Log Buffer #429: A Carnival of the Vanities for DBAs

This Log Buffer Edition gathers a wide sample of blogs and then purifies the best ones from Oracle, SQL Server and MySQL.


  • If you take a look at the “alter user” command in the old 9i documentation, you’ll see this: DEFAULT ROLE Clause.
  • There’s been an interesting recent discussion on the OTN Database forum regarding “Index blank blocks after a large update that was rolled back.”
  • 12c Parallel Execution New Features: 1 (more...)

Modirum Authenticates Transactions with MySQL

Modirum is a software and consulting company specializing in secure authentication software products, card payment solutions, consulting and SaaS hosted processing services. The company was founded in 1998 in Finland and has offices in Finland, Norway, Estonia, the UK and elsewhere.

Modirum has worked closely with organisations including Visa and Nokia for the development of authentication protocols such as the 3D-Secure protocol and mobile commerce projects over the years. 3-D Secure is an XML-based protocol (more...)

Log Buffer #428: A Carnival of the Vanities for DBAs

The Log Buffer Edition once again is sparkling with some gems, hand-picked from Oracle, SQL Server and MySQL.


  • Oracle GoldenGate  is now certified with Unity 14.10.  With this certification, customers can use Oracle GoldenGate to deliver data to Teradata Unity which can then automate the distribution of data to multiple Teradata databases.
  • How do I change DNS servers on Exadata storage servers.
  • Flushing Shared Pool Does Not Slow (more...)

Coverting MySQL database character set to UTF8

Recently I was engaged to convert the character set for few MySQL databases from latin1 to UTF8 collation utf8_general_ci. This article describes the approach taken for doing the same.

First I will describe various levels at which we can change the character set and collation and then we will see how to convert existing data in a database to required character set.

Backup your database:

Before even thinking about changing character set for your database, (more...)

Log Buffer #427: A Carnival of the Vanities for DBAs

This Log Buffer Edition covers various blog posts from the last week regarding Oracle, SQL Server and MySQL.


  • Merging Overlapping Date Ranges with MATCH_RECOGNIZE
  • The latest version of Enterprise Manager, EM, has been announced!
  • Kdump is the Linux kernel crash-dump mechanism. In the event of a server crash, Kdump creates a memory image (vmcore) that can help in determining the cause of the crash.
  • APEX Connect Presentation and Download of (more...)

Blog Roundup: Oracle, SQL Server, MySQL

This Log Buffer edition transcends beyond ordinary and loop in few of the very good blog posts from Oracle, SQL Server and MySQL.


  • Variable selection also known as feature or attribute selection is an important technique for data mining and predictive analytics.
  • The Oracle Utilities SDK V4. has been released and is available from My Oracle Support for download.
  • This article provides a high level list of the new features (more...)

Bash Arrays & MySQL

Student questions are always interesting! They get me to think and to write. The question this time is: “How do I write a Bash Shell script to process multiple MySQL script files?” This post builds the following model (courtesy of Download MySQL Workbench) by using a bash shell script and MySQL script files, but there’s a disclaimer on this post. It shows both insecure and secure approaches and you should avoid the insecure (more...)

Pointing MySQL Read-Replica to new master after failover

Here I am describing a simple scenario where we have a read replica (other than slave) which is currently pointing to master mysql instance.
We have another slave which is also pointing to same master. What we are going to see is, how to point read replica to new master after failover.


To make you familier with environment, we have 3 instances of mysql

mysql_a -> Current master
mysql_b -> Current slave
mysql_c -> read replica  (more...)

Eclipse on Fedora

While I previously blogged about installing Netbeans 8, some of my students would prefer to use the Eclipse IDE. This post shows how to install and configure Eclipse IDE, include the mysql-connector-java.jar, and write Java to access the MySQL.

You can download Eclipse IDE and then open it in Fedora’s Archive Manager. You can use the Archive Manager to Extract the Eclipse IDE to a directory of your choice. I opted to extract (more...)

“show slave hosts” on master not reporting hostname

If you have multiple MySQL slaves or complex topology, its difficult to remember what slaves are replicating from which master.

We can go to slave servers and check “show slave status” which list master host, but if we want to find out other way, we have can run “show slave hosts” from master.
This will list down all the slaves that are getting replicated from this master.

Only problem I faced was, “show slave (more...)

Restoring Slave when GTID is enabled on master

This is a quick post on issues I faced while restoring a slave when GTID was enabled on master.

I have master created few days back and now I am trying to create a slave. I have GTID enabled on master.

Master status:

root [mysql] >show master status G
*************************** 1. row ***************************
             File: bin_log.000002
         Position: 16682
Executed_Gtid_Set: f7718b80-c237-11e4-baa8-a0369f370a52:1-59
1 row in set (0.00 sec)
root [mysql] >show  (more...)

Test MySQL on AWS quickly

Using sysbench to performance test AWS RDS MySQL hardware is an easy three step  operation. 

Sysbench creates synthetic tests and they are done on a 1 mil row 'sbtest' table that sysbench creates in the MySQL database you indicate. The test doesn't intrude with your database schema, and it doesn't use your data, so it is quite safe. The test is an OLTP test trying to simulate event operations in the database as it (more...)

MariaDB – Measure Replicaton Lag and Check / Fix Replication Inconsistencies using Percona tools

Percona Toolkit is collection of command-line tools to perform many MySQL tasks like creating backups, finding duplicate indexes, managing replication, etc.

In this post I will talk about how to measure replication lag and check/fix replication inconsistencies with this tools:

I am using environment from previous blog post.
Master-Master replication with MariaDB 10.0.16 database on Debian 7.

Install Percona Toolkit on both nodes:

$ sudo wget percona.com/get/percona-toolkit.deb

$ (more...)

MariaDB(MySQL) Master-Master Replication

The simplest and probably most common replication method is master-slave replication. Basically, data is replicated from master database to the slave. In case of master database failure you must get the slave database up-to-date before failover and then promote slave to be new master.

Another method is to set up replication in both directions called master-master replication. But you must be aware that this setup brings some potential issues as data changes are happening on (more...)

MySQL Locking

Have you ever wondered if MySQL does Row Level Locking? Or wondered why are you getting the error:

ERROR 1205 (HY000) : Lock wait timeout exceeded; try restarting transaction

You get the error because your allocated time to hold a DML lock in a transaction exceeds the set limit. Usually the default limit to hold a DML row lock, set by innodb_lock_wait_timeout db parameter, is 50 seconds. If your transaction doesn't commit/rollback within 50 seconds (more...)

Thoughts and notes, Thanksgiving weekend 2014

I’m taking a few weeks defocused from work, as a kind of grandpaternity leave. That said, the venue for my Dances of Infant Calming is a small-but-nice apartment in San Francisco, so a certain amount of thinking about tech industries is inevitable. I even found time last Tuesday to meet or speak with my clients at WibiData, MemSQL, Cloudera, Citus Data, and MongoDB. And thus:

1. I’ve been sloppy in my terminology around “geo-distribution”, in (more...)


I've never had a tool I really liked that would extract a chunk of a large production database for testing purposes while respecting the database's foreign keys. This past week I finally got to write one: rdbms-subsetter.

rdbms-subsetter postgresql://user:passwd@host/source_db postgresql://user:passwd@host/excerpted_db 0.001

Getting it to respect referential integrity "upward" - guaranteeing every needed parent record would be included for each child row - took less than a day. Trying to get it to also guarantee (more...)

%sql: To Pandas and Back

A Pandas DataFrame has a nice to_sql(table_name, sqlalchemy_engine) method that saves itself to a database.

The only trouble is that coming up with the SQLAlchemy Engine object is a little bit of a pain, and if you're using the IPython %sql magic, your %sql session already has an SQLAlchemy engine anyway. So I created a bogus PERSIST pseudo-SQL command that simply calls to_sql with the open database connection:

%sql PERSIST mydataframe

The result is (more...)

auto-generate SQLAlchemy models

PyOhio gave my lightning talk on ddlgenerator a warm reception, and Brandon Lorenz got me thinking, and PyOhio sprints filled my with py-drenaline, and now ddlgenerator can inspect your data and spit out SQLAlchemy model definitions for you:

$ cat merovingians.yaml
name: Clovis I
from: 486
to: 511
name: Childebert I
from: 511
to: 558
$ ddlgenerator --inserts sqlalchemy merovingians.yaml

from sqlalchemy import create_engine, Column, Integer, Table, Unicode
engine (more...)

21st Century DBMS success and failure

As part of my series on the keys to and likelihood of success, I outlined some examples from the DBMS industry. The list turned out too long for a single post, so I split it up by millennia. The part on 20th Century DBMS success and failure went up Friday; in this one I’ll cover more recent events, organized in line with the original overview post. Categories addressed will include analytic RDBMS (including data (more...)