kflushd & update

[Christos Ricudis]

Hello Linux-greek-users!

In <LINUX-USERS.GR> Linux-greek-users wrote:

 L> enhmeroseis (px anadiorganosh olou tou arxeiou) oti eno sthn zrxh
 L> paei me "xilia", ksafnka arxizei na "kathizei" me sinexh kflushd,
 L> kai update. Yparxei tropos na rithmiso ta megethi ton buffers, h/kai
 L> ton xrono pou ginetai to flush ?

Bebaiws, ola briskontai sto /proc/sys/vm:

cat /proc/sys/vm/bdflush:
40      500     64      256     15      3000    500     1884    2

40: % of dirty cache buffers to cause flushing
500: Max number of dirty blocks to write at once
64: Number of clean bufers we try to obtain at each refill cycle
256: den katalabainw akribws ti einai
15: unused
3000: Time for normal buffers to age before flushing (seconds*HZ, to HZ einai
synh8ws 100)
500: Time for superblock to age before we flush it
1884: unused
2: unused

Sthn periptwsh soy 8a soy elega na dokimaseis na aykshseis LIGO to 40 kai
perissoero to 3000. Isws na 8elhsei kai kapoia allagh to 500, blepontas kai
kanontas.

<figoura>

Ena apo ta sobarotera problhmata toy linux poy se ena meros ofeiletai aplws se
stenokefalia toy Torvalds, einai oti den exei yposthriksh gia raw disk devices.
Prin apokthsei tetoia yposthriksh (pragma poy 8a ginei meta apo arketes pieseis
kyriws toy Dave Miller) APOKLEIETAI na doyme kapoia apo tis megales commercial
databases na ginontai port sto linux, kai hdh exoyn xa8ei arketes "doyleies"
eksaitias aytoy toy gegonotos. Ayth einai epishs h aitia gia thn opoia den
exoyme akoma logging/journalling filesystems sto linux, opws to LFS toy BSD h
to JFS ths IBM. 

To linux einai isws to mono monterno UNIX poy den dinei sthn efarmogh thn
dynatothta na exei direct prosbash sto disko, xwris thn parembolh ths buffer
cache toy leitoyrgikou kai xwris reordering apo to leitoyrgiko twn I/O
requests. Ayta ta dyo features einai ousiwdh gia thn yposthriksh megalwn RDBMS
efarmogwn, oi opoies afenos xrhsimopoioyn poly pio eksypnoys kai
prosarmosmenoys sth sygkekrimenh efarmogh algori8mous gia data caching,
afeterou xreiazontai opwsdhpote th dynatothta na ka8orizoyn th seira me thn
opoia ekteloyntai ta I/O requests, etsi wste na exoyn plhrh gnwsh ths
katastashs ths database ana pasa stigmh (wste na epitrepoyn transaction
rollback kai integrity checks meta apo ptwseis toy systhmatos). Oi allages
aytes 8a apaithsoyn kapoia arketa shmantikh anadiorganwsh sto VM kai to IO
subsystem toy linux, alla einai aparaithtes an 8eloyme na exoyme thn elpida na
doyme kapote thn Linux ekdosh ths Oracle. 

</figoura>

Christos Ricudis, ricudis at paiko.the.forthnet.gr         2:413/11.0.
--
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