Mongo cache vs database objects

Am 27.11.2013 um 13:20 schrieb Sabine Knöfel <[hidden email]>:

> Hi Esteban, all,
>
> I work with mongo daily an it works fine, I am very happy with it.
>
> As you told me, with
>>> VORepository current reset.
> I can force re loading all objects from database and resetting the cache
> completely.
> This is helpful for development eg. after changing the magritte
> descriptions.
>

Indeed. You need to flush/reset the repository in order to have new descriptions to take effect.

> My question:
> Is there a possibility to make a query and tell voyage that THIS query
> should be done within the database and NOT within the cached objets? And
> that all objects and the child objects from this query are loaded freshly
> from database into the cache.
>

All queries go to the database. The cache is just used at resolve time. And it is necessary to have identical objects. Meaning you query the database directly and then objects are materialized. If the object is already in the cache the cached one is returned. Otherwise you would lose identity because having two requests containing the same object as a result would lead to two objects instead of one. You could only load trees instead of a graph.

> My concrete situation:
> I want that if the user logs in, his objects are loaded from database and
> NOT from cache. This means the person, his trips etc.
>
> And the question coming along with this:
> How long does the cache keeps objects/when are they reseted (except the
>>> VORepository current reset)?
> If I would never take a new image and never make a reset, would all objects
> remain in the image (and the database objects wold never be read)? In this
> case what about the size of the image?
>

I’m not sure on this one. I think the cache does not clean anything. The thing about being able to load a graph I wrote above has also the constraint that all loaded objects that are still participating in the active graph need to be in the cache. But then the cache is a weak dictionary meaning that all objects leaving the active graph are removed from the cache (well at GC time, I think)

Norbert
 
> Regards
> Sabine
>
>
>
> --
> View this message in context: http://forum.world.st/Mongo-cache-vs-database-objects-tp4725554.html
> Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.
>

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Am 27.11.2013 um 14:05 schrieb Sabine Knöfel <[hidden email]>:

Hi Norbert,

thank you very much for the clarification. 

I had to read it several times  but now I understand and I know what to change in my model for this (something with references to objects which have been deleted by the user).

Yep, it _is_ a horrible explanation but the only one I can come up in a short timeframe :) Making it easily readably and clear would talk some more time.

Perhaps your answer is also interesting for the documentation of Johan.

Uh? I’ve never seen a documentation about Johan. That is a nice idea! I was always thinking about how to use him!

Norbert

Greets

Sabine

On Wed, Nov 27, 2013 at 1:44 PM, Norbert Hartl [via Smalltalk] <<a href="x-msg://256/user/SendEmail.jtp?type=node&amp;node=4725585&amp;i=0" target="_top" rel="nofollow" link="external">[hidden email]> wrote:

Am 27.11.2013 um 13:20 schrieb Sabine Knöfel <[hidden email]>: 

> Hi Esteban, all, 
> 
> I work with mongo daily an it works fine, I am very happy with it. 
> 
> As you told me, with 
>>> VORepository current reset. 
> I can force re loading all objects from database and resetting the cache 
> completely. 
> This is helpful for development eg. after changing the magritte 
> descriptions. 
>

Indeed. You need to flush/reset the repository in order to have new descriptions to take effect.

> My question: 
> Is there a possibility to make a query and tell voyage that THIS query 
> should be done within the database and NOT within the cached objets? And 
> that all objects and the child objects from this query are loaded freshly 
> from database into the cache. 
> 

All queries go to the database. The cache is just used at resolve time. And it is necessary to have identical objects. Meaning you query the database directly and then objects are materialized. If the object is already in the cache the cached one is returned. Otherwise you would lose identity because having two requests containing the same object as a result would lead to two objects instead of one. You could only load trees instead of a graph. 

> My concrete situation: 
> I want that if the user logs in, his objects are loaded from database and 
> NOT from cache. This means the person, his trips etc. 
> 
> And the question coming along with this: 
> How long does the cache keeps objects/when are they reseted (except the 
>>> VORepository current reset)? 
> If I would never take a new image and never make a reset, would all objects 
> remain in the image (and the database objects wold never be read)? In this 
> case what about the size of the image? 
>

I’m not sure on this one. I think the cache does not clean anything. The thing about being able to load a graph I wrote above has also the constraint that all loaded objects that are still participating in the active graph need to be in the cache. But then the cache is a weak dictionary meaning that all objects leaving the active graph are removed from the cache (well at GC time, I think)

Norbert 
  
> Regards 
> Sabine 
> 
> 
> 
> -- 
> View this message in context: http://forum.world.st/Mongo-cache-vs-database-objects-tp4725554.html
> Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. 
> 

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Am 27.11.2013 um 14:28 schrieb Sabine Knöfel <[hidden email]>:

Hi Norbert,

ooh sorry, it was absolutely NOT  my intention to critisize your explanation I wanted to say it is  complicated for my small brain ;-) I am very happy about your quick answer which helped me finding a solution for my problem!!! sorry!

No pun taken. In fact _I_ was criticizing my explanation because it sucks :) So now let’s stop it because we are germans not canadians. No more sorrys needed.

This was the post FROM Johan about the documentation:

http://forum.world.st/Cleaning-up-Voyage-Documentation-td4723834.html

LOL now, after writing the answer I understand the joke ;-) (of Johan, from johan)

Ah, the other Johan! It is good to know because I did some changes to MongoTalk so I see what I can add.

Norbert

Sabine

On Wed, Nov 27, 2013 at 2:17 PM, Norbert Hartl [via Smalltalk] <<a href="x-msg://257/user/SendEmail.jtp?type=node&amp;node=4725597&amp;i=0" target="_top" rel="nofollow" link="external">[hidden email]> wrote:

Am 27.11.2013 um 14:05 schrieb Sabine Knöfel <[hidden email]>:

Hi Norbert,

thank you very much for the clarification. 

I had to read it several times  but now I understand and I know what to change in my model for this (something with references to objects which have been deleted by the user).

Yep, it _is_ a horrible explanation but the only one I can come up in a short timeframe :) Making it easily readably and clear would talk some more time.

Perhaps your answer is also interesting for the documentation of Johan.

Uh? I’ve never seen a documentation about Johan. That is a nice idea! I was always thinking about how to use him!

Norbert

Greets

Sabine

On Wed, Nov 27, 2013 at 1:44 PM, Norbert Hartl [via Smalltalk] <<a href="<a href="x-msg://256/user/SendEmail.jtp?type=node&amp;amp;node=4725585&amp;amp;i=0">x-msg://256/user/SendEmail.jtp?type=node&amp;node=4725585&amp;i=0" target="_top" rel="nofollow" link="external">[hidden email]> wrote:

Am 27.11.2013 um 13:20 schrieb Sabine Knöfel <[hidden email]>: 

> Hi Esteban, all, 
> 
> I work with mongo daily an it works fine, I am very happy with it. 
> 
> As you told me, with 
>>> VORepository current reset. 
> I can force re loading all objects from database and resetting the cache 
> completely. 
> This is helpful for development eg. after changing the magritte 
> descriptions. 
>

Indeed. You need to flush/reset the repository in order to have new descriptions to take effect.

> My question: 
> Is there a possibility to make a query and tell voyage that THIS query 
> should be done within the database and NOT within the cached objets? And 
> that all objects and the child objects from this query are loaded freshly 
> from database into the cache. 
> 

All queries go to the database. The cache is just used at resolve time. And it is necessary to have identical objects. Meaning you query the database directly and then objects are materialized. If the object is already in the cache the cached one is returned. Otherwise you would lose identity because having two requests containing the same object as a result would lead to two objects instead of one. You could only load trees instead of a graph. 

> My concrete situation: 
> I want that if the user logs in, his objects are loaded from database and 
> NOT from cache. This means the person, his trips etc. 
> 
> And the question coming along with this: 
> How long does the cache keeps objects/when are they reseted (except the 
>>> VORepository current reset)? 
> If I would never take a new image and never make a reset, would all objects 
> remain in the image (and the database objects wold never be read)? In this 
> case what about the size of the image? 
>

I’m not sure on this one. I think the cache does not clean anything. The thing about being able to load a graph I wrote above has also the constraint that all loaded objects that are still participating in the active graph need to be in the cache. But then the cache is a weak dictionary meaning that all objects leaving the active graph are removed from the cache (well at GC time, I think)

Norbert 

  
> Regards 
> Sabine 
> 
> 
> 
> -- 
> View this message in context: http://forum.world.st/Mongo-cache-vs-database-objects-tp4725554.html
> Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. 
> 

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