IBM 000-8697 Instrukcja Użytkownika Pobierz pdf (Strona 170)

100

101

2-76 IBM Informix OnLine Database Server Administrator’s Guide

Write Types Describe Flushing Activity

Data is always written to the primary chunk ﬁrst. If a mirror chunk is

associatedwiththeprimarychunk,thewriteisrepeatedonthemirrorchunk.

The write to the mirror chunk is also included in these counts.

Refer to page 5-17 for a discussion of tuning OnLine performance by

monitoring write-type statistics.

Refer to page 7-87 for information about monitoring write types (and buffer

ﬂushing) using tbstat -F.

Sorted Write

AnyOnLineprocessthatiswritingmorethanonepagetothesamedisksorts

the pages into disk sequence and writes the pages in disk-sequence order.

(The disk-sequence information is contained in the physical address of the

page, whichis containedin thepage header.) This technique is referredto as

a sorted write.

Sorted writes are more efﬁcient than either idle writes or foreground writes

because they minimize head movement (disk seek time) on the disk. In

addition, a sorted write enables the page cleaners to use the big buffers

during the write, if possible. (Refer to page 2-55 for more information about

big buffers.)

Chunk writes, which occur during checkpoints, are performed as sorted

writes.(Chunk writes arethe most efﬁcientwrites available toOnLine.Refer

to page 2-77.)

Idle Write

Writes that are initiated by the page cleaners are called idle writes. The page-

cleaner daemon wakes periodically and searches through the MLRU queues

to determine ifthe number ofmodiﬁed buffers is equalto or greater than the

value represented by LRU_MAX_DIRTY.

If a page cleaner determines that the buffer pool should be ﬂushed, it marks

a page for ﬂushing, ﬂushes the page (after ﬁrst checking to determine if the

physical log buffer must be ﬂushed ﬁrst), and then rechecks the percentage.

This process repeats until the number of modiﬁed buffers is less than the

value represented by LRU_MIN_DIRTY.

1 2 ... 165 166 167 168 169 170 171 172 173 174 175 ... 701 702

Komentarze do niniejszej Instrukcji

Brak uwag

IBM 000-8697 Instrukcja Użytkownika Strona 170

Komentarze do niniejszej Instrukcji

Powiązane produkty i podręczniki dla Oprogramowanie bazy danych IBM 000-8697