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I specialise MySQL Server performance as well as in performance of application stacks using MySQL, especially LAMP. Web sites handling millions of visitors a day dealing with terabytes of data and hundreds of servers is king of applications I love the most. Peter is a DZone MVB and is not an employee of DZone and has posted 272 posts at DZone. You can read more from them at their website. View Full User Profile

Looking Out for Max Values in Integer-Based Columns in MySQL

07.16.2014
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Originally written by

Yay! My first blog post! As long as at least 1 person finds it useful, I’ve done my job. ;) Recently, one of my long-term clients was noticing that while their INSERTs were succeeding, a particular column counter was not incrementing. A quick investigation determined the column was of type int(11) and they had reached the maximum value of 2147483647. We fixed this by using pt-online-schema-change to change the column to int(10) unsigned, thus allowing values up to 4294967295.

My client was now concerned about all his other integer-based columns and wanted me to check them all. So I wrote a quick-n-dirty script in Go to check all integer-based columns on their current value compared to the maximum allowed for that column type.

You can find the full source code in my git repo.

Here’s a quick overview; the code is pretty simple.

First we connect to MySQL and verify the connection:

db, err := sql.Open("mysql", fmt.Sprintf("%s:%s@tcp(%s:3306)/%s", mysqlUn, mysqlPw, hostToCheck, dbToCheck))
if err != nil {
	fmt.Printf("Error connecting to MySQL on '%s': n", hostToCheck, err)
	db.Close()
	os.Exit(1)
}
// Check connection is alive.
err = db.Ping()
if err != nil {
	fmt.Printf("Unable to ping mysql at '%s': %sn", hostToCheck, err)
	db.Close()
	os.Exit(1)
}

Next, we query the information_schema.columns table for the names of all integer-based columns and calculate what their maximum value can be (credit for the clever SQL goes to Peter Boros).

// Construct our base i_s query
var tableExtraSql string
if tableToCheck != "" {
	tableExtraSql = fmt.Sprintf("AND TABLE_NAME = '%s'", tableToCheck)
}
baseSql := fmt.Sprintf(`
	SELECT TABLE_NAME, COLUMN_NAME, COLUMN_TYPE, (CASE DATA_TYPE
   	  WHEN 'tinyint' THEN 255
    	  WHEN 'smallint' THEN 65535
    	  WHEN 'mediumint' THEN 16777215
    	  WHEN 'int' THEN 4294967295
    	  WHEN 'bigint' THEN 18446744073709551615
   	END >> IF(LOCATE('unsigned', COLUMN_TYPE) > 0, 0, 1)) AS MAX_VALUE
	FROM information_schema.columns
	WHERE TABLE_SCHEMA = '%s' %s
	AND DATA_TYPE IN ('tinyint', 'int', 'mediumint', 'bigint')`, dbToCheck, tableExtraSql)

Now that we have this list of columns to check, we simply loop over this result set, get the MAX() of each column and print a pretty report.

// Loop over rows received from i_s query above.
for columnsToCheck.Next() {
	err := columnsToCheck.Scan(&tableName, &columnName, &columnType, &maxValue)
	if err != nil {
		log.Fatal("Scanning Row Error: ", err)
	}
	// Check this column
	query := fmt.Sprintf("SELECT MAX(%s), ROUND((MAX(%s)/%d)*100, 2) AS ratio FROM %s.%s",
		columnName, columnName, maxValue, dbToCheck, tableName)
	err = db.QueryRow(query).Scan(¤tValue, &ratio)
	if err != nil {
		fmt.Printf("Couldn't get MAX(%s.%s): %sn", tableName, columnName, err)
		fmt.Println("SQL: ", query)
		continue
	}
	// Print report
	if ratio.Valid && ratio.Float64 >= float64(reportPct) {
		fmt.Printf("'%s'.'%s' - Type: '%s' - ", tableName, columnName, columnType)
		fmt.Printf("ColumMax: '%d'", maxValue)
		fmt.Printf(" - CurVal: '%d'", currentValue.Int64)
		fmt.Printf(" - FillRatio: '%.2f'n", ratio.Float64)
	}
}

There are more options to the app that allow you to silence some of the verbosity and to only print report lines where the value-to-max ratio is > a user-defined threshold. If you have frequently changing schemas, this should allow you to cron the app and only receive email reports when there is a potential problem. Otherwise, this tool could be useful to run once a month/quarter, just to verify things are in good standing.

Like I said before, hopefully this helps at least 1 person catch a potential problem sooner rather than later.


Published at DZone with permission of Peter Zaitsev, author and DZone MVB. (source)

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