IBM 000-8697 Instrukcja Użytkownika Pobierz pdf (Strona 208)

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2-114 IBM Informix OnLine Database Server Administrator’s Guide

Structure of an Extent

Cleanup

Explicit temporary tables are dropped when the OnLine user process exits.

Implicit temporary tables may be dropped at any time during processing.

Ifthe OnLine databaseservershuts down withoutadequatetime to cleanup

temporarytables, the tbinitdaemonperformsthecleanup as partofthenext

OnLine initialization. (To request shared-memory initialization without

temporary table cleanup, executetbinit with the-p option. Referto page 2-8

for further information about initialization commands.)

Structure of an Extent

An extent is a collection of pages within a dbspace. Every permanent

database table has two extent sizes associated with it. The initial extent size

is the number of kilobytes allocated to the table when it is ﬁrst created. The

next extent size is the number of kilobytes allocated to the table when the

initial extent, and every extent thereafter, becomes full.

Blobspaces do not employ the concept of an extent.

Refer to page 2-117 for a description of next extent allocation. Refer to

IBM InformixGuide to SQL:Tutorial for speciﬁcinstructionshow to specifyand

calculate the size of an extent.

Extent Size

The minimum size of an extent is four pages. No maximum limit exists,

although a practical limit is about two gigabytes (or as much space as is

available within the chunk). Extent sizes must be an even multiple of the

page size, speciﬁedasBUFFSIZE in theconﬁguration ﬁle. Thedefaultsize of

an extent is eight pages.

The maximum size of an extent is determined by the largest page number

that can be accommodated in a rowid. (Refer to page 2-123 for further infor-

mation about rowids.) Since the page number in a rowid cannot exceed

16,777,215, this is the upper limit of the number of pages that a single extent

can contain.

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