> 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
> > Postgres can provide the PK from a record before it is committed.
> >
> > transaction
> > begin
> > insert record
> > retrieve PK (I will assume that is a serial data type).
> > insert record
> > retrieve PK
> > continue
> >
> > commit or rollback
> >
> > I realize that Dabo does not do it but I do it all the time with Dabo
> temp
> > cursors.
> >
> > Johnf
>
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On Friday, May 04, 2012 03:06:30 PM Vineet Deodhar wrote:
> Anyway, I am using MySQL and I am very much comfortable with it.
>
> -- Vineet\
Tell me how MySQL does it differently?
Johnf
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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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