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From Selcuk AYA <ayasel...@gmail.com>
Subject Re: [index] OneLevelIndex removal
Date Thu, 12 Apr 2012 16:00:05 GMT
On Thu, Apr 12, 2012 at 7:14 AM, Alex Karasulu <akarasulu@apache.org> wrote:
>
>
> On Thu, Apr 12, 2012 at 4:35 PM, Emmanuel Lécharny <elecharny@gmail.com>
> wrote:
>>
>> Forgot to reply to this mail, which raises interesting points.
>>
>> More inside.
>>
>> Le 4/11/12 10:38 PM, Alex Karasulu a écrit :
>>>
>>> On Wed, Apr 11, 2012 at 4:04 PM, Emmanuel
>>> Lécharny<elecharny@gmail.com>wrote:
>>>
>>>> I think we should add some mechanism in the server to check that
>>>> automatically, to avoid doing it by hand (there are hundreds of tests to
>>>> check...). One solution would be to keep a track of every cursor
>>>> construction in a HashMap, and to remove them when the cursor is closed.
>>>> The remaining cursors are likely not closed.
>>>
>>>
>>> It would be nice to have a Cursor monitor that every opened Cursor
>>> registers with but this needs to happen automatically. Then when out of
>>> the
>>> creation scope the Cursor is expected to be closed and if not this is
>>> handled automatically. However does creation scope work well since
>>> sometimes we create Cursors and pass them up?
>>
>> We do have a monitor, which is currently used to check that the cursor is
>> not closed when we try to use it. We certainly can use this monitor for more
>> than just checking such thing.
>>
>> Now, the pb is that the scope is not as easy to determinate than for a
>> variable in Java. For instance, if we consider persistent searches, or paged
>> searches, or even an abandonned search request, the scope is pretty wide...
>>
>> Though we can have a set of rules that help us to close the cursor
>> automatically :
>> - if we get an exception during a SearchRequest, then the cursors must be
>> closed immediately. As soon as we store the cursors into the SearchContext,
>> this is pretty easy to do
>> - an AbandonRequest will close the cursor automatically too (getting the
>> cursor from the abandonned request)
>> - when we process the SearchResultDone, we can also close the cursor for
>> the current search request (this work for PagedSearch too)
>> - for pagedSearch, if the user reset the search by sending 0 as the
>> expected number of entries to return, then the cursor will be freed
>> - for persistent searches, as it will be closed by an unbind or an abandon
>> request, we are fine
>> - when a client unbinds, then all the pending cursors will be closed.
>>
>> All in all, we have everything needed to close the cursors automatically,
>> assuming we keep all the cursors into the session.

For the server side, I would suggest policing this with a test. When
cursors open, they can bump a global counter atomically. When they
close, they can decrement it. We can have a test such that after a
bunch of operations, this counter at the server side should be zero.

>>
>
> These are really great suggestions and make the ideas I tried to express
> really tangible. Thanks for it Emmanuel.
>
> One technical point, we need to make Cursor close() operations idempotent if
> they are not already - meaning if we close a second time this should not
> cause an exception or change the outcome.
>
>>
>> On the client side, this is another issue... As cursors are created by the
>> client code, we have no easy way to determinate when we should close the
>> cursors, except when the connection is closed or an abandon request/unbind
>> request is sent. Of course, when the server returns a searchResultDone we
>> could also close the cursor. Remains the situations where the client has
>> fetched some entries (but not all), and haven't unbind nor abandonned the
>> search.
>>
>
> I think the aspect for automatic closing of cursors is left to be managed
> inside the server even though the API overlaps here.
>
>>
>> In any case, this is less critical as we don't have to deal with the txn
>> layer. The client will just blow away with some nasty OOM sooner or later...
>> but this is not worse than what we get with NamingEnumeration in JNDI, nah ?
>>
>
> Yup +1
>
>>
>> Have I covered all the server options ? Or did I miss something ?
>>
>>>
>>> This sounds like something that can be handled nicely using an aspect
>>> oriented solution. Now these things are heavy if you use AspectJ or
>>> something like that but other simpler solutions exist to bytecode splice
>>> compiled code to automatically handle these things. Maybe our past
>>> experiences with Aspects might make us reconsider.
>>
>> A bit overkilling, IMO?
>>
>
> I'm feeling the same but thought it should be just put out there. However we
> can achieve the same results perhaps with code or using a lighter mechanism
> with Proxy's via CGlib or something similar. These are just raw thought
> dumps so it's not a we SHOULD recommendation. Something to think about.
>
> --
> Best Regards,
> -- Alex
>

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