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Re: Inserts and row chaining

From: Frank Abney <abneyf_at_osshe.edu>
Date: 1997/01/16
Message-ID: <Pine.SOL.3.91.970116142656.13429D-100000-100000@osshe.edu>#1/1

My understanding of PCTFREE is that as soon as a block is filled above this point, the block is taken off the free list. What needs to be realized is if you add a 100 byte record that goes over PCTFREE, it is simply using part of the free space you left for growth. So it you have a 2k block and PCTFREE of 10, then you have roughly 200 bytes to work with in each block, so the entire 100 bytes is added, but your 200 bytes for updates is reduced. It is always recommended that your PCTFREE always allow enough bytes for an entire record. If you ensure this, you will not have to worry about a single insert chainging blocks, unless a single record is larger than your block.


Frank Abney                              Email: abneyf_at_osshe.edu
Oregon State System of Higher Education Phone: (541) 737-6269

On 16 Jan 1997, Unknown wrote:

> : According to the instructor in the DBA-1 class that I took, it won't
> : spread a row across multiple blocks unless it has too. If the block
> : has not reached the pctfree threshold, it'll insert it into another
> : block. (i.e. It'll grab the free block in the extent, or allocate a
> : new extent.)
>
> Chuck, thanks for your reply. However, I am still a little unclear.
> Lets say I have a 100-byte row that I wish to insert and the next
> block on the freelist will exceed (or go under) the PCTFREE value
> in 75 bytes. My boss insists that Oracle will place 75 bytes into
> this block and 25 into the following block. I cannot believe Oracle
> would do that because we would have chained rows all over the place.
>
> However, if it doesn't do that, what does it do ? Does it look
> throughout the freelist to find a block that won't cause that
> to happen ? A book I read said something about taking the block
> off the freelist, but it didn't say it would use it !!
Received on Thu Jan 16 1997 - 00:00:00 CST

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