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Commit08d2d58

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author
Etsuro Fujita
committed
postgres_fdw: Fix costing of pre-sorted foreign paths with local stats.
Commitaa09cd2 modified estimate_path_cost_size() so that it reusescached costs of a basic foreign path for a given foreign-base/joinrelation when costing pre-sorted foreign paths for that relation, but itincorrectly re-computed retrieved_rows, an estimated number of rowsfetched from the remote side, which is needed for costing both the basicand pre-sorted foreign paths. To fix, handle retrieved_rows the same wayas the cached costs: store in that relation's fpinfo the retrieved_rowsestimate computed for costing the basic foreign path, and reuse it whencosting the pre-sorted foreign paths. Also, reuse the rows/widthestimates stored in that relation's fpinfo when costing the pre-sortedforeign paths, to make the code consistent.In commitffab494, to extend the costing mentioned above to theforeign-grouping case, I made a change to add_foreign_grouping_paths() tostore in a given foreign-grouped relation's RelOptInfo the rows estimatefor that relation for reuse, but this patch makes that change unnecessarysince we already store the row estimate in that relation's fpinfo, whichthis patch reuses when costing a foreign path for that relation with thesortClause ordering; remove that change.In passing, fix thinko in commit7012b13: in estimate_path_cost_size(),the width estimate for a given foreign-grouped relation to be stored inthat relation's fpinfo was reset incorrectly when costing a basic foreignpath for that relation with local stats.Apply the patch to HEAD only to avoid destabilizing existing plan choices.Author: Etsuro FujitaDiscussion:https://postgr.es/m/CAPmGK17jaJLPDEkgnP2VmkOg=5wT8YQ1CqssU8JRpZ_NSE+dqQ@mail.gmail.com
1 parentbe2e024 commit08d2d58

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2 files changed

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‎contrib/postgres_fdw/postgres_fdw.c

Lines changed: 56 additions & 39 deletions
Original file line numberDiff line numberDiff line change
@@ -661,10 +661,11 @@ postgresGetForeignRelSize(PlannerInfo *root,
661661
cost_qual_eval(&fpinfo->local_conds_cost,fpinfo->local_conds,root);
662662

663663
/*
664-
* Set cached relation costs to some negative value, so that we can detect
665-
* when they are set to some sensiblecosts during one (usually the first)
666-
* of the calls to estimate_path_cost_size().
664+
* Set# of retrieved rows andcached relation costs to some negative
665+
*value, so that we can detectwhen they are set to some sensiblevalues,
666+
*during one (usually the first)of the calls to estimate_path_cost_size.
667667
*/
668+
fpinfo->retrieved_rows=-1;
668669
fpinfo->rel_startup_cost=-1;
669670
fpinfo->rel_total_cost=-1;
670671

@@ -2623,7 +2624,6 @@ estimate_path_cost_size(PlannerInfo *root,
26232624
intwidth;
26242625
Coststartup_cost;
26252626
Costtotal_cost;
2626-
Costcpu_per_tuple;
26272627

26282628
/* Make sure the core code has set up the relation's reltarget */
26292629
Assert(foreignrel->reltarget);
@@ -2736,26 +2736,20 @@ estimate_path_cost_size(PlannerInfo *root,
27362736
*/
27372737
Assert(param_join_conds==NIL);
27382738

2739-
/*
2740-
* Use rows/width estimates made by set_baserel_size_estimates() for
2741-
* base foreign relations and set_joinrel_size_estimates() for join
2742-
* between foreign relations.
2743-
*/
2744-
rows=foreignrel->rows;
2745-
width=foreignrel->reltarget->width;
2746-
2747-
/* Back into an estimate of the number of retrieved rows. */
2748-
retrieved_rows=clamp_row_est(rows /fpinfo->local_conds_sel);
2749-
27502739
/*
27512740
* We will come here again and again with different set of pathkeys or
27522741
* additional post-scan/join-processing steps that caller wants to
2753-
* cost. We don't need to calculate thecosts of the underlying scan,
2754-
* join, or grouping each time. Instead, usethe costs if we have
2755-
* cached them already.
2742+
* cost. We don't need to calculate thecost/size estimates for the
2743+
*underlying scan,join, or grouping each time. Instead, usethose
2744+
*estimates if we havecached them already.
27562745
*/
27572746
if (fpinfo->rel_startup_cost >=0&&fpinfo->rel_total_cost >=0)
27582747
{
2748+
Assert(fpinfo->retrieved_rows >=1);
2749+
2750+
rows=fpinfo->rows;
2751+
retrieved_rows=fpinfo->retrieved_rows;
2752+
width=fpinfo->width;
27592753
startup_cost=fpinfo->rel_startup_cost;
27602754
run_cost=fpinfo->rel_total_cost-fpinfo->rel_startup_cost;
27612755

@@ -2785,6 +2779,10 @@ estimate_path_cost_size(PlannerInfo *root,
27852779
QualCostremote_conds_cost;
27862780
doublenrows;
27872781

2782+
/* Use rows/width estimates made by the core code. */
2783+
rows=foreignrel->rows;
2784+
width=foreignrel->reltarget->width;
2785+
27882786
/* For join we expect inner and outer relations set */
27892787
Assert(fpinfo->innerrel&&fpinfo->outerrel);
27902788

@@ -2793,7 +2791,12 @@ estimate_path_cost_size(PlannerInfo *root,
27932791

27942792
/* Estimate of number of rows in cross product */
27952793
nrows=fpinfo_i->rows*fpinfo_o->rows;
2796-
/* Clamp retrieved rows estimate to at most size of cross product */
2794+
2795+
/*
2796+
* Back into an estimate of the number of retrieved rows. Just in
2797+
* case this is nuts, clamp to at most nrow.
2798+
*/
2799+
retrieved_rows=clamp_row_est(rows /fpinfo->local_conds_sel);
27972800
retrieved_rows=Min(retrieved_rows,nrows);
27982801

27992802
/*
@@ -2871,9 +2874,8 @@ estimate_path_cost_size(PlannerInfo *root,
28712874

28722875
ofpinfo= (PgFdwRelationInfo*)outerrel->fdw_private;
28732876

2874-
/* Get rowsand widthfrom input rel */
2877+
/* Get rows from input rel */
28752878
input_rows=ofpinfo->rows;
2876-
width=ofpinfo->width;
28772879

28782880
/* Collect statistics about aggregates for estimating costs. */
28792881
MemSet(&aggcosts,0,sizeof(AggClauseCosts));
@@ -2920,6 +2922,9 @@ estimate_path_cost_size(PlannerInfo *root,
29202922
rows=retrieved_rows=numGroups;
29212923
}
29222924

2925+
/* Use width estimate made by the core code. */
2926+
width=foreignrel->reltarget->width;
2927+
29232928
/*-----
29242929
* Startup cost includes:
29252930
* 1. Startup cost for underneath input relation, adjusted for
@@ -2966,7 +2971,17 @@ estimate_path_cost_size(PlannerInfo *root,
29662971
}
29672972
else
29682973
{
2969-
/* Clamp retrieved rows estimates to at most foreignrel->tuples. */
2974+
Costcpu_per_tuple;
2975+
2976+
/* Use rows/width estimates made by set_baserel_size_estimates. */
2977+
rows=foreignrel->rows;
2978+
width=foreignrel->reltarget->width;
2979+
2980+
/*
2981+
* Back into an estimate of the number of retrieved rows. Just in
2982+
* case this is nuts, clamp to at most foreignrel->tuples.
2983+
*/
2984+
retrieved_rows=clamp_row_est(rows /fpinfo->local_conds_sel);
29702985
retrieved_rows=Min(retrieved_rows,foreignrel->tuples);
29712986

29722987
/*
@@ -3043,18 +3058,20 @@ estimate_path_cost_size(PlannerInfo *root,
30433058
}
30443059

30453060
/*
3046-
* Cache the costs for scans, joins, or groupings without any
3047-
* parameterization, pathkeys, or additional post-scan/join-processing
3048-
* steps, before adding the costs for transferring data from the foreign
3049-
* server. These costs are useful for costing remote joins involving this
3050-
* relation or costing other remote operations for this relation such as
3051-
* remote sorts and remote LIMIT restrictions, when the costs can not be
3052-
* obtained from the foreign server. This function will be called at
3053-
* least once for every foreign relation without any parameterization,
3054-
* pathkeys, or additional post-scan/join-processing steps.
3061+
* Cache the retrieved rows and cost estimates for scans, joins, or
3062+
* groupings without any parameterization, pathkeys, or additional
3063+
* post-scan/join-processing steps, before adding the costs for
3064+
* transferring data from the foreign server. These estimates are useful
3065+
* for costing remote joins involving this relation or costing other
3066+
* remote operations on this relation such as remote sorts and remote
3067+
* LIMIT restrictions, when the costs can not be obtained from the foreign
3068+
* server. This function will be called at least once for every foreign
3069+
* relation without any parameterization, pathkeys, or additional
3070+
* post-scan/join-processing steps.
30553071
*/
30563072
if (pathkeys==NIL&&param_join_conds==NIL&&fpextra==NULL)
30573073
{
3074+
fpinfo->retrieved_rows=retrieved_rows;
30583075
fpinfo->rel_startup_cost=startup_cost;
30593076
fpinfo->rel_total_cost=total_cost;
30603077
}
@@ -5157,10 +5174,11 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
51575174
fpinfo->user=NULL;
51585175

51595176
/*
5160-
* Set cached relation costs to some negative value, so that we can detect
5161-
* when they are set to some sensiblecosts, during one (usually the
5162-
* first) of the calls to estimate_path_cost_size().
5177+
* Set# of retrieved rows andcached relation costs to some negative
5178+
*value, so that we can detectwhen they are set to some sensiblevalues,
5179+
*during one (usually thefirst) of the calls to estimate_path_cost_size.
51635180
*/
5181+
fpinfo->retrieved_rows=-1;
51645182
fpinfo->rel_startup_cost=-1;
51655183
fpinfo->rel_total_cost=-1;
51665184

@@ -5708,10 +5726,11 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
57085726
fpinfo->pushdown_safe= true;
57095727

57105728
/*
5711-
* Set cached relation costs to some negative value, so that we can detect
5712-
* when they are set to some sensiblecosts, during one (usually the
5713-
* first) of the calls to estimate_path_cost_size().
5729+
* Set# of retrieved rows andcached relation costs to some negative
5730+
*value, so that we can detectwhen they are set to some sensiblevalues,
5731+
*during one (usually thefirst) of the calls to estimate_path_cost_size.
57145732
*/
5733+
fpinfo->retrieved_rows=-1;
57155734
fpinfo->rel_startup_cost=-1;
57165735
fpinfo->rel_total_cost=-1;
57175736

@@ -5853,8 +5872,6 @@ add_foreign_grouping_paths(PlannerInfo *root, RelOptInfo *input_rel,
58535872
fpinfo->startup_cost=startup_cost;
58545873
fpinfo->total_cost=total_cost;
58555874

5856-
grouped_rel->rows=fpinfo->rows;
5857-
58585875
/* Create and add foreign path to the grouping relation. */
58595876
grouppath=create_foreign_upper_path(root,
58605877
grouped_rel,

‎contrib/postgres_fdw/postgres_fdw.h

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -59,12 +59,17 @@ typedef struct PgFdwRelationInfo
5959
/* Selectivity of join conditions */
6060
Selectivityjoinclause_sel;
6161

62-
/* Estimated size and cost for a scanorjoin. */
62+
/* Estimated size and cost for a scan, join,orgrouping/aggregation. */
6363
doublerows;
6464
intwidth;
6565
Coststartup_cost;
6666
Costtotal_cost;
67-
/* Costs excluding costs for transferring data from the foreign server */
67+
/*
68+
* Estimated number of rows fetched from the foreign server, and costs
69+
* excluding costs for transferring those rows from the foreign server.
70+
* These are only used by estimate_path_cost_size().
71+
*/
72+
doubleretrieved_rows;
6873
Costrel_startup_cost;
6974
Costrel_total_cost;
7075

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