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Report a fraud if voter tries to vote twice

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.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;

0

2

I have a list of candidateId, voterId as incoming request to the "backendService".

This backend service checks if the voterID has not already been voted to any of the candidateId, if so it will increment the candidateId count in the cache as below :

| CandidateId | count |

| ABC | 5 |

| XYZ | 10 |

| MNO | 100 |

The problem with above approach is if we scale up the "backendService" to 3 - 4 instances and the same voterID tries to vote to many candidates as below incoming request and all of the below comes at a SAME TIME:

 candidateId : 1, voterId : "ABC"
 candidateId : 2, voterId : "ABC"
 candidateId : 3, voterId : "ABC"

Each of the "backendService" will pick one of the above request to process.

In this case all 3 instances check that VoterID has not already voted to any candidate in the cache at a same time ( where are the voter's ID who has already give there vote is being stored) and then all the 3 service instance will wrongly updates the count at a same time for all the 3 candidateId which is casted by the same voterID in the cache which is wrong.

I am looking for a solution on how to avoid such cases.

Currently all the details are stored in distributed cache (REDIS).

java caching concurrency system-design

share|improve this question

edited Mar 8 at 9:25

Yathish Manjunath

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How do you keep votes in memory ? Can you use a map in a synchronized block where its key is voterId and the value is vote as a cache, and return exception if the specified key exists while putting in it ?
  
  – Emre Acar
  Mar 8 at 6:03
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Use database locking. If such a conflict is less likely to occur, you can improve performance by using optimistic locking.
  
  – Kartik
  Mar 8 at 6:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  All the details are stored in REDIS cache and serializing the updates would slow down.
  
  – Yathish Manjunath
  Mar 8 at 6:14
  

  
  
  
  

add a comment | 

0

2

I have a list of candidateId, voterId as incoming request to the "backendService".

This backend service checks if the voterID has not already been voted to any of the candidateId, if so it will increment the candidateId count in the cache as below :

| CandidateId | count |

| ABC | 5 |

| XYZ | 10 |

| MNO | 100 |

The problem with above approach is if we scale up the "backendService" to 3 - 4 instances and the same voterID tries to vote to many candidates as below incoming request and all of the below comes at a SAME TIME:

 candidateId : 1, voterId : "ABC"
 candidateId : 2, voterId : "ABC"
 candidateId : 3, voterId : "ABC"

Each of the "backendService" will pick one of the above request to process.

In this case all 3 instances check that VoterID has not already voted to any candidate in the cache at a same time ( where are the voter's ID who has already give there vote is being stored) and then all the 3 service instance will wrongly updates the count at a same time for all the 3 candidateId which is casted by the same voterID in the cache which is wrong.

I am looking for a solution on how to avoid such cases.

Currently all the details are stored in distributed cache (REDIS).

java caching concurrency system-design

share|improve this question

edited Mar 8 at 9:25

Yathish Manjunath

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How do you keep votes in memory ? Can you use a map in a synchronized block where its key is voterId and the value is vote as a cache, and return exception if the specified key exists while putting in it ?
  
  – Emre Acar
  Mar 8 at 6:03
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Use database locking. If such a conflict is less likely to occur, you can improve performance by using optimistic locking.
  
  – Kartik
  Mar 8 at 6:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  All the details are stored in REDIS cache and serializing the updates would slow down.
  
  – Yathish Manjunath
  Mar 8 at 6:14
  

  
  
  
  

add a comment | 

I have a list of candidateId, voterId as incoming request to the "backendService".

This backend service checks if the voterID has not already been voted to any of the candidateId, if so it will increment the candidateId count in the cache as below :

| CandidateId | count |

| ABC | 5 |

| XYZ | 10 |

| MNO | 100 |

The problem with above approach is if we scale up the "backendService" to 3 - 4 instances and the same voterID tries to vote to many candidates as below incoming request and all of the below comes at a SAME TIME:

 candidateId : 1, voterId : "ABC"
 candidateId : 2, voterId : "ABC"
 candidateId : 3, voterId : "ABC"

Each of the "backendService" will pick one of the above request to process.

In this case all 3 instances check that VoterID has not already voted to any candidate in the cache at a same time ( where are the voter's ID who has already give there vote is being stored) and then all the 3 service instance will wrongly updates the count at a same time for all the 3 candidateId which is casted by the same voterID in the cache which is wrong.

I am looking for a solution on how to avoid such cases.

Currently all the details are stored in distributed cache (REDIS).

java caching concurrency system-design

share|improve this question

edited Mar 8 at 9:25

Yathish Manjunath

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515

 candidateId : 1, voterId : "ABC"
 candidateId : 2, voterId : "ABC"
 candidateId : 3, voterId : "ABC"

share|improve this question

edited Mar 8 at 9:25

Yathish Manjunath

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515

share|improve this question

edited Mar 8 at 9:25

Yathish Manjunath

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515

asked Mar 8 at 5:57

Yathish ManjunathYathish Manjunath

1,2861515