RE: dbanalyzer output/optimization

Hi Jon,
With 1Gb or RAM, 15000 for data cache is very low, only 100Mb ! If your
database is alone on your server, you can increase data cache to 100000,
leaving approx 200 Mb for OS and other stuffs.
For your information, i use 25000 for data cache on our test system (
2Gb RAM, and 1Gb database with only 300Mb on data ), and there are other
databases on this server ( Progress and SQLServer ).

OTH
Fred.

-----Message d'origine-----
De : Jon Loken [mailto:j.loken@xxxxxxxxx]
Envoyé : vendredi 26 novembre 2004 15:31
À : maxdb@xxxxxxxxxxxxxxx
Objet : dbanalyzer output/optimization


Hi all, 

We have a database instance that has recently grown to around 9Gb in
size. We recently encountered some performance issues. This mail is
about suitable strategies to address this issue. 
*We have started adding indexes, but are not quite sure how to optimize
them in terms of using UNIQUE, multitable indices. Does anyone have a
link to a suitable tutorial?
*Is there a recommended size for each data volume file? For us each data
volume is 200Mb. Ram is 1Gb.
*what should the 'data cache' be set to? The default is 10000. I
increased it to 15000 and performance increased dramatically! Very
impressive! Any general tips?


------


Your documentation page about 'Tips on database design'
(http://dev.mysql.com/doc/maxdb/en/45/f31c53e95511d5995d00508b5d5211/con
tent.htm) covering amongst other things indexing and sql statements
mentions:
'Before you define your tables, examine the structures and use the
results in your table definitions.  When you define the key columns,
ensure that any especially selective columns, and any columns for which
search conditions are specified particularly often, are placed at the
"beginning of the key". This gives the system the option of considering
only a very small part of the table when processing a SELECT statement.'

In this paragraph, what does 'beginning of the key' mean? Could anyone
exemplify this?

Similarly in paragraph:
'Only columns with as high a selectivity as possible "should be
inverted". Do not choose columns such as gender or marital status as
index keys, due to their low number of different values. These columns
can only be used very rarely for a non-sequential search, since these
searches would usually be more costly than a sequential search.'

In this paragraph, what does a column 'being inverted' mean? Could
anyone exemplify this?

Many thanks for your help.
Regards
Jon Loken




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