Introduction In this article, I’m going to explain how to do query profiling using the MySQL Performance Schema. The Performance Schema has been available since MySQL 5.5.3 and allows MySQL to instrument SQL queries and store their trace information in various tables that you can later inspect in order to determine why a given SQL statement is slow. On older versions of MySQL, you might have used the SHOW PROFILE command, but since this feature has been deprecated, you should now use the Performance Schema for SQL query profiling. Enabling the MySQL... Read More
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In this blog post, we’ll look at some of the available PMP profiling tools.
While debugging or analyzing issues with Percona Server for MySQL, we often need a quick understanding of what’s happening on the server. Percona experts frequently use the pt-pmp tool from Percona Toolkit (inspired by http://poormansprofiler.org).
tool collects application stack traces GDB and then post-processes them. From this you get a condensed, ordered list of the stack traces. The list helps you understand where the application spent most of the time: either running something or waiting for something.
Getting a profile with
With the changes to performance_schema in MySQL 5.7 Development
Milestone Release it is now possible to analyze and profile the
execution of stored programs. This is highly useful if you
develop more complex stored procedures and try to find the
bottlenecks. The "old" performance_schema up to MySQL 5.6 only
reported a CALL statement with a runtime, but no information on
statements that were executed WITHIN the stored procedure. Now
let's try this in the latest MySQL 5.7.6 DMR release. After
creating some test table and a test stored procedure we need to
activate the events_statements_history_long consumer, which is
OFF by default:
mysql> UPDATE setup_consumers SET ENABLED="YES"
WHERE NAME = "events_statements_history_long";
Then let's call the stored procedure that we want to inspect:
mysql> CALL …
Section 6: "Profile a real case" 6.1 INTRODUCTION
Profiling & Debugging is an argument that would require an entire book, the aim of this(and the others) posts of this series is to give you the basic knowledge on how to work with these tools and techniques withing Eclipse. For instance if you want to learn to profile with OProfile you should study on the abundant and separate resources, you may start from: http://OProfile.sourceforge.net
6.2 ABOUT NAMING THE PROJECT
Today we had an interesting situation where the same query was executed significantly slower when it was written with GROUP BY instead of DISTINCT and I saw many people still had the assumption that these two types of queries are actually equivalent which is simply not true. Although DISTINCT queries can be implemented using GROUP BY but not every GROUP BY query can be translated to DISTINCT. Depending on the brand and the optimizer the database server may actually use group by internally for the execution of distinct but that won’t make them equivalent. Let’s see why…
GROUP BY as the name suggest groups the result by some set of parameters and evaluate the whole result set. In most databases group by is implemented based on sorting and the same rules applies to it as well.
DISTINCT will make sure that the same row won’t be returned in the result set twice. Distinct doesn’t necessary …[Read more]
Profiling mysqld on windows using visual studio 2012 profiler tool (vsperfcmd)
Recently, when I was doing performance assessment of one innodb feature using sysbench standard tool then I observed performance drop in the feature. I had some hands on experience with codeanalyst (AMD's tool) so I did sampling profiling. I attached profiler vsperf to mysqld when sysbench client was doing transaction with some concurrent threads and captured the data for 1 minute. Just for information, there are 2 technique of profiling -1 sampling and instrumentation. For instrumentation, I had limitation because a)our test framework starts mysqld in instrumentation profiler needs to start mysqld b) in-between framework does shutdown for some clean-up of data and c) instrumentation profiling requires debug build. The codeanalyst does not provide very detailed data like 'vsperf' provides. Using visual studio IDE, we can profile (sampling or instrumentation). In my …[Read more]
The story happened with a webshop application running on Amazon EC2 microinstances. Actually on two instance. Amazon business model is basically simple, they ask money for only three things: Cpu time, IOPS and network traffic. Everybody (including me) thinks for the first time network traffic will be the bottleneck until they got the first bill (it can be even after one year considering the free tier). Actually in this category the IOPS is the most expensive.
On the cacti diagrams I saw strange datas. The created temp tables on disk and created temp files were much higher than created temp tables. The 67% of temporary tables were created on disk. This is very far from optimal.
Temporary objects in MySQL
II increased the max_heap_table_size and tmp_table_size from …[Read more]
This guide will get you up and running with how to identify the bottleneck queries using the excellent tool pt-query-digest. You will learn how to use and analyze the output returned by pt-query-digest. You will also learn some differences between slow query logging in various MySQL versions. Later on in the post I will also show you how to make use of the extra diagnostic data available with Percona Server.
The post Profiling your slow queries using pt-query-digest and some love from Percona Server appeared first on ovais.tariq.
MySQL is needlessly slow at accepting new connections. People usually work around that by having various sorts of connection pools, but there’s always a scale at which connection pools are not feasible. Sometimes connection avalanches come unexpected, and even if MySQL would have no trouble dealing with queries, it will have problems letting clients in. Something has to be done about it.
Lots of these problems have been low hanging fruits for years – it ‘was not detected’ by benchmarks because everyone who benchmarks MySQL would know that persistent connections are much faster and therefore wouldn’t look at connection speeds anymore.
Usually people attribute most of slowness to the LOCK_thread_count mutex – they are only partially right. This mutex does not just handle the counter of active running connections, but pretty much every operation that deals with increase or decrease of threads (thread cache, active thread …[Read more]
There are multiple metrics that are really useful for read workload analysis, that should all be tracked and looked at in performance-critical environments.
The most commonly used is of course Questions (or ‘Queries’, ‘COM_Select’) – this is probably primary finger-pointing metric that can be used in communication with different departments (“why did your qps go up by 30%?”) – it doesn’t always reveal actual cost, it can be increase of actual request rates, it can be new feature, it can be fat fingers error somewhere in the code or improperly handled cache failure.
Another important to note is Connections – MySQL’s costly bottleneck. Though most of users won’t be approaching ~10k/s area – at that point connection pooling starts actually making sense – it is worth to check for other reasons, such as “maybe we connect when we shouldn’t”, or needlessly reconnect, or …[Read more]
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