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Displaying posts with tag: System Administration (reset)
Temporary table naming scheme in 5.6 and before

Benchmarking is a popular topic. People love drawing graphs as much as watching how X is 10% faster than Y; there must be something special in measurements.

For a DBA, however, more tangible improvements come from less popular area of database maintenance. While MariaDB spreads FUD around InnoDB (nonetheless still uses it) I have to admit InnoDB gets more friendly to DBAs.

In MySQL 5.6 new temporary table naming scheme was introduced – one of improvements. Invisible, yet important.

Temporary table names became more random and should not ever be reused.

Some time ago I wrote a post about how to remove …

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Resolving ERROR 1050 (42S01) at line 1: Table ‘sakila/#sql-ib712′ already exists

When ALTER TABLE crashes MySQL server it leaves orphaned records in InnoDB dictionary. It is annoying because next time you run the same ALTER TABLE query it will fail with error:

ERROR 1050 (42S01) at line 1: Table 'sakila/#sql-ib712' already exists

The post explains why it happens and how to fix it.

When you run ALTER table InnoDB follows the plan:

  1. Block the original table
  2. Create an empty temporary table with the new structure. The name of the new table is something like #sql-ib712.
  3. Copy all records from the original table to the temporary one
  4. Swap the temporary and original tables
  5. Unblock the original table

The temporary table is a normal InnoDB table except it’s not visible to a user. InnoDB creates a record in the dictionary for the temporary table as for any other table.

If MySQL crashes in the middle of the …

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Installing MySQL on Mac OS X easily

Installing MySQL Database on Ubuntu or CentOS is a trivial operation as long as they have nice package managers as Aptitute and YUM. Otherwise, in Mac OS X is a hard operation from downloading the correct package, apllying with several steps and it can break the whole install, if you But, with Homebrew, the install... Read More

The post Installing MySQL on Mac OS X easily appeared first on Devops for Dummies.

The network is reliable

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.

Stuck at "copying to tmp table"

I have a fairly lightly loaded MySQL server with a few tables that are updated every five minutes. Other than these updates, there are very few queries run against the database. The data is queried just a few times per month. Ever so often, one of the more complicated queries will result in the process getting hung in the "copying to tmp table" state. To be honest, the queries that get hung aren't even that complicated. Usually there's one or two joins, a GROUP BY, and an ORDER BY.

Apache Can't Use Remote MySQL Server When SELinux is Enabled

I don't know why SELinux problems seem so frustrating. The problem almost certainly is related to the fact that there is frequently no error message. This is exactly the problem I ran into while turning up a new Apache web server on Red Hat Enterprise Linux 6 (RHEL6) with SELinux enabled.

InnoDB disabled if ib_logfile files corrupted


I recently came across a dev VM running MySQL 5.0.77 (an old release, 28 January 2009) that didn’t have InnoDB available. skip-innodb wasn’t set, SHOW VARIABLES LIKE '%innodb%' looked as expected, but with one exception: the value of have-innodb was DISABLED.

I confirmed this with SHOW ENGINES:

(root@localhost) [(none)]> show engines;
+------------+----------+----------------------------------------------------------------+
| Engine     | Support  | Comment                                                        |
+------------+----------+----------------------------------------------------------------+
| MyISAM     | DEFAULT  | Default engine as of MySQL 3.23 with great performance         |
| MEMORY     | YES      | Hash based, stored in memory, useful for temporary tables      |
| InnoDB     | DISABLED | Supports transactions, row-level locking, and …
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What's New in CFEngine 3: Making System Administration Even More Powerful

CFEngine is both the oldest and the newest of the popular tools for automating site administration. Mark Burgess invented it as a free software project in 1993, and years later, as deployments in the field outgrew its original design he gave it a complete rethink and developed the powerful concept of promise theory to make it modular and maintainable. In this guise as version 3, CFEngine stands along with two other pieces of free software, Puppet and Chef, as key parts of enterprise computing. Along the way, Burgess also started a commercial venture, CFEngine AS, that maintains both the open source and proprietary versions of CFEngine.

Diego Zamboni has recently taken the position of Senior Security Advisor at CFEngine AS and is writing a book for O'Reilly on CFEngine 3. I talked to him this week about the recent new …

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SNMP Traps into MySQL is Sublime

I use snmptrapd to catch SNMP traps and then put them into a MySQL database using a pretty generic trap handler. This gives me the opportunity to generate such useful information as: > SELECT HOUR(time) AS "hour", COUNT(*) AS "bounces" FROM snmptraps WHERE hostname = 'XXX' AND time > '2011-07-25' AND trap_oid = 'SNMPv2-MIB::snmpTrapOID.0 IF-MIB::linkDown' […]

Clear Windows DNS Server Cache From the CLI

Clearing the Windows DNS Server cache from the command line is an easy task.

C:\> dnscmd . /clearcache

The . indicates the local DNS server. You can use this command to clear the cache of remote DNS servers by replacing the . with the hostname or IP address of the remote server.


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