Comments on: MySQL's query cache explained http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/ Words of wisdom from a server administrator Sat, 11 Feb 2012 23:43:21 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: tom3k http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-13988 tom3k Tue, 31 Mar 2009 09:01:27 +0000 http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-13988 well writen. thanks! well writen.

thanks!

]]> By: Moe http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-13962 Moe Wed, 18 Mar 2009 19:21:51 +0000 http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-13962 I know this is off topic, but I was wondering if you have ever seen the following: [MySQL][ODBC 3.51 Driver]Can't create a new thread (errno 12); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug The server is a W2k3 server, with Dual Xeon Duo Core with 12 gb ram. Memory usage is at 10gb available when it crashes. I don’t think this is a hardware limitation. I have attached our my.ini file. Currently, the system crashes at 1280 connections. Is there any way we can adjust the file so we can maximize the connections until we re-develop our software? The My.ini has the following settings: max_connections=2047 I know this is off topic, but I was wondering if you have ever seen the following:

[MySQL][ODBC 3.51 Driver]Can't create a new thread (errno 12); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug

The server is a W2k3 server, with Dual Xeon Duo Core with 12 gb ram. Memory usage is at 10gb available when it crashes. I don’t think this is a hardware limitation.

I have attached our my.ini file. Currently, the system crashes at 1280 connections. Is there any way we can adjust the file so we can maximize the connections until we re-develop our software?

The My.ini has the following settings:

max_connections=2047

]]> By: major http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-12843 major Sun, 01 Feb 2009 15:45:11 +0000 http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-12843 Moe, The query cache only holds the results of the queries, but it is very picky. For example, these two queries are seen as completely different by the query cache: SELECT column FROM table; select column from table; If you make a large select, and then make a smaller select later, the second query will not be able to utilize the cached result from the first. When tables are removed or rows are updated, the related data in the query cache is removed, which can be an expensive operation when multiplied over thousands of queries. Moe,

The query cache only holds the results of the queries, but it is very picky. For example, these two queries are seen as completely different by the query cache:

SELECT column FROM table;
select column from table;

If you make a large select, and then make a smaller select later, the second query will not be able to utilize the cached result from the first. When tables are removed or rows are updated, the related data in the query cache is removed, which can be an expensive operation when multiplied over thousands of queries.

]]> By: Moe http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-12842 Moe Sun, 01 Feb 2009 15:41:32 +0000 http://rackerhacker.com/2007/08/08/mysqls-query-cache-explained/#comment-12842 We make medical systems for physicians which store a fair amount of data in MySQL. However, only a small portion of the data (<1%) is used on a given day. So here is my question related to the article. Is only the results of the query stored using the query cache or is MySQL aware that the data is in memory and will seek it there first. For example, when someone selects a patient and goes into their record, we run a query to look up that patients information specifying the patient exactly. Could I run a larger query resulting in all the patients for a given day, and then when I run the query for that specific patient it would give the response I am looking for? My second question is, what happens if the underlying data changes, does the query cache up date itself? Thanks Moe. We make medical systems for physicians which store a fair amount of data in MySQL. However, only a small portion of the data (<1%) is used on a given day.

So here is my question related to the article. Is only the results of the query stored using the query cache or is MySQL aware that the data is in memory and will seek it there first. For example, when someone selects a patient and goes into their record, we run a query to look up that patients information specifying the patient exactly.

Could I run a larger query resulting in all the patients for a given day, and then when I run the query for that specific patient it would give the response I am looking for?

My second question is, what happens if the underlying data changes, does the query cache up date itself?

Thanks
Moe.

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