REPOST: Re: Need an easy explain on Inittrans and Maxtrans

When you want to update, insert or delete a row, you have to be allowed access to the body of the block wherein that piece of DML is about to take place. To gain access, you have to acquire a 'transaction slot'. INITRANS and MAXTRANS tell us how many slots are available to start with (1 by default on a table) and how many we can dynamically expand to as the number of concurrent transactions increase (255 by default, if memory serves).

If there's a lot of concurrent activity on a block, we have to start creating the second, third, fourth and so on transaction slots. Since each slot takes up space (it's about 20 or so bytes per slot), that means (effectively) that the header of the block expands downwards towards the data. Increasing INITRANS (which you would do when first creating a table) would thus have the effect of reducing the amount of useable space within the block, because it would make the header of the block bigger from the word go.

On hugely concurrent systems, there might be a requirement to increase maxtrans to permit greater access to the data by multiple users simultaneously -but it would have to be a really popular block, and have a hell of a lot of concurrent transactions before the need would arise. Still, if you get lots of buffer busy waits because of contention for the block, it's an option.

Frankly, I've never had a need to change either setting from their default values. My own suspicion is that unless you were working in a large Parallel Server enviroment with thousands of users, you'd be unlikely to need to either.

Regards
HJR

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"frank" <frankw_at_qd.lucent.com> wrote in message
news:a0j3fh$kk4_at_nntpa.cb.lucent.com...


> Hello,

>

> Can you give me a easy explain on how these parameters are used. I am in a

> puzzle about these two parameters

>

> Thanks in advance

> Frank

>

>


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