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Why the MySQL EXPLAIN Output can be Wrong
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Infinite Replication Loop
Last week I helped 2 different customers with infinite replication loops. I decided to write a blog post about these infinite loop of binary log statements in MySQL Replication. To explain what they are, how to identify them… and how to fix them. An infinite replication loop is one or more transactions that are replicating over and over in a Multi Master Replication relationship. This happens beca
When Do InnoDB Table Statistics Update?
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Disaster: MySQL 5.5 Flushing
We raised topic of problems with flushing in InnoDB several times, some links: InnoDB Flushing theory and solutions MySQL 5.5.8 in search of stability This was not often recurring problem so far, however in my recent experiments, I observe it in very simple sysbench workload on hardware which can be considered as typical nowadays. Hardware: HP ProLiant DL380 G6, with 72GB of RAM and RAID10 on 8 di
Percona Toolkit 1.0.1 released
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MySQL caching methods and tips
“The least expensive query is the query you never run.”Data access is expensive for your application. It often requires CPU, network and disk access, all of which can take a lot of time. Using less computing resources, particularly in the cloud, results in decreased overall operational costs, so caches provide real value by avoiding using those resources. You need an efficient and reliable cache i
How to debug long-running transactions in MySQL
Among the many things that can cause a “server stall” is a long-running transaction. If a transaction remains open for a very long time without committing, and has modified data, then other transactions could block and fail with a lock wait timeout. The problem is, it can be very difficult to find the offending code so that it can be fixed. I see this much too often, and have developed a favorite
MySQL on Amazon RDS part 1: insert performance
Amazon’s Relational Database Service (RDS) is a cloud-hosted MySQL solution. I’ve had some clients hitting performance limitations on standard EC2 servers with EBS volumes (see SSD versus EBS death match), and one of them wanted to evaluate RDS as a replacement. It is built on the same technologies, but the hardware and networking are supposed to be dedicated to RDS, not shared with the general us
How to Identify Bad Queries in MySQL
Finding bad queries is a big part of optimization. A scientific optimization process can be simplified to “can anything be improved for less than it costs not to improve it? – if not, we’re done.” In databases, we care most about the work the database is doing. That is, queries. There are other things we care about, but not as much as queries. The key here is that the question “can anything be imp
Shard-Query adds parallelism to queries
Preamble: On performance, workload and scalability: MySQL has always been focused on OLTP workloads. In fact, both Percona Server and MySQL 5.5.7rc have numerous performance improvements which benefit workloads that have high concurrency. Typical OLTP workloads feature numerous clients (perhaps hundreds or thousands) each reading and writing small chunks of data. The recent improvements to MySQL m
MySQL Limitations Part 4: One Thread per Connection
This is the third in a series on what’s seriously limiting MySQL in core use cases (links: part 1, 2, 3). This post is about the way MySQL handles connections, allocating one thread per connection to the server. MySQL Limitations: ConnectionsMySQL is a single process with multiple threads. Not all databases are architected this way; some have multiple processes that communicate through shared memo
InnoDB, InnoDB-plugin vs XtraDB on fast storage
To continue fun with FusionIO cards, I wanted to check how MySQL / InnoDB performs here. For benchmark I took MySQL 5.1.42 with built-in InnoDB, InnoDB-plugin 1.0.6, and XtraDB 1.0.6-9 ( InnoDB with Percona patches). As benchmark engine I used tpcc-mysql with 1000 warehouses ( which gives around 90GB of data + indexes) on my workhourse Dell PowerEdge R900 ( details about box ). On storage configur
Upgrading to MySQL 8: Embrace the Challenge
Nobody likes change, especially when that change may be challenging. When faced with a technical challenge, I try to remember this comment from Theodore Roosevelt: “Nothing in the world is worth having or worth doing unless it means effort, pain, difficulty.” While this is a bit of an exaggeration, in this case, the main concept is still valid. We shouldn’t shy away from an upgrade path because
Multi Column indexes vs Index Merge
The mistake I commonly see among MySQL users is how indexes are created. Quite commonly people just index individual columns as they are referenced in where clause thinking this is the optimal indexing strategy. For example if I would have something like AGE=18 AND STATE=’CA’ they would create 2 separate indexes on AGE and STATE columns. The better strategy is often to have combined multi-column i
Using netcat to copy MySQL Database
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Conflict Avoidance with auto_increment_increment and auto_increment_offset
How well do your tables fit in buffer pool
xtrabackup-1.1
Finding your MySQL High-Availability solution - The definitions
check-unused-keys: A tool to interact with INDEX_STATISTICS