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10 Newer Entries Showing entries 31 to 40 of 367 10 Older Entries

Displaying posts with tag: Insight for DBAs (reset)

Advanced MySQL Query Tuning (Aug. 6) and MySQL 5.6 Performance Schema (Aug. 13) webinars
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I will be presenting two webinars in August:

This Wednesday’s webinar on advanced MySQL query tuning will be focused on tuning the “usual suspects”: queries with “Group By”, “Order By” and subqueries; those query types are usually perform bad in MySQL and add an additional load as MySQL may need to create a temporary table(s) or perform a filesort.

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Examining the TokuDB MySQL storage engine file structure
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As we know different storage engines in MySQL have different file structures. Every table in MySQL 5.6 must have a .frm file in the database directory matching the table name. But where the rest of the data resides depends on the storage engine.

For MyISAM we have .MYI and .MYD files in the database directory (unless special settings are in place); for InnoDB we might have data stored in the single table space (typically ibdata1 in the database directory) or as file per table (or better said file per partition) producing a single file with .ibd extension for each table/partition. TokuDB as of this version (7.1.7) has its own innovative approach to storing the table contents.

I have created the table in the database test having the following

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Prevent MySQL downtime: Set max_user_connections
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One of the common causes of downtime with MySQL is running out of connections. Have you ever seen this error? “ERROR 1040 (00000): Too many connections.” If you’re working with MySQL long enough you surely have. This is quite a nasty error as it might cause complete downtime… transient errors with successful transactions mixed with failing ones as well as only some processes stopping to run properly causing various kinds of effects if not monitored properly.

There are number of causes for running out of connections, the most common ones involving when the Web/App server is creating unexpectedly large numbers of connections due to a miss-configuration or some script/application leaking connections or creating too many connections in error.

The solution I see some people employ is just to increase

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What I learned while migrating a customer MySQL installation to Amazon RDS
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Hi, I recently had the experience of assisting with a migration of a customer MySQL installation to Amazon RDS (Relational Database Service). Amazon RDS is a great platform for hosting your MySQL installation and offers the following list of pros and cons:

  • You can scale your CPU, IOPS, and storage space separately by using Amazon RDS. Otherwise you need to take downtime and upgrade physical components of a rack-mounted server.
  • Backups, software version patching, failure detection, and (some) recovery is automated with Amazon RDS.
  • You lose shell access to your DB instance
  • You lose SUPER privilege for regular users. Many SUPER-type statements and commands are provided for as a Stored Procedure.
  • It is easy to set up multiple read
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Monitoring MySQL flow control in Percona XtraDB Cluster 5.6
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Monitoring flow control in a Galera cluster is very important. If you do not, you will not understand why writes may sometimes be stalled. Percona XtraDB Cluster 5.6 provides 2 status variables for such monitoring: wsrep_flow_control_paused and wsrep_flow_control_paused_ns. Which one should you use?

What is flow control?

Flow control does not exist with regular MySQL replication, but only with Galera replication. It is simply the mechanism nodes are using when they are not able to keep up with the write load: to keep replication synchronous, the node that is starting to lag instructs the other nodes that writes should be paused for some time so it does not get too far behind.

If you are not familiar with this notion, you

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Reference architecture for a write-intensive MySQL deployment
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We designed Percona Cloud Tools (both hardware and software setup) to handle a very high-intensive MySQL write workload. For example, we already observe inserts of 1bln+ datapoints per day. So I wanted to share what kind of hardware we use to achieve this result.

Let me describe what we use, and later I will explain why.

Server:

  • Chassis: Supermicro SC825TQ-R740LPB 2U Rackmount Chassis
  • Motherboard: Supermicro X9DRI-F dual socket
  • CPU: Dual Intel Xeon Ivy Bridge E5-2643v2 (6x 3.5Ghz cores, 12x HT cores, 25M L3)
  • Memory: 256GB (16x 16GB 256-bit quad-channel) ECC registered DDR3-1600
  • Raid: LSI MegaRAID 9260-4i 4-port 6G/s hardware RAID controller, 512M buffer
  • MainStorage: PCIe SSD HGST FlashMAX II 4.8TB
  • Secondary
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A schema change inconsistency with Galera Cluster for MySQL
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I recently worked on a case where one node of a Galera cluster had its schema desynchronized with the other nodes. And that was although Total Order Isolation method was in effect to perform the schema changes. Let’s see what happened.

Background

For those of you who are not familiar with how Galera can perform schema changes, here is a short recap:

  • Two methods are available depending on the value of the wsrep_OSU_method setting. Both have benefits and drawbacks, it is not the main topic of this post.
  • With TOI (Total Order Isolation), a DDL statement is performed at the same point in the replication flow on all nodes, giving strong guarantees that the schema is always identical on all nodes.
  • With RSU (Rolling Schema Upgrade), a DDL statement is not replicated to the other nodes.
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Systemtap solves phantom MySQLd SIGTERM / SIGKILL issue
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The Percona Managed Services team recently faced a somewhat peculiar client issue. We’d receive pages about their MySQL service being unreachable. However, studying the logs showed nothing out of the ordinary…. for the most part it appeared to be a normal shutdown and there was nothing in anyone’s command history nor a cron task to speak of that was suspicious.

This is one of those obscure and peculiar (read: unique) issues that triggered an old memory; I’d seen this behavior before and I had just the tool to catch the culprit in the act.

Systemtap made diagnostics of this issue possible and I can’t state enough how much of a powerful and often under-utilized tool set systemtap really is.

cat >

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Managing shards of MySQL databases with MySQL Fabric
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This is the fourth post in our MySQL Fabric series. In case you’re joining us now, we started with an introductory post, and then discussed High Availability (HA) using MySQL Fabric here (Part 1) and here (Part 2). Today we will talk about how MySQL Fabric can help you scale out MySQL databases with sharding.

Introduction

At the time of writing, MySQL Fabric includes support for range- and hash-based sharding. As with HA, the functionality is split between client, through a MySQL Fabric-aware connector; and server, through the

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TokuDB gotchas: slow INFORMATION_SCHEMA TABLES
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We are using Percona Server + TokuDB engine extensively in Percona Cloud Tools and getting real usage operational experience with this engine. So I want to share some findings we came across, in hope it may help someone in their work with TokuDB.

So, one problem I faced is that SELECT * FROM INFORMATION_SCHEMA.TABLES is quite slow when I have thousands tables in TokuDB. How slow? For example…

select * from information_schema.tables limit 1000;
...
1000 rows in set (18 min 31.93 sec)

This is very similar to what InnoDB faced a couple years back. InnoDB solved it by adding

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10 Newer Entries Showing entries 31 to 40 of 367 10 Older Entries

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