MDEV-16188 Use in-memory PK filters built from range index scans

This patch contains a full implementation of the optimization
that allows to use in-memory rowid / primary filters built for range  
conditions over indexes. In many cases usage of such filters reduce  
the number of disk seeks spent for fetching table rows.

In this implementation the choice of what possible filter to be applied  
(if any) is made purely on cost-based considerations.

This implementation re-achitectured the partial implementation of
the feature pushed by Galina Shalygina in the commit
8d5a11122c32f4d9eb87536886c6e893377bdd07.

Besides this patch contains a better implementation of the generic  
handler function handler::multi_range_read_info_const() that
takes into account gaps between ranges when calculating the cost of
range index scans. It also contains some corrections of the
implementation of the handler function records_in_range() for MyISAM.

This patch supports the feature for InnoDB and MyISAM.

1 files changed, 2 insertions, 1 deletions

diff --git a/mysql-test/main/type_blob.test b/mysql-test/main/type_blob.test
index 2c74d4ea241..4b5f3578e3a 100644
--- a/mysql-test/main/type_blob.test
+++ b/mysql-test/main/type_blob.test
@@ -360,7 +360,8 @@ select * from t1 where txt >= 'Chevy';
 drop table t1;
 
 create table t1 (id integer primary key auto_increment, txt text, index txt_index (txt (20)));
-insert into t1 (txt) values ('Chevy'), ('Chevy '), (NULL);
+insert into t1 (txt) values
+  ('Chevy'), ('Chevy '), (NULL), ('Honda'), ('Subaru'), ('Honda');
 select * from t1 where txt='Chevy' or txt is NULL;
 explain select * from t1 where txt='Chevy' or txt is NULL;
 select * from t1 where txt='Chevy ';