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| author | unknown <heikki@hundin.mysql.fi> | 2004-07-15 09:08:51 +0300 |
|---|---|---|
| committer | unknown <heikki@hundin.mysql.fi> | 2004-07-15 09:08:51 +0300 |
| commit | 9e6f619834527dfa031df16cf494765de3098720 (patch) | |
| tree | 233122fef912777383bfbfdcfa7e3c3cf833d29b /innobase | |
| parent | 5eb3dc3223b20f72f799923db541f6fd585aabed (diff) | |
| download | mariadb-git-9e6f619834527dfa031df16cf494765de3098720.tar.gz | |
btr0cur.c:
Do not add + 1 to the InnoDB index cardinality estimate if the B-tree just contains one page; the fix made in March 2004 caused InnoDB systematically to overestimate the cardinality of empty or small tables by 1
innobase/btr/btr0cur.c:
Do not add + 1 to the InnoDB index cardinality estimate if the B-tree just contains one page; the fix made in March 2004 caused InnoDB systematically to overestimate the cardinality of empty or small tables by 1
Diffstat (limited to 'innobase')
| -rw-r--r-- | innobase/btr/btr0cur.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/innobase/btr/btr0cur.c b/innobase/btr/btr0cur.c index 8974200efe8..b07b06765e6 100644 --- a/innobase/btr/btr0cur.c +++ b/innobase/btr/btr0cur.c @@ -2707,8 +2707,11 @@ btr_estimate_number_of_different_key_vals( rec = page_rec_get_next(rec); } + if (n_cols == dict_index_get_n_unique_in_tree(index)) { - /* We add one because we know that the first record + + /* If there is more than one leaf page in the tree, + we add one because we know that the first record on the page certainly had a different prefix than the last record on the previous index page in the alphabetical order. Before this fix, if there was @@ -2716,7 +2719,11 @@ btr_estimate_number_of_different_key_vals( algorithm grossly underestimated the number of rows in the table. */ - n_diff[n_cols]++; + if (btr_page_get_prev(page, &mtr) != FIL_NULL + || btr_page_get_next(page, &mtr) != FIL_NULL) { + + n_diff[n_cols]++; + } } total_external_size += |