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Home -> Community -> Usenet -> c.d.o.misc -> Re: Help with Freelists
A copy of this was sent to Arthur Merar <amerar_at_unsu.com>
(if that email address didn't require changing)
On Thu, 15 Oct 1998 20:57:30 -0500, you wrote:
>
>Hello,
>
>I have a question. I am a bit confused about freelists and the data
>buffer cache.
>
>The book I have says that all data is kept in the buffer cache. But it
no its not. all data is kept on disk and sometimes it might appear in the buffer cache.
>also says that if you have a lot of inserts, then you should increase
>your freelists.
>
When you do an insert into a table, you need to get a block that has space. The place we will go is a freelist. Think of this like a shared data structure that has a list of blocks that have space free on them and must be updated in order for us to get a block to put a new row on. Since this is a data structure, for the point in time that we are looking for a block in it and then getting that block off the freelist -- no one else can be doing that (else corruption occurrs). We get the freelist -- blocking others from getting it -- and then unget the freelist when we get our block. During that small period of time we had the freelist other inserts would be held up.
If we have more then one freelist -- when someone comes along to get a free block and someone else is doing the same -- they can process in parallel, each using a different freelist to get storage from.
The effect on a table that is heavily inserted into can be dramatic.
>I'm confused......data is held in the buffer cache.....so what do
>freelists have to do with anything?
>
>Please e-mail your replies........
>
>Thank you,
Thomas Kyte
tkyte_at_us.oracle.com
Oracle Government
Herndon VA
--
http://govt.us.oracle.com/ -- downloadable utilities
Anti-Anti Spam Msg: if you want an answer emailed to you, you have to make it easy to get email to you. Any bounced email will be treated the same way i treat SPAM-- I delete it. Received on Fri Oct 16 1998 - 08:29:37 CDT
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