This blog describes how to identify queries that cause a sudden spike in system resources as well as the user and host who executed the culprit query using the Monyog MySQL Monitor and Advisor.

How many times have you seen a system go live and perform much worse than it did in testing? There could be several reasons behind bad performance. For instance, a slow running query in MySQL can be caused by a poor database design or may be due to higher-than-normal latency in network communication. Other issues such as using too few or too many indexes may also be a factor. This blog will identify the types of poorly performing queries and outline some concrete strategies for identifying them using monitoring. Finally, some tips for improving performance will be presented.

The Effects of Misbehaving Queries

Typically, misbehaving queries will result in two possible outcomes: high CPU usage and/or slow execution. The two …

This blog describes how to identify queries that cause a sudden spike in system resources as well as the user and host who executed the culprit query using the Monyog MySQL Monitor and Advisor.

How many times have you seen a system go live and perform much worse than it did in testing? There could be several reasons behind bad performance. For instance, a slow running query in MySQL can be caused by a poor database design or may be due to higher-than-normal latency in network communication. Other issues such as using too few or too many indexes may also be a factor. This blog will identify the types of poorly performing queries and outline some concrete strategies for identifying them using monitoring. Finally, some tips for improving performance will be presented.

The Effects of Misbehaving Queries

Typically, misbehaving queries will result in two possible outcomes: high CPU usage and/or slow execution. The two …

This blog compares how PostgreSQL and MySQL handle millions of queries per second.

Anastasia: Can open source databases cope with millions of queries per second? Many open source advocates would answer “yes.” However, assertions aren’t enough for well-grounded proof. That’s why in this blog post, we share the benchmark testing results from Alexander Korotkov (CEO of Development, Postgres Professional) and Sveta Smirnova (Principal Technical Services Engineer, Percona). The comparative research of PostgreSQL 9.6 and MySQL 5.7 performance will be especially valuable for environments with multiple databases.

The idea behind this research is to provide an honest comparison for the two popular RDBMSs. Sveta and Alexander wanted to test the most recent versions of both MySQL and PostgreSQL with the same tool, under the same challenging …

Join us for our latest webinar on Thursday, April 7, at 10 am PDT (UTC-7) on Introduction to Troubleshooting Performance: What Affects Query Execution?

MySQL installations experience a multitude of issues: server hangs, wrong data stored in the database, slow running queries, stopped replications, poor user connections and many others. It’s often difficult not only to troubleshoot these issues, but to even know which tools to use.

Slow running queries, threads stacking for ages during peak times, application performance suddenly lagging: these are some of the things on a long list of possible database performance issues. How can you figure out why your MySQL installation isn’t …

Too often developers and DBAs struggle to pinpoint the root cause of MySQL database performance issues, and then spend too much time in trying to fix them. Wouldn’t it be great to bypass wasted guesswork and get right to the issue?

In our upcoming webinar Tired of MySQL Making You Wait? we’re going to help you discover how to significantly increase the performance of your applications and reduce database response time.

In this webinar, Principal Architect Alexander Rubin and Database Evangelist Janis Griffin will provide the key steps needed to identify, prioritize, and improve query performance.

They will discuss the following topics:

• Wait time analytics using …

When it is not possible to eliminate an SQL statement to improve performance, it might be possible to simplify the statement. Consider the following questions:

• Are all columns required?
• Can a table join be removed?
• Is a join or WHERE restriction necessary for additional SQL statements in a given function?

Column Improvement

An important requirement of simplification is to capture all SQL statements in order for a given executed function. Using a sampling process will not identify all possible improvements. Here is an example of a query simplification:

mysql> SELECT fid, val, val
    -> FROM table1
    -> WHERE fid = X;

This query returned 350,000 rows of data that was cached by the application server during system startup. For this query, …

When it’s not possible to remove SQL statements that are unnecessary and the rate of change of common data is relatively low, caching SQL results can provide a significant performance boost to your application and enable additional scalability of your database server.

MySQL Caching

The MySQL query cache can provide a boost in performance for a high read environment and can be implemented without any additional application overhead. The following is an example using the profiling functionality to show the execution time and the individual complexity of a regular SQL statement and a subsequent cached query:

SET GLOBAL query_cache_size=1024*1024*16;
SET GLOBAL query_cache_type=1;
SET PROFILING=1;
SELECT name FROM firms WHERE id=727;
SELECT name FROM firms WHERE id=727;
SHOW PROFILES;

…

Eliminating overhead that adds unnecessary load to database servers when SQL statements are unnecessary can improve MySQL performance, including removing duplicate, repeating or unnecessary statements.

Removing Duplicate SQL Statements

Capture of all SQL statements for a given function or process will highlight any duplicate SQL statements that are executed to complete a specific request. The best practice is to enable the general query log in development environments. Analysis of all SQL statements should be the responsibility of the developer to ensure that only necessary SQL statements are executed. Adding instrumentation to your application to report the number of SQL statements and provide debugging for dynamic viewing of all SQL statements easily enables more information to identify duplicate statements. The use of application frameworks can be a primary cause of unnecessary duplicate SQL statements.

Removing …

Adding indexes can provide significant performance benefits. However, the most effective SQL optimization for a relational database is to eliminate the need to execute the SQL statement completely. For a highly tuned application, the greatest amount of time for the total execution of the statement is the network overhead.

Removing SQL statements can reduce the application processing time. Additional steps necessary for each SQL statement include parsing, permission security checks, and generation of the query execution plan.

These are all overheads that add unnecessary load to the database server when statements are unnecessary. You can use the profiling functionality to get detailed timing of steps within the execution of a query.

Here is an example:

mysql> show profile source for query 7;

…

You might need to restore corrupted tables (or even an entire database) from your backups and use the update logs if a table gets damaged or deleted by accident. In case of relatively minor damage, however, MySQL provides several options for table repair. This next section deals with what you can do if this is the case.

Checking Tables for Errors

The first thing to do if you suspect something is wrong is to check the table for errors. The myisamchk utility is one way to check a table. To invoke this utility, execute the command myisamchk table-file.

Because myisamchk requires exclusive access to the tables, a good idea is to take the server offline before running it. This way, you needn’t worry about coordinating access between clients. In addition, you can run several options when you check a table for errors, as shown in Table 1.

The following example runs myisamchk with the …