Re: [HACKERS] Partition-wise aggregation/grouping - Mailing list pgsql-hackers
| From | Jeevan Chalke |
|---|---|
| Subject | Re: [HACKERS] Partition-wise aggregation/grouping |
| Date | |
| Msg-id | CAM2+6=U-B5AOGmU0s8sRVYFqoHq+fXF2FsmUVexCMF0VA3D5gw@mail.gmail.com Whole thread Raw |
| In response to | Re: [HACKERS] Partition-wise aggregation/grouping (Robert Haas <robertmhaas@gmail.com>) |
| Responses |
Re: [HACKERS] Partition-wise aggregation/grouping
|
| List | pgsql-hackers |
Hi Robert,
On Fri, Feb 23, 2018 at 2:53 AM, Robert Haas <robertmhaas@gmail.com> wrote:
I have reviewed and tested the patch and here are my couple of points:
/*
- * If the input rel belongs to a single FDW, so does the grouped rel.
+ * If the input rel belongs to a single FDW, so does the grouped rel. Same
+ * for the partially_grouped_rel.
*/
grouped_rel->serverid = input_rel->serverid;
grouped_rel->userid = input_rel->userid;
grouped_rel->useridiscurrent = input_rel->useridiscurrent;
grouped_rel->fdwroutine = input_rel->fdwroutine;
+ partially_grouped_rel->serverid = input_rel->serverid;
+ partially_grouped_rel->userid = input_rel->userid;
+ partially_grouped_rel->useridiscurrent = input_rel->useridiscurrent;
+ partially_grouped_rel->fdwroutine = input_rel->fdwroutine;
In my earlier mail where I have posted a patch for this partially grouped rel changes, I forgot to put my question on this.
I was unclear about above changes and thus passed grouped_rel whenever we wanted to work on partially_grouped_rel to fetch relevant details.
One idea I thought about is to memcpy the struct once we have set all required fields for grouped_rel so that we don't have to do similar stuff for partially_grouped_rel.
---
+ * Insert a Sort node, if required. But there's no point in
+ * sorting anything but the cheapest path.
*/
- if (root->group_pathkeys)
+ if (!pathkeys_contained_in(root->group_pathkeys, path->pathkeys))
+ {
+ if (path != linitial(partially_grouped_rel->pathlist))
+ continue;
Paths in pathlist are added by add_path(). Though we have paths is pathlist is sorted with the cheapest total path, we generally use RelOptInfo->cheapest_total_path instead of using first entry, unlike partial paths. But here you use the first entry like partial paths case. Will it better to use cheapest total path from partially_grouped_rel? This will require calling set_cheapest on partially_grouped_rel before we call this function.
Attached top-up patch doing this along with few indentation fixes.
Rest of the changes look good to me.
Once this gets in, I will re-base my other patches accordingly.
And, thanks for committing 0006.
Thanks
On Thu, Feb 8, 2018 at 8:05 AM, Jeevan Chalke
<jeevan.chalke@enterprisedb.com> wrote:
> In this attached version, I have rebased my changes over new design of
> partially_grouped_rel. The preparatory changes of adding
> partially_grouped_rel are in 0001.
I spent today hacking in 0001; results attached. The big change from
your version is that this now uses generate_gather_paths() to add
Gather/Gather Merge nodes (except in the case where we sort by group
pathkeys and then Gather Merge) rather than keeping all of the bespoke
code. That turned up to be a bit less elegant than I would have liked
-- I had to an override_rows argument to generate_gather_paths to make
it work. But overall I think this is still a big improvement, since
it lets us share code instead of duplicating it. Also, it potentially
lets us add partially-aggregated but non-parallel paths into
partially_grouped_rel->pathlist and that should Just Work; they will
get the Finalize Aggregate step but not the Gather. With your
arrangement that wouldn't work.
Please review/test.
I have reviewed and tested the patch and here are my couple of points:
/*
- * If the input rel belongs to a single FDW, so does the grouped rel.
+ * If the input rel belongs to a single FDW, so does the grouped rel. Same
+ * for the partially_grouped_rel.
*/
grouped_rel->serverid = input_rel->serverid;
grouped_rel->userid = input_rel->userid;
grouped_rel->useridiscurrent = input_rel->useridiscurrent;
grouped_rel->fdwroutine = input_rel->fdwroutine;
+ partially_grouped_rel->serverid = input_rel->serverid;
+ partially_grouped_rel->userid = input_rel->userid;
+ partially_grouped_rel->useridiscurrent = input_rel->useridiscurrent;
+ partially_grouped_rel->fdwroutine = input_rel->fdwroutine;
In my earlier mail where I have posted a patch for this partially grouped rel changes, I forgot to put my question on this.
I was unclear about above changes and thus passed grouped_rel whenever we wanted to work on partially_grouped_rel to fetch relevant details.
One idea I thought about is to memcpy the struct once we have set all required fields for grouped_rel so that we don't have to do similar stuff for partially_grouped_rel.
---
+ * Insert a Sort node, if required. But there's no point in
+ * sorting anything but the cheapest path.
*/
- if (root->group_pathkeys)
+ if (!pathkeys_contained_in(root->group_pathkeys, path->pathkeys))
+ {
+ if (path != linitial(partially_grouped_rel->pathlist))
+ continue;
Paths in pathlist are added by add_path(). Though we have paths is pathlist is sorted with the cheapest total path, we generally use RelOptInfo->cheapest_total_path instead of using first entry, unlike partial paths. But here you use the first entry like partial paths case. Will it better to use cheapest total path from partially_grouped_rel? This will require calling set_cheapest on partially_grouped_rel before we call this function.
Attached top-up patch doing this along with few indentation fixes.
Rest of the changes look good to me.
Once this gets in, I will re-base my other patches accordingly.
And, thanks for committing 0006.
Thanks
--
Jeevan Chalke
Technical Architect, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company
Technical Architect, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company
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