Planet MySQL Planet MySQL: Meta Deutsch Español Français Italiano 日本語 Русский Português 中文
Showing entries 1 to 10 of 29 10 Older Entries

Displaying posts with tag: error (reset)

Changes in Configuration of Global Variables between MySQL 5.6.20 and MySQL 5.7.4 “Milestone 14″
+0 Vote Up -0Vote Down

While doing some testing (that I have pending to show you) on the still-in-development MySQL 5.7 I wanted to do some analysis on the configuration to see if the changes in performance were due to the code changes or just to the new MySQL defaults (something that is very common in the migration from 5.5 to 5.6 due to the default transaction log size and other InnoDB parameters). This is a quick post aiming to identify the global variables changed between these two versions.

You could tell me that you could just read the release notes, but my experience (and this is not an exception,

  [Read more...]
The network is reliable
+2 Vote Up -0Vote Down

A fascinating post-mortem on high profile network failures:

This post is meant as a reference point–to illustrate that, according to a wide range of accounts, partitions occur in many real-world environments. Processes, servers, NICs, switches, local and wide area networks can all fail, and the resulting economic consequences are real. Network outages can suddenly arise in systems that are stable for months at a time, during routine upgrades, or as a result of emergency maintenance. The consequences of these outages range from increased latency and temporary unavailability to inconsistency, corruption, and data loss. Split-brain is not an academic concern: it happens to all kinds of systems–sometimes for days on end. Partitions deserve serious consideration.

Diagnosing problems with SQL imports
+0 Vote Up -0Vote Down

Importing a text file containing a list of SQL commands into MySQL is a straightforward task. All you need to do is simply feed the file contents through pipe into MySQL command line client. For example: mysql app_production .

The reasons for doing such imports can be very different - restoring MySQL backups created with mysqldump, manually replaying binary log events or performing database migrations during software roll-outs.

While the task is simple, the import may not end successfully and when this happens, how to tell what the problem was?

MySQL errors

Whenever database hits an error, MySQL produces an error message that describes the problem and the import process stops immediately. If the message is not clear enough, you can always refer to the reported line number, which is the line number inside the source SQL file. This

  [Read more...]
SQLSTATE[HY000]: General error: 2006 MySQL server has gone away
+1 Vote Up -0Vote Down

This would have to be one of the most common MySQL error messages that is misleading to the end user developer. The MySQL Manual page confirms the broad range of possible conditions, but offers little to a PHP developer that does not speak MySQL Geek. I am commonly asked to help solve this issue from a developer.

The problem is that there are several conditions that can cause this error, and a more meaningful explanation to the end user would help in addressing the issue. In general terms, this actually means “Your SQL statement has failed because the connection to the database has been disconnected because of ???”.

Here are a few common situations and how to check for what “???” is.

1. Your MySQL server really did go away.

  [Read more...]
The hidden mistake
+5 Vote Up -0Vote Down

There are mistakes that drive you crazy when you try to understand what went wrong.

One of the most annoying and hard to catch was this, apparently harmless line:

tungsten-sandbox -m 5.5.24 --topology all-masters -n 2 -p 7300 -l 12300 -r 10300 –t $HOME/mm -d tsb-mm

The person reporting the error told me that the installation directory (indicated by "-t") was not taken into account.

I usually debug by examples, so I copied the line, and pasted it into one of my servers. Sure enough, the application did not take trat option into account. The installation kept happening in the default directory.

I knew that I had done a good job at making the application configurable, but I checked the code nonetheless. The only place where the default directory is mentioned is when the related variable is initialized. Throughout the code, there are no


  [Read more...]
A small rant on Galera & XtraDB Cluster
+3 Vote Up -0Vote Down

I had to install Percona XtraDB Cluster, I think for the first time since it was announced stable. I remembered many problems I faced with beta releases, which was understandable given they were only for a preview, but this time I hoped for significant improvements.

I have to say I am generally quite sensitive about simple problems that could/should be easily discovered and corrected. Well, it didn’t take five minutes to see a few of such problems. These minutes I spent installing the database binaries from Percona Yum repository. It turned out that was enough to see a lot of errors for no reason. Not a good thing.

[..]
  Installing : 1:Percona-XtraDB-Cluster-server-5.5.23-23.5.333.rhel6.x86_64         5/5
ls: cannot access /var/lib/mysql/*.err: No such file or directory
ls: cannot access /var/lib/mysql/*.err: No such file or directory
  [Read more...]
MySQL, OOM Killer, and everything related
+1 Vote Up -0Vote Down

Do the operating systems kill your MySQL instances from time to time? Are some database servers swapping constantly? These are relatively common problems. Why? How to prevent them?

Memory allocation

When a running program needs some additional memory, it can typically allocate it dynamically with malloc() function. It finds an unused continuous block that is at least as large as the requested size, reserves as much as it needs, and returns a pointer to that space. No initialization of the memory contents is performed at the time. When malloc() returns NULL instead of a valid address, it is an information to the calling program that there wasn’t enough memory available and the call has failed to allocate anything. In such cases applications typically take appropriate actions to notify users about the problem and terminate some of their

  [Read more...]
An elaborate way to break a MySQL server with XtraBackup
+2 Vote Up -0Vote Down

XtraBackup is a great piece of software from Percona, which allows creating (nearly) lock-less MySQL/InnoDB backups. The tool has been around for quite some time and recently even received a major version bump. I have relied on it many times over the years. As it turns out, using it in some configurations may lead to heavy swapping or prevent MySQL from running queries.

So far I only kept complaining about the wrapper script XtraBackup has been distributed with and which was taken from Oracle’s InnoDB Hot Backup. The infamous innobackupex-1.5.1 was neither well written, nor was it even fully compatible with the XtraBackup’s feature set. This sometimes led to weird problems where there should not be any.

This time the problem can appear elsewhere. Mostly when one using the tool does not understand how it works in

  [Read more...]
How To – Fix MySQL Option Without Preceding Group
+0 Vote Up -0Vote Down

Background Knowledge


You try starting, stopping or connecting to MySQL and receive the following error, “Error: Found option without preceding group in config file: /etc/mysql/conf.d/char_collation_set.cnf at line: 1″. The error message my vary but comes to the same issue. MySQL may not start or might experience connectivity issues.

This issue was experienced on Debian Squeeze v6.04 AMD64 system with MySQL v14.14 Distrib 5.1.61.

Solution


This issue is caused by a improperly formatted MySQL configuration file(s) and refers to one missing the group heading (e.g. [mysqld], [mysqld_safe], etc.).

Source:   [Read more...]

Running out of disk space on MySQL partition? A quick rescue.
+2 Vote Up -0Vote Down

No space left on device – this can happen to anyone. Sooner or later you may face the situation where a database either has already or is only minutes away from running out of disk space. What many people do in such cases, they just start looking for semi-random things to remove – perhaps a backup, a few older log files, or pretty much anything that seems redundant. However this means acting under a lot of stress and without much thinking, so it would be great if there was a possibility to avoid that. Often there is. Or what if there isn’t anything to remove?

While xfs is usually the recommended filesystem for a MySQL data partition on Linux, the extended filesystem family continues to be very popular as it is used as default in all major Linux distributions. There is a feature

  [Read more...]
Showing entries 1 to 10 of 29 10 Older Entries

Planet MySQL © 1995, 2014, Oracle Corporation and/or its affiliates   Legal Policies | Your Privacy Rights | Terms of Use

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.