diff options
| author | unknown <sergefp@mysql.com> | 2005-10-18 14:04:14 +0400 |
|---|---|---|
| committer | unknown <sergefp@mysql.com> | 2005-10-18 14:04:14 +0400 |
| commit | 8ff8fac53dc7423d1fbe229dfb2f112236b7cf2a (patch) | |
| tree | b67aef0810c2a280d19c1888ea8171c81fdbedf3 /sql/opt_range.cc | |
| parent | 1fe423aebaaefdae815662ce555703eb66b3f9e0 (diff) | |
| download | mariadb-git-8ff8fac53dc7423d1fbe229dfb2f112236b7cf2a.tar.gz | |
BUG#12915: post-review fixes
Diffstat (limited to 'sql/opt_range.cc')
| -rw-r--r-- | sql/opt_range.cc | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/sql/opt_range.cc b/sql/opt_range.cc index 29994c14d3e..71f937f90c6 100644 --- a/sql/opt_range.cc +++ b/sql/opt_range.cc @@ -584,8 +584,7 @@ SEL_ARG *SEL_ARG::clone_tree() /* - Find an index that allows to retrieve first #limit records in the given - order cheaper then one would retrieve them using full table scan. + Find the best index to retrieve first N records in given order SYNOPSIS get_index_for_order() @@ -594,10 +593,13 @@ SEL_ARG *SEL_ARG::clone_tree() limit Number of records that will be retrieved DESCRIPTION + Find the best index that allows to retrieve first #limit records in the + given order cheaper then one would retrieve them using full table scan. + + IMPLEMENTATION Run through all table indexes and find the shortest index that allows - records to be retrieved in given order. If there is such index and - reading first #limit records from it is cheaper then scanning the entire - table, return it. + records to be retrieved in given order. We look for the shortest index + as we will have fewer index pages to read with it. This function is used only by UPDATE/DELETE, so we take into account how the UPDATE/DELETE code will work: |