MySQL how to release memory used up by SELECT I executed an INSERT IGNORE combined with SELECT from large table. The SELECT took up 16GB of memory and went into SWAP before I terminated it with CTRL+C.

INSERT IGNORE INTO sid(sid) 
SELECT sid FROM data WHERE sid != "";


The data contains 64 million rows.

Data type of sid is VARCHAR(13). There were 28.2M records that matched the SELECT (I ran it afterwards). That results in around 350MB of data that needs to be SELECTed and INSERTed.

Is it possible to release memory allocated by MySQL? The query was terminated and there is no longer a need for that memory. Why is it still lingering?

Here are some config details:

max_allowed_packet=1024M

# Memory Table

max_heap_table_size=8192M


Everything else is default.

MySQL version 5.5.25, using MyISAM

Inserts into ndbcluster 7.2.7

NDB Config

SharedGlobalMemory=256M
DataMemory=2048M
IndexMemory=512M


My box runs 1/3 SQL nodes, management node. 2 other servers run data nodes.
You could run RESET QUERY CACHE to eliminate collected result sets in the query cache. You could also be more aggressive and drop the query cache and recreate it a different size. For example, to set the query_cache_size to 512M, do the following

SET GLOBAL query_cache_size = 0;
SELECT SLEEP(30);
SET GLOBAL query_cache_size = 1024 * 1024 * 512;


Unfortunately, you can't release the MyISAM Key Buffer and InnoDB Buffer Pool in the same manner. You would have to resize them in /etc/my.cnf (or my.ini for Windows) and restart mysql.

Reading your comments, I can confidently say that MyISAM does not cache data pages. The query cache is the only thing I can think of that grabs and holds result sets. If you are loading in bulk, there should be a lot of query cache invalidations going on.

I am not Cluster Certified, but I will take shot at saying this: Since you are using MySQL Cluster, you may want to try shutting down any mysqld processes or having the cluster disconnect data nodes. Also, be aware of the transmission speed that data hops around the Cluster.