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  • Programmer's Guide
  • Setting Up Development Environment
    • .NET
      • Client API Prerequisites
      • Server-side API Prerequisites
    • Java
      • Client API Prerequisites
      • Server-side API Prerequisites
    • Python
      • Client API Prerequisites
    • Node.js
      • Client API Prerequisites
  • Client Side API Programming
    • Error Handling
    • Troubleshooting
    • Cache Keys and Data
    • How to Connect to Cache
    • Basic Operations - An Overview
      • Add Data
      • Update/Insert Data
      • Retrieve Data
      • Remove Data
    • Groups
      • Overview
      • Add/Update Data with Groups
      • Retrieve Data with Groups
      • Remove Data with Group
      • Search Group Data Using SQL
      • Delete Group Data Using SQL
    • Tags
      • Overview
      • Add/Update Data with Tags
      • Retrieve Data with Tags
      • Remove Data with Tags
      • Search Tag Data Using SQL
      • Delete Tag Data Using SQL
    • Named Tags
      • Overview
      • Add/Update Data with Named Tags
      • Remove Data with Named Tags
      • Search Data with Named Tags Using SQL
      • Delete Data with Named Tags Using SQL
    • Expirations
      • Overview
      • Absolute Expiration
      • Sliding Expiration
    • Data Dependency
      • Key Dependency
      • Multi-Cache Dependency
    • Dependency on Database
      • SQL Server
      • Oracle
      • OleDB with Polling
      • CLR Procedures in SQL Server
    • Dependency on External Source
      • File Dependency
      • Custom Dependency
      • Aggregate Dependency
    • Locks
      • Types of Locking
      • Pessimistic Locking
      • Optimistic Locking
    • SQL Query
      • Overview
      • Define Indexes Programmatically
      • Query with ExecuteReader and ExecuteScalar
      • Delete Data with ExecuteNonQuery
      • SQL Reference
    • LINQ Query
      • Overview
      • LINQ Query for Objects
      • LINQ Reference
    • Data Structures
      • Overview
      • List
      • Queue
      • Set
      • Dictionary
      • Counter
      • Invalidation Attributes
      • Searchable Attributes
      • Query on Data Structures
      • Remove from Data Structure
    • Events
      • Cache Level Events
      • Item Level Events
      • Management Level Events
    • Pub/Sub Messaging
      • Overview
      • Topics
      • Publish Messages
      • Subscribe to a Topic
      • Pub/Sub Events
    • Continuous Query
      • Overview
      • Use Continuous Query
    • Stream Processing
      • Add/Update Stream Data
      • Retrieve Stream Data
    • JSON
      • Overview
      • Use JSON Objects
      • Query JSON Data
    • Security API
      • Login with Credentials
    • Management API
    • Clear Cache
    • Error Logging
    • Location Affinity
  • Server-side API Programming
    • Loader and Refresher
      • Overview
      • Implement Loader and Refresher
      • Components of Loader/Refresher
    • Data Source Providers
      • Read-through
        • Implement Read-through
        • Use Read-through
      • Write-through
        • Implement Write-through
        • Use Write-through
        • Use Write-behind
    • Custom Dependency
      • Implement Extensible Dependency
      • Implement Bulk Extensible Dependency
      • Implement Notify Extensible Dependency
    • Bridge Conflict Resolver
    • Entry Processor
      • Overview
      • Implement Entry Processor
    • MapReduce
      • Overview
      • Implement MapReduce
      • Use MapReduce
    • MapReduce Aggregator
      • Overview
      • Implement and Use Aggregator
    • Compact Serialization
  • Client Side Features
    • ASP.NET Core Caching
      • Session Storage
        • Session Provider
        • IDistributedCache
        • Sessions Usage
        • Multi-site Session Provider
        • Session Sharing with ASP.NET
      • SignalR
        • NCache Extension for SignalR Core
      • Response Caching
        • Configure and Use
        • Configure with IDistributedCache
      • Data Caching
        • NCache API
        • IDistributedCache API
      • Data Protection Provider
        • Configure
    • Java Web App Caching
      • Web Sessions
        • Overview
        • Configure App
          • Add Maven Dependencies
          • Deploy Application
        • Multi-site Sessions
    • Node.js App Caching
      • Web Sessions
    • ASP.NET Caching Benefits and Overview
      • ASP.NET Session State Provider Properties
      • Multi-region ASP.NET Session State Provider Configuration
      • Session Sharing between ASP.NET and ASP.NET Core
      • ASP.NET SignalR Backplane
        • NCache Extension for SignalR
      • ASP.NET View State Caching
        • View State Content Optimization Configuration
        • Group View State with Sessions
        • Limit View State Caching
        • Page Level Grouping
      • ASP.NET Output Cache
        • Output Caching Provider Overview
        • Output Cache with Custom Hooks
  • .NET Third Party Integrations
    • Entity Framework (EF) Core
      • Installation
      • Configure
      • EF Core Extension Methods
        • Extension Methods
        • Cache Handle
        • Caching Options
        • Query Deferred API
      • Logging in EF Core
    • Entity Framework EF 6
      • EF Second Level Cache
      • EF Caching Resync Provider
      • EF Caching Configuration File
    • NHibernate
      • Second Level Cache
      • Query Caching
      • Synchronize Database with Cache
    • Debug NCache Providers in Visual Studio
  • Java Third Party Integrations
    • Hibernate
      • Second Level Cache
      • Configure Cacheable Objects and Regions
      • Configure Application
      • Query Caching
    • Spring
      • Overview
      • Use NCache with Spring
        • Configure Generic Provider
        • Configure JCache Spring Caching Provider
        • Configure Caching Declaration
        • Configure Spring Sessions
    • JCache API
      • CRUD Operations
      • Expiration
      • Events
  • Third-Party Wrappers
    • AppFabric to NCache Migration
      • AppFabric API vs. NCache API
      • Configuration Differences Between AppFabric and NCache
      • Migrating from an AppFabric Application to NCache
    • Redis to NCache Migration
      • Redis to NCache Migration
    • Memcached Wrapper
      • Memcached Gateway Approach
      • Memcached Client Plugin for .NET

Error Handling in Cache

There are scenarios where NCache client operations may fail due to various errors, as demonstrated below.

Specified Key Exists in Cache

  • Type of Exception: OperationFailedException
  • Message: "Specified key already exists in cache."

  • Reason: This exception is specific to the Add API if the same key is used with the object. The operation only adds an item to the cache if the given key does not exist previously. It adds data to the cache for the first time when the key does not exist within the cache.

You can handle this in the following ways according to your business requirements:

  • Specify a new key for the object you are trying to add.
  • Use Insert API if the same key is used with the object.
  • Use Remove API if the same key is used with the object. Remove the object first and then add it again to the cache with the same key.

Connection Failure

  • Type of exception: OperationFailedException
  • Message: "The operation has been interrupted due to a loss of connectivity between the server and the client."

  • Reason: Operations can fail in case a connection is lost between the server and the client. This could be due to a network glitch or a physical interruption between the client and server.

    You may encounter this exception if an already established connection is broken with the server. In such a case, it is advised to resolve the network cause first and then retry the operation if it is highly needed.

No Server Available to Process the Request

  • Type of exception: OperationFailedException
  • Message: "No server is available to process the request".

  • Reason: You may encounter this exception if the cache is unavailable due to stoppage and inaccessibility.

Operation Timeout

  • Type of Exception: OperationFailedException
  • Message: "Operation timed out."

  • Reason: In case of heavy transactions on the server, incoming client operations can be queued while the server processes the current operations. Each cache client operation has a configurable timeout value associated with it. This means that if the cache server does not respond to the operation within the given time, the operation will be considered as failed even though it has not really failed - or succeeded - for that matter.

It is not advised to immediately retry a timed-out operation as it may still result in timeout again if the server is still processing the previous operations. Hence, it is recommended that if your business allows, you extend the timeout value before retrying the operation.

In NCache, the default timeout value is 90 seconds during which a client operation must be completed. In case you want the operation to wait longer, you can configure the client-request-timeout value from the client.ncconf file.

Operation Performed During State Transfer

  • Type of Exception: OperationFailedException
  • Message: "Operation could not be completed due to state transfer."

  • Reason: Once the distribution state of the cluster changes, it requires immediate data consistency across the cluster, especially for Partitioned and Partition-Replica topologies. This change of state occurs due to the nodes joining or leaving the cluster. This means that once a node joins the cluster, the newly added node needs to be provided with the data of the cache according to the distribution. Similarly, if a node leaves the cluster, the data is re-distributed among the remaining nodes.

To cater to this issue, NCache internally initiates a state transfer - a node-level data transfer mechanism, that is triggered after the distribution of data is changed across a clustered cache.

A state transfer can occur between two nodes of a single cluster, where data is transferred bucket by bucket. The requesting node initiates the state transfer by locking that specific bucket. Any operations that are performed on this bucket during state transfer are logged. These operations can result in duplicates or fewer results than expected, as the same bucket might exist on both nodes during transfer or none. Once a bucket is transferred completely, the logged operations are transferred to the requesting node.

It is advised to monitor State Transfer PerfMon counters for your cache after every change in the cluster. Once the counters depict that the state transfer is complete, you can proceed with performing operations on the cache.

See Also

How to Connect to Cache
Add Data to Cache
Retrieve Existing Cache Data
Remove Data from Cache
Create Cache

In This Article
  • Specified Key Exists in Cache
  • Connection Failure
  • No Server Available to Process the Request
  • Operation Timeout
  • Operation Performed During State Transfer
  • See Also

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