Introduction

In the realm of SQL Server replication, encountering errors can be a daunting aspect of database management. One such error that frequently perplexes database administrators is the replication error 20598. This error typically arises during transactional replication when an UPDATE command is applied to a subscriber that cannot find the corresponding row. This blog post aims to demystify this error, exploring its causes and providing a step-by-step resolution to help you maintain the integrity and performance of your SQL Server replication environment.

Issue

The error message in question is as follows:

Command attempted:

if @@trancount > 0 rollback tran
(Transaction sequence number: 0x00TAd26800029780003600000000, Command ID: 2)
Error messages:
The row was not found at the Subscriber when applying the replicated UPDATE command for Table ‘[dbo].[Table1]’ with Primary Key(s): [Col1] = 45852653, [Col2] = FT_GT_DF (Source: MSSQLServer, Error number: 20598)
Get help: http://help/20598
The row was not found at the Subscriber when applying the replicated UPDATE command for Table ‘[dbo].[Table1]’ with Primary Key(s): [Col1] = 45852653, [Col2] = FT_GT_DF (Source: MSSQLServer, Error number: 20598)
Get help: http://help/20598

This error surfaces during the replication process, specifically when an UPDATE operation is being replicated from the publisher to the subscriber, and the system cannot locate the target row on the subscriber side to apply the update.

Understanding the Error

Error 20598 is a symptom of a larger issue where data synchronization between the publisher and subscriber has been compromised. This discrepancy can occur for several reasons:

1. Manual Changes: Direct modifications made to the subscriber that bypass replication can lead to inconsistencies.
2. Failed Replication Commands: Previous commands that failed to replicate successfully can result in missing data on the subscriber.
3. Initial Snapshot Issues: Problems with the initial snapshot or schema changes that were not correctly replicated can cause missing rows.
4. Data Cleanup Scripts: Scripts that unintentionally remove data from the subscriber can also contribute to this error.

Identifying the root cause is crucial for applying the correct resolution strategy.

Resolution

Resolving error 20598 involves ensuring that the data between the publisher and subscriber is synchronized. Here are the steps to troubleshoot and fix the issue:

1. Validate Subscriptions: Use the Replication Monitor or execute the sp_validatemergepublication stored procedure to check for data inconsistencies between the publisher and the subscriber.
2. Identify the Missing Row: Confirm that the row indicated in the error message is indeed missing from the subscriber. This verification helps in understanding whether it’s a singular issue or part of a larger synchronization problem.
3. Reinitialize the Subscription: If the data discrepancy is extensive or the missing row is part of a larger issue, consider reinitializing the subscription. This process involves generating a new snapshot of the publication and reapplying it to the subscriber. Be cautious, as this can be resource-intensive for large datasets.
4. Manually Apply Missing Data: For isolated incidents where only a few rows are affected, manually inserting or updating the missing data on the subscriber can be a quick fix. Ensure the replication agent jobs are stopped while making manual changes to avoid conflicts.
5. Investigate and Address the Root Cause: After resolving the immediate error, investigate the root cause of the data inconsistency. This may involve reviewing data modification practices, ensuring all changes go through replication, and setting up alerts for failed replication commands.

To address this challenge comprehensively, including identifying the cause of missing rows on the subscriber, implementing a monitoring strategy is paramount. We will employ a trigger on the publisher’s table to monitor write operations. This approach aids in determining whether rows are being deleted or otherwise modified in a manner that could lead to replication errors. Here’s how to set up the monitoring:

Monitoring Setup

First, create a tracking table to log changes:

CREATE TABLE table1_Tracking
(
    TrackingID INT IDENTITY(1,1) PRIMARY KEY,
    OperationType VARCHAR(10),
    ChangedData NVARCHAR(MAX),
    PreviousData NVARCHAR(MAX),
    ExecutedBy SYSNAME,
    ApplicationName NVARCHAR(128),
    HostName NVARCHAR(128),
    ChangeTime DATETIME DEFAULT GETDATE()
);

Next, establish a trigger to capture insert, update, and delete operations:

CREATE TRIGGER trg_table1_WriteOperations
ON table1
AFTER INSERT, UPDATE, DELETE
NOT FOR REPLICATION
AS
BEGIN
    SET NOCOUNT ON;

    DECLARE @ExecutedBy SYSNAME = SUSER_SNAME();
    DECLARE @ApplicationName NVARCHAR(128) = APP_NAME();
    DECLARE @HostName NVARCHAR(128) = HOST_NAME();

    IF EXISTS (SELECT * FROM inserted)
    BEGIN
        IF EXISTS (SELECT * FROM deleted)
        BEGIN
            -- Handle UPDATE
            INSERT INTO table1_Tracking(OperationType, ChangedData, PreviousData, ExecutedBy, ApplicationName, HostName)
            SELECT 'UPDATE', 
                   (SELECT * FROM inserted FOR JSON AUTO), 
                   (SELECT * FROM deleted FOR JSON AUTO), 
                   @ExecutedBy, @ApplicationName, @HostName;
        END
        ELSE
        BEGIN
            -- Handle INSERT
            INSERT INTO table1_Tracking(OperationType, ChangedData, ExecutedBy, ApplicationName, HostName)
            SELECT 'INSERT', 
                   (SELECT * FROM inserted FOR JSON AUTO), 
                   @ExecutedBy, @ApplicationName, @HostName;
        END
    END
    ELSE
    BEGIN
        -- Handle DELETE
        INSERT INTO table1_Tracking(OperationType, PreviousData, ExecutedBy, ApplicationName, HostName)
        SELECT 'DELETE', 
               (SELECT * FROM deleted FOR JSON AUTO), 
               @ExecutedBy, @ApplicationName, @HostName;
    END
END;

This trigger captures the nature of the operation (insert, update, delete), the data before and after the change, who executed the operation, from which application, and from which host. This comprehensive tracking enables administrators to analyze patterns that could lead to replication errors, such as unauthorized deletions or updates that bypass replication mechanisms.

Conclusion

Error 20598 in SQL Server replication highlights the challenges of maintaining data consistency across distributed databases. By understanding the underlying causes and meticulously applying the appropriate resolution steps, database administrators can ensure the integrity and reliability of their replication setup. Remember, the key to effectively managing replication errors lies in proactive monitoring, thorough investigation, and understanding the intricacies of SQL Server’s replication mechanisms.

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Thank You,
Vivek Janakiraman

Disclaimer:
The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.