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| ajith_company |
 Posted: Wed May 30, 2012 12:42 am Post subject: Cache node over shared variable |
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Newbie
Joined: 30 May 2012
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| What is the advantage of cache node over shared variable? |
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| mqjeff |
| Posted: Wed May 30, 2012 2:33 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| The cache node can share data between execution groups. |
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| lancelotlinc |
| Posted: Wed May 30, 2012 5:53 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
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Location: Bloomington, IL USA
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The cache node uses a Singleton and queues internally to share data. If you are an experienced Java programmer, you can use a Singleton directly and avoid the overhead of using queues to store cache data.
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| Esa |
| Posted: Wed May 30, 2012 6:07 am Post subject: |
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Grand Master
Joined: 22 May 2008
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Location: Finland
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| lancelotlinc wrote: |
| The cache node uses a Singleton and queues internally to share data. If you are an experienced Java programmer, you can use a Singleton directly and avoid the overhead of using queues to store cache data. |
And then you cannot share data between execution groups.
But with shared variables you can only share data within one flow file in one execution group. |
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| lancelotlinc |
| Posted: Wed May 30, 2012 6:10 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
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Location: Bloomington, IL USA
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| Esa wrote: |
| lancelotlinc wrote: |
| The cache node uses a Singleton and queues internally to share data. If you are an experienced Java programmer, you can use a Singleton directly and avoid the overhead of using queues to store cache data. |
And then you cannot share data between execution groups.
But with shared variables you can only share data within one flow file in one execution group. |
We use a Singleton, and we share data between EGs. Why cannot you?
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| Esa |
| Posted: Wed May 30, 2012 6:15 am Post subject: |
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Grand Master
Joined: 22 May 2008
Posts: 1387
Location: Finland
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| lancelotlinc wrote: |
| Esa wrote: |
| lancelotlinc wrote: |
| The cache node uses a Singleton and queues internally to share data. If you are an experienced Java programmer, you can use a Singleton directly and avoid the overhead of using queues to store cache data. |
And then you cannot share data between execution groups.
But with shared variables you can only share data within one flow file in one execution group. |
We use a Singleton, and we share data between EGs. Why cannot you? |
Well, it has never crossed my mind to share a Singleton across JVM's. I must admit that I thought it's not possible. |
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| lancelotlinc |
| Posted: Wed May 30, 2012 6:17 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
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Location: Bloomington, IL USA
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| Esa wrote: |
| lancelotlinc wrote: |
| Esa wrote: |
| lancelotlinc wrote: |
| The cache node uses a Singleton and queues internally to share data. If you are an experienced Java programmer, you can use a Singleton directly and avoid the overhead of using queues to store cache data. |
And then you cannot share data between execution groups.
But with shared variables you can only share data within one flow file in one execution group. |
We use a Singleton, and we share data between EGs. Why cannot you? |
Well, it has never crossed my mind to share a Singleton across JVM's. I must admit that I thought it's not possible. |
You have never created any application that used inter-process communication? You've never used mutexes, or semaphores? Named-pipes?
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| mqjeff |
| Posted: Wed May 30, 2012 6:25 am Post subject: |
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The use of a Singleton does not provide any automatic mechanism that requires no programming to provide data that is available in more than one DFE.
The use of ESQL shared variables or of Java static variables does not provide any automatic mechanism that requires no programming to provide data that is available in more than one DFE.
The use of the Cache node supportPac allows for an administrative configuration, that can be made after development is complete, that provides data that is available in more than one DFE without any additional programming.
That is the advantage of the Cache node supportPac. |
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| Esa |
| Posted: Wed May 30, 2012 6:26 am Post subject: |
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Grand Master
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| lancelotlinc wrote: |
You have never created any application that used inter-process communication? You've never used mutexes, or semaphores? Named-pipes? |
I haven't needed to.
I guess your Singleton lives outside the broker. Do you share data accross brokers, too? |
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| lancelotlinc |
| Posted: Wed May 30, 2012 6:28 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
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Location: Bloomington, IL USA
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Very well stated, mqjeff. The support pak provides a way to cache data through administrative configuration. I like your synopsis.
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| lancelotlinc |
| Posted: Wed May 30, 2012 6:31 am Post subject: |
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Jedi Knight
Joined: 22 Mar 2010
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Location: Bloomington, IL USA
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| Esa wrote: |
| lancelotlinc wrote: |
You have never created any application that used inter-process communication? You've never used mutexes, or semaphores? Named-pipes? |
I haven't needed to.
I guess your Singleton lives outside the broker. Do you share data accross brokers, too? |
The inter-process communication mechanism has no restrictions on boundaries, as long as you can access the interface through TCP/IP. We use JMX managed beans as cache objects, which can also be browsed by an adminstrator as cache data is being held, using either a standard web browser or jconsole, which ever suits your taste.
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| rekarm01 |
| Posted: Wed May 30, 2012 11:51 pm Post subject: Re: Cache node over shared variable |
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Grand Master
Joined: 25 Jun 2008
Posts: 1415
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| lancelotlinc wrote: |
| We use a Singleton, and we share data between EGs. |
A Singleton? It seems like it would require more than one.
In this case, what is the advantage of singletons, over static class methods/variables? |
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| Esa |
| Posted: Thu May 31, 2012 12:01 am Post subject: Re: Cache node over shared variable |
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Grand Master
Joined: 22 May 2008
Posts: 1387
Location: Finland
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| rekarm01 wrote: |
| A Singleton? It seems like it would require more than one. |
This has been discussed above...
| rekarm01 wrote: |
In this case, what is the advantage of singletons, over static class methods/variables? |
A singleton is just a pattern for synchronizing access to the (cache) object to make sure that everyone is accessing the same object and that only one thread at a time is allowed to update it. A standard way of using static varibles/methods for a certain purpose. |
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| mqjeff |
| Posted: Thu May 31, 2012 1:24 am Post subject: Re: Cache node over shared variable |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| Esa wrote: |
| rekarm01 wrote: |
In this case, what is the advantage of singletons, over static class methods/variables? |
A singleton is just a pattern for synchronizing access to the (cache) object to make sure that everyone is accessing the same object and that only one thread at a time is allowed to update it. A standard way of using static varibles/methods for a certain purpose. |
An ESQL shared variable wrapped in method calls that enforce BEGIN ATOMIC probably counts as a Singleton. |
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| Esa |
| Posted: Thu May 31, 2012 1:27 am Post subject: Re: Cache node over shared variable |
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Grand Master
Joined: 22 May 2008
Posts: 1387
Location: Finland
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| mqjeff wrote: |
An ESQL shared variable wrapped in method calls that enforce BEGIN ATOMIC probably counts as a Singleton. |
 The only major difference being a more limited scope. |
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