---
title: "Solving the Mystery of the Slow Hash Table"
url: https://daily.dev/posts/solving-the-mystery-of-the-slow-hash-table-y20tqe7we
source_url: https://engineering.blackrock.com/solving-the-mystery-of-the-slow-hash-table-616627a270c5
type: article
source: "Blackrock Engineering"
published: 2024-07-29T19:07:39.320Z
updated: 2026-03-15T06:42:58.774Z
tags: ["apache-spark", "general-programming", "java", "performance"]
reading_time: 11
upvotes: 2
comments: 0
language: en
---

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# Solving the Mystery of the Slow Hash Table

**[Blackrock Engineering](https://daily.dev/sources/blackrock)** · 11 min read · 2 upvotes · 0 comments

## Summary

The post discusses a case study from Aladdin Wealth Tech, detailing how they identified and fixed a performance issue with a Java hash table handling very large portfolios in an Apache Spark job. It was discovered that hash collisions in the Apache Commons Lang3 Pair class were causing quadratic time complexity (O(N2)). By restructuring their map keys and avoiding the use of problematic hash functions, they restored the expected performance. This experience underscores the importance of understanding data structures and their underlying mechanics to prevent such issues.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://engineering.blackrock.com/solving-the-mystery-of-the-slow-hash-table-616627a270c5>

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---

Tags: [#apache-spark](https://daily.dev/tags/apache-spark), [#general-programming](https://daily.dev/tags/general-programming), [#java](https://daily.dev/tags/java), [#performance](https://daily.dev/tags/performance)

[View this post on daily.dev](https://daily.dev/posts/solving-the-mystery-of-the-slow-hash-table-y20tqe7we)