Hi nagaraj,
sorry.. Since the cardinality is low MySQL has chosen *not to use* a Index that can give the best performance. i missed that.


Regards,
Pradeep chandru.



Nagaraj S wrote:
Pradeep,
Can you be clear on your statement. Becoz i read in few links if the cardinality is low also mysql doen't use the index. It depends up on the where condition used.. Regards,
Naga.

On Thu, Sep 18, 2008 at 12:22 PM, chandru <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> wrote:

    Hi Dilip,
      I dont think forcing MySQL to use Index can improve your
    performance. MySQL decides on the index to be used based on the
    cardinality. Since the cardinality is low MySQL has chosen a Index
    that can give the best performance. Forcing that can only increase
    the volume of data that is fetched.

    Regards,
    Pradeep chandru.



    Parikh, Dilip Kumar wrote:
    Hi johan,

    U can use and try to write a query to use index in it (like use index(index 
name) before where condition.
    And other variables also looks like ok seems let me check, Please try to 
send the output of global status.

    Show global status;



    Thanks & Regards,
    Dilipkumar

    -----Original Message-----
From: chandru [mailto:[EMAIL PROTECTED] Sent: Thursday, September 18, 2008 11:36 AM
    To: Johan Thorvaldsson
    Cc: mysql@lists.mysql.com <mailto:mysql@lists.mysql.com>
    Subject: Re: Fwd: Why dont my query use the index keys?

    Hi Johan,
      the query is going for a temporary table creation  "Using temporary; Using 
filesort"

In case your sort_buffer_size is too low please try increasing the same. Be cautious don't try to increase it massively, since it is a per thread memory allocation.

    please let me know what is your sort_buffer_size by using the command  show 
global variables like 'sort%';



    Regards,
    Pradeep Chandru.


    Johan Thorvaldsson wrote:
    So query and index:es are ok ? Because the query runs very slow.

    Vidarebefordrat brev:

    Från: "Ananda Kumar" <[EMAIL PROTECTED]> <mailto:[EMAIL PROTECTED]>
    Datum: ti 16 sep 2008 13.19.43 GMT+02:00
    Till: "Johan Thorvaldsson" <[EMAIL PROTECTED]> <mailto:[EMAIL PROTECTED]>
    Kopia: mysql@lists.mysql.com <mailto:mysql@lists.mysql.com>
    Ämne: Re: Why dont my query use the index keys?

    Hi Johan,
    Its doing a range based search, so its using index.

    regards
    anandkl


    On 9/16/08, Johan Thorvaldsson <[EMAIL PROTECTED]> <mailto:[EMAIL 
PROTECTED]> wrote:
    But this one doesnt use any indexes?
SIMPLE tm range is_active,ad_id,tag_id * tag_id* 4 NULL 15353 Using where; Using temporary; Using filesort

    Thanks for your replies.

    Vidarebefordrat brev:

    Från: chandru <[EMAIL PROTECTED]> <mailto:[EMAIL PROTECTED]>
    Datum: ti 16 sep 2008 10.13.53 GMT+02:00
    Till: Johan Thorvaldsson <[EMAIL PROTECTED]> <mailto:[EMAIL PROTECTED]>
    Kopia: mysql@lists.mysql.com <mailto:mysql@lists.mysql.com>
    Ämne: Re: Why dont my query use the index keys?


    Hi johan,
    i find that the query is using a index already.
    Explain version:
1 SIMPLE tm range is_active,ad_id,tag_id * tag_id* 4 NULL 15353 Using where; Using temporary; Using filesort 1 SIMPLE ad eq_ref PRIMARY,ad_id,is_removed,is_active,whitelisted,ant_feedback_alert *PRIMARY* 4 rubbt.tm.ad_id 1 I have bold the index names that are being used. Can you please clarify is that the one you are trying to find?

    Regards,
    Pradeep Chandru.




    Johan Thorvaldsson wrote:
    AD

    Create Table: CREATE TABLE `ad` (
`ad_id` int(11) NOT NULL auto_increment, `ad_key` varchar(32) collate utf8_swedish_ci NOT NULL default '', `pris` varchar(32) collate utf8_swedish_ci NOT NULL default '', `pris_original` varchar(32) collate utf8_swedish_ci NOT NULL default '', `dt_pub` datetime NOT NULL default '0000-00-00 00:00:00', `dt_updated` datetime NOT NULL default '0000-00-00 00:00:00', `ad_password` varchar(32) collate utf8_swedish_ci NOT NULL default '', `adtext` text collate utf8_swedish_ci NOT NULL, `unique_key` varchar(32) collate utf8_swedish_ci NOT NULL default '', `is_removed` int(11) NOT NULL default '0', `is_active` int(11) NOT NULL default '0', `num_images` int(11) default NULL, `sh_phone` int(11) default '0', `postalcode` varchar(32) collate utf8_swedish_ci default NULL, `ad_url` varchar(128) collate utf8_swedish_ci NOT NULL default '', `source_id` int(11) default '0', `youtube_link` text collate utf8_swedish_ci, `ad_sections` varchar(128) collate utf8_swedish_ci default NULL, `flickr_link` text collate utf8_swedish_ci, `ant_feedback_good` int(32) default '0', `ant_feedback_alert` int(32) default '0', `whitelisted` int(11) default '0', `adtext_plain` text collate utf8_swedish_ci NOT NULL, `dt_img_path` datetime NOT NULL default '0000-00-00 00:00:00', PRIMARY KEY (`ad_id`), KEY `sortkey` (`dt_pub`,`pris`), KEY `webbid` (`ad_key`), KEY `ad_id` (`ad_id`) ) ENGINE=MyISAM AUTO_INCREMENT=18721 DEFAULT CHARSET=utf8 COLLATE=utf8_swedish_ci

+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
    | Table | Non_unique | Key_name | Seq_in_index | Column_name |
Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | ad | 0 | PRIMARY | 1 | ad_id | A | 18691 | NULL | NULL | | BTREE | | | ad | 1 | sortkey | 1 | dt_pub | A | 3115 | NULL | NULL | | BTREE | | | ad | 1 | sortkey | 2 | pris | A | 3115 | NULL | NULL | | BTREE | | | ad | 1 | webbid | 1 | ad_key | A | 18691 | NULL | NULL | | BTREE | | | ad | 1 | ad_id | 1 | ad_id | A | 18691 | NULL | NULL | | BTREE | | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+


    Tag_ad_map
Create Table: CREATE TABLE `tag_ad_map` ( `ad_id` int(11) NOT NULL default '0', `tag_id` int(11) NOT NULL default '0', `termfreq` int(11) NOT NULL default '0', `weight` int(11) NOT NULL default '0', `is_active` int(11) NOT NULL default '0', PRIMARY KEY (`tag_id`,`ad_id`), KEY `tag_id` (`tag_id`), KEY `ad_id` (`ad_id`)
    ) ENGINE=MyISAM DEFAULT CHARSET=utf8

+------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | tag_ad_map | 0 | PRIMARY | 1 | tag_id | A | 35921 | NULL | NULL | | BTREE | | | tag_ad_map | 0 | PRIMARY | 2 | ad_id | A | 215531 | NULL | NULL | | BTREE | | | tag_ad_map | 1 | tag_id | 1 | tag_id | A | 35921 | NULL | NULL | | BTREE | | | tag_ad_map | 1 | ad_id | 1 | ad_id | A | 17960 | NULL | NULL | | BTREE | | +------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+

    16 sep 2008 kl. 09.01 skrev Ananda Kumar:

    can u please do

    show index for ad;

    show index for tag_ad_map;

and past the output. I am not able to understand the index setup on these two tables.

    regards
    anandkl


    On 9/15/08, Johan Thorvaldsson <[EMAIL PROTECTED]> <mailto:[EMAIL 
PROTECTED]> wrote:
My query dont use the indexes for the 2 tables that I have joined. Is there someone nice and helpful that could help me optimize this query and make it use the indexes?

    Query:

SELECT SQL_NO_CACHE COUNT(*) antal, ad.ad_url, ad.adtext_plain FROM ad

    LEFT JOIN tag_ad_map tm ON tm.ad_id=ad.ad_id

    WHERE  tm.tag_id IN (99, 10807, 20728, 447, 807)

AND ad.is_removed = 0 AND ad.is_active=1 AND (ad.ant_feedback_alert <= 5 OR ad.whitelisted = 1) AND tm.is_active=1 AND ad.ad_id != 13687 GROUP BY ad.ad_id ORDER BY antal DESC LIMIT 10;

    Explain version:
1 SIMPLE tm range is_active,ad_id,tag_id tag_id 4 NULL 15353 Using where; Using temporary; Using filesort 1 SIMPLE ad eq_ref PRIMARY,ad_id,is_removed,is_active,whitelisted,ant_feedback_alert PRIMARY 4 rubbt.tm.ad_id 1 Using where

    Indexes:
ad 0 PRIMARY 1 ad_id A 18679 NULL NULL BTREE ad 1 is_removed 1 is_removed A 1 NULL NULL BTREE ad 1 is_active 1 is_active A 1 NULL NULL BTREE ad 1 source_id 1 source_id A 3 NULL NULL YES BTREE ad 1 whitelisted 1 whitelisted A 1 NULL NULL YES BTREE ad 1 ant_feedback_alert 1 ant_feedback_alert A 1 NULL NULL YES BTREE ad 1 dt_pub 1 dt_pub A 3113 NULL NULL BTREE ad 1 dt_updated 1 dt_updated A 3113 NULL NULL BTREE ad 1 ad_url 1 ad_url A 18679 NULL NULL BTREE ad 1 adtext_plain 1 adtext_plain NULL 1 NULL NULL FULLTEXT


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Kristinebergsvägen 17, S-30241 HALMSTAD Telefon +46(0)35-13 68 00 | Fax +46(0)35-13 68 01


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