updatable ResultSet: inserted row "may" become visible?

[Michelle Caisse <Mi...@Sun.COM>]

The Derby Developer's Guide states:

    Rows inserted to the table may become visible in the result set. (p. 57)

    If the inserted row satisfies the query predicate, it may become
    visible in the result set. (p. 58)

What does "may" mean? Are there no circumstances in which the insert is 
guaranteed to become visible in the result set?

-- Michelle

Re: updatable ResultSet: inserted row "may" become visible?

[Michelle Caisse <Mi...@Sun.COM>]

Thank you for the responses. No guarantees is clearly the answer.

-- Michelle

Jørgen Løland wrote:

> Michelle Caisse wrote:
>
>> The Derby Developer's Guide states:
>>
>>    Rows inserted to the table may become visible in the result set. 
>> (p. 57)
>>
>>    If the inserted row satisfies the query predicate, it may become
>>    visible in the result set. (p. 58)
>>
>> What does "may" mean? Are there no circumstances in which the insert 
>> is guaranteed to become visible in the result set?
>>
>> -- Michelle
>>
>
> This looks similar to a discussion on derby-dev for update operations 
> and open cursors a few months back:
>
> http://www.nabble.com/Updating-rows-with-an-open-cursor...what-is-the-expected-behavior--t3908926.html#a11083342 
>
>
> In that discussion, it became clear that the cursor would return rows 
> that satisfied the query at the time the row was retrieved. That could 
> be any point in time between the cursor creation and when the cursor 
> reached that record in the result set. Hence, updates *may* be visible 
> to open cursors, but with no guarantees.
>

Re: updatable ResultSet: inserted row "may" become visible?

[Jørgen Løland <Jo...@Sun.COM>]

Michelle Caisse wrote:
> The Derby Developer's Guide states:
> 
>    Rows inserted to the table may become visible in the result set. (p. 57)
> 
>    If the inserted row satisfies the query predicate, it may become
>    visible in the result set. (p. 58)
> 
> What does "may" mean? Are there no circumstances in which the insert is 
> guaranteed to become visible in the result set?
> 
> -- Michelle
> 

This looks similar to a discussion on derby-dev for update operations 
and open cursors a few months back:
 
http://www.nabble.com/Updating-rows-with-an-open-cursor...what-is-the-expected-behavior--t3908926.html#a11083342

In that discussion, it became clear that the cursor would return rows 
that satisfied the query at the time the row was retrieved. That could 
be any point in time between the cursor creation and when the cursor 
reached that record in the result set. Hence, updates *may* be visible 
to open cursors, but with no guarantees.

-- 
Jørgen Løland

Re: updatable ResultSet: inserted row "may" become visible?

[Stanley Bradbury <St...@gmail.com>]

Michelle Caisse wrote:
> The Derby Developer's Guide states:
>
>    Rows inserted to the table may become visible in the result set. 
> (p. 57)
>
>    If the inserted row satisfies the query predicate, it may become
>    visible in the result set. (p. 58)
>
> What does "may" mean? Are there no circumstances in which the insert 
> is guaranteed to become visible in the result set?
>
> -- Michelle
>
Hi -
I think I found the passage you refer to but it is not on pg 57 in the 
10.3 Developers guide I looked at.  Please indicate the version of the 
manuals or better yet, the section of the document.  I found the text  
you mentioned in the section "Updatable result sets".

I believe whether the row becomes visible depends on how many rows are 
cached at the time the insert is performed.  If the entire ResultSet is 
already cached you will not see the inserted row because Derby will not 
do another read from disk.  If, however, you are stepping down through a 
large ResultSet where all the records have not been read and the 
inserted record sorts below the current position the new record could be 
read from the disk when it is reached. 

I don't believe there is anyway to predict this behavior.