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Large Tables, Very Slow Deletes.


I've been using MySQL for a while now and are starting to run into limitations. Either my own, or something else.

I have this really large table, it stores images, it has a mediumblob field, an unsigned id integer field and a timestamp field. This table contains up to a few million rows and is constantly filled real time. It grows up to sizes between 50 and 100 gb and in the future probably even larger.

This data is not supposed to be stored for all time, therefor when a certain treshhold is reached, the oldest 5000 rows are deleted to make room for newer rows. This is where my problem kicks in. Whenever I try to delete those rows, it can take for ever to complete. 500 rows I can delete without problem, 2500 becomes slow, 5000 rows takes several seconds and 10.000 rows or more makes it looks like things are frozen.

Now the temporary solution I have is to delete 500 rows at time, but this means I must do that every 10 seconds just to maintain status quo. I would much rather check every 5 minutes or so, and if needed delete 15.000 rows in one go.

I use MyISAM tables and tried setting the key size to 128M, no luck. I run this on a dual Opteron system with a GB of memory and WinXP-SP2 Proffesional.




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UID mediumint(8) unsigned PRI NULL auto_increment
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(
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UNION (

SELECT usernames.UID AS `UID` , usernames.Name AS `result` , auth.username AS `playername` , usernames.Uses AS `Uses` , 0 AS `clan_id` , '' AS `clan_abbrev` , '' AS `clan_name` , 0 AS `clan_icon` , stats.kills AS `kills`
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)
ORDER BY `Uses` DESC
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Slow Performance
On my index.php page, I have a simple query that checks the session_id against a table where I store other session_id'. If it's not there, it records it (unique hit). If it's there, it doesn't record it (not a unique hit.) This usually goes off without a hitch, and every month or so I empty the table.

Right now I only have about 2500 rows, and it's taking forever to load the page. Is there something possibly server related that could be causing this? My host charges an arm and a leg just to see if there's something wrong if I bring up an issue, so I'd like some insight as to whether there's a commonly known server-side issue that can bog down performance.

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Slow Queries!
I have a website which has a users table in a mySQL database. This users table is large (It has about 25 columns - most varchar(100)) but only has about 10000 records. The records contain user information which is searched with a javascript form.
My problem is that when I click to 'view all', it takes about 7 seconds to load. This seems a lot?
Does 25 cloums seem sxcessive in a table? Can anyone point me to some good tutorials / docs on improving query performance? I have defined the colums as best as I can, but I am using SELECT * from table, would selecting individual columns make a big difference?

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Slow Subquery
Can anyone tell me why the following query with sub-query takes forever to finish? (I've le it run for 20 minutes, and it still hasn't finished)

select date from temps where date in (select distinct date from observations where camera like "a")

The sub query returns 10 dates. The outer query is on a table that contains about 40,000 rows. What's the big deal here? All I'm trying to do is select rows from "temps" that match a small range of 10 dates. Is there another way to do this? Is a sub-query the wrong approach?

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Slow Connection
I build an application and installed it on many machines. In every machine except two, the program works without problems. On this two, the connection with database is too slow.

I saw the opened doors with 'netstat' and the computer opens about 5 or 6 ports (to the port 3306 of the mysql server) before sucessfuly connect with MySql Database and execute the sql. I don't know what could be happening. I realy need to fix this because the progrm is too slow with this error. Could anyone know what could be happening??

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Slow Query Log
my slow log is catching a slow query, however the timestamp for the query is "0". I also placed a timestamp on the query to echo out to the results page, and it is about 4 thousands of a second. Why is it showing in the slow log?

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Slow Query Using NOT IN
I am migrating a MSSQL server to MySQL. I know the following SQL is valid for both servers, but MSSQL finishes execution of the query almost instantly, and MySQL has been running the query for the past ten minutes and still is not finished. There is basically the same amount of data in each database. Does anyone know ....

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