diff options
Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 31 |
1 files changed, 13 insertions, 18 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 6bf34c6a25a..22eb4d3e53d 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -7,7 +7,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.35 1999/04/30 04:01:44 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.36 1999/05/01 19:47:41 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -167,28 +167,23 @@ cost_index(Oid indexid, /* * cost_sort * Determines and returns the cost of sorting a relation by considering - * 1. the cost of doing an external sort: XXX this is probably too low + * the cost of doing an external sort: XXX this is probably too low * disk = (p lg p) * cpu = *CPU-PAGE-WEIGHT* * (t lg t) - * 2. the cost of reading the sort result into memory (another seqscan) - * unless 'noread' is set * * 'pathkeys' is a list of sort keys * 'tuples' is the number of tuples in the relation * 'width' is the average tuple width in bytes - * 'noread' is a flag indicating that the cost of reading the sort - * source data should not be included (i.e., the caller - * will account for it separately). * * NOTE: some callers currently pass NULL for pathkeys because they - * can't conveniently supply sort keys. Since this routine doesn't + * can't conveniently supply the sort keys. Since this routine doesn't * currently do anything with pathkeys anyway, that doesn't matter... + * but if it ever does, it should react gracefully to lack of key data. * * Returns a flonum. - * */ Cost -cost_sort(List *pathkeys, int tuples, int width, bool noread) +cost_sort(List *pathkeys, int tuples, int width) { Cost temp = 0; int npages = page_size(tuples, width); @@ -200,6 +195,8 @@ cost_sort(List *pathkeys, int tuples, int width, bool noread) /* We want to be sure the cost of a sort is never estimated as zero, * even if passed-in tuple count is zero. Besides, mustn't do log(0)... */ + if (tuples <= 0) + tuples = 1; if (npages <= 0) npages = 1; @@ -210,13 +207,10 @@ cost_sort(List *pathkeys, int tuples, int width, bool noread) temp += npages * log_npages; /* - * could be base_log(pages, NBuffers), but we are only doing 2-way + * could be base_log(tuples, NBuffers), but we are only doing 2-way * merges */ - temp += _cpu_page_wight_ * tuples * log_npages; - - if (!noread) - temp += cost_seqscan(_NONAME_RELATION_ID_, npages, tuples); + temp += _cpu_page_wight_ * tuples * base_log((double) tuples, 2.0); Assert(temp > 0); @@ -282,7 +276,8 @@ cost_nestloop(Cost outercost, * 'outercost' and 'innercost' are the (disk+cpu) costs of scanning the * outer and inner relations * 'outersortkeys' and 'innersortkeys' are lists of the keys to be used - * to sort the outer and inner relations + * to sort the outer and inner relations (or NIL if no explicit + * sort is needed because the source path is already ordered) * 'outertuples' and 'innertuples' are the number of tuples in the outer * and inner relations * 'outerwidth' and 'innerwidth' are the (typical) widths (in bytes) @@ -309,9 +304,9 @@ cost_mergejoin(Cost outercost, temp += outercost; temp += innercost; if (outersortkeys) /* do we need to sort? */ - temp += cost_sort(outersortkeys, outersize, outerwidth, true); + temp += cost_sort(outersortkeys, outersize, outerwidth); if (innersortkeys) /* do we need to sort? */ - temp += cost_sort(innersortkeys, innersize, innerwidth, true); + temp += cost_sort(innersortkeys, innersize, innerwidth); temp += _cpu_page_wight_ * (outersize + innersize); Assert(temp >= 0); |