Postgresql

A while ago I read a paper about Optimizer Benchmarks: How Good Are Query Optimizers, Really? by Viktor Leis from Fakultät für Informatik of the Technische Universität München.

Because we have from time to time problems with slow queries of customers especially after upgrading to new database releases it is interesting for me, how different optimizers cope with a query. Sometimes it is not clear to me why the query is slow or how I can make it faster. So the mentioned paper inspired me to compare the same …

For a fancy application we want to query a chunk of rows from a table and therefore we need the minimum and the maximum of the Primary Key of these rows.
Because InnoDB is an Index Organized Table or Index Clustered Table we know that this access will use the Primary Key. But to be sure and to be compliant with the standard (and compatible) we use and ORDER BY on the Primary Key.

MySQL 5.7

First we create some test data:

mysql> CREATE TABLE t_my (
  ID CHAR(32) NOT NULL PRIMARY KEY
) ENGINE = InnoDB; …

See also our former articles:

• Do not underestimate performance impacts of swapping on NUMA database systems
• MariaDB and MySQL swap analysis

When we do analysis of MariaDB Database servers we also check the memory (RAM and Swap) available:

# free --kilo --wide
              total        used        free      shared     buffers       cache   available
Mem:       16106252     4329952      703356      199008      307872    10765072    11042748
Swap:      31250428      528684    30721744

The values for …

If your MariaDB or MySQL database system is swapping it can have a significant impact on your database query performance! Further it can also slow down your database shutdown and thus influence the whole reboot of your machine. This is especially painful if you have only short maintenance windows or if you do not want to spend the whole night with operation tasks.

When we do reviews of our customer MariaDB or MySQL database systems one of the items to check is Swap Space and swapping. With the free command …

# free
              total        used        free      shared  buff/cache   available
Mem:       16106332     3914228      367072      296508    11825032    11441608
Swap:      31250428      182924    31067504

# cat /proc/meminfo | grep ^Swap
SwapCached:        10056 kB
SwapTotal:      31250428 kB
SwapFree:       31067504 kB

# for file in /proc/*/status ; do
  awk '/VmSwap|Name/{
    if ( $2 != "0" )
      printf $2 " " $3
  }END{ print ""}' $file
done | grep kB | sort -k 2 …

Database migration tools

A generic database migration tool to MySQL and MariaDB is the MySQL Workbench.

An alternative is the old MySQL Migration Tool Kit.

Recommended by MariaDB Foundation: Sqlines.

Adabas D to MariaDB migration

Project migrating an Adabas D database to MariaDB is in progress. More information are expected before end of 2015.

Oracle to MySQL or MariaDB migration

Data Migration Tools

• MyOraDump is a tool to export data from an Oracle database to MySQL or MariaDB. …

Im Admin-Magazin 2011/06 hat es einen netten Artikel über MySQL und PostgreSQL Performance Tuning: Duell der Datenbanken: In einem Shootout messen sich MySQL und PostgreSQL

Susanne hat dabei PostgreSQL, wir MySQL betreut…