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Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
-rw-r--r-- | src/backend/optimizer/path/costsize.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 8e4caeba0a..4917922ab5 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -1432,8 +1432,8 @@ cost_recursive_union(Path *runion, Path *nrterm, Path *rterm) * total, but we will also need to write and read each tuple once per * merge pass. We expect about ceil(logM(r)) merge passes where r is the * number of initial runs formed and M is the merge order used by tuplesort.c. - * Since the average initial run should be about twice sort_mem, we have - * disk traffic = 2 * relsize * ceil(logM(p / (2*sort_mem))) + * Since the average initial run should be about sort_mem, we have + * disk traffic = 2 * relsize * ceil(logM(p / sort_mem)) * cpu = comparison_cost * t * log2(t) * * If the sort is bounded (i.e., only the first k result tuples are needed) @@ -1509,7 +1509,7 @@ cost_sort(Path *path, PlannerInfo *root, * We'll have to use a disk-based sort of all the tuples */ double npages = ceil(input_bytes / BLCKSZ); - double nruns = (input_bytes / sort_mem_bytes) * 0.5; + double nruns = input_bytes / sort_mem_bytes; double mergeorder = tuplesort_merge_order(sort_mem_bytes); double log_runs; double npageaccesses; |