GemFire: Data Visibility Issues in Partitioned Regions due to Hash Code Mismatch with PDX Serialization

Products

• VMware Tanzu Data
• Pivotal GemFire
• VMware Tanzu Gemfire
• VMware Tanzu Data Suite
• VMware Tanzu Data Suite

Issue/Introduction

In GemFire environments, users may encounter scenarios where data successfully loaded into GemFire regions appears "missing" during standard lookup operations. Although logs may indicate that data ingestion completed without errors, specific keys cannot be retrieved by the application.

This behavior is typically observed when using complex objects as region keys in conjunction with PDX serialization.

Cause

The root cause is a hash code mismatch between the client and server or between the serialized and deserialized states of a key object.

• When read-serialized is set to true on the server, GemFire stores and compares keys in their serialized PDX form.

• GemFire identifies the bucket location and performs lookups based on the key's hash code. If the hashCode() or equals() implementation of a complex key object is not consistent when serialized, the server may calculate a different hash than the client.

• This results in the key being placed in a specific bucket during ingestion, but failing to be located during a get operation because the lookup hash points to a different location or fails the equality check.

Using complex objects as keys is generally considered a non-recommended practice unless specific serialization requirements are met.

Resolution

To resolve and prevent data visibility issues related to hash code mismatches, implement the following strategies:

• Use a String or a primitive type as the key. These types have consistent, built-in hash code and equality logic that is not affected by PDX serialization settings.
• If complex objects must be used as keys, avoid relying on the standard PdxSerializer. Instead, the key objects should implement the DataSerializable 
• In some instances, matching read-serialized configuration on the server and client can act as a workaround. This forces the server to deserialize the object before performing equality checks, though it may incur a performance overhead.

 

Additional Information

https://techdocs.broadcom.com/us/en/vmware-tanzu/data-solutions/tanzu-gemfire/10-1/gf/developing-data_serialization-gemfire_pdx_serialization.html