The postmaster has commanded
this server process to roll back the current transaction and exit, because
another server process exited abnormally and possibly corrupted shared
memory.
2018-03-01 18:38:38.670 IST [50076] HINT:  In a moment you should be able
to reconnect to the database and repeat your command.
2018-03-01 18:38:38.675 IST [50071] LOG:  all server processes terminated;
reinitializing
2018-03-01 18:38:38.702 IST [51712] LOG:  database system was interrupted;
last known up at 2018-03-01 18:37:36 IST
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shut down; automatic recovery in progress
2018-03-01 18:38:38.724 IST [51712] LOG:  redo starts at 0/1639510
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0/1669488: 

Re: parallel append vs. simple UNION ALL

[Amit Khandekar]

> On Sat, Feb 24, 2018 at 2:55 AM, Robert Haas  wrote:
>>
>> 0001 is pretty much the same as the subquery-smarts.patch file I
>> attached to the previous email.  I don't see much reason not to go
>> ahead and commit this, although it could use a test case.  It makes
>> the simple/flattened case work.  After some study I think that the
>> gather-parameter handling is correct, although if somebody felt like
>> reviewing that portion especially I wouldn't say no.

I had a look at 0001 patch. Other than the issue raised by Rajkumar,
it looks good functionally.

Regarding the finalize_plan() changes, I see that in the patch, the
Gather rescan param is now included in the valid_params while calling
finalize_plan() for the SubqueryScan, which looks correct. But I was
thinking that instead of doing that just before the recursive
finalize_plan(), it looks better if we do that at the initial section
of finalize_plan(). We already add initSetParam to valid_params. There
itself we can also add gather_params. Something like this :

@@ -2314,6 +2314,10 @@ finalize_plan(PlannerInfo *root, Plan *plan,
if (initSetParam)
valid_params = bms_union(valid_params, initSetParam);

+   /* Same applies for Gather rescan param */
+   if (gather_param >= 0)
+   valid_params = bms_add_member(valid_params, gather_param);


On 27 February 2018 at 16:51, Rajkumar Raghuwanshi
 wrote:
>
>
> I have applied 0001 on pg-head, and while playing with regression tests, it
> crashed with below test case.
>
> postgres=# SET min_parallel_table_scan_size=0;
> SET
> postgres=# SELECT * FROM information_schema.foreign_data_wrapper_options
> ORDER BY 1, 2, 3;
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> The connection to the server was lost. Attempting reset: Failed.

This is happening because there is a ProjectionPath as one of the
subpaths, and that is not parallel safe.

 Sort
   Sort Key: ((current_database())::information_schema.sql_identifier),
((w.fdwname)::information_schema.sql_identifier),
pg_options_to_table(w.fdwoptions))).option_name)::information_schema.sql_identifier)
   ->  Result
 ->  ProjectSet
   ->  Hash Join
 Hash Cond: (w.fdwowner = u.oid)
 ->  Seq Scan on pg_foreign_data_wrapper w
   Filter: (pg_has_role(fdwowner,
'USAGE'::text) OR has_foreign_data_wrapper_privilege(oid,
'USAGE'::text))
 ->  Hash
   ->  Seq Scan on pg_authid u

In grouping_planner() where partial paths are generated for final_rel,
we can skip non-parallel-safe paths.

-- 
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company

Re: parallel append vs. simple UNION ALL

[Rajkumar Raghuwanshi]

On Sat, Feb 24, 2018 at 2:55 AM, Robert Haas  wrote:

> 0001 is pretty much the same as the subquery-smarts.patch file I
> attached to the previous email.  I don't see much reason not to go
> ahead and commit this, although it could use a test case.  It makes
> the simple/flattened case work.  After some study I think that the
> gather-parameter handling is correct, although if somebody felt like
> reviewing that portion especially I wouldn't say no.
>

I have applied 0001 on pg-head, and while playing with regression tests, it
crashed with below test case.

postgres=# SET min_parallel_table_scan_size=0;
SET
postgres=# SELECT * FROM information_schema.foreign_data_wrapper_options
ORDER BY 1, 2, 3;
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

--logfile
2018-02-26 22:06:07.331 IST [43508] LOG:  database system is ready to
accept connections
TRAP: FailedAssertion("!(subpath->parallel_safe)", File: "pathnode.c",
Line: 1813)
2018-02-26 22:06:42.345 IST [43508] LOG:  server process (PID 43519) was
terminated by signal 6: Aborted
2018-02-26 22:06:42.345 IST [43508] DETAIL:  Failed process was running:
SELECT * FROM information_schema.foreign_data_wrapper_options ORDER BY 1,
2, 3;

Thanks & Regards,
Rajkumar Raghuwanshi
QMG, EnterpriseDB Corporation

Re: parallel append vs. simple UNION ALL

[Robert Haas]

On Sat, Dec 23, 2017 at 4:53 PM, Robert Haas  wrote:
> As I mentioned in the commit message for the Parallel Append commit
> (ab72716778128fb63d54ac256adf7fe6820a1185), it's kind of sad that this
> doesn't work with UNION ALL queries, which are an obvious candidate
> for such parallelization.  It turns out that it actually does work to
> a limited degree: assuming that the UNION ALL query can be converted
> to a simple appendrel, it can consider a parallel append of
> non-partial paths only.  The attached patch lets it consider a
> parallel append of partial paths ...

Here's an extended series of patches that now handles both the simple
UNION ALL case (where we flatten it) and the unflattened case:

0001 is pretty much the same as the subquery-smarts.patch file I
attached to the previous email.  I don't see much reason not to go
ahead and commit this, although it could use a test case.  It makes
the simple/flattened case work.  After some study I think that the
gather-parameter handling is correct, although if somebody felt like
reviewing that portion especially I wouldn't say no.

0002 rewrites recurse_union_children to work iteratively rather than
recursively and renames it to plan_union_children.  This probably
isn't 100% necessary, but it seems to me that the resulting code is
easier to understand, and it reduces the risk of blowing out the
stack.  There should be no user-visible behavior change.

0003 rewrites the setop planner to create a separate upper rel for
each stage of setop planning and uses them to return paths instead of
returning paths directly.  This is necessary preparatory work for
anything that wants to consider multiple possible paths for queries
that go through the full setop planner, but it shouldn't have any
visible impact all by itself.

0004 causes generate_union_path() to consider both the traditional
method and also Gather -> Parallel Append -> [partial path for each
subquery].  This is still a bit rough around the edges and there's a
lot more that could be done here, but I'm posting what I have for now
in the (perhaps vain) hope of getting some feedback.  With this, you
can use Parallel Append for the UNION ALL step of a query like SELECT
.. UNION ALL .. SELECT ... EXCEPT SELECT ...

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


0004-Consider-Parallel-Append-as-a-way-to-implement-a-uni.patch
Description: Binary data


0003-Generate-a-separate-upper-relation-for-each-stage-of.patch
Description: Binary data


0002-Rewrite-recurse_union_children-to-iterate-rather-tha.patch
Description: Binary data


0001-Let-Parallel-Append-over-simple-UNION-ALL-have-parti.patch
Description: Binary data