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Re: one hour checkpoints

From: Christo Kutrovsky <kutrovsky.oracle_at_gmail.com>
Date: Wed, 24 Jan 2007 11:17:12 -0500
Message-ID: <52a152eb0701240817s2147efevf48664dfd8e391b5@mail.gmail.com>


Well, in theory, 600mb of redo log could be 1'228'800 blocks changed. That's 629145600 bytes of redo log, with a redo record been 512 bytes.

That's only an approximation, since you could have merged records, multiple changes in a single record and etc.

Let's assume a typical IO time of 5 ms. That would be 1228800*5ms = 6'144'000 ms = 6'144 seconds = 1.7 hours.

So it could've taken 1.7 hours. And that's been optimistic about the 5ms IO. It could've been 10 ms during busy times.

It's not as bad as it sounds.

-- 
Christo Kutrovsky
Senior Database/System Administrator
The Pythian Group - www.pythian.com
I blog at http://www.pythian.com/blogs/


On 1/18/07, amonte <ax.mount_at_gmail.com> wrote:

> Hello all
>
> I have a quite busy Oracle APPS database running in HPUX. Today during peak
> hour I saw this in alert
>
> Thu Jan 18 10:19:50 2007
> Beginning log switch checkpoint up to RBA [0x17d1.2.10], SCN:
> 0x0784.b14a52c1
> Thu Jan 18 10:22:09 2007
> Beginning log switch checkpoint up to RBA [0x17d2.2.10], SCN:
> 0x0784.b14a8673
> Thu Jan 18 10:26:18 2007
> Beginning log switch checkpoint up to RBA [0x17d3.2.10], SCN:
> 0x0784.b14aee22
> Thu Jan 18 10:51:32 2007
> Beginning log switch checkpoint up to RBA [0x17d4.2.10], SCN:
> 0x0784.b14d0ddb
> Thu Jan 18 11:09:24 2007
> Beginning log switch checkpoint up to RBA [0x17d5.2.10], SCN:
> 0x0784.b14ea5dd
> .........................
> Thu Jan 18 11:12:04 2007
> Completed checkpoint up to RBA [0x17d1.2.10], SCN: 0x0784.b14a52c1
> Thu Jan 18 11:16:19 2007
> Completed checkpoint up to RBA [0x17d2.2.10], SCN: 0x0784.b14a8673
> Thu Jan 18 11:16:45 2007
> Completed checkpoint up to RBA [0x17d3.2.10], SCN: 0x0784.b14aee22
> Thu Jan 18 11:18:22 2007
> Completed checkpoint up to RBA [0x17d4.2.10], SCN: 0x0784.b14d0ddb
> Thu Jan 18 11:23:56 2007
> Completed checkpoint up to RBA [ 0x17d5.2.10], SCN: 0x0784.b14ea5dd
>
>
>
> From v$log_histroty I see the log switch frequency
>
> select * from v$log_history
> where FIRST_TIME > ('20070118 090000');
>
> RECID STAMP THREAD# SEQUENCE# FIRST_CHANGE#
> FIRST_TIME NEXT_CHANGE#
> ---------- ---------- ---------- ---------- ----------------------
> --------------- ----------------
> 6096 612181190 1 6096 8266491016370 20070118
> 090018 8266491515585
> 6097 612181328 1 6097 8266491515585 20070118
> 101949 8266491528819
> 6098 612181578 1 6098 8266491528819 20070118
> 102208 8266491555362
> 6099 612183092 1 6099 8266491555362 20070118
> 102618 8266491694555
> 6100 612184164 1 6100 8266491694555 20070118
> 105132 8266491799005
> 6101 612185404 1 6101 8266491799005 20070118
> 110923 8266491936643
>
>
> Redo log are 600MB each.
>
> How can a checkpoint take so long?
>
>
>
> Cheers
>
> Alex
>
>
-- Christo Kutrovsky Senior Database/System Administrator The Pythian Group - www.pythian.com I blog at http://www.pythian.com/blogs/ -- http://www.freelists.org/webpage/oracle-l
Received on Wed Jan 24 2007 - 10:17:12 CST

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