Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit7a7ba33

Browse files
committed
Clean up some bogosities in path cost estimation, like
sometimes estimating an index scan of a table to be cheaper than asequential scan of the same tuples...
1 parent11a0027 commit7a7ba33

File tree

1 file changed

+49
-28
lines changed

1 file changed

+49
-28
lines changed

‎src/backend/optimizer/path/costsize.c‎

Lines changed: 49 additions & 28 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/costsize.c,v 1.34 1999/04/05 02:07:07 tgl Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.35 1999/04/30 04:01:44 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -129,28 +129,36 @@ cost_index(Oid indexid,
129129
intindextuples,
130130
boolis_injoin)
131131
{
132-
Costtemp;
133-
doubletemp2;
134-
135-
temp= (Cost)0;
132+
Costtemp=0;
136133

137134
if (!_enable_indexscan_&& !is_injoin)
138135
temp+=_disable_cost_;
139136

137+
/* We want to be sure we estimate the cost of an index scan
138+
* as more than the cost of a sequential scan (when selec == 1.0),
139+
* even if we don't have good stats. So, disbelieve zero index size.
140+
*/
141+
if (expected_indexpages <=0)
142+
expected_indexpages=1;
143+
if (indextuples <=0)
144+
indextuples=1;
145+
140146
/* expected index relation pages */
141147
temp+=expected_indexpages;
142148

143-
/* expected base relation pages */
144-
temp2= (reltuples==0) ? (double)0 : (double)relpages /reltuples;
145-
temp2=temp2* (double)selec*indextuples;
146-
147-
temp+=Min(relpages, (int)ceil(temp2));
149+
/* expected base relation pages
150+
* XXX this isn't really right, since we will access the table
151+
* nonsequentially and might have to fetch the same page
152+
* more than once. This calculation assumes the buffer cache
153+
* will prevent that from happening...
154+
*/
155+
temp+=ceil(((double)selec)* ((double)relpages));
148156

149157
/* per index tuples */
150-
temp=temp+ (_cpu_index_page_wight_*selec*indextuples);
158+
temp+=_cpu_index_page_wight_*selec*indextuples;
151159

152160
/* per heap tuples */
153-
temp=temp+ (_cpu_page_wight_*selec*reltuples);
161+
temp+=_cpu_page_wight_*selec*reltuples;
154162

155163
Assert(temp >=0);
156164
returntemp;
@@ -168,8 +176,13 @@ cost_index(Oid indexid,
168176
* 'pathkeys' is a list of sort keys
169177
* 'tuples' is the number of tuples in the relation
170178
* 'width' is the average tuple width in bytes
171-
* 'noread' is a flag indicating that the sort result can remain on disk
172-
*(i.e., the sort result is the result relation)
179+
* 'noread' is a flag indicating that the cost of reading the sort
180+
*source data should not be included (i.e., the caller
181+
*will account for it separately).
182+
*
183+
* NOTE: some callers currently pass NULL for pathkeys because they
184+
* can't conveniently supply sort keys. Since this routine doesn't
185+
* currently do anything with pathkeys anyway, that doesn't matter...
173186
*
174187
* Returns a flonum.
175188
*
@@ -179,28 +192,33 @@ cost_sort(List *pathkeys, int tuples, int width, bool noread)
179192
{
180193
Costtemp=0;
181194
intnpages=page_size(tuples,width);
182-
Costpages= (Cost)npages;
183-
CostnumTuples=tuples;
195+
doublelog_npages;
184196

185197
if (!_enable_sort_)
186198
temp+=_disable_cost_;
187-
if (tuples==0||pathkeys==NULL)
188-
{
189-
Assert(temp >=0);
190-
returntemp;
191-
}
192-
temp+=pages*base_log((double)pages, (double)2.0);
199+
200+
/* We want to be sure the cost of a sort is never estimated as zero,
201+
* even if passed-in tuple count is zero. Besides, mustn't do log(0)...
202+
*/
203+
if (npages <=0)
204+
npages=1;
205+
206+
log_npages=ceil(base_log((double)npages,2.0));
207+
if (log_npages <=0.0)
208+
log_npages=1.0;
209+
210+
temp+=npages*log_npages;
193211

194212
/*
195213
* could be base_log(pages, NBuffers), but we are only doing 2-way
196214
* merges
197215
*/
198-
temp+=_cpu_page_wight_*numTuples*
199-
base_log((double)pages, (double)2.0);
216+
temp+=_cpu_page_wight_*tuples*log_npages;
200217

201218
if (!noread)
202-
temp=temp+cost_seqscan(_NONAME_RELATION_ID_,npages,tuples);
203-
Assert(temp >=0);
219+
temp+=cost_seqscan(_NONAME_RELATION_ID_,npages,tuples);
220+
221+
Assert(temp>0);
204222

205223
returntemp;
206224
}
@@ -290,9 +308,12 @@ cost_mergejoin(Cost outercost,
290308

291309
temp+=outercost;
292310
temp+=innercost;
293-
temp+=cost_sort(outersortkeys,outersize,outerwidth, false);
294-
temp+=cost_sort(innersortkeys,innersize,innerwidth, false);
311+
if (outersortkeys)/* do we need to sort? */
312+
temp+=cost_sort(outersortkeys,outersize,outerwidth, true);
313+
if (innersortkeys)/* do we need to sort? */
314+
temp+=cost_sort(innersortkeys,innersize,innerwidth, true);
295315
temp+=_cpu_page_wight_* (outersize+innersize);
316+
296317
Assert(temp >=0);
297318

298319
returntemp;

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp