MySQL Calculate How Much Disk Space You Wasted
Bhuvanesh
by Bhuvanesh
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Its not the new term for DBAs. MySQL has an awesome parameter innodb-file-per-tables allows MySQL to create separate files for each tables. This helped a lot to manage the disk space in more efficient way. But when we perform a large batch job for delete or update the data in MySQL tables, you may face this fragmentation issue. Comparing with SQL server, MySQL’s fragmentation is not high. I had a similar situation where my Disk space was consuming 80% and when I check the huge files in OS, one table’s idb file consumed 300GB+. I know it has some wasted blocks(but not actually wasted, MySQL will use this space, it’ll not return this to OS) Then I checked the information schema to find out the data size and its index size. It was 27GB only. Then I realize, we did a batch operation to delete many billions of records in that table.

Thanks to Rolando - MySQL DBA:

When I searched the similar issue on dba stackexchange, I found this great script by Rolando. He had given this script to calculate the wasted size for a single table. I just add some South Indian Masala on top of it.(just for fun). You can use the below script to identify the wasted space/fragmented space in GB for all tables in a database.

Parameters:

  • DB - Your Database Name
  • MYSQL_DATA_DIR - Your Data directory for MySQL
  • MYSQL_USER - MySQL user to query the information schema.
  • MYSQL_PASS - Password for the MySQL user.
    DB='mydb'
    MYSQL_DATA_DIR='/mysqldata'
    MYSQL_USER=sqladmin
    MYSQL_PASS='mypass!'
    MYSQL_CONN="-u${MYSQL_USER} -p${MYSQL_PASS}"
    
    Tables=`ls -l $MYSQL_DATA_DIR/$DB/ | grep ibd | awk -F' ' '{print $9}' | sed -e 's/\.ibd//g'`
    for x in `echo $Tables`
    do
    TB=$x
    SQL="SELECT data_length+index_length FROM information_schema.tables"
    SQL="${SQL} WHERE table_schema='${DB}' AND table_name='${TB}'"
    TBLSIZE_OPER=`ls -l $MYSQL_DATA_DIR/${DB}/${TB}.ibd | awk -F' ' '{print $5}'`
    TBLSIZE_INFO=`mysql ${MYSQL_CONN} -ANe"${SQL}"`
    TBLSIZE_FRAG=$(($TBLSIZE_OPER - $TBLSIZE_INFO))
    TBLSIZE_FRAG_GB=$(($TBLSIZE_FRAG / 1073741824))
    echo ${TB} ${TBLSIZE_FRAG_GB}
    done

Execution

Its better to create the script as a shell file and print the output in a file.

./script.sh > output.txt

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