[Xapian-discuss] Why the Database object cannot see changes made by other WritableDatabase object which has been flushed?

[岳帅杰]

Hi, Tom:

   Thanks very much! Now I understand it. That is to say, if there are
concurrant read and write operations, there will be no problem.


2009/11/12 Tom <tom at lemurconsulting.com>

> 2009/11/12 岳帅杰 <ysj.ray at gmail.com>:
> > Hi, All:
> >
> >    I was using xapian with python. But I didn't understand the following
> > code:
> > ...
> >    I think this piece of code is quite simple for understanding.
> >
> >    I don't understand why reader1 cannot see the changes make by writter.
> >    I see the document says:
> >    "From the point of view of a separate process (or a separate database
> > object in the same process) reading the database, all modifications made
> to
> > a database are invisible until the modifications is committed."
> >    But the writter had committed its change( by calling flush())
> >
> >    And why reader2 can see the change?
>
> Hi Ray,
>
> Database readers continue to see the version of the database that
> existed when they opened it, even if the database is changed. That's
> why reader2 sees changes that are invisible to reader1. (It's
> implemented by multiple, versioned paths through the B-trees).
>
> To make a reader see the latest flushed version of the database, you
> can call Database::reopen().
>
> cheers,
> Tom
>



-- 
Best wishes from Ray ...