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Commit0b8b1fe

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Tighten coding in new_join_pathkey, which seems to be a hotspot
for GEQO ...
1 parent1332c1e commit0b8b1fe

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1 file changed

+53
-96
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1 file changed

+53
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‎src/backend/optimizer/path/pathkeys.c‎

Lines changed: 53 additions & 96 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
*
88
*
99
* IDENTIFICATION
10-
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.8 1999/04/30 03:59:06 tgl Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.9 1999/05/17 00:26:33 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -29,42 +29,51 @@ static int match_pathkey_joinkeys(List *pathkey, List *joinkeys,
2929
intouter_or_inner);
3030
staticList*new_join_pathkey(List*pathkeys,List*join_rel_tlist,
3131
List*joinclauses);
32-
staticList*get_joinvars_for_var(Var*pathkey,List**considered_pathkeys,
33-
List*join_rel_tlist,List*joinclauses);
3432

3533

36-
/*
34+
/*--------------------
3735
*Explanation of Path.pathkeys
3836
*
3937
*Path.pathkeys is a List of List of Var nodes that represent the sort
4038
*order of the result generated by the Path.
4139
*
4240
*In single/base relation RelOptInfo's, the Path's represent various ways
43-
*of generate the relation. Sequential scan Paths have a NIL pathkeys.
44-
*Index scans have Path.pathkeys that represent the chosen index. A
45-
*single-key index pathkeys would be { {tab1_indexkey1} }. The pathkeys
46-
*entry for a multi-key index would be { {tab1_indexkey1}, {tab1_indexkey2} }.
41+
*of generating the relation and the resulting ordering of the tuples.
42+
*Sequential scan Paths have NIL pathkeys, indicating no known ordering.
43+
*Index scans have Path.pathkeys that represent the chosen index.
44+
*A single-key index pathkeys would be { {tab1_indexkey1} }. For a
45+
*multi-key index pathkeys would be { {tab1_indexkey1}, {tab1_indexkey2} },
46+
*indicating major sort by indexkey1 and minor sort by indexkey2.
4747
*
4848
*Multi-relation RelOptInfo Path's are more complicated. Mergejoins are
49-
*only performed withequajoins("="). Because of this, the multi-relation
49+
*only performed withequijoins("="). Because of this, the multi-relation
5050
*path actually has more than one primary Var key. For example, a
5151
*mergejoin Path of "tab1.col1 = tab2.col1" would generate a pathkeys of
52-
*{ {tab1.col1, tab2.col1} }. This allows future joins to use either Var
53-
*as a pre-sorted key to prevent Mergejoins from having to re-sort the Path.
54-
*They are equal, so they are both primary sort keys. This is why pathkeys
55-
*is a List of Lists.
52+
*{ {tab1.col1, tab2.col1} }, indicating that the major sort order of the
53+
*Path can be taken to be *either* tab1.col1 or tab2.col1.
54+
*They are equal, so they are both primary sort keys. This allows future
55+
*joins to use either Var as a pre-sorted key to prevent upper Mergejoins
56+
*from having to re-sort the Path. This is why pathkeys is a List of Lists.
57+
*
58+
*Note that while the order of the top list is meaningful (primary vs.
59+
*secondary sort key), the order of each sublist is arbitrary.
5660
*
5761
*For multi-key sorts, if the outer is sorted by a multi-key index, the
5862
*multi-key index remains after the join. If the inner has a multi-key
5963
*sort, only the primary key of the inner is added to the result.
6064
*Mergejoins only join on the primary key. Currently, non-primary keys
6165
*in the pathkeys List are of limited value.
6266
*
63-
*HashJoin has similar functionality. NestJoin does not perform sorting,
64-
*and allows non-equajoins, so it does not allow useful pathkeys.
67+
*Although Hashjoins also work only with equijoin operators, it is *not*
68+
*safe to consider the output of a Hashjoin to be sorted in any particular
69+
*order --- not even the outer path's order. This is true because the
70+
*executor might have to split the join into multiple batches.
71+
*
72+
*NestJoin does not perform sorting, and allows non-equijoins, so it does
73+
*not allow useful pathkeys. (But couldn't we use the outer path's order?)
6574
*
6675
*-- bjm
67-
*
76+
*--------------------
6877
*/
6978

7079
/****************************************************************************
@@ -228,7 +237,7 @@ get_cheapest_path_for_joinkeys(List *joinkeys,
228237
intouter_or_inner)
229238
{
230239
Path*matched_path=NULL;
231-
List*i=NIL;
240+
List*i;
232241

233242
foreach(i,paths)
234243
{
@@ -337,16 +346,16 @@ new_join_pathkeys(List *outer_pathkeys,
337346
List*join_rel_tlist,
338347
List*joinclauses)
339348
{
340-
List*outer_pathkey=NIL;
341349
List*final_pathkeys=NIL;
342-
List*new_pathkey;
343-
List*i=NIL;
350+
List*i;
344351

345352
foreach(i,outer_pathkeys)
346353
{
347-
outer_pathkey=lfirst(i);
354+
List*outer_pathkey=lfirst(i);
355+
List*new_pathkey;
356+
348357
new_pathkey=new_join_pathkey(outer_pathkey,join_rel_tlist,
349-
joinclauses);
358+
joinclauses);
350359
if (new_pathkey!=NIL)
351360
final_pathkeys=lappend(final_pathkeys,new_pathkey);
352361
}
@@ -355,104 +364,52 @@ new_join_pathkeys(List *outer_pathkeys,
355364

356365
/*
357366
* new_join_pathkey
358-
* Finds new vars that become pathkeys due to qualification clauses that
359-
* contain any previously considered pathkeys. These new pathkeys plus the
360-
* pathkeys from 'pathkeys' form a new pathkey for the join relation.
367+
* Generate an individual pathkey sublist, consisting of the outer vars
368+
* already mentioned in 'pathkey' plus any inner vars that are joined to
369+
* them (and thus can now also be considered path keys, per discussion
370+
* at the top of this file).
361371
*
362372
* Note that each returned pathkey is the var node found in
363373
* 'join_rel_tlist' rather than the joinclause var node.
374+
* (Is this important?) Also, we return a fully copied list
375+
* that does not share any subnodes with existing data structures.
376+
* (Is that important, either?)
364377
*
365-
* 'pathkeys' is a list of pathkeys for which matching pathkeys are to be
366-
*found
367-
* 'considered_pathkeys' is the current list of all pathkeys corresponding
368-
*to a given pathkey
369-
*
370-
* Returns a new pathkey(list of pathkeys).
378+
* Returns a new pathkey (list of pathkey variables).
371379
*
372380
*/
373381
staticList*
374382
new_join_pathkey(List*pathkey,
375383
List*join_rel_tlist,
376384
List*joinclauses)
377385
{
378-
List*final_pathkey=NIL;
379-
List*i=NIL;
380-
List*considered_pathkeys=NIL;
386+
List*new_pathkey=NIL;
387+
List*i,
388+
*j;
381389

382390
foreach(i,pathkey)
383391
{
384392
Var*key= (Var*)lfirst(i);
385-
List*joined_keys;
386393
Expr*tlist_key;
387394

388395
Assert(key);
389-
joined_keys=get_joinvars_for_var(key,&considered_pathkeys,
390-
join_rel_tlist,joinclauses);
391-
if (joined_keys)
392-
{
393-
considered_pathkeys=nconc(considered_pathkeys,joined_keys);
394-
final_pathkey=nconc(final_pathkey,joined_keys);
395-
}
396396

397397
tlist_key=matching_tlist_var(key,join_rel_tlist);
398-
if (tlist_key&& !member(tlist_key,considered_pathkeys))
399-
{
400-
/*
401-
*If pathkey is in the target list, and not considered,
402-
*add it
403-
*/
404-
considered_pathkeys=lcons(tlist_key,considered_pathkeys);
405-
final_pathkey=lcons(tlist_key,final_pathkey);
406-
}
407-
}
408-
returncopyObject(final_pathkey);
409-
}
398+
if (tlist_key&& !member(tlist_key,new_pathkey))
399+
new_pathkey=lcons(copyObject(tlist_key),new_pathkey);
410400

411-
/*
412-
* get_joinvars_for_var
413-
* Returns a list of new pathkeys:
414-
* (1) which are not listed in 'considered_pathkeys'
415-
* (2) for which the "other" variable in some clause in 'joinclauses' is
416-
* 'pathkey'
417-
* (3) which are mentioned in 'join_rel_tlist'
418-
*
419-
* Note that each returned pathkey is the var node found in
420-
* 'join_rel_tlist' rather than the joinclause var node.
421-
*
422-
* 'pathkey' is the var node for which we are trying to find matching
423-
*clauses
424-
*
425-
* Returns a list of new pathkeys.
426-
*
427-
*/
428-
staticList*
429-
get_joinvars_for_var(Var*key,
430-
List**considered_pathkeys,
431-
List*join_rel_tlist,
432-
List*joinclauses)
433-
{
434-
List*final_pathkey=NIL;
435-
Expr*joinclause;
436-
List*i;
437-
Expr*tlist_other_var;
438-
439-
foreach(i,joinclauses)
440-
{
441-
joinclause=lfirst(i);
401+
foreach(j,joinclauses)
402+
{
403+
Expr*joinclause=lfirst(j);
404+
Expr*tlist_other_var;
442405

443-
tlist_other_var=matching_tlist_var(
406+
tlist_other_var=matching_tlist_var(
444407
other_join_clause_var(key,joinclause),
445408
join_rel_tlist);
446-
if (tlist_other_var&&
447-
!member(tlist_other_var,*considered_pathkeys))
448-
{
449-
/*
450-
*The key has a join variable that is in the target list,
451-
*and has not been considered.
452-
*/
453-
*considered_pathkeys=lcons(tlist_other_var,*considered_pathkeys);
454-
final_pathkey=lcons(tlist_other_var,final_pathkey);
409+
if (tlist_other_var&& !member(tlist_other_var,new_pathkey))
410+
new_pathkey=lcons(copyObject(tlist_other_var),new_pathkey);
455411
}
456412
}
457-
returnfinal_pathkey;
413+
414+
returnnew_pathkey;
458415
}

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