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Showing entries 1 to 10 of 34741 10 Older Entries
on ORDER BY optimization | Domas Mituzas
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http://dom.as/2015/07/30/on-order-by-optimization/

An insightful exploration by Domas (Facebook) on how some of the MySQL optimiser’s decision logic is sometimes naive, in this case regarding ORDER BY optimisation.

Quite often, “simple” logic can work better than complex logic as chasing all the corner cases can just make things worse – but sometimes, logic can be too simple.

Everything must be made as simple as possible, but no simpler.
— Albert Einstein / Roger Sessions

Log Buffer #434: A Carnival of the Vanities for DBAs
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This Log Buffer Edition throws spotlight on some of the salient blog posts from Oracle, SQL Server and MySQL.

Oracle:

  • STANDARD date considerations in Oracle SQL and PL/SQL
  • My good friend, Oracle icon Karen Morton passed away.
  [Read more...]
MariaDB automatic failover with MaxScale and MariaDB Replication Manager
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Fri, 2015-07-31 12:14guillaumelefranc

Mandatory disclaimer: the techniques described in this blog post are experimental, so use at your own risk. Neither me nor MariaDB Corporation will be held responsible if anything bad happens to your servers.

Context

MaxScale 1.2.0 and above can call external scripts on monitor events. In the case of a classic Master-Slave setup, this can be used for automatic failover and promotion using MariaDB Replication Manager. The following use case is exposed using three MariaDB servers (one master, two slaves) and a MaxScale server. Please refer to my …

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MySQL QA Episode 10: Reproducing and Simplifying: How to get it Right
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Welcome to the 10th episode in the MySQL QA series! Today we’ll talk about reproducing and simplifying: How to get it Right.

Note that unless you are a QA engineer stuck on a remote, and additionally difficult-to-reproduce or difficult-to-reduce bug, this episode will largely be non-interesting for you.

However, what you may like to see – especially if you watched episodes 7 (and possibly 8 and 9) – is how reducer automatically generates handy start/stop/client (cl) etc. scripts, all packed into a handy bug tarball, in combination with the reduced SQL testcase.

This somewhat separate part is covered …

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Shinguz: Max_used_connections per user/account
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Taxonomy upgrade extras: max_used_connectionsuseraccountconnectionconfiguration

How many connections can be opened concurrently against my MySQL or MariaDB database can be configured and checked with the following command:

SHOW GLOBAL VARIABLES LIKE 'max_connections';
+-----------------+-------+
| Variable_name …
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on ORDER BY optimization
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Generally in MySQL we send queries massaged to a point where optimizer doesn’t have to think about anything. In our major user database environment 99.9% of queries don’t have alternative query plans available (either because of forced indexes or just straightforward Primary Key read). We have various other systems and from time to time we have to do SQL work there and chase optimizer errors.

There’re multiple places where optimizer can make a choice in very basic queries, for example:

  • Which index returns less rows
  • Which index can be used for ORDER BY

A query that I was looking asked a very basic question, on a job …

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Webinar-on-demand: Learn how to add HA and DR to MySQL operating on-prem and in VMware's vCloud Air public cloud
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Learn how VMware Continuent adds HA, DR and real-time data warehouse loading to off-the-shelf MySQL operating on-prem and in VMware vCloud Air public cloud. 

We introduce vCloud Air basics, then do a deep dive into the VMware Continuent system architecture covering important issues like fail-over, zero-downtime maintenance, and load scaling. We will conclude with a demonstration of using

MySQL replication monitoring 101
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Replication is the process that transfers data from an active master to a slave server, which reproduces the data stream to achieve, as best as possible, a faithful copy of the data in the master.

To check replication health, you may start with sampling the service, i.e. committing some Sentinel value in the master and retrieving it from the slave.


Sentinel data: Tap tap… Is this thing on?

If you want to make sure that replication is working, the easiest test is using replication itself to see …






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Unknown column ‘smth’ in ‘field list’ -> Oldie but goodie error
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There is an error which is definitely new to people which have encountered such situation at first time.
It was reported a long time before:
#1689 -> 28 Oct 2003 4:46
#1478 -> 4 Oct 2003 10:58
#7501 -> 23 Dec 2004 5:35

Error is -> ERROR 1054 (42S22): Unknown column ‘c2′ in ‘field list’
The Place where you can encounter …





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Why base64-output=DECODE-ROWS does not print row events in MySQL binary logs
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Lately I saw many cases when users specified option

--base64-output=DECODE-ROWS

  to print out a statement representation of row events in MySQL binary logs just to get nothing. Reason for this is obvious: option

--base64-output=DECODE-ROWS

  does not convert row events into its string representation, this is job of option

--verbose

. But why users mix these two options so often? This blog post is result of my investigations.

There are already two great blog posts about printing row events on the …

  [Read more...]
Showing entries 1 to 10 of 34741 10 Older Entries

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