I see that index_ref_start is defined on Ref_Id and Start_Position. Mysql only uses the left-most column of this index. Drop and re-add this key only defined as
INDEX idx_ref_start(start_position) and see if that helps. Your explain you sent this time is not even using the index. In your previous explain output, mysql said the key_len is 5. Since both columns in this key are INT (4-bytes), it says it's only using the left-most column, REF_ID. I'm not sure why it says 5 and not 4, maybe someone else can explain this. I'd redefine the index to only use the a single column, then define a new index on REF_ID if you use that in JOINs. On Mon, Jul 13, 2009 at 9:07 AM, TianJing <tianj...@genomics.org.cn> wrote: > the REF_SEQ is defined below, the col DNA_SEQ is a string such as > "ATGCGGTTA", > > | REF_SEQ | CREATE TABLE `REF_SEQ` ( > `SEQ_ID` int(11) NOT NULL auto_increment, > `REF_ID` int(11) NOT NULL, > `START_POSITION` int(11) NOT NULL, > `END_POSITION` int(11) NOT NULL, > `DNA_SEQ` text, > `DNA_QUALITY` text, > PRIMARY KEY (`SEQ_ID`), > KEY `index_ref_start` (`REF_ID`,`START_POSITION`) > ) ENGINE=MyISAM DEFAULT CHARSET=utf8 | > > i create a index on cols REF_ID and START_POSITION, i also use analyze > table REF_SEQ to optimization the query, > and now the explain output is: > > > mysql> explain select * from REF_SEQ where START_POSITION between 30000 > and 8030000; > > +----+-------------+---------+------+---------------+------+---------+------+--------+-------------+ > | id | select_type | table | type | possible_keys | key | key_len | ref > | rows | Extra | > > +----+-------------+---------+------+---------------+------+---------+------+--------+-------------+ > | 1 | SIMPLE | REF_SEQ | ALL | NULL | NULL | NULL | NULL > | 219728 | Using where | > > +----+-------------+---------+------+---------------+------+---------+------+--------+-------------+ > > > > > 2009/7/13 Johnny Withers <joh...@pixelated.net> > >> Can you show the CREATE TABLE for your REF_SEQ table? >> >> The explain output says "using where" which means that MySQL will have to >> post-filter rows after the storage engine retrieves them. It also means the >> query may benefit from different/better indexing. >> >> >> On Mon, Jul 13, 2009 at 12:04 AM, TianJing <tianj...@genomics.org.cn>wrote: >> >>> i do not use text for start_postion,i use int for it. the only col which >>> defined to text is characters such as "ABTGDSDFSGFDG" etc. >>> >>> 2009/7/13 Darryle Steplight <dstepli...@gmail.com> >>> >>> > Numeric indexing is a lot faster. You definitely shouldn't use text or >>> > varchar types as column types for you min and max values. Do an ALTER >>> > TABLE on any column only hold numeric values and switch them to int >>> > or mediumint. >>> > >>> > On Mon, Jul 13, 2009 at 12:36 AM, TianJing<tianj...@genomics.org.cn> >>> > wrote: >>> > > sorry fo that, but i really need all cols in the table, i think the >>> > problem >>> > > maybe caused by one of the col which is text type, each record of >>> this >>> > col >>> > > has 2000 characters. this makes the size of record more biger. >>> > > >>> > > 2009/7/13 Darryle Steplight <dstepli...@gmail.com> >>> > >> >>> > >> You are still doing SELECT * . Do you really need to return all of >>> the >>> > >> columns in that table or just COL1, COL2, COL5 for example. Only >>> grab >>> > >> the columns you are actually going to use. >>> > >> >>> > >> On Mon, Jul 13, 2009 at 12:23 AM, TianJing<tianj...@genomics.org.cn >>> > >>> > >> wrote: >>> > >> > thanks for reply, >>> > >> > >>> > >> > i hava an index on the start_position,the min_postion and the >>> > >> > max_postion is >>> > >> > constant value, the output of the query is: >>> > >> > >>> > >> > explain select * from REF_SEQ where START_POSITION between 30000 >>> and >>> > >> > 8030000; >>> > >> > >>> > >> > >>> > >> > >>> > >>> +----+-------------+---------+-------+-----------------+-----------------+---------+------+-------+-------------+ >>> > >> > | id | select_type | table | type | possible_keys | key >>> > >> > | >>> > >> > key_len | ref | rows | Extra | >>> > >> > >>> > >> > >>> > >>> +----+-------------+---------+-------+-----------------+-----------------+---------+------+-------+-------------+ >>> > >> > | 1 | SIMPLE | REF_SEQ | range | index_seq_start | >>> > index_seq_start >>> > >> > | >>> > >> > 5 | NULL | 90886 | Using where | >>> > >> > >>> > >> > >>> > >>> +----+-------------+---------+-------+-----------------+-----------------+---------+------+-------+-------------+ >>> > >> > >>> > >> > index_seq_start is the index on start_postion, >>> > >> > >>> > >> > 2009/7/13 Darryle Steplight <dstepli...@gmail.com> >>> > >> >> >>> > >> >> 1. Don't use SELECT *. Only grab the cols that you only need. >>> Also >>> > >> >> make sure you have an index on min_position and max_position. >>> After >>> > >> >> that if your query isn't faster please show us the output of >>> running >>> > >> >> EXPLAIN select * from table_name where start_postion between >>> > >> >> min_postion and >>> > >> >> max_postion" . >>> > >> >> >>> > >> >> On Mon, Jul 13, 2009 at 12:03 AM, JingTian< >>> jingtian.seu...@gmail.com >>> > > >>> > >> >> wrote: >>> > >> >> > Hi all, >>> > >> >> > >>> > >> >> > i use "select * from table_name where start_postion between >>> > >> >> > min_postion >>> > >> >> > and >>> > >> >> > max_postion" to select all the record in the ranges, >>> > >> >> > when the ranges is very large,such as 8000000(about 1000 record >>> in >>> > >> >> > it), >>> > >> >> > the >>> > >> >> > query is so slow, >>> > >> >> > >>> > >> >> > when i use mysql administrator i find that traffic is higher >>> when >>> > the >>> > >> >> > query >>> > >> >> > is begin, >>> > >> >> > >>> > >> >> > could you please give me some advice on how to optimization the >>> > >> >> > query? >>> > >> >> > >>> > >> >> > thanks, >>> > >> >> > >>> > >> >> > -- >>> > >> >> > Tianjing >>> > >> >> > >>> > >> >> >>> > >> >> >>> > >> >> >>> > >> >> -- >>> > >> >> A: It reverses the normal flow of conversation. >>> > >> >> Q: What's wrong with top-posting? >>> > >> >> A: Top-posting. >>> > >> >> Q: What's the biggest scourge on plain text email discussions? >>> > >> > >>> > >> > >>> > >> > >>> > >> > -- >>> > >> >>> > >> >>> > >> -- >>> > >> A: It reverses the normal flow of conversation. >>> > >> Q: What's wrong with top-posting? >>> > >> A: Top-posting. >>> > >> Q: What's the biggest scourge on plain text email discussions? >>> > >> >>> > >> -- >>> > >> MySQL General Mailing List >>> > >> For list archives: http://lists.mysql.com/mysql >>> > >> To unsubscribe: >>> > >> http://lists.mysql.com/mysql?unsub=jingtian.seu...@gmail.com >>> > >> >>> > > >>> > > >>> > > >>> > > -- >>> > > Tianjing >>> > > >>> > > >>> > >>> > >>> > >>> > -- >>> > A: It reverses the normal flow of conversation. >>> > Q: What's wrong with top-posting? >>> > A: Top-posting. >>> > Q: What's the biggest scourge on plain text email discussions? >>> > >>> >>> >>> >> -- >> ----------------------------- >> Johnny Withers >> 601.209.4985 >> joh...@pixelated.net >> > > > > -- > Tianjing > > -- ----------------------------- Johnny Withers 601.209.4985 joh...@pixelated.net
