Re: [dabo-users] postgres pkid before commit

El 04/05/12 06:36, Vineet Deodhar escribió:

>> On 5/3/12 9:06 PM, Vineet Deodhar wrote:

>>> Isn't it dangerous to get a pkid from the db before commit?

>>> Consider a situation where UserA gets a pkid "2564' for a table "tbl1".

>>> Before this change is committed, UserB inserts a record to tbl1& gets

>>> "2564".

>>>

>>> Wouldn't is cause a mess?

>> No, postgres knows it handed out 2564 already, even though it isn't

>> committed yet.

>> Paul

> I see.

> In that case, it would lead to further trouble such as -->

> UserA, after getting pkid 2564 for tbl1, cancels the addition.

> So 5264 is unutilized.

> If the no. of users & data-traffic is quite low, no issue.

> But consider a case where hundreds of users are interacting with tbl1 and

> there are a lot of cases for cancelled additions to tbl1.

> In effect, even if the smallint data-type for this pkid is sufficient, the

> DBA has to opt for maybe mediumint !

> Anyway, I am using MySQL and I am very much comfortable with it.

> -- Vineet

I'd never use smallint or mediumint for a pkid!

If the table is small enough then you are not saving much space. If it

is big then it will not scale properly. I guess RDBMs define pkid type

according to maximum database size in records, and then some in order to

have ample space to cover for what you specify.

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