Faith & Code | Reflections by Errong

Fix “Value Too Long for Column” Error: UTF-8 String Truncation by Bytes in Java If you've ever encountered the "value too long for column" database error, especially in a Java backend, the root cause may not be obvious. In this post, we’ll walk through a real production issue caused by UTF-8 encoding , explain why string length is not equal to byte length , and show how to correctly truncate strings by bytes without breaking multibyte characters. The Production Issue We hit a production error during a database insert: value too long for column Database column limit: 50 bytes Input string length: 53 characters Code already truncated to 50 characters At first glance, everything looked correct—but the insert still failed. Root Cause: UTF-8 Encoding The issue comes down to this: 50 characters does NOT equal 50 bytes in UTF-8 In UTF-8 encoding: ASCII characters → 1 byte Chinese characters → 3 bytes Emoji → 4 bytes This mean...

A Lesson Learned: Slow DELETE Caused by Missing FK Indexes Recently, I was working on a data purge task. The logic itself was simple: delete old records based on certain conditions. I had done similar work before, so I did not expect any major issues. However, this time the DELETE operation got stuck . No errors were reported, but the SQL just kept running without making progress. What Happened? With help from our DBA, we started investigating the issue at the database level. After some analysis, we identified the root cause: Several foreign key (FK) columns were missing supporting indexes. Because of this, every DELETE on a parent table forced Oracle to perform full table scans on related child tables to validate referential integrity. As data volume increased, the performance impact became severe. The Fix After adding indexes on the missing foreign key columns (across related tables), the results were immediate: DELETE operations completed much faster ...

Why PostgreSQL Idle Connections Remain After Vercel Deployments If you are running a Next.js application on Vercel with PostgreSQL , you may have encountered this error: remaining connection slots are reserved for roles with the SUPERUSER attribute This issue often appears right after a redeploy or during traffic spikes, even when your application traffic is relatively low. The Symptom PostgreSQL shows many connections in idle state Connections remain even after Vercel instances are shut down New requests fail with connection slot errors Manually terminating idle connections only fixes the problem temporarily What Is Really Happening This behavior is expected in serverless environments . Here is what happens behind the scenes: Vercel spins up serverless function instances Each instance creates its own PostgreSQL connection or connection pool When the instance finishes, it may shut down without gracefully closing the DB connection Post...

How a JPA save() Call Silently Overwrote My Data (and How to Fix It) I recently encountered a subtle but dangerous issue in a Spring Boot + JPA application. There were no errors, no exceptions, and no failed transactions — yet a database column was silently overwritten with NULL . If you are using Spring Data JPA and updating the same table from multiple endpoints, this is something you should be aware of. The Simplified Scenario We had two REST endpoints updating the same entity, but different fields. The code below is simplified and mangled for illustration. Endpoint A – updates an external reference EntityX entity = repository.findByKey(refId); // update external reference entity.setExternalRef("ABC123"); repository.save(entity); Endpoint B – updates customer email EntityX entity = repository.findByKey(refId); // update email only entity.setEmail("user@example.com"); repository.save(entity); The assumption was that Endpoint B would ...