IBM 000-8697 Manuel d'utilisateur télécharger pdf (Page 204)

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2-110 IBM Informix OnLine Database Server Administrator’s Guide

OnLine Limits for Databases

The size limits that apply to databases are related to their location in a

dbspace.

Youcanspecifythedbspacewhereadatabaseresides,butyoucannotcontrol

the placement of database tables within the dbspace chunks. If you want to

be certain that all tables in a database are created on a speciﬁc physical

device, assign only one chunk to the device and create a dbspace that

contains only that chunk. Place your database in that dbspace. (This also

limits the size of the database to the size of the chunk.)

Tables cannot grow beyondthe spaceavailable in the dbspace. You can limit

the growth of a table by refusing to add a chunk to the dbspace when it

becomes full.

DB-Monitor displays the ﬁrst 100 databases you create through the Status

menu,Databasesoption.Althoughyoucancontinuetocreatedatabases,you

are unable to view them through DB-Monitor. It is possible that, without

documentation,youcould lose track ofthenamesoftheseunseen databases.

Forthisreason,Informixrecommendsthatyou keep recordsof the databases

you create. Although the tbcheck -pe listing includes all databases, it could

be time-consuming to assemble a database list from the tbcheck -pe output.

Create a Table: What Happens on Disk

After the rootdbspace existsand adatabase hasbeen created, users with the

necessary SQL privileges can create a database table.

The table attributes are speciﬁed in the SQL statement CREATE TABLE. Users

can place the table in a speciﬁc dbspace by naming the dbspace in the

statement. Otherwise, by default, the table is created in the dbspace where

the database resides.

When users create a table, OnLine allocates disk space for the table in units

called extents.

An extent is a block of physically contiguous pages from the dbspace. The

CREATETABLE statementcanspecifyasize(inkilobytes)fortheinitialextent

and for every next extent that follows. Otherwise, the default value for each

extentiseightpages.(Refer to page 2-114formoreinformationaboutextents

and to page page 2-117 for more information about next extent allocation.)

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IBM 000-8697 Manuel d'utilisateur Page 204

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