IBM 000-8697 Bedienungsanleitung PDF herunterladen (Seite 448)

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5-8 IBM Informix OnLine Database Server Administrator’s Guide

Apply Effective Criteria

Looking at the efﬁciency information for blobspace bspc1 in Figure 5-1, an

administrator might decide that a better blob-storage strategy would be to

doubletheblobpagesizefrom2048bytesto4096bytes.(Recallthatblobpage

size isalways a multiple of theOnLine page size.) If theadministrator made

this change, the measure of page fullness would remain the same but the

number of locks needed during a blob update or modiﬁcation would be

reduced by half.

The efﬁciency information for blobspace blobPIC reveals no obvious

suggestion forimprovement. The two blobsin blobPIC differ greatly in size

and there is no optimal storage strategy. In general, blobs of similar size can

be stored more efﬁciently than blobs of different sizes.

Eliminate User-Created Resource Bottlenecks

OnLine manages limited resources such as locks, latches, buffers, and log

space. Users can adversely affect OnLine performance by inadvertently

creating resource bottlenecks in an otherwise efﬁciently tuned OnLine

system. (You can monitor the shared-memory resources being held by user

processes by executing tbstat -u. Refer to page 3-86 or page page 7-99.)

KnowledgeableusersareabletoavoidactivitiesthatcanslowOnLineperfor-

mancefor everyone. Asadministrator, you shouldencourageuserstofollow

these four guidelines:

■ Do not leave a transactionopen withoutcommitting or rolling backwithin

a reasonable period of time.

Ifauserleavesatransactionopen, theresourcesheldbythedatabase

serverprocessareunavailabletootherusers.Inaddition,ifthetrans-

action is left open for an extended period, this user action can

become responsible for a long transaction error.

■ Do not stop a process using job control unless you are certain you can

terminate the job.

Astopped job doesnotreleaseresourcesheld by thedatabaseserver

process. These resources might remain unavailable to other users. If

an application process is stopped while OnLine is engaged in data-

base activity on its behalf, serious concurrency delays can result.

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