Dear Stefan,
Thanks for your help. I didn't know MySQL doesn't
automatically create index on primary key (I probably
should create UNIQUE index on them now).
About not mixing char and varchar in one table, I
don't find that info in the on-line documents. I could
successfully create a test table
create table testTable(
Seq_ID char(20),
Title varchar(100)
);
Qunfeng
--- "Stefan Hinz, iConnect (Berlin)"
<[EMAIL PROTECTED]> wrote:
> Qunfeng,
>
> > A simple left join on two big table took 5 mins to
> > finish.
>
> These lines tell about the cause of the problem:
>
> > | table | type | possible_keys | key |
> key_len |
> > | s | index | NULL | PRIMARY |
> 50 |
>
> MySQL has no key (index) which it can use to speed
> up the search on the
> first table, newSequence (alias s). So, it has to
> scan all of the rows:
>
> > ref | rows | Extra |
> > NULL | 2684094 | Using index |
>
> MySQL will still use the primary key, _trying_ to be
> faster than without.
>
> Does the Seq_ID have to be VARCHAR? This column type
> isn't very easy to
> index, especially without a length specification.
>
> As you cannot have CHAR (> 3) and VARCHAR in one
> table, I would suggest you
> split up table newSequence into two tables (one
> fixed-length (i.e. without
> VARCHAR/TEXT columns), the other variable-length).
> This will speed up
> count() queries (and others) amazingly.
>
> If you can use something like INT instead of CHAR,
> it's even faster.
>
> If, for any reason, you have to stick to VARCHAR,
> you should index the
> column separately. Leave the primary key as is, but
> add another key (index)
> like that:
>
> CREATE INDEX make_it_fast ON newSequence
> (Seq_ID(10));
>
> This will only make sense if the first 10 characters
> can tell the difference
> between different records. If not, you can
> experiment setting the index size
> to 20, 30, ...
>
> I hope this will give you some ideas on how you can
> improve performance.
>
> Regards,
> --
> Stefan Hinz <[EMAIL PROTECTED]>
> CEO / Gesch�ftsleitung iConnect GmbH
> <http://iConnect.de>
> Heesestr. 6, 12169 Berlin (Germany)
> Telefon: +49 30 7970948-0 Fax: +49 30 7970948-3
>
>
> ----- Original Message -----
> From: "Qunfeng Dong" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Monday, December 16, 2002 6:42 PM
> Subject: How can I speed up the Left Join on big
> tables?
>
>
> > Hi,
> >
> > A simple left join on two big table took 5 mins to
> > finish.
> >
> > Here is the "explain"
> > mysql> explain select count(*) from newSequence s
> left
> > join newSequence_Homolog h on s.Seq_ID = h.Seq_ID;
> >
>
+-------+--------+---------------+---------+---------+----------+---------+-
> ------------+
> > | table | type | possible_keys | key |
> key_len |
> > ref | rows | Extra |
> >
>
+-------+--------+---------------+---------+---------+----------+---------+-
> ------------+
> > | s | index | NULL | PRIMARY |
> 50 |
> > NULL | 2684094 | Using index |
> > | h | eq_ref | PRIMARY | PRIMARY |
> 50 |
> > s.Seq_ID | 1 | Using index |
> >
>
+-------+--------+---------------+---------+---------+----------+---------+-
> ------------+
> > 2 rows in set (0.00 sec)
> >
> > here are the two tables' definitaion
> > mysql> describe newSequence;
> >
>
+-------------+-------------------------------------------------------------
>
-------------------------------------------+------+-----+------------+------
> -+
> > | Field | Type
> >
> > | Null | Key | Default | Extra |
> >
>
+-------------+-------------------------------------------------------------
>
-------------------------------------------+------+-----+------------+------
> -+
> > | Seq_ID | varchar(50)
> >
> > | | PRI | | |
> > | GenBank_Acc | varchar(10)
> >
> > | YES | MUL | NULL | |
> > | Organism | varchar(50)
> >
> > | | MUL | | |
> > | Seq_Type | enum('EST','GSS','EST Contig','EST
> > Singlet','GSS Contig','GSS Singlet','GSS Plasmid
> > Contig','Protein') | | MUL | EST |
> |
> > | Seq_Length | int(11)
> >
> > | | | 0 | |
> > | Seq_Title | text
> >
> > | | MUL | | |
> > | Comment | text
> >
> > | YES | MUL | NULL | |
> > | Entry_Date | date
> >
> > | | | 0000-00-00 | |
> >
>
+-------------+-------------------------------------------------------------
>
-------------------------------------------+------+-----+------------+------
> -+
> > 8 rows in set (0.00 sec)
> >
> > There are 2684094 records on this table.
> >
> > mysql> describe newSequence_Homolog;
> >
>
+------------------+-------------+------+-----+---------+-------+
> > | Field | Type | Null | Key |
> > Default | Extra |
> >
>
+------------------+-------------+------+-----+---------+-------+
> > | Seq_ID | varchar(50) | | PRI |
> > | |
> > | Homolog1_PID | varchar(20) | YES | MUL |
> NULL
> > | |
> > | Homolog1_Desc | varchar(50) | YES | MUL |
> NULL
> > | |
> > | Homolog1_Species | varchar(50) | YES | |
> NULL
> > | |
> > | Homolog2_PID | varchar(20) | YES | MUL |
> NULL
> > | |
> > | Homolog2_Desc | varchar(50) | YES | MUL |
> NULL
> > | |
> > | Homolog2_Species | varchar(50) | YES | |
> NULL
> > | |
> > | Homolog3_PID | varchar(20) | YES | MUL |
> NULL
> > | |
> > | Homolog3_Desc | varchar(50) | YES | MUL |
> NULL
> > | |
> > | Homolog3_Species | varchar(50) | YES | |
> NULL
> > | |
> >
>
+------------------+-------------+------+-----+---------+-------+
> > 10 rows in set (0.00 sec)
> > There are 357944 records in this tables.
> >
> > I've already copied
> > /usr/share/doc/mysql-server-3.23.49/my-huge.cnf as
> > /etc/my.cnf
> >
> > Is there any other thing I can do to improve the
> speed
> > of join? I really hate to merge the two tables
> > together. I am running MySQL3.23.49 on redhat
> > linux7.3. My MySQL Server has 4 GB memory.
> >
> > Eventually, I need to do (select *) instead of the
> > above select count(*)
>
=== message truncated ===
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