Re: How many rollback segments

Each rollback segment can handle multiple transactions simultaineously.

The number depends on your block size and your OS.

Still, you can exceed the transaction capacity of all your rollback segments. When that happens, new transactions wait.

You can monitor this with the v$rollstat view. The gets / waits should exceed 500; otherwise, add more segments.

Kenneth C Stahl wrote:

> I work with a system that has upwards of 50-100 users all logged in with
> client applications. In the normal process of what they do the
> application adds records, updates records and occasionally deletes
> records. The chances of everyone having an active transaction at the
> same time is pretty minimal, but in theory some day it just might work
> out that I have 50 workstations all trying to insert/update/delete at
> the same time (different records however, since each operator would only
> see records that belong to them).
>
> Right now I have 4 rollback segments. To date I have not seen any
> problems that have occurred because of this. But what I'm wondering is
> whether I shouldn't have more.
>
> Let me pose this. Suppose that it occurs that I have ten operators who
> are doing things at will insert/update/delete simulaneously. Will the
> first four operators get the rollback segments and the other six will
> see the application hang while the rdbms waits for a rollback segment
> that it can assign to them? If so, would I see lag time (that is, the
> time between the moment they hit the enter key and the time that they
> can continue with the next operation) decrease if there were more
> rollback segments available? Typically, the transactions performed by
> the client application are small (a couple rows at the most), so once
> processing starts it tends to complete a transaction pretty quickly, but
> I'm wondering that if things really get busy will there be a queue
> waiting for rollback segments if there are more outstanding transactions
> waiting to occur then there are rollback segments?
>
> Thoughts?
>
> Ken
Received on Fri Jun 18 1999 - 08:32:24 CDT