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Displaying posts with tag: slow query log (reset)
Advanced MySQL Slow Query Logging Part 2: pt-query-digest report

Proper MySQL Query Optimization starts with a proper Slow Query Logging session. And MySQL Query Optimization is where I spend 70-80% of my time when doing MySQL performance optimization.

Here in part 2, we will go over the pt-query-digest report, that we have prepared in part 1.

The post Advanced MySQL Slow Query Logging Part 2: pt-query-digest report appeared first on Speedemy.

Advanced MySQL Slow Query Logging

Proper MySQL Query Optimization starts with a proper Slow Query Logging session. And MySQL Query Optimization is where I spend 70-80% of my time when doing MySQL performance optimization. In this short series I will show you how to do Slow Query Logging the right way.

UPDATE: Part 2 is now available. You can find it here:

Advanced MySQL Slow Query Logging Part 2: pt-query-digest report

Stay tuned for Part 3, as well as the cheat sheet mentioned in the video.

The post Advanced MySQL Slow Query Logging appeared first on Speedemy.

Slow Query Log Rotation

Some time ago, Peter Boros at Percona wrote this post: Rotating MySQL slow logs safely. It contains good info, such as that one should use the rename method for rotation (rather than copytruncate), and then connect to mysqld and issue a FLUSH LOGS (rather than send a SIGHUP signal).

So far so good. What I do not agree with is the additional construct to prevent slow queries from being written during log rotation. The author’s rationale is that if too many items get written while the rotation is in process, this can block threads. I understand this, but let’s review what actually happens.

Indeed, if one were to do lots of writes to the slow query log in a short space of time, a write could block while waiting.

Is the risk of this occurring greater during a logrotate operation? I doubt it. A FLUSH LOGS has to …

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Howto automate MySQL slow query analysis with amazon RDS

If you’ve used relational databases for more than ten minutes, I hope you’ve heard of slow queries. Those are those pesky little gremlins that are slowing down your startup, and preventing scalability you so desperately need. Luckily there’s a solution. What I’ve found is if I send a report to developers every week, it keeps […]

How to log slow queries on Slave in MySQL 5.0 with pt-query-digest

Working as a Percona Support Engineer, every day we are seeing lots of issues related to MySQL replication. One very common issue is slave lagging. There are many reasons for slave lag but one common reason is that queries are taking more time on slave then master. How to check and log those long-running queries?  From MySQL 5.1, log-slow-slave-statements variable was introduced, which you can enable on slave and log slow queries. But what if you want to log slow queries on slave in earlier versions like MySQL 5.0?  There is a good solution/workaround: pt-query-digest. How? …

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Tools and tips for analysis of MySQL’s Slow Query Log

MySQL has a nice feature, slow query log, which allows you to log all queries that exceed a predefined about of time to execute. Peter Zaitsev first wrote about this back in 2006 – there have been a few other posts here on the MySQL Performance Blog since then (check this and this, too) but I wanted to revisit his original subject in today’s post.

Query optimization is essential for good database …

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PERFORMANCE_SCHEMA vs Slow Query Log

A couple of weeks ago, shortly after Vadim wrote about Percona Cloud Tools and using Slow Query Log to capture the data, Mark Leith asked why don’t we just use Performance Schema instead? This is an interesting question and I think it deserves its own blog post to talk about.

First, I would say main reason for using Slow Query Log is compatibility. Basic Slow query log with microsecond query time precision is available starting in MySQL 5.1, while events_statements_summary_by_digest table was only added in MySQL 5.6 which was out for …

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Scalability Tips & Greatest Hits

Join 8000 others and follow Sean Hull on twitter @hullsean. In the past two years we’ve written a ton of material on scalability. Here’s the greatest hits… Why Generalists Are Better at Scaling the Web The internet stack is a complex infrastructure of interlocking components. An scalability engineer must be adept at Linux, plus webservers, […]

The post Scalability Tips & Greatest Hits appeared first on Scalable Startups.

Scalability Happiness – A Quiet Query Log

Join 7500 others and follow Sean Hull on twitter @hullsean.

There’s a lot of talk on the web about scalability. Making web applications scale is not easy. The modern web architecture has so many moving parts. How can we grapple with the underlying problem?

Also: Why Are MySQL DBAs So Hard to Find?

The LAMP stack scales well

The truth that is half right. True there are a lot of moving parts, and a lot to setup. The internet stack made up of Linux, Apache, MySQL & PHP. LAMP as it’s called, was built to be resilient, dynamic, and scalable. It’s essentially why Amazon works. Why what they’re doing is possible. Windows …

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How LOCK TABLES interacts with the MySQL slow query log

Here’s a little trivia that you might find helpful. Suppose that I have the following in the MySQL slow query log (abbreviated for clarity):


# User@Host: root[root] @ localhost [127.0.0.1]
# Time: 100919 17:58:52
# Query_time: 9.648427  Lock_time: 8.648039
select sleep(1) from t limit 1;

To get this into the slow query log, I set the long_query_time to 0 and opened two sessions. In one session I ran LOCK TABLES t WRITE, and in the other I tried to select from that table. As you can see above, 1) LOCK TABLES contributes to the Lock_time number, and 2) the Query_time is the sum of execution time and lock time.

Now, I’ll set long_query_time = 2 and run the same test. What happens? Nothing shows up in the slow query log, because 3) the time spent waiting for table locks doesn’t count towards the slow query time threshold.

A final note: …

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