Tablespaces in MySQL, Oracle and Postgres

If you are not familiar with tablespaces you may be wondering what the big deal about them is. Tablespaces are a logical addition to a database that helps maintenance, and potentially, can improve performance.

In Oracle and MySQL, a tablespace is a logical unit meant to store segments (i.e. tables and indexes). In Postgres, a tablespace is a physical unit. It is a symbolic link to a directory. Postgres does not allow tablespaces on operating systems that do not support symbolic links (such as windows).

The data file is the actual physical storage mechanism in Oracle and MySQL. Postgres stores tables in individual files. Postgres support of tablespaces is minimal. In MySQL and Oracle, performance can be improved by a more granular spread of data across disks. Ease of maintenance is maintained due to the logical grouping of tablespaces.

Oracle syntax for creating a tablespace is much the same as MySQL but with many more options. Oracle also allows a single tablespace to be made up of many data files.

Below is a very simple example of creating and using a tablespace in MySQL:

mysql> create tablespace testts

-> add datafile 'myfirstfile'

-> engine = falcon;

Query OK, 0 rows affected (0.48 sec)

mysql> create table testmyts (

-> abc integer )

-> tablespace testts;

Query OK, 0 rows affected (0.11 sec)

mysql>

The first command creates the tablespace (naming it testts) and assigning it a file name of myfirstfile. Of course, we are using the falcon engine. If you look in your MySQL data directory after running this command, you should a new file named myfirstfile.

The second command creates a table using our new tablespace. If you look at the tablespace now, it should be bigger. If not, insert a bunch of rows and watch it grow.

Oracle syntax, in its simplest form, is very close to MySQL syntax. Here is the same example in Oracle.

SQL> create tablespace testts

2 datafile 'myfirstfile'

3 size 10M;

Tablespace created.

SQL> create table testmyts (

2 abc integer )

3 tablespace testts;

Table created.

SQL> 

In Oracle, we leave off the engine keyword and we need to declare a size. We can create a small data file and use autoextend if we want, but we MUST declare an initial size.

In Oracle, it is possible to create each partition of a partitioned table in its own tablespace. I'm not sure if that's possible with MySQL, but I plan to try it out!

Falcon Test

I just downloaded Falcon and was running some tests. I was getting an error:

C:\MySQL\bin>mysqladmin version status proc 
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'ODBC'@'localhost' 
                             (using password: NO)'

To fix this error, just add a -u parameter, i.e.:

C:\MySQL\bin>mysqladmin version status proc -u root
mysqladmin  Ver 8.42 Distrib 6.0.2-alpha, for Win32 on ia32
Copyright (C) 2000-2006 MySQL AB
This software comes with ABSOLUTELY NO WARRANTY. This is free 
software, and you are welcome to modify and redistribute it 
under the GPL license

Server version          6.0.2-alpha-community-nt-debug
Protocol version        10
Connection              localhost via TCP/IP
TCP port                3306
Uptime:                 27 min 43 sec

Threads: 1  Questions: 4  Slow queries: 0  Opens: 15  Flush tables: 1  
Open tables: 8  Queries per second avg: 0.2
Uptime: 1663  Threads: 1  Questions: 4  Slow queries: 0  Opens: 15  
Flush tables: 1  Open tables: 8 
 Queries per second avg: 0.2
+----+------+----------------+----+---------+------+-------+------------------+
| Id | User | Host           | db | Command | Time | State | Info             |
+----+------+----------------+----+---------+------+-------+------------------+
| 5  | root | localhost:4682 |    | Query   | 0    |       | show processlist |
+----+------+----------------+----+---------+------+-------+------------------+

I'm going to be blogging about my attempts to use some of the newer enterprise features of Falcon, as well as general MySQL programming info. LewisC

MySQL 6.0 in Alpha Test

I just found out that MySQL 6.0 with the Falcon Storage Engine is available as Alpha. Falcon adds ACID compliance, tablespaces and performance improvements. It's supposed to also simplify administration but I'm not sure how MySQL can be simplified. It's pretty simple now. I've always thought that the ability to swap out the storage engine is the best feature of MySQL. It reminds me of the replaceable database drivers from my clipper days in the late 80s and early 90s. From my reading about Falcon, it looks like one advantage will be the fact that Falcon has been engineered to take advantage of 64 bit architectures and large memory caches. User data files in Falcon can be up to 100 terabytes. That should pretty much cover most uses. It looks like you only get a single data file per Falcon database. Falcon has what it calles the Falcon serial Log. It's the equivalent of the Redo Log in Oracle or the Write Ahead Log (WAL) in Postgres/EnterpriseDB. This log file is also used for crash recovery (which I believe is completely automated in MySQL 6.0). Falcon uses 4 different memory caches: log, system and index, page and record. It uses a sophisticated algorithm to determine what data remains when the max is hit. Supposedly this algorithm is faster and more complex that the LRU.